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Living crocodylians possess acute sensory capabilities, e.g., vision, audition, olfaction, gustation, and tactile sensation. In many species, multi-modal communication is common, particularly in intra-specific social interactions. To... more
Living crocodylians possess acute sensory capabilities, e.g., vision, audition, olfaction, gustation, and tactile sensation. In many species, multi-modal communication is common, particularly in intra-specific social interactions. To date, chemical signaling studies have been rudimentary and exploratory, and confined to sampling isolated captives, typically in zoos. We studied the chemical composition of gular (chin) and paracloacal (cloaca vent) glands, using secretory samples (flash frozen, liquid nitrogen) from 97 gharial, representing differing sizes-ages and sexes, and residing in upstream and downstream stretches (~348 km total) of National Chambal Sanctuary, India. Using gas chromotography mass spectrometry (GCMS), we identified 182 glandular compounds (gular and paracloacal). Using multi-variant analyses (Partial least-squares Discriminant Analyses=PLS-DA), we focused on 47 of 182 compounds based on presence/ absence. Significant differences were detected in size-age, sex, and river residence cohorts. Of these compounds, 21 were previously identified as putative pheromones, and 26 are phytochemicals. We observed clusters in PLS-DA analyses that clearly separated adult females vs. males on the bases of gular as well as paracloacal secretions; unique male-specific chemicals predominated in sex comparisons. This result suggests that sex-specific glandular products may facilitate communication amongst reproductively active gharial. In addition, within groups of adult males and females, upstream vs. downstream residence was a significant factor in discriminating between adult females as well as between adult males in the paracloacal secretions. Habitat-specific features in two regions sampled may account for observed within-sex differences due to location. In brief, this study provides an initial, comprehensive inventory of gharial chemo-signals, and suggests that these compounds may have functional roles as significant discriminatory elements in multi-modal communications. Management implications include both attractant as well as repellent possibilities, and also potential ways to enhance reproduction in rare, endangered populations/species. Future studies will likely reveal that chemo-signals are an understudied, but important component of crocodylian communication.
The National Chambal Sanctuary in Northern India has the world's largest free-living population of Gharials and an estimated 2,000 of the total wild population of 2,500 in the world. I asked if this was driven by the Chambal River being... more
The National Chambal Sanctuary in Northern India has the world's largest free-living population of Gharials and an estimated 2,000 of the total wild population of 2,500 in the world. I asked if this was driven by the Chambal River being the cleanest river in North India. Jeff wholeheartedly agreed that the Chambal was special, particularly "clean" compared to other Indian rivers, but also unimpeded, with no dams or barrages, except in its headwaters. However, the radio telemetry work and the GPS data downloads were revealing that in the National Chambal Sanctuary, adult female Gharials were able to make long distance movements of a magnitude that had not been appreciated before. The gharials' requirement for an open river system is shared with other endangered wildlife such as the South Asian River Dolphins, large river turtles, and big species of river fish. I would undertake three river safaris to see more of the mighty Chambal River and its riverine animal residents. I learned two types of data loggers were in use. I had noticed one type, VHF transmitters, on my first river safari. The small radios were attached to the tails of gharials, just behind the legs, and sent out beeping signals that could be detected with special radio receivers. This required researchers to patrol the river, typically on a boat (but also on foot), using a five element directional Yagi antenna and receiver. Each transmitter has a unique signal allowing the individual to be identified. However, this method is not perfect as the signal range is limited, to four to five kilometres. If the researchers go in one direction and the animal has gone in another, it will not be picked up at all. Significant movements by the animals can be missed by the movements of the researchers and the animals not coinciding. This became all the more apparent when some of the animals were also fitted with a second type of transmitter that also logged location information via GPS. These units are more sophisticated and can be calibrated to capture and store GPS points multiple times each day. These GPS loggers also transmit a
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Gharial were historically distributed throughout the major channels of the Indus, Ganges, Mahanadi, Brahmaputra-Meghna and possibly Irrawaddy drainages, to elevations of <500 m, an estimated combined linear river distance of >20,000 km,... more
Gharial were historically distributed throughout the major channels of the Indus, Ganges, Mahanadi, Brahmaputra-Meghna and possibly Irrawaddy drainages, to elevations of <500 m, an estimated combined linear river distance of >20,000 km, or an historic occupancy area of 80,000 km² (using Red List standard 4 km² resolution). The species is currently extirpated from the Indus, Irrawaddy and most rivers and tributaries of the Ganges and Brahmaputra-Meghna systems, but persists in fourteen sites within the Ganges drainage (6 major and 8 minor), with confirmed breeding at only five locations (Table 1 in the Supplementary Information). Surveys and counts in 2010-2017 indicate an adult global metapopulation conservatively estimated at 650 (median) with a range of 300-900. The largest and most populous location, the protected National Chambal Sanctuary in north India, spans 625 river km, with approximately 500 mature adults, comprising 77% of the global total, producing >410 nests annually, or >86% of the global total. Five other locations reporting breeding are small and highly disturbed. The remaining 8 minor locations together contain less than 10% of the world population (<50 mature adults), with no recent breeding. During the next decade, gharial will likely be extirpated from some of the minor/non-breeding sites, including three sanctuaries in India designed for their protection (Son, Ken, Satkosia Gorge), as well as the Padma-Jamuna, Brahmaputra-Meghna, and Bhagirathi-Hooghly drainages, based on the infrequent sightings in these regions. Generation time is estimated at 25 years giving a period of decline of 75 years or since 1943. Cause of declines have been principally dams and barrages disrupting river hydrology, mortality in fishing nets, and historically, unregulated hide-hunting. Current serious threats include major water control and extraction activities, mortality in fishing gear, and increased anthropogenic river-bank disruptions, especially sand mining and boulder removal. These threats are known, continuing and not reversible, therefore criterion A2 applies. The expansion of threats and major declines have intensified since the 1950s, and continue presently with increasing demand for river resources. Past population levels are inferred to be >20,000 adult gharial globally. Calculating across the range of current and past population estimates, exponential declines are 94% or greater. Even a very conservative calculation of 5,000 in 1943 and 1,000 currently gives a decline of 80%. Decline in 3 generations is confidently inferred to exceed the criterion A2bc 80% for Critically Endangered. Toxins/pollutants were strongly suspected to play a role in the death of >110 gharial in the size range of 2-4m during the winter of 2008-2009 on the lower Chambal (Whitaker et al. 2008), and possibly the loss of additional gharial in 2012 (<10-15 individuals; Nair et al. 2013). This initial major loss suggested a species-specific sensitivity to whatever caused the deaths, which were localized geographically, most occurring rapidly within 2-15 weeks. These deaths were related to articular and visceral gout, related to kidney failure, associated with low ambient temperatures. Despite the absence of a re-occurrence, the susceptibility of gharial to whatever resulted in gout in the first instance warrants the application of criterion A2e. Extent of occurrence (EOO) exceeded 80,000km² historically. Area of occupancy (AOO) is generously estimated for the six major locations with sizeable resident populations at 4,400 km², a reduction of 94%. A population estimate of 300-900 mature individuals meets criterion C1 for Endangered if we infer that the decline is continuing at a rate of at least 20% in two generations/50 years i.e. since 1967. Gharial meets criterion D1 Vulnerable (population size <1,000 mature individuals). The species does not meet criteria E.
Gharial (Gavialis gangeticus) is listed as critically endangered, and the historical range loss suggests severe genetic bottleneck events that might have occurred in the remnant populations. We used 14 species-specific microsatellite... more
Gharial (Gavialis gangeticus) is listed as critically endangered, and the historical range loss suggests severe genetic bottleneck events that might have occurred in the remnant populations. We used 14 species-specific microsatellite markers to
investigate the genetic diversity of the largest breeding population of gharials in Chambal River in India. From 104 gharial scute samples collected during catching and tagging by Gharial Ecology Project team, DNA was isolated. Genotyping was done and results were analyzed using GeneMaper 5.0. The average number of alleles per marker was found be lower in the Chambal population (2.64 alleles, range = 1 to 8) than in the ex-situ population (6 alleles, range = 2 to 8). Five markers were monomorphic in the Chambal population, which were polymorphic in the ex-situ population. Average observed and expected heterozygosity (using Cervus 3.0) was 0.442 and 0.444 respectively. Although the Chambal population was found to be in Hardy-Weinberg equilibrium (no inbreeding), low allelic diversity indicates the role of genetic bottleneck events. These findings inform that remnant breeding populations need to be
genotyped and new species-specific markers need to be standardized for developing effective conservation strategies for the species.
investigate the genetic diversity of the largest breeding population of gharials in Chambal River in India. From 104 gharial scute samples collected during catching and tagging by Gharial Ecology Project team, DNA was isolated. Genotyping was done and results were analyzed using GeneMaper 5.0. The average number of alleles per marker was found be lower in the Chambal population (2.64 alleles, range = 1 to 8) than in the ex-situ population (6 alleles, range = 2 to 8). Five markers were monomorphic in the Chambal population, which were polymorphic in the ex-situ population. Average observed and expected heterozygosity (using Cervus 3.0) was 0.442 and 0.444 respectively. Although the Chambal population was found to be in Hardy-Weinberg equilibrium (no inbreeding), low allelic diversity indicates the role of genetic bottleneck events. These findings inform that remnant breeding populations need to be
genotyped and new species-specific markers need to be standardized for developing effective conservation strategies for the species.
The Indian narrow-headed softshell turtle, Chitra indica, is a riverine species restricted to south Asia. We studied movements as well as seasonal activities of 11 adults and one subadult in the lower Chambal and Yamuna Rivers near their... more
The Indian narrow-headed softshell turtle, Chitra indica, is a riverine species restricted to south Asia. We studied movements as well as seasonal activities of 11 adults and one subadult in the lower Chambal and Yamuna Rivers near their confluence in north India. Each turtle was radio-tagged with a VHF transmitter attached to the rear carapace, and tracked at o.5-2km range, multiple times per week. Behavioral observations were made visually and/or by monitoring radio signals for 1-4 hrs. daily. In November 2017, 5 adults (IM:4F) and 1 subadult (F), ranging from 7-15 kg wight, and from 36-53 cm carapace length were tagged. In May 2018, 6 more turtles, all females, ranging from 11-50kg weight, and size from 46-79 cm carapace length were tagged. Here, we present preliminary results from the initial tagged group. We logged 697 observations over 389 turtle-days on 4 resident turtles, released at their capture sites (=448 obs.), and on 2 transplanted turtles, shifted 62 river kms from their capture site to a release location within the protected National Chambal Sanctuary (=249 obs.). These observations were made on 165 days, from Dec 2017 thru May 2018 (=180 days study period). Four resident females (3 adults;1 subadult) occupied 2.6, 2.7, 7.3 and 11.7 river kms; two transplants occupied 13.1 and 14.3 river kms during the same period. Winter (Dec-mid Mar)behaviors consisted of daytime movements into shallow water (0.5-1m depth), and nighttime retreats to moderate depths (2-4m). Tracking signals were strong and detectable day and night. In constrast, summer (mid-Mar thru May) behaviors consisted of movements into shallow water only at night, and daytime retreats to deep pools (>5m depths) where tracking signals were undetectable. The single male turtle, a transplant, moved more frequently from pool to pool, over longer distances (>5 kms) than any of the tracked females. Transmitter ambient temperatures for 2 turtles ranged from 7-7.5 to 23.3-24.2 C in winter, and from 20.3-21.5 to 29.6-29.9 Cin summer. When fishing occurred nearby, tagged turtles moved to adjacent undisturbed areas
Abstract: Living crocodilians are known to communicate using visual, acoustic, chemical, and/or tactile signals. As adults, gharials (Gavialis gangeticus) vocalize only rarely, and reportedly do not produce infrasound. On-going... more
Abstract: Living crocodilians are known to communicate using visual, acoustic, chemical, and/or tactile signals. As adults, gharials (Gavialis gangeticus) vocalize only rarely, and reportedly do not produce infrasound. On-going ecological and behavioral studies of the largest remaining wild pop-ulation of gharials, living in the Chambal River, North India, indicate that gharials breed in well-defined arenas established by dominant males, and then reproductive females assemble and nest in large colonies nearby. Detailed behavioral observations, supported by 24hr acoustic data and still and video imagery, at breeding and nesting sites, at multiple locations in successive years, have documented complex social interactions, including acoustic signaling between and amongst adults, as well as by young. Adult male gharials produce explosive, concussive “pop” sounds underwater, in 1-3 short, loud, audible bursts. A “pop” is always sudden and high in volume. Using hydro-phones and aerial mics, we recorded over 500 samples of “pop” signals of 14 male gharials, behav-ing normally under natural conditions. Each male gharial produced a stereo-typed series of 1-3 “pops” underwater. Temporal patterning, rather than frequency differences, appears to be the pri-mary feature of this unique crocodilian signal which presumably facilitates individual recognition. Immediately preceding a pop, infrasound is produced. Duration ranges from 0.013 to 0.036 se-conds, and the time interval between syllables ranges from 0.045 to 0.745 secs. Distinctive low and high frequencies were characteristic, ranging from 100-2400 Hz to 10,000-22,000 Hz. During breeding (late Feb-early Mar), popping occurs in four distinct contexts, namely 1) external disturb-ances, 2) patrolling, 3) male-male interactions, and 4) courtship between potential mates. At one site frequented by a breeding male, with relatively few (<10 in 2017) vs. many (>30 in 2018) fe-males, “recruiting” pops directed at females dominated in 2017, whereas “challenging” pops domi-nated in 2018, when challengers visited. During hatching until ~4-6 weeks afterwards (late May-early July), at each communal nesting site, a guardian male will “pop” often to 1) alert and recruit hatchlings, and 2) announce his presence and location to females in the vicinity of the crèche. Each guardian male can be identified by his distinctive “popping” at a specific crèche, year after year.
Executive Summary An earlier field report (GEP 2017) established on a 425 km stretch of the National Chambal Sanctuary (NCS) from Pali to the Yamuna confluence, based on actual counts, the adult gharial population was 72 males with gharas... more
Executive Summary An earlier field report (GEP 2017) established on a 425 km stretch of the National Chambal Sanctuary (NCS) from Pali to the Yamuna confluence, based on actual counts, the adult gharial population was 72 males with gharas (>4.5m), and at least 411 were reproductive females, based nest counts in 2017, immediately after hatching (GEP 2017). At that time, we estimated very conservatively a total of 483 mature adult gharial inhabit the NCS. Furthermore, these data firmly established that this minimum estimated population (revised upward by 20+ to 500+ adults, and by 4+ to 415+ nests, with the addition of the Parvati tributary population; Khandel et al. 2017) inhabits ALL of the 425 km of NCS surveyed where they reside most of the year, and also nest from Pali (near Ranthambore) to the Yamuna confluence (Bareh), at approximately 30 riverside locations identified in nest surveys. These recent counts provided the bases for highlighting the Chambal gharial population in the recently updated Red List assessment, as the single most important extant gharial population, by a factor of ten (10x larger than the next largest of 5 remaining breeding populations), and the only open-river, self-sustaining remnant of this CR species alive today (Lang et al. 2018). In January-March 2018, various surveys were conducted to make additional actual counts of gharial in the National Chambal Sanctuary (NCS), as noted above, in a manner similar to those conducted in 2017 (GEP 2017). In the upper Chambal, prior to the boat survey, the static survey counted 393 gharial, specifically 19 males, 183 females, 120 subadults, 56 juveniles, and 15 yearlings. The boat survey tallied 456 gharial in the same upper stretch. In the lower Chambal, immediately prior to the boat survey, 1330 gharial were directly observed and tallied by the static survey. These consisted of 53 males, 391 females, 370 subadults, 318 juveniles, and 198 yearlings. On the same stretch of lower Chambal, the boat survey counted 1225 gharial. Thus, the overall number of gharial living on the 425 km of Chambal River counted by boat survey was 1681, and by static survey was 1676, based on Jan-Feb direct counts of observed animals. Adjusted for accuracy in size categories, these counts included 75 mature males (with ghara), 464 reproductive females plus 52 " near reproductive " females, 462 subadults, 366 juveniles, and 208 yearlings. In 2017, in the NCS, we tallied 417 nests at 28 sites, of which 358 hatched and 59 were lost. In 2018, a total of 443 nests at 37 sites were observed, of which 318 hatched and 115 were lost. The relative importance of the Chambal gharial population cannot be overstated. Now, with realistic size estimates of the other subpopulations, totaling approximately 650 total adults globally, the NCS population comprises 85% of the global total (550/650). It also represents ~90% (450/500) of the global yearly nesting. Importantly, the Chambal population is the ONLY self-sustaining population living in an open river, protected habitat. Major threats are, in order of importance, a) dams and river-linking, b) water extraction, c) sand mining, and d) net fishing.
Historic accounts indicate that gharial (Gavialis gangeticus) were common and abundant throughout the Indus, Ganges, Mahanadi, Brahmaputra-Meghna drainages. Large scale water control and extraction, widespread hunting, and intensive... more
Historic accounts indicate that gharial (Gavialis gangeticus) were common and abundant throughout the Indus, Ganges, Mahanadi, Brahmaputra-Meghna drainages. Large scale water control and extraction, widespread hunting, and intensive fishing during the 19 th and 20 th centuries reduced gharial numbers dramatically throughout the species' former range. At present, the species has been extirpated from the Indus, Irrawaddy and most rivers and tributaries of the Ganges and Brahamaputra-Meghna systems. Today, gharial are limited to only 14 widely spaced, restricted localities in north India and lowland Nepal. Only 5 subpopulations exhibit recent reproduction/recruitment. Nesting is commensurate with the estimated adult females only on Chambal River and at Katerniaghat Reservoir. Limited nesting, relative to adult females at these localities, occurs at Chitwan, Corbett, and on Gandak River. Nesting at Babai River (Bardia NP in Nepal) may have occurred previously, but not recently. The other 8 minor locations where gharial have been sighted show no evidence of reproduction. The number of extant gharial is estimated conservatively at ~650 (300-900 mature adults). The Chambal River subpopulation, inhabiting ~625 river km within the National Chambal Sanctuary, contains 77% of the global total (=500/650 mature adults; conservatively 425 females, 75 males). In 2017, the nesting on the Chambal River and its tributaries accounted for ~89% of the global total nesting (425/475). In 2018, the IUCN Red List re-assessment of gharial, a decade after its initial listing as CR in 2007, recommends no change in status. In 2007, the primary basis for CR were low population numbers, <250 mature adults. In 2018, multiple counts estimate current numbers at 2-3X those previous. However, the recent increase is due entirely to a demonstrable increase in the Chambal subpopulation. Elsewhere, despite evidence of reproduction, numbers remain stable or have decreased. Of the 8 minor subpopulations, 3-6 will likely be extirpated within the next decade. The updated CR status of gharial is based upon a 1) 94% exponential decline in adult numbers, within 3 generations (using 25 yrs/generation, =from1943), from>20,000 adults historicially (based on 1 gharial / river km) to 650 adults today, and 2) 94% exponential decline in occupancy area from 80,000 km 2 historically to 4400 km 2 today. Continuing major threats include: dams/barrages, water extraction/irrigation, river inter-linking, fishing net mortality, sand/boulder mining, and introduced species. Conservation actions have included captive breeding and head-starting in past decades, but now require smart, site-specific programs with local river communities to reduce multiple threats in-situ. Oral presentation (30 mn requested) : J.W. Lang is registered for, and attending the meeting.
The gharial (Gavialis gangeticus) is a Critically Endangered, river dwelling crocodylian, with a piscivorous diet, a specialized elongated and narrow snout, and a distinct phylogeny. The documented drastic decline (>90%) in the species'... more
The gharial (Gavialis gangeticus) is a Critically Endangered, river dwelling crocodylian, with a piscivorous diet, a specialized elongated and narrow snout, and a distinct phylogeny. The documented drastic decline (>90%) in the species' geographic range, as well as in its numberical abundance, are strongly suggestive of severe genetic bottleneck(s) in the recent history of the few extant populations today (~5; total adults=600-900). Ongoing ecological and behavioral studies of the largest remaining wild population of gharials, living in the Chambal River, north India, indicate that the gharials nest in large colonies. When nests at these sites hatch pre-monsoon, hatchlings remain together for 4-6 weeks in large creches (100-1000+ young) guarded by adults, typically multiple females and a single adult male. Detailed behavioral observations, supported by 24hr acoustic and still/video imagery, at these large creches, at multiple sites in successive years, have documented complex social interactions. These are frequent amongst creche members, and involve young-young, young-adult, and adult-adult interactions. Here we outline a strategy for genotyping the Chambal gharial population in order to 1) examine the underlying genetic bases for creche behaviors, 2) provide baseline " relatedness " values within and amongst gharial populations, 3) test the efficacy of using " Next-Generation Sequencing " (NGS) vs. conventional genotyping for such analyses, and 4) set the stage for scaling up " genetic " monitoring of all extant gharial populations. In 2017, we collected ~3000 eggshells and tissue samples from a subset of breeding adults, at nine colonial nesting sites along ~100 km of the lower Chambal River. As a " proof of concept " in the first instance, we are isolating DNA from samples from one large creche site (~34 nests), which likely contained eggs sired by 2-4+ males from nearby breeding sites. Microsatellite markers (18) will be screened, and polymerase chain reactions optimized, and the samples will be genotyped with 15 markers via NGS. To assign clutch parentage, adult profiles will be matched to egg profiles, clutchwise. Additionally, capillary electrophoresis based genotype data of a small sample of egg shells from each nest will be calibrated along with few complete nests. The number of adult males and females will be estimated using a double sampling approach. The use of NGS over conventional method of genotyping with double sampling approach will be evaluated for cost effectiveness for the accuracy and precision of population inferences. This is an interim report of progress to date.
Living crocodilians communicate using visual, acoustic, chemical, and/or tactile signals. As adults, gharials (Gavialis gangeticus) vocalize only rarely, and reportedly do not produce infrasound. Ongoing ecological and behavioral studies... more
Living crocodilians communicate using visual, acoustic, chemical, and/or tactile signals. As adults, gharials (Gavialis gangeticus) vocalize only rarely, and reportedly do not produce infrasound. Ongoing ecological and behavioral studies of the largest remaining wild population of gharials, living in the Chambal River, north India, indicate that gharials breed at well defined arenas established by dominant males, and then reproductive females assemble and nest in large colonies nearby. Detailed behavioral observations, supported by 24hr acoustic and still/video imagery, at breeding and nesting sites, at multiple locations in successive years, have documented complex social interactions, including acoustic signaling between and amongst adults, as well as young. Male gharial produce an explosive, concussive " pop " sound underwater, in 1-3 short, loud audible bursts. A " pop " is always sudden and high volume, resembling a stoppered bottle being opened rapidly, like a wine bottle being uncorked. We used hydrophones and aerial mics, to record the " pop " signals of 15+ male gharial, totaling in excess of 500 samples. Spontaneous recordings were obtained as gharials behaved normally under natural conditions. At one site frequented by a breeding male, with few females (<10 in 2017) vs. many (>30 in 2018), " recruiting " pops directed at females predominated in 2017, whereas " challenging " pops were frequent in 2018, when other males were present. In 2018, at this site, overall pop frequency more than doubled, relative to 2017. During hatching and afterwards (~4-6 wks), at each crèche site, a guardian male " pops " often to 1) alert and recruit hatchlings, and 2) announce his presence and location to females in the vicinity of the creche. Each male gharial produces a stereoptypic and characteristic series of " pops, " performed underwater, and consisting of 1, 2, or 3 pops. Temporal patterning, rather than frequency differences, appears to be the primary feature of this unique signal, not known in other crocodilians, that presumably facilitates individual recognition. The " pop " or syllable duration ranged from 0.013 to 0.023 seconds, and the time interval between syllables ranged from 0.103 to 0.555 seconds. Distinctive low and high frequencies were characteristic of each pop, ranging from >100-2400 Hz to >10,000-22,000 Hz. Immediately preceding a pop, infrasound is produced. Signal analyses: Raven Pro & Avisoft software. This is an interim progress report for 2017-18.
This is a general audience story commissioned by the BBC WILDLIFE magazine which features images taken by Dhritiman M. at Kasaua, one of our study sites during the 2017 hatching period.
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In certain reptiles with temperature-dependent sex determination (TSD), estrogens act as a signal for female differentiation. Because aromatase produces estrogens from androgens, this enzyme plays a pivotal role in TSD. Whether androgens... more
In certain reptiles with temperature-dependent sex determination (TSD), estrogens act as a signal for female differentiation. Because aromatase produces estrogens from androgens, this enzyme plays a pivotal role in TSD. Whether androgens act as the signal for male differentiation in TSD species in not yet clear. We manipulated the hormonal environment in eggs of the common snapping turtle (Chelydra serpentina) to determine the effects of an estrogen (estradiol 17-beta), an aromatase inhibitor (fadrozole; CGS 16949A), and androgens (testosterone and dihydrotestosterone) on sex determination in this TSD species. Test solutions were applied topically to representative eggs (total tested = 1054 from 27 clutches) and incubated at two male-producing temperatures (24 and 26.5 degrees) and at a predominantly female-producing temperature (29 degrees). In this species, application of an estrogen induced female development at all temperatures tested. In contrast, the aromatase inhibitor had no effect at the male-producing temperatures, but induced male development at the predominantly female-producing temperature. At this temperature, aromatase inhibitor plus testosterone had a similar male-producing effect, but when applied alone, testosterone failed to augment male production. Dihydrotestosterone had a similar effect, in contrast to its reported androgenic effects in other TSD species. In the snapping turtle, male differentiation may not be androgen dependent; rather, it may proceed in the absence of female differentiation. In this species, female development is clearly estrogen-dependent and is altered by aromatase inhibition at female-producing temperatures. Our results not only provide additional evidence that sex steroids mediate gonadal differentiation in TSD species, but also suggest caution with respect to generalizations about the proximal mechanisms of TSD in reptiles.
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Ambient temperatures during embryonic development determine gonadal sex in many reptiles. The temperature sensitive period for sex determination has been defined by shifting eggs between female- and male-producing temperatures in a few... more
Ambient temperatures during embryonic development determine gonadal sex in many reptiles. The temperature sensitive period for sex determination has been defined by shifting eggs between female- and male-producing temperatures in a few species. This phase spans 20-35% of embryogenesis in most species, which makes it difficult to define the mechanisms that transduce temperature into a signal for ovarian versus testicular development. We present an extensive set of studies that define a brief period when high temperature specifies, and then determines, ovarian fate in a northern population of snapping turtles, Chelydra serpentina. We shifted embryos from male to female temperatures, or vice versa, at various stages of development. Gonads in embryos incubated at female temperatures commit to ovarian fate earlier (by stage 18) than gonads in embryos incubated at male temperatures commit to testicular fate (by stages 19-21). In double shift studies, embryos were incubated at a female temperature, exposed to a male temperature for set times, and shifted back to the original temperature, or vice versa. The time required to induce ovarian development (≤6 days at female temperatures) was much shorter than the time required to induce testicular formation (&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;20 days at male temperatures). Differentiation of the gonads at the histological level occurred after the sex-determining period. Nevertheless, we found that a change in temperature rapidly (within 24h) influenced expression and splicing of WT1 mRNA: the absolute abundance of WT1 mRNA, the relative abundance of +KTS versus -KTS isoforms, as well as the ratio of +KTS:-KTS isoforms was higher in gonads at a male versus a female temperature. In conclusion, ovarian fate is more readily determined than testicular fate in snapping turtle embryos. The short sex-determining period in this species (6-8% of embryogenesis) will facilitate studies of molecular mechanisms for specification and determination of gonad fate by temperature.
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Page 1. OIKOS 86: 311-319. Copenhagen 1999 Incubation temperature and sex affect mass and energy reserves of hatchling snapping turtles, Chelydra serpentina Turk Rhen and Jeffrey W. Lang Rhen, T. and Lang, JW 1999. ...
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... Off-spring size is also positively correlated with maternal body size in other species of Tham-... We anticipate that small females produce smaller, predominately female young whereas large fe-males produce larger, predominately male... more
... Off-spring size is also positively correlated with maternal body size in other species of Tham-... We anticipate that small females produce smaller, predominately female young whereas large fe-males produce larger, predominately male young. ... CREWS, D., AND W. GARSTKA. ...
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... Sex-reversed individuals appear to have normal sex steroid profiles of T and Ez, both at basal levels and in response to ... macroscopically us-ing a dissecting microscope (Yntema, &amp;#x27;76) and also examined microscopically... more
... Sex-reversed individuals appear to have normal sex steroid profiles of T and Ez, both at basal levels and in response to ... macroscopically us-ing a dissecting microscope (Yntema, &amp;#x27;76) and also examined microscopically after histological prepa-ration (Lance and Bogart, &amp;#x27;92). ...
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Wild animals are captured or taken opportunistically, and the meat, body parts, and/or eggs are consumed for local subsistence or used for traditional purposes to some extent across most of the world, particularly in the tropics and... more
Wild animals are captured or taken opportunistically, and the meat, body parts, and/or eggs are consumed for local subsistence or used for traditional purposes to some extent across most of the world, particularly in the tropics and subtropics. The consumption of aquatic animals is widespread, in some places has been sustained for millennia, and can be an important source of nutrition, income, and cultural identity to communities. Yet, economic opportunities to exploit wildlife at higher levels have led to unsustainable exploitation of some species. In the literature, there has been limited focus on the exploitation of aquatic non-fish animals for food and other purposes. Understanding the scope and potential threat of aquatic wild meat exploitation is an important first step toward appropriate inclusion on the international policy and conservation management agenda. Here, we conduct a review of the literature, and present an overview of the contemporary use of aquatic megafauna (ce...
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The gharial (Gavialis gangeticus Gmelin) is a fish-eating specialist crocodylian, endemic to south Asia, and critically endangered in its few remaining wild localities. A secondary gharial population resides in riverine-reservoir habitat... more
The gharial (Gavialis gangeticus Gmelin) is a fish-eating specialist crocodylian, endemic to south Asia, and critically endangered in its few remaining wild localities. A secondary gharial population resides in riverine-reservoir habitat adjacent to the Nepal border, within the Katerniaghat Wildlife Sanctuary (KWS), and nests along a 10 km riverbank of the Girwa River. A natural channel shift in the mainstream Karnali River (upstream in Nepal) has reduced seasonal flow in the Girwa stretch where gharials nest, coincident with a gradual loss of nest sites, which in turn was related to an overall shift to woody vegetation at these sites. To understand how these changes in riparian vegetation on riverbanks were related to gharial nesting, we sampled vegetation at these sites from 2017 to 2019, and derived an Enhanced Vegetation Index (EVI) from LANDSAT 8 satellite data to quantify riverside vegetation from 1988 through 2019. We found that sampled sites transitioned to woody cover, the ...
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In Minnesota, the small lizard Eumeces septentrionalis oviposits 6-14 eggs in a subterranean nest; she remains in contact with her eggs (=brooding) for 3-6 weeks. In natural nests, ambient temperatures range from &lt;20 to &gt;45... more
In Minnesota, the small lizard Eumeces septentrionalis oviposits 6-14 eggs in a subterranean nest; she remains in contact with her eggs (=brooding) for 3-6 weeks. In natural nests, ambient temperatures range from &lt;20 to &gt;45 C. Relocations of eggs within nest cavities, tunnels, and trackways correspond to daily thermal cycles. In experimental terraria with thermal gradients but uniform soil moisture, gravid females (N=30) selected nest sites near heat sources. Each individual excavated a cavity, laid eggs, and brooded them. When the heat source was moved, the parent repeatedly moved her eggs 10-50 cm to &quot;new&quot; thermal locations that favored rapid embryonic development (28-32C). When heat intensity was increased or decreased, females shifted eggs away from or towards heat source over short distances (&lt;10 cm) by sinuous body movements within hours. In this study, brooding behavior clearly had a thermoregulatory function. The resultant warm temperatures accelerated development and hatching by days. [videotape; NSF supported]
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Abstract. We compared the spatial biology of Blanding's turtle (Emydoidea blandingii) in typical and highly disturbed habitats in the Weaver Dunes area of Wabasha County, Minnesota. The typical habitat (Old Zumbro River Wetlands) is a... more
Abstract. We compared the spatial biology of Blanding's turtle (Emydoidea blandingii) in typical and highly disturbed habitats in the Weaver Dunes area of Wabasha County, Minnesota. The typical habitat (Old Zumbro River Wetlands) is a large area of riparian forest with open shallow wetlands containing emergent vegetation, whereas the highly disturbed area (Weaver Bottoms) is a large shallow wetland that was previously vegetated but at the time of this study was mostly open water. Between 15 April 1999 and 1 April 2000, we used radiotelemetry to determine the distance and rate of movements of 35 adult turtles (23 females, 12 males). We used ArcView GIS to examine movements, activity areas, and home ranges of 16 females and 8 males with the most complete records. During the activity season, males made more and shorter-distance movements and had more activity areas (mean = 3.13, standard error = 0.40) than did females (mean = 1.75, standard error = 0.19), although females made longer overland movements typically associated with nesting. Mean home range estimates, calculated using the minimum convex polygon, bivariate normal density kernel, and poly-buff methods, averaged 91.59 ha (standard error = 29.95) for males and 46.0 ha (standard error = 7.40) for females. Poly-buff home ranges of adults in Old Zumbro River Wetlands were significantly smaller than in Weaver Bottoms. Average home ranges of adults at Old Zumbro River Wetlands were typical of Blanding's turtles and home ranges reported at other locations across their range, whereas the average home ranges of adults at Weaver Bottoms were approximately 7 times larger than that found in Old Zumbro River Wetlands and larger than reported for any other population of Blanding's turtles. The large home ranges at Weaver Bottoms were associated with expanses of open water and fragmented vegetated areas, which suggests that the maintenance of or even an increase in emergent vegetation in the Weaver Bottoms is important for the long-term stability of the Blanding's turtle population at the Weaver Dunes area.
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Egg inundation often results in poor hatching success in crocodylians. However, how tolerant eggs are to submergence, and/or how eggshell ultrastructure may affect embryo survival when inundated, are not well understood. In this study,... more
Egg inundation often results in poor hatching success in crocodylians. However, how tolerant eggs are to submergence, and/or how eggshell ultrastructure may affect embryo survival when inundated, are not well understood. In this study, our objective was to determine if embryo survival in Caiman latirostris is affected by eggshell surface roughness, when eggs are submerged under water. Tolerance to inundation was tested early (day 30) versus late (day 60) in development, using eight clutches (four per time treatments), subdivided into four groups: (N = 9 per clutch per treatment; 9 × 4 = 36 eggs per group). 'Rough' eggshell represented the natural, unmodified eggshell surface structure. 'Smooth' eggshell surface structure was created by mechanically sanding the natural rough surface to remove surface columnar elements and secondary layer features, e.g. irregularities that result in 'roughness'. When inundated by submerging eggs under water for 10 h at day 30, ...
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Abstract Over half of all crocodylians are threatened with extinction, with many species considered to be functionally extinct throughout their historical ranges. How such losses impact crocodylian functional diversity (FD) and its... more
Abstract
Over half of all crocodylians are threatened with extinction, with many species considered to be functionally extinct throughout their historical ranges. How such losses impact crocodylian functional diversity (FD) and its conservation is poorly understood, but can be investigated using measurable traits. Where such information is unavailable, phylogenetic diversity (PD) has been proposed as an effective strategy to capture FD, but this assumption is not well tested.
We constructed a global trait database for 28 extant crocodylians, and quantified their FD, distinctiveness and groupings. Functionally distinctive crocodylians include the most and least evolutionarily distinct species, likely because unusual trait values and combinations can be produced by both evolutionary isolation and evolutionarily recent adaptive radiation. We identified four functional groups of crocodylians, within which species have similar ecological roles. Highly distinctive species, such as the gharial, fit less well into functional groups.
We combined functional distinctiveness (FUD) and threat ranking scores to prioritise species for conservation. The metric is termed Ecologically Distinct and Globally Endangered (EcoDGE), and we tested how well it operates to preserve crocodylian FD among extant Crocodylia. Under current extinction scenarios, 32%–38% of crocodylian FD might be lost within 100 years. Losses increase to 48% if all threatened species go extinct, with Asia identified as a hotspot of threatened FD in crocodylians. Highly threatened distinctive species lead this extinction scenario, exacerbated by clusters of species sharing traits linked to high extinction risk. These traits include habitat specialism and lower reproductive investment; in contrast, species that tolerate climate extremes are more resilient.
Prioritising at-risk species based on FUD and threat status appears to be an effective way to conserve present-day crocodylian diversity. Conservation prioritisation based on the EcoDGE metric performed well to minimise projected losses in FD. Among extant crocodylians, FD losses are projected when high diversity overlaps with high extrinsic threats.
We then examined the utility of PD-based measures as surrogates for FD conservation, to better understand the advantages and drawbacks of such substitutions. A PD-based measure such as the Evolutionarily Distinct and Globally Endangered metric provided an effective tool to capture FD in our tests.
Over half of all crocodylians are threatened with extinction, with many species considered to be functionally extinct throughout their historical ranges. How such losses impact crocodylian functional diversity (FD) and its conservation is poorly understood, but can be investigated using measurable traits. Where such information is unavailable, phylogenetic diversity (PD) has been proposed as an effective strategy to capture FD, but this assumption is not well tested.
We constructed a global trait database for 28 extant crocodylians, and quantified their FD, distinctiveness and groupings. Functionally distinctive crocodylians include the most and least evolutionarily distinct species, likely because unusual trait values and combinations can be produced by both evolutionary isolation and evolutionarily recent adaptive radiation. We identified four functional groups of crocodylians, within which species have similar ecological roles. Highly distinctive species, such as the gharial, fit less well into functional groups.
We combined functional distinctiveness (FUD) and threat ranking scores to prioritise species for conservation. The metric is termed Ecologically Distinct and Globally Endangered (EcoDGE), and we tested how well it operates to preserve crocodylian FD among extant Crocodylia. Under current extinction scenarios, 32%–38% of crocodylian FD might be lost within 100 years. Losses increase to 48% if all threatened species go extinct, with Asia identified as a hotspot of threatened FD in crocodylians. Highly threatened distinctive species lead this extinction scenario, exacerbated by clusters of species sharing traits linked to high extinction risk. These traits include habitat specialism and lower reproductive investment; in contrast, species that tolerate climate extremes are more resilient.
Prioritising at-risk species based on FUD and threat status appears to be an effective way to conserve present-day crocodylian diversity. Conservation prioritisation based on the EcoDGE metric performed well to minimise projected losses in FD. Among extant crocodylians, FD losses are projected when high diversity overlaps with high extrinsic threats.
We then examined the utility of PD-based measures as surrogates for FD conservation, to better understand the advantages and drawbacks of such substitutions. A PD-based measure such as the Evolutionarily Distinct and Globally Endangered metric provided an effective tool to capture FD in our tests.
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The gharial (Gavialis gangeticus Gmelin) is a fish-eating specialist crocodylian, endemic to south Asia, and critically endangered in its few remaining wild localities. A secondary gharial population resides in riverine-reservoir habitat... more
The gharial (Gavialis gangeticus Gmelin) is a fish-eating specialist crocodylian, endemic to south Asia, and critically endangered in its few remaining wild localities. A secondary gharial population resides in riverine-reservoir habitat adjacent to the Nepal border, within the Katerniaghat Wildlife Sanctuary (KWS), and nests along a 10 km riverbank of the Girwa River. A natural channel shift in the mainstream Karnali River (upstream in Nepal) has reduced seasonal flow in the Girwa stretch where gharials nest, coincident with a gradual loss of nest sites, which in turn was related to an overall shift to woody vegetation at these sites. To understand how these changes in riparian vegetation on riverbanks were related to gharial nesting, we sampled vegetation at these sites from 2017 to 2019, and derived an Enhanced Vegetation Index (EVI) from LANDSAT 8 satellite data to quantify riverside vegetation from 1988 through 2019. We found that sampled sites transitioned to woody cover, the ...
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Page 1. Herpetologica, 51(3), 1995, 314-325 X 1995 by The Herpetologists&amp;amp;#x27; League, Inc. SEXUAL DIMORPHISM IN THE GENITAL MORPHOLOGY OF YOUNG AMERICAN ALLIGATORS, ALLIGATOR MISSISSIPPIENSIS JOHN ...
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The gharial (Gavialis gangeticus Gmelin) is a fish-eating specialist crocodylian, endemic to south Asia, and critically endangered in its few remaining wild localities. A secondary gharial population resides in riverine-reservoir habitat... more
The gharial (Gavialis gangeticus Gmelin) is a fish-eating specialist crocodylian, endemic to south Asia, and critically endangered in its few remaining wild localities. A secondary gharial population resides in riverine-reservoir habitat adjacent to the Nepal border, within the Katerniaghat Wildlife Sanctuary (KWS), and nests along a 10 km riverbank of the Girwa River. A natural channel shift in the mainstream Karnali River (upstream in Nepal) has reduced seasonal flow in the Girwa stretch where gharials nest, coincident with a gradual loss of nest sites, which in turn was related to an overall shift to woody vegetation at these sites. To understand how these changes in riparian vegetation on riverbanks were related to gharial nesting, we sampled vegetation at these sites from 2017 to 2019, and derived an Enhanced Vegetation Index (EVI) from LANDSAT 8 satellite data to quantify riverside vegetation from 1988 through 2019. We found that sampled sites transitioned to woody cover, the number of nesting sites declined, and the number of nests were reduced by > 40%. At these sites, after the channel shift, woody vegetation replaced open sites that predominated prior to the channel shift. Our findings indicate that the lack of open riverbanks and the increase in woody vegetation at potential nesting sites threatens the reproductive success of the KWS gharial population. This population persists today in a regulated river ecosystem, and nests in an altered riparian habitat which appears to be increasingly unsuitable for the continued successful recruitment of breeding adults. This second-ranking, critically endangered remnant population may have incurred an "extinction debt" by living in a reservoir that will lead to its eventual extirpation. Freshwater habitats occupy less than one percent of the Earth's surface, yet a tenth of all known species inhabit these areas, including a third of all vertebrate species 1. Intense human pressures threaten the rich biodiversity in freshwater environments worldwide 2,3 , particularly the megafauna species which are at greater risk of declines and extinctions, than their smaller taxonomic counterparts 4. The main threats include overexploitation, dam construction, habitat degradation, pollution and species invasion 5. For example, dams not only interrupt river channel connectivity, but also have profound effects on riverine landscapes 6,7. The major driver or grand struc-turing factor of river ecosystems is the natural flow regime, pulsating seasonally with floods and droughts 8-10. River studies, firmly grounded in landscape-level perspectives 11,12 , are increasingly focused on dynamic models and management strategies that help predict restoration outcomes 13-16. For river-adapted habitat specialists, threats associated with loss of channel connectivity, altered flow regimes, and water extraction schemes are often direct and immediate and include increased harvest, restricted foraging opportunities, or loss of aquatic habitats. If the resultant impacts of these freshwater infrastructures, such as dams and irrigation canals, remain unaddressed, they can lead to species' reductions, fragmentations, local extirpations (e.g., Indus River dolphins 17), and regional extinctions (e.g., gharial in the Indus 18). Spatially, freshwater megafauna show the largest range contractions, approaching 99%, in the Indomalaya realm, higher than other regions 19. Natural flood events can result in channel shifts altering river discharge dynamics, and ultimately affect species composition, distribution and abundance. A recent example occurred within the Karnali River basin, the third largest riverine system originating in Nepal and flowing into India. In 2010, after monsoon floods, the active OPEN
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ABSTRACT. –We compared the spatial biology of Blanding’s turtle (Emydoidea blandingii) in highly disturbed habitats in the Weaver Dunes area of Wabasha County, Minnesota. The typical habitat (Old Zumbro River Wetlands) is a large area of... more
ABSTRACT. –We compared the spatial biology of Blanding’s turtle (Emydoidea blandingii) in highly disturbed habitats in the Weaver Dunes area of Wabasha County, Minnesota. The typical habitat (Old Zumbro River Wetlands) is a large area of riparian forest with open shallow wetlands containing emergent vegetation, whereas the highly disturbed area (Weaver Bottoms) is a large shallow wetland that was previously vegetated but at the time of this study was mostly open water. Between 15 April 1999 and 1 April 2000, we used radiotelemetry to determine the distance and rate of movements of 35 adult turtles (23 females, 12 males). We used ArcView GIS to examine movements, activity areas, and home ranges of 16 females and 8 males with the most complete records. During the activity season, males made more and shorter-distance movements and had more activity areas (mean = 3.13, standard error = 0.40) than did females (mean = 1.75, standard error = 0.19), although females made longer overland movements typically associated
with nesting. Mean home range estimates, calculated using the minimum convex polygon, bivariate normal density kernel, and poly-buff methods, averaged 91.59 ha (standard error = 29.95) for males and 46.0 ha (standard error = 7.40) for females. Poly-buff home ranges of adults in Old Zumbro River Wetlands were significantly smaller than in Weaver Bottoms. Average home ranges of adults at Old Zumbro River Wetlands were typical of Blanding’s turtles and home ranges reported at other locations across their range, whereas the average home ranges
of adults at Weaver Bottoms were approximately 7 times larger than that found in Old Zumbro River Wetlands and larger than reported for any other population of Blanding’s turtles. The large home ranges at Weaver Bottoms were associated with expanses of open water and fragmented
vegetated areas, which suggests that the maintenance of or even an increase in emergent vegetation in the Weaver Bottoms is important for the long-term stability of the Blanding’s turtle population at the Weaver Dunes area.
with nesting. Mean home range estimates, calculated using the minimum convex polygon, bivariate normal density kernel, and poly-buff methods, averaged 91.59 ha (standard error = 29.95) for males and 46.0 ha (standard error = 7.40) for females. Poly-buff home ranges of adults in Old Zumbro River Wetlands were significantly smaller than in Weaver Bottoms. Average home ranges of adults at Old Zumbro River Wetlands were typical of Blanding’s turtles and home ranges reported at other locations across their range, whereas the average home ranges
of adults at Weaver Bottoms were approximately 7 times larger than that found in Old Zumbro River Wetlands and larger than reported for any other population of Blanding’s turtles. The large home ranges at Weaver Bottoms were associated with expanses of open water and fragmented
vegetated areas, which suggests that the maintenance of or even an increase in emergent vegetation in the Weaver Bottoms is important for the long-term stability of the Blanding’s turtle population at the Weaver Dunes area.
JUSTIFICATION Gharial were historically distributed throughout the major channels of the Indus, Ganges, Mahanadi, Brahmaputra-Meghna and possibly Irrawaddy drainages, to elevations of <500 m, an estimated combined linear river distance of... more
JUSTIFICATION
Gharial were historically distributed throughout the major channels of the Indus, Ganges, Mahanadi, Brahmaputra-Meghna and possibly Irrawaddy drainages, to elevations of <500 m, an estimated combined linear river distance of >20,000 km, or an historic occupancy area of 80,000 km² (using Red List standard 4 km² resolution). The species is currently extirpated from the Indus, Irrawaddy and most rivers and tributaries of the Ganges and Brahmaputra-Meghna systems, but persists in fourteen sites within the Ganges drainage (6 major and 8 minor), with confirmed breeding at only five locations (Table 1 in the Supplementary Information).
Surveys and counts in 2010-2017 indicate an adult global metapopulation conservatively estimated at 650 (median) with a range of 300-900. The largest and most populous location, the protected National Chambal Sanctuary in north India, spans 625 river km, with approximately 500 mature adults, comprising 77% of the global total, producing >410 nests annually, or >86% of the global total. Five other locations reporting breeding are small and highly disturbed. The remaining 8 minor locations together contain less than 10% of the world population (<50 mature adults), with no recent breeding. During the next decade, gharial will likely be extirpated from some of the minor/non-breeding sites, including three sanctuaries in India designed for their protection (Son, Ken, Satkosia Gorge), as well as the Padma-Jamuna, Brahmaputra-Meghna, and Bhagirathi-Hooghly drainages, based on the infrequent sightings in these regions.
Generation time is estimated at 25 years giving a period of decline of 75 years or since 1943. Cause of declines have been principally dams and barrages disrupting river hydrology, mortality in fishing nets, and historically, unregulated hide-hunting. Current serious threats include major water control and extraction activities, mortality in fishing gear, and increased anthropogenic river-bank disruptions, especially sand mining and boulder removal. These threats are known, continuing and not reversible, therefore criterion A2 applies. The expansion of threats and major declines have intensified since the 1950s, and continue presently with increasing demand for river resources.
Past population levels are inferred to be >20,000 adult gharial globally. Calculating across the range of current and past population estimates, exponential declines are 94% or greater. Even a very conservative calculation of 5,000 in 1943 and 1,000 currently gives a decline of 80%. Decline in 3 generations is confidently inferred to exceed the criterion A2bc 80% for Critically Endangered.
Toxins/pollutants were strongly suspected to play a role in the death of >110 gharial in the size range of 2-4m during the winter of 2008-2009 on the lower Chambal (Whitaker et al. 2008), and possibly the loss of additional gharial in 2012 (<10-15 individuals; Nair et al. 2013). This initial major loss suggested a species-specific sensitivity to whatever caused the deaths, which were localized geographically, most occurring rapidly within 2-15 weeks. These deaths were related to articular and visceral gout, related to kidney failure, associated with low ambient temperatures. Despite the absence of a re-occurrence, the susceptibility of gharial to whatever resulted in gout in the first instance warrants the application of criterion A2e.
Extent of occurrence (EOO) exceeded 80,000km² historically. Area of occupancy (AOO) is generously estimated for the six major locations with sizeable resident populations at 4,400 km², a reduction of 94%.
A population estimate of 300-900 mature individuals meets criterion C1 for Endangered if we infer that the decline is continuing at a rate of at least 20% in two generations/50 years i.e. since 1967. Gharial meets criterion D1 Vulnerable (population size <1,000 mature individuals). The species does not meet criteria E.
Gharial were historically distributed throughout the major channels of the Indus, Ganges, Mahanadi, Brahmaputra-Meghna and possibly Irrawaddy drainages, to elevations of <500 m, an estimated combined linear river distance of >20,000 km, or an historic occupancy area of 80,000 km² (using Red List standard 4 km² resolution). The species is currently extirpated from the Indus, Irrawaddy and most rivers and tributaries of the Ganges and Brahmaputra-Meghna systems, but persists in fourteen sites within the Ganges drainage (6 major and 8 minor), with confirmed breeding at only five locations (Table 1 in the Supplementary Information).
Surveys and counts in 2010-2017 indicate an adult global metapopulation conservatively estimated at 650 (median) with a range of 300-900. The largest and most populous location, the protected National Chambal Sanctuary in north India, spans 625 river km, with approximately 500 mature adults, comprising 77% of the global total, producing >410 nests annually, or >86% of the global total. Five other locations reporting breeding are small and highly disturbed. The remaining 8 minor locations together contain less than 10% of the world population (<50 mature adults), with no recent breeding. During the next decade, gharial will likely be extirpated from some of the minor/non-breeding sites, including three sanctuaries in India designed for their protection (Son, Ken, Satkosia Gorge), as well as the Padma-Jamuna, Brahmaputra-Meghna, and Bhagirathi-Hooghly drainages, based on the infrequent sightings in these regions.
Generation time is estimated at 25 years giving a period of decline of 75 years or since 1943. Cause of declines have been principally dams and barrages disrupting river hydrology, mortality in fishing nets, and historically, unregulated hide-hunting. Current serious threats include major water control and extraction activities, mortality in fishing gear, and increased anthropogenic river-bank disruptions, especially sand mining and boulder removal. These threats are known, continuing and not reversible, therefore criterion A2 applies. The expansion of threats and major declines have intensified since the 1950s, and continue presently with increasing demand for river resources.
Past population levels are inferred to be >20,000 adult gharial globally. Calculating across the range of current and past population estimates, exponential declines are 94% or greater. Even a very conservative calculation of 5,000 in 1943 and 1,000 currently gives a decline of 80%. Decline in 3 generations is confidently inferred to exceed the criterion A2bc 80% for Critically Endangered.
Toxins/pollutants were strongly suspected to play a role in the death of >110 gharial in the size range of 2-4m during the winter of 2008-2009 on the lower Chambal (Whitaker et al. 2008), and possibly the loss of additional gharial in 2012 (<10-15 individuals; Nair et al. 2013). This initial major loss suggested a species-specific sensitivity to whatever caused the deaths, which were localized geographically, most occurring rapidly within 2-15 weeks. These deaths were related to articular and visceral gout, related to kidney failure, associated with low ambient temperatures. Despite the absence of a re-occurrence, the susceptibility of gharial to whatever resulted in gout in the first instance warrants the application of criterion A2e.
Extent of occurrence (EOO) exceeded 80,000km² historically. Area of occupancy (AOO) is generously estimated for the six major locations with sizeable resident populations at 4,400 km², a reduction of 94%.
A population estimate of 300-900 mature individuals meets criterion C1 for Endangered if we infer that the decline is continuing at a rate of at least 20% in two generations/50 years i.e. since 1967. Gharial meets criterion D1 Vulnerable (population size <1,000 mature individuals). The species does not meet criteria E.
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Egg inundation often results in poor hatching success in crocodylians. However, how tolerant eggs are to submergence, and/or how eggshell ultrastructure may affect embryo survival when inundated, are not well understood. In this study,... more
Egg inundation often results in poor hatching success in crocodylians. However, how tolerant eggs are to submergence, and/or how eggshell
ultrastructure may affect embryo survival when inundated, are not well
understood. In this study, our objective was to determine if embryo survival
in Caiman latirostris is affected by eggshell surface roughness, when eggs are submerged under water. Tolerance to inundation was tested early (day 30) versus late (day 60) in development, using eight clutches (four per time
treatments), subdivided into four groups: (N ¼ 9 per clutch per treatment;
9 4 ¼ 36 eggs per group). ‘Rough’ eggshell represented the natural, unmodified eggshell surface structure. ‘Smooth’ eggshell surface structure was created by mechanically sanding the natural rough surface to remove surface columnar elements and secondary layer features, e.g. irregularities that result in ‘roughness’. When inundated by submerging eggs under water
for 10 h at day 30, ‘smooth’ eggshell structure resulted in more than twice
as many dead embryos (16 versus 6, smooth versus rough; N ¼ 36), and
fewer than half as many healthy embryos (6 versus 13, smooth versus
rough, respectively; N ¼ 36). By contrast, at day 60, inundation resulted in
very low hatching success, regardless of eggshell surface structure. Only
two hatchlings survived the inundation, notably in the untreated group
with intact, rough eggshells. Inundation produced a high rate of malformations (58% at day 30), but did not affect hatchling size. Our results
indicate that eggshell roughness enhances embryo survival when eggs are
inundated early in development, but not late in development. Apparently,
the natural surface ‘roughness’ entraps air bubbles at the eggshell surface
during inundation, thereby facilitating gas exchange through the eggshell
even when the egg is submerged under water.
ultrastructure may affect embryo survival when inundated, are not well
understood. In this study, our objective was to determine if embryo survival
in Caiman latirostris is affected by eggshell surface roughness, when eggs are submerged under water. Tolerance to inundation was tested early (day 30) versus late (day 60) in development, using eight clutches (four per time
treatments), subdivided into four groups: (N ¼ 9 per clutch per treatment;
9 4 ¼ 36 eggs per group). ‘Rough’ eggshell represented the natural, unmodified eggshell surface structure. ‘Smooth’ eggshell surface structure was created by mechanically sanding the natural rough surface to remove surface columnar elements and secondary layer features, e.g. irregularities that result in ‘roughness’. When inundated by submerging eggs under water
for 10 h at day 30, ‘smooth’ eggshell structure resulted in more than twice
as many dead embryos (16 versus 6, smooth versus rough; N ¼ 36), and
fewer than half as many healthy embryos (6 versus 13, smooth versus
rough, respectively; N ¼ 36). By contrast, at day 60, inundation resulted in
very low hatching success, regardless of eggshell surface structure. Only
two hatchlings survived the inundation, notably in the untreated group
with intact, rough eggshells. Inundation produced a high rate of malformations (58% at day 30), but did not affect hatchling size. Our results
indicate that eggshell roughness enhances embryo survival when eggs are
inundated early in development, but not late in development. Apparently,
the natural surface ‘roughness’ entraps air bubbles at the eggshell surface
during inundation, thereby facilitating gas exchange through the eggshell
even when the egg is submerged under water.
The Gharial Ecology Project (GEP) is now in its 15th field season (2022), since its initiation in 2008, following the mass die-off of Gharial (Gavialis gangeticus) in the winter of 2007-08. Our research, supported by the international zoo... more
The Gharial Ecology Project (GEP) is now in its 15th field season (2022), since its initiation in 2008, following the mass die-off of Gharial (Gavialis gangeticus) in the winter of 2007-08. Our research, supported by the international zoo community and private donations, is sanctioned under the NGO umbrella of the Madras Crocodile Bank Trust (MCBT). The GEP programs are facilitated by the State Forest Departments of Uttar Pradesh, Madhya Pradesh, and Rajasthan, as well as the Ministry of Environment, Forests, and Climate Change, Government of India. The GEP is the present day avatar of the Gharial Conservation Alliance, and our media presence has increased through active Facebook and Instagram pages, a dedicated YouTube Channel, and soon to be inaugurated new website, now under construction. What follows is a brief summary of recent activities, updating Lang et al. (2018, 2021).
Assessment Rationale Reasons for Change Reason(s) for Change in Red List Category from the Previous Assessment: Status is unchanged, but the criteria have been modified based on recent information by removing criterion C1 and adding... more
Assessment Rationale Reasons for Change Reason(s) for Change in Red List Category from the Previous Assessment: Status is unchanged, but the criteria have been modified based on recent information by removing criterion C1 and adding criterion A2e. This species is the sole living representative of the family Gavialidae, which represents an ancient third lineage in the order Crocodylia (in addition to Alligatoridae and Crocodylidae). Therefore, gharial extinction would eliminate the only remaining representative of an Archosaur group related to birds and dinosaurs.
Figures to accompany Gharial Ecology Project Progress Report 2020-2021
The Gharial Ecology Project (GEP) is now in its 15th field season (2022), since its initiation in 2008, following the mass die-off of Gharial (Gavialis gangeticus) in the winter of 2007-08. Our research, supported by the international zoo... more
The Gharial Ecology Project (GEP) is now in its 15th field season (2022), since its initiation in 2008, following the mass die-off of Gharial (Gavialis gangeticus) in the winter of 2007-08. Our research, supported by the international zoo community and private donations, is sanctioned under the NGO umbrella of the Madras Crocodile Bank Trust (MCBT). The GEP programs are facilitated by the State Forest Departments of Uttar Pradesh, Madhya Pradesh, and Rajasthan, as well as the Ministry of Environment, Forests, and Climate Change, Government of India. The GEP is the present day avatar of the Gharial Conservation Alliance, and our media presence has increased through active Facebook and Instagram pages, a dedicated YouTube Channel, and soon to be inaugurated new website, now under construction. What follows is a brief summary of recent activities, updating Lang et al. (2018, 2021).
Research Interests:
Gharials produce a sudden, high amplitude, pulsatile, underwater sound, referred to as a POP. The gharial POP has durations ranging from 4 to 72 milliseconds, and is clearly audible on land and in water at ~ 200-500m distances. POPs were... more
Gharials produce a sudden, high amplitude, pulsatile, underwater sound, referred to as a POP. The gharial POP has durations ranging from 4 to 72 milliseconds, and is clearly audible on land and in water at ~ 200-500m distances. POPs were performed only underwater by adult males possessing a sex-specific, cartilaginous narial excrescence, the ghara. Adult males produce single, double, or triple POPs. We recorded 531 POP events for 9 wild adult males resident in 115 km stretch of the Chambal River during 2017-2019, using hydrophones and aerial mics. Here we present the acoustic features of the gharial POP signal. These include its incorporation as the initial component in a complex breathing display, its reliance on temporal rather than spectral elements, its dependence on a specific social context, its consistency within an individual, and its individually distinctive patterning specific to a particular male. The breathing display consisted of sub audible vibrations (SAV) preceding each underwater POP, then a stereotyped exhalation-inhalation-exhalation sequence, concluding typically with bubbling & submergence. Each POP signal was performed in a specific social setting. Four contexts were identified: ALERT, PATROL, MALE-MALE, MALE-FEMALE. In each context, male identities were examined using Discriminant Function Analysis (DFA) and Random Forest (RF) models. Within each context, all of the males exhibited individually distinctive POP patterns which were context-specific, as well as contextdependent. Two dominant males each showed 11 POP patterns, each one male-specific and context-specific. In our study, 96% of the total variation in POP signal parameters was explained by POP signal timings (92%) and number of POPs (4%), and only 2% was related to frequency (spectral) differences. POP signal features were stable for individual males, from one year to the next; extensive POP recordings (n=403) of a single male over 3 breeding seasons were consistent and nearly identical within contexts.
Gharials produce a sudden, high amplitude, pulsatile, underwater sound, referred to as a POP. The gharial POP has durations ranging from 4 to 72 milliseconds, and is clearly audible on land and in water at ~ 200-500m distances. POPs were... more
Gharials produce a sudden, high amplitude, pulsatile, underwater sound, referred to as a POP. The gharial POP has durations ranging from 4 to 72 milliseconds, and is clearly audible on land and in water at ~ 200-500m distances. POPs were performed only underwater by adult males possessing a sex-specific, cartilaginous narial excrescence, the ghara. Adult males produce single, double, or triple POPs. We recorded 531 POP events for 9 wild adult males resident in 115 km stretch of the Chambal River during 2017-2019, using hydrophones and aerial mics. Here we present the acoustic features of the gharial POP signal. These include its incorporation as the initial component in a complex breathing display, its reliance on temporal rather than spectral elements, its dependence on a specific social context, its consistency within an individual, and its individually distinctive patterning specific to a particular male. The breathing display consisted of sub audible vibrations (SAV) preceding each underwater POP, then a stereotyped exhalation-inhalation-exhalation sequence, concluding typically with bubbling & submergence. Each POP signal was performed in a specific social setting. Four contexts were identified: ALERT, PATROL, MALE-MALE, MALE-FEMALE. In each context, male identities were examined using Discriminant Function Analysis (DFA) and Random Forest (RF) models. Within each context, all of the males exhibited individually distinctive POP patterns which were context-specific, as well as contextdependent. Two dominant males each showed 11 POP patterns, each one male-specific and context-specific. In our study, 96% of the total variation in POP signal parameters was explained by POP signal timings (92%) and number of POPs (4%), and only 2% was related to frequency (spectral) differences. POP signal features were stable for individual males, from one year to the next; extensive POP recordings (n=403) of a single male over 3 breeding seasons were consistent and nearly identical within contexts.
Living crocodylians possess acute sensory capabilities, e.g., vision, audition, olfaction, gustation, and tactile sensation. In many species, multi-modal communication is common, particularly in intra-specific social interactions. To... more
Living crocodylians possess acute sensory capabilities, e.g., vision, audition, olfaction, gustation, and tactile sensation. In many species, multi-modal communication is common, particularly in intra-specific social interactions. To date, chemical signaling studies have been rudimentary and exploratory, and confined to sampling isolated captives, typically in zoos. We studied the chemical composition of gular (chin) and paracloacal (cloaca vent) glands, using secretory samples (flash frozen, liquid nitrogen) from 97 gharial, representing differing sizes-ages and sexes, and residing in upstream and downstream stretches (~348 km total) of National Chambal Sanctuary, India. Using gas chromotography mass spectrometry (GCMS), we identified 182 glandular compounds (gular and paracloacal). Using multi-variant analyses (Partial least-squares Discriminant Analyses=PLS-DA), we focused on 47 of 182 compounds based on presence/ absence. Significant differences were detected in size-age, sex, and river residence cohorts. Of these compounds, 21 were previously identified as putative pheromones, and 26 are phytochemicals. We observed clusters in PLS-DA analyses that clearly separated adult females vs. males on the bases of gular as well as paracloacal secretions; unique male-specific chemicals predominated in sex comparisons. This result suggests that sex-specific glandular products may facilitate communication amongst reproductively active gharial. In addition, within groups of adult males and females, upstream vs. downstream residence was a significant factor in discriminating between adult females as well as between adult males in the paracloacal secretions. Habitat-specific features in two regions sampled may account for observed within-sex differences due to location. In brief, this study provides an initial, comprehensive inventory of gharial chemo-signals, and suggests that these compounds may have functional roles as significant discriminatory elements in multi-modal communications. Management implications include both attractant as well as repellent possibilities, and also potential ways to enhance reproduction in rare, endangered populations/species. Future studies will likely reveal that chemo-signals are an understudied, but important component of crocodylian communication.
Gharials produce a sudden, high amplitude, pulsatile, underwater sound, referred to as a POP. The gharial POP has durations ranging from 4 to 72 milliseconds, and is clearly audible on land and in water at ~ 200-500m distances. POPs were... more
Gharials produce a sudden, high amplitude, pulsatile, underwater sound, referred to as a POP. The gharial POP has durations ranging from 4 to 72 milliseconds, and is clearly audible on land and in water at ~ 200-500m distances. POPs were performed only underwater by adult males possessing a sex-specific, cartilaginous narial excrescence, the ghara. Adult males produce single, double, or triple POPs. We recorded 531 POP events for 9 wild adult males resident in 115 km stretch of the Chambal River during 2017-2019, using hydrophones and aerial mics. Here we present the acoustic features of the gharial POP signal. These include its incorporation as the initial component in a complex breathing display, its reliance on temporal rather than spectral elements, its dependence on a specific social context, its consistency within an individual, and its individually distinctive patterning specific to a particular male. The breathing display consisted of sub audible vibrations (SAV) preceding each underwater POP, then a stereotyped exhalation-inhalation-exhalation sequence, concluding typically with bubbling & submergence. Each POP signal was performed in a specific social setting. Four contexts were identified: ALERT, PATROL, MALE-MALE, MALE-FEMALE. In each context, male identities were examined using Discriminant Function Analysis (DFA) and Random Forest (RF) models. Within each context, all of the males exhibited individually distinctive POP patterns which were context-specific, as well as contextdependent. Two dominant males each showed 11 POP patterns, each one male-specific and context-specific. In our study, 96% of the total variation in POP signal parameters was explained by POP signal timings (92%) and number of POPs (4%), and only 2% was related to frequency (spectral) differences. POP signal features were stable for individual males, from one year to the next; extensive POP recordings (n=403) of a single male over 3 breeding seasons were consistent and nearly identical within contexts.
In Minnesota, the small lizard Eumeces septentrionalis oviposits 6-14 eggs in a subterranean nest; she remains in contact with her eggs (=brooding) for 3-6 weeks. In natural nests, ambient temperatures range from <20 to >45 C.... more
In Minnesota, the small lizard Eumeces septentrionalis oviposits 6-14 eggs in a subterranean nest; she remains in contact with her eggs (=brooding) for 3-6 weeks. In natural nests, ambient temperatures range from <20 to >45 C. Relocations of eggs within nest cavities, tunnels, and trackways correspond to daily thermal cycles. In experimental terraria with thermal gradients but uniform soil moisture, gravid females (N=30) selected nest sites near heat sources. Each individual excavated a cavity, laid eggs, and brooded them. When the heat source was moved, the parent repeatedly moved her eggs 10-50 cm to "new" thermal locations that favored rapid embryonic development (28-32C). When heat intensity was increased or decreased, females shifted eggs away from or towards heat source over short distances (<10 cm) by sinuous body movements within hours. In this study, brooding behavior clearly had a thermoregulatory function. The resultant warm temperatures accelerated development and hatching by days. [videotape; NSF supported]
Research Interests:
The Gharial Ecology Project has continued to survey adults and nests of gharial, and extended surveying and tracking to the entire NCS, from Pali to Pachnada. At present, 1600+ gharial of all ages/sizes reside in the NCS, where 400-500... more
The Gharial Ecology Project has continued to survey adults and nests of gharial, and extended surveying and tracking to the entire NCS, from Pali to Pachnada. At present, 1600+ gharial of all ages/sizes reside in the NCS, where 400-500 females nest every year, and 100+ big ghara males maintain residences. Recent field studies have focused on the upstream segment where about one third of the gharial live and breed.