Videos by Jeffrey W . Lang
This video summarizes our research on the largest, self-sustaining wild population of gharial (Ga... more This video summarizes our research on the largest, self-sustaining wild population of gharial (Gavialis gangeticus) in the National Chambal Sanctuary, north India. The Gharial Ecology Project is a conservation-focused initiative of Madras Crocodile Bank Trust, its parent NGO. Since 2008, GEP has been studying ecology & natural history of the 1600+ resident gharial in the 425+ km stretch of the Chambal River and its tributaries. Now, we are concentrating on understanding how the upstream resident gharial utilize different riverine habitats, including rocky stretches traversed by the river, with rapids and waterfalls. Major threats to Chambal gharial are water extraction schemes, as well as extensive, industrial scale sand mining in recent years. Elaborate social behaviors amongst gharials of all ages, colonial nesting, and large creches guarded by adults, both parents and relatives are common. Supported by zoos and individuals--
https://madrascrocodilebank.org/web/make_a_donation 12 views
Despite periodic lockdowns and covid restrictions, the field team of the Gharial Ecology Project ... more Despite periodic lockdowns and covid restrictions, the field team of the Gharial Ecology Project has continued its surveys of the population of gharial residing in the National Chambal Sanctuary, north India, and the breeding behaviors, activities, and ecology of the largest, last self-sustaining gharials living in an open, large river habitat. This video describes recent project activities and findings, and outlines the scope of the project, now in its 14th field season. Logistic and operational support is provided by the Forest Depts of UP, MP, and Rajasthan, and the Madras Crocodile Bank Trust. Financial support is generously provided by the international zoo community, especially the Prague Zoo, WCS, Berlin Zoo, Krokodyli Zoo Protivin, Montgomery Zoo (Alabama), Los Angeles County Zoo, and the donors to CrocFests 2016 and 2018. 8 views
Teaching Documents by Jeffrey W . Lang
CSG27 Darwin, 2024
Living crocodylians possess acute sensory capabilities, e.g., vision, audition, olfaction, gustat... 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.
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
Wall Street International , 2020
The National Chambal Sanctuary in Northern India has the world's largest free-living population ... 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
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
Crocodile Specialists Group Newsletter 2019 Apr-Jun, 2019
Bookmarks Related papers MentionsView impact
The Red List of Threatened Species, 2019
Gharial were historically distributed throughout the major channels of the Indus, Ganges, Mahanad... 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.
Bookmarks Related papers MentionsView impact
ICCB 19th Mtg, Kuala Lampur, Malaysia, 2019
Gharial (Gavialis gangeticus) is listed as critically endangered, and the historical range loss s... 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.
Bookmarks Related papers MentionsView impact
Turtle Survival Alliance, Annual Meeting, August 2018, 2018
The Indian narrow-headed softshell turtle, Chitra indica, is a riverine species restricted to sou... 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
Bookmarks Related papers MentionsView impact
Proceedings 13th Western Pacific Acoustics Conference, 11-15 Nov2018 New Delhi, 2019
Abstract: Living crocodilians are known to communicate using visual, acoustic, chemical, and/or t... 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.
Bookmarks Related papers MentionsView impact
Executive Summary An earlier field report (GEP 2017) established on a 425 km stretch of the Natio... 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.
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
Historic accounts indicate that gharial (Gavialis gangeticus) were common and abundant throughout... 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.
Bookmarks Related papers MentionsView impact
The gharial (Gavialis gangeticus) is a Critically Endangered, river dwelling crocodylian, with a ... 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.
Bookmarks Related papers MentionsView impact
Living crocodilians communicate using visual, acoustic, chemical, and/or tactile signals. As adul... 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.
Bookmarks Related papers MentionsView impact
This is a general audience story commissioned by the BBC WILDLIFE magazine which features images ... more 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.
Bookmarks Related papers MentionsView impact
Papers by Jeffrey W . Lang
Journal of Thermal Biology, Feb 1, 1999
Bookmarks Related papers MentionsView impact
General and Comparative Endocrinology, Nov 1, 1994
In certain reptiles with temperature-dependent sex determination (TSD), estrogens act as a signal... 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.
Bookmarks Related papers MentionsView impact
Uploads
Videos by Jeffrey W . Lang
https://madrascrocodilebank.org/web/make_a_donation
Teaching Documents by Jeffrey W . Lang
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.
Papers by Jeffrey W . Lang
https://madrascrocodilebank.org/web/make_a_donation
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.