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- JAVIER MANJARREZ received a B.S. in Biology, M.Sc., and Ph.D. in Ecology from the Universidad Nacional Autónoma de Me... moreJAVIER MANJARREZ received a B.S. in Biology, M.Sc., and Ph.D. in Ecology from the Universidad Nacional Autónoma de Mexico (UNAM). He is currently a Professor of Biological Sciences at the Universidad Autonoma del Estado de Mexico. Most of his research interests have centered on the behavioral ecology of snakes and evolutionary processes that shape ecological diversity in sympatric species. Although he prefers working with snakes, his research has involved a variety of animals ranging from hylid frogs to domestic birds and mammals. Javier teaches courses in ecology, animal ecology, and statistics.edit
are determinants for success in individual fitness. Interspecific interactions among species can potentially benefit the individual by reducing the probability of predation, increasing reproductive success, and facilitating thermoand... more
are determinants for success in individual fitness. Interspecific interactions among species can potentially benefit the individual by reducing the probability of predation, increasing reproductive success, and facilitating thermoand hydro-regulation (Krause and Ruxton, 2002). Although reptiles have been stereotyped as solitary and, in some cases, territorial animals, there are many studies that report on gatherings (Graves and Duvall; 1995; Giles et al., 2009; Davis et al., 2011; Clark et al., 2012). In the case of snakes, intra and interspecific aggregations have been mostly associated with reproductive and thermoregulatory events (Huey et al., 1989; Gregory, 2004; Amarello, 2012; Amarello and Smith, 2012; Clark et al., 2012, Meek, 2014). On October 14, 2017, at 0910 h, we recorded an aggregation of 16 adult Thamnophis scaliger Jan, 1863; one adult T. eques Reuss, 1834 (Colubridae), and one adult Crotalus polystictus Cope, 1865 (Viperidae), all under the same shelter. They were in...
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Semi-aquatic snakes integrate visual and chemical stimuli, and prey detection and capture success are therefore linked to the display of visual predatory behavior. The snake Tham-nophis melanogaster responds preferentially to individuals... more
Semi-aquatic snakes integrate visual and chemical stimuli, and prey detection and capture success are therefore linked to the display of visual predatory behavior. The snake Tham-nophis melanogaster responds preferentially to individuals of the fish Xenotoca variata with a greater number of bright, colorful spots (lateral speckles) compared with those with a smaller number; however, water turbidity can reduce underwater visibility and effect the vul-nerability of fish. In this study, we tested whether the presence of iridescent speckles on the flanks of male X. variata interacted with water turbidity to modify the predatory behavior dis-played by the snake T.melanogaster. We predicted that in an experimental laboratory test, the snakes would increase the frequency of their predatory behavior to the extent that the water turbidity decreases. The snakes were tested at six different levels of water turbidity, in combination with three categories of male fish (with few, a median number ...
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Research Interests: Evolutionary Biology, Zoology, Ethology, Psychology, Mate Choice, and 3 moreBiology, Aggression, and Lizard
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We describe the seasonal activity and use of shelters in a population of Aspidoscelis costata in an area of central Mexico. We visited this locality each month from July of 2013 to April of 2015, and during each visit observed the... more
We describe the seasonal activity and use of shelters in a population of Aspidoscelis costata in an area of central Mexico. We visited this locality each month from July of 2013 to April of 2015, and during each visit observed the frequency in which the shelters were used and the microhabitats where they were located. We recorded the climatic conditions (dry or rain), use of the shelters (temporary or permanent), and their respective position (sun or shade). The lizards chose to use temporary shelters and those exposed to the sun more frequently (63% and 53% respectely, of 90 lizards), with similar frequencies shown during the dry and rainy seasons. These results suggest that A. costata chooses refuges with characteristics that allow them to maximize such resources as the availability of sunlight, access to food, and protection from predators. Nonetheless, we believe these results should be reexamined in future studies, especially those conducted in different locations.
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To characterize head structure in snakes of Thamnophis melanogaster (crayfish-eating and non-crayfish-eating individuals), Thamnophis eques, Regina grahamii and R. septemvittata, we measured (1) jaw length (distance from the posterior... more
To characterize head structure in snakes of Thamnophis melanogaster (crayfish-eating and non-crayfish-eating individuals), Thamnophis eques, Regina grahamii and R. septemvittata, we measured (1) jaw length (distance from the posterior edge of the posterior-most supralabial scale to the anterior tip of the rostrum), (2) head length (distance from the snout tip to the posterior-most portion of the parietal bone), (3) head width (widest part measured while applying pressure on the posterior portion of the head to spread the quadrates and mandibles laterally), and (4) number of maxillary teeth
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Morphological convergence is expected when organisms which differ in phenotype experience similar functional demands, which lead to similar associations between resource utilization and performance. To consume prey with hard exoskeletons,... more
Morphological convergence is expected when organisms which differ in phenotype experience similar functional demands, which lead to similar associations between resource utilization and performance. To consume prey with hard exoskeletons, snakes require either specialized head morphology, or to deal with them when they are vulnerable, e.g. during molting. Such attributes may in turn reduce the efficiency with which they prey on soft-bodied, slippery animals such as fish. Snakes which consume a range of prey may present intermediate morphology, such as that of Thamnophiine (Natricidae) which may be classified morphometrically across the soft-hard prey dietary boundary. In this study, we compared the dentition and head structure of populations of Thamnophis melanogaster that have entered the arthropod-crustacean (crayfish)-eating niche and those that have not, and tested for convergence between the former and two distantly related crayfish specialists of the genus Regina (R. septemvittata and R. grahamii). As a control, we included the congener T. eques. Multivariate analysis of jaw length, head length, head width, and number of maxillary teeth yielded three significant canonical variables that together explained 98.8 % of the variance in the size-corrected morphological data. The first canonical variable significantly discriminated between the three species. The results show that head dimensions and number of teeth of the two Regina species are more similar to those of crayfish-eating T. melanogaster than to non-crayfish-eating snakes or of T. eques. It is unclear how particular head proportions or teeth number facilitates capture of crayfish, but our results and the rarity of soft crayfish ingestion by T. melanogaster may reflect the novelty of this niche expansion, and are consistent with the hypothesis that some populations of T. melanogaster have converged in their head morphology with the two soft crayfish-eating Regina species, although we cannot rule out the possibility of a morphological preadaptation to ingest crayfish
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Declarations can be found on page 10 DOI 10.7717/peerj.1274 Copyright 2015 Cruz-Ruiz et al.
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The prediction of fuel load areas and species associated with these events reduces the response time to fight forest fires. The objective of this study was to estimate the annual fuel load from 2009–2013, predict the annual fuel load in... more
The prediction of fuel load areas and species associated with these events reduces the response time to fight forest fires. The objective of this study was to estimate the annual fuel load from 2009–2013, predict the annual fuel load in the rest of the ecosystem, identify species that contribute most to this load and compare the percentage of area by risk category in the temperate forests of Tamaulipas. Fuel load was estimated with inventory data using three models. Fuel load was predicted with elevation, total annual precipitation, mean annual temperature, and enhanced vegetation index from satellite scenes using partial least squares regression. The highest concentration of fuel load was associated with the oak, oak-pine, pine forest and mountain mesophyll forest ecosystems. The contribution of genera to fuel load was different. Quercus contributed the most variation among clusters, and the contribution among Quercus species was similar. The results highlight the importance of foc...
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En este trabajo se examina el uso que hace Sceloporus horridus de los diferentes microhábitats durante el día, año, por sexo, por edad, en diferentes intervalos de altura y sus implicaciones para la termorregulación y la conservación. El... more
En este trabajo se examina el uso que hace Sceloporus horridus de los diferentes microhábitats durante el día, año, por sexo, por edad, en diferentes intervalos de altura y sus implicaciones para la termorregulación y la conservación. El 49.5% de las lagartijas usan árboles, 32.62% rocas y 2.3% arbustos (χ2 = 216.06, gl 3, p < 0.05). El uso de microhábitat por edades, con los sexos separados, reveló diferencias significativas entre crías, subadultos y adultos. En hembras, las crías utilizan con mayor frecuencia las rocas, mientras que las subadultas y adultas utilizan árboles (χ2 = 13.38, gl 6, p < 0.05). En machos, las crías y subadultos usan rocas, y los adultos árboles (χ2 = 15.22, gl 4, p < 0.05). La distribución altitudinal tiene efectos en el uso de hábitat; en el intervalo altitudinal de 800 a 1,100 m, estas lagartijas tienden a ser más arborícolas, y entre los 1,100 y 1,400 m usan con mas frecuencia las rocas (χ2 = 36.21, gl 6, p < 0.05). En la época de sequía hu...
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El dimorfismo sexual, es un fenómeno común en lagartijas del género Sceloporus, lo que permite identificar diferencias en el tamaño de cuerpo, y diseño morfológico, entre machos y hembras. Lo más común es que ocurran variaciones en el... more
El dimorfismo sexual, es un fenómeno común en lagartijas del género Sceloporus, lo que permite identificar diferencias en el tamaño de cuerpo, y diseño morfológico, entre machos y hembras. Lo más común es que ocurran variaciones en el color disociadas de la morfología. Utilizando ANDEVA de una vía y análisis discriminante, obtuvimos diferencias significativas en seis caracteres morfológicos en correlación con color de la garganta; lo que permite reconocer tres diferentes fenotipos (amarillo,azul y naranja). Sin embargo, no observamos diferencias en el uso de microhábitats. Los machos con garganta de color azul (44.35 %) fueron los más grandes y robustos, y tienen similar abundancia que los machos con garganta de color amarillo (48.5%). Los machos con garganta naranja solo representaron el 8 % del total. Sugerimos que los mecanismos de selección de machos por parte de las hembras y las oportunidades de realizar cópula, por parte de los tres morfos, pueden inducir variaciones en la in...
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The demographic characteristics of an amphibian population fluctuate independently over time, mainly in response to the temporal variation of environmental factors, especially precipitation and temperature. These temporal fluctuations may... more
The demographic characteristics of an amphibian population fluctuate independently over time, mainly in response to the temporal variation of environmental factors, especially precipitation and temperature. These temporal fluctuations may contribute to the size of an amphibian population and could be used to determine the current conservation status of a species. During a five year (2004–2008) period, we studied the relative abundance, sex ratio, and age-sex structure of a population of metamorphosed individuals of the endemic treefrogHyla eximiain Central Mexico. We also studied the species’ relationship with climatic variables such as temperature and precipitation. We found an interannual constant abundance during the study period. However, interannual differences were observed in the population structure by age-sex category (males, females, or juveniles), with decreased abundance of males and juveniles during the rainy months (August–November). The annual abundance ofH. eximiawas...
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Abstract: In temperate zones, offspring born earlier in the breeding season might have more time to acquire resources before hibernation and consequently have higher survival rates. In this study, we tested the hypothesis that neonates... more
Abstract: In temperate zones, offspring born earlier in the breeding season might have more time to acquire resources before hibernation and consequently have higher survival rates. In this study, we tested the hypothesis that neonates born earlier in the birth season are smaller (in body size, mass, or both combined as body condition) than neonates born later, but that they have more time to acquire resources before hibernation. We used 43 laboratory-born litters of Thamnophis melanogaster and 21 litters of T. eques obtained from females collected from syntopic field sites. For both species, neonate body condition at birth differed within the birth season, such that sizes were smaller in the early portion, and larger in the later portion, of the season. When compared, only the snout–vent length and mass of neonates, averaged for each litter, did not change throughout the birth season. The temporal variation in neonate body condition found in the two species could explain increased offspring survival when neonates face challenging environmental conditions. If these differences reflect variations in the environment throughout the birth season, then body condition at birth could be relevant for neonate survival.
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Research Interests: Evolutionary Biology, Zoology, Ethology, Psychology, Biology, and 3 moreTemperature, Stream, and Field Study
Amarillo fish females (Girardinichthys multiradiatus) vibrate when conspecific males approach them; the reason behind this behaviour is unclear. Hypotheses are that females vibrate either to avoid aggression from males or to court them.... more
Amarillo fish females (Girardinichthys multiradiatus) vibrate when conspecific males approach them; the reason behind this behaviour is unclear. Hypotheses are that females vibrate either to avoid aggression from males or to court them. We prevented females from vibrating by temporarily blocking their lateral line organs and eyes, on the assumption that they rely on these senses to detect approaching males. Females with the lateral line organs obstructed vibrated less frequently than females with the lateral line intact, indicating that the mechanosensory lateral line system is necessary for perceiving approaching males. Males displayed more courtship behaviour to sighted females with the lateral line organs obstructed than to sighted females with the lateral line intact. A general tendency indicated that the less the females vibrated the more the males courted them. These findings indicate that female vibration discourages male courtship behaviour.
Research Interests: Psychology, Cognitive Science, Biology, Vibration, Medicine, and 5 moreFemale, Animals, Male, Courtship, and Cyprinodontiformes
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In this study, we explored chemosensory, ingestive and prey-catching responses of neonate Mexican Black-bellied Gartersnakes (Thamnophis melanogaster) to crayfish (Cambarellus montezumae). By comparing snakes from a recently discovered... more
In this study, we explored chemosensory, ingestive and prey-catching responses of neonate Mexican Black-bellied Gartersnakes (Thamnophis melanogaster) to crayfish (Cambarellus montezumae). By comparing snakes from a recently discovered crayfish-eating population and a typical non-crayfish-eating population, we asked which behavioral components change as a species enlarges its feeding niche. In the crayfish-eating population chemosensory responsiveness to crayfish was not enhanced but its heritability was higher. Neonates of both populations showed similar preference for freshly-molted versus unmolted crayfish, and whereas the tendency to ingest both crayfish stages remained stable between ages 15 and 90 days in the non-crayfish-eating population, in the crayfish-eating population it actually decreased. Techniques to catch and manipulate molted crayfish were similar in the two populations. We discuss the possibility that there is no increase in the behavioral response to eat crayfish...
Land-use and climate change are affecting the abundance and distribution of species. The Trans-Mexican Volcanic Belt (TMVB) is a very diverse region due to geological history, geographic position and climate, however, is one of the most... more
Land-use and climate change are affecting the abundance and distribution of species. The Trans-Mexican Volcanic Belt (TMVB) is a very diverse region due to geological history, geographic position and climate, however, is one of the most disturbed regions in Mexico. Reptiles are particularly sensitive to environmental changes due to their low dispersal capacity and thermal ecology. In this study, we define the environmental niche (a part of it; considering climatic, topographic and land use variables) and potential distribution (present and future) of the five Thamnophis species present in TMVB. To do so, we used the maximum entropy modelling software (MAXENT). First, we modeled to select the most important variables to explain the distribution of each species, then we modeled again only with the most important variables and projected these models to the future (year 2050) considering a middle-moderate climate change scenario (rcp45) and the land use and vegetation variables for year...
The sensory systems of Boidae and Crotalinae snakes detect subtle differences of thermal infrared energy. The complexity of this ability involves neurophysiological mechanisms with interspecific differences in the anatomy of... more
The sensory systems of Boidae and Crotalinae snakes detect subtle differences of thermal infrared energy. The complexity of this ability involves neurophysiological mechanisms with interspecific differences in the anatomy of thermoreceptor organs and functionally in thermal detection ranges and thermal thresholds, with ecological correlations that influence the thermo-reception. However, little is known about the information these snakes obtain and use from infrared radiation. We analyzed the behavioral response of adult Mexican Lance-head Rattlesnakes (Crotalus polystictus) to static thermal stimuli, evaluating the influence of distance from the snake of the thermal stimuli, and its lizard-like or mouse-like shape. The results reveal that C. polystictus is able to detect static thermal stimuli located from 20 to 200 cm away. Head movements and tongue-flicks were the most frequently performed behaviors, which suggests they are behaviors that can facilitate the detection of subtle di...
Figures 1-2 from: Soria-Díaz L, Rábago-Castro JL, Domínguez-Vega H, Gómez-Ortíz Y, Manjarrez J, Garrido-Olvera L (2019) Parasites in feces of the endemic rattlesnake, Crotalus triseriatus (Serpentes: Viperidae), from Mexican highlands. Zoologia 36: 1-6. https://doi.org/10.3897/zoologia.36.e29587more