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The majority of lizards and snakes lay flexible-shelled eggs with high water vapor permeability and which absorb water during incubation and increase in mass, volume, and surface area (water uptake is necessary for successful embryonic development). In contrast, one clade of gekkotans lay rigid-shelled eggs with low permeability which, like bird eggs, lose water during incubation and incubate successfully under low moisture conditions. Anecdotal accounts suggest that eggs of some New Caledonian diplodactylids, a family of gekkotans characterized by flexible-shelled eggs, are ‘hard-shelled.' I made observations on the eggs of Correlophus ciliatus (= Rhacodactylus ciliatus) to test the idea that New Caledonian diplodactylid eggs exhibit features unlike those of other squamates that lay flexible-shelled eggs. I found that C. ciliatus eggs are flexible-shelled; they have relatively high water vapor permeability and they increase in mass during incubation as the result of water uptake. Nonetheless, egg characteristics fall outside the range of values observed for squamates that lay flexible-shelled eggs. While C. ciliatus eggs increase in mass (as expected of flexible-shelled eggs), the magnitude of increase is substantially lower than in eggs of other squamates. Moreover, water vapor permeability of C. ciliatus eggs is about 40% that of flexible-shelled eggs of the same mass. Therefore, shell characteristics appear to be transitional between flexible- and rigid-shelled eggs. This suggests that the diplodactylid geckos of New Caledonia may provide a unique opportunity to explore the nature of the evolutionary transition between two disparate shell types.
Chemically mediated interactions are an important component of reptile life. Tuatara (Sphenodon punctatus) have been documented to locate prey by olfaction, and the recent discovery of a cloacal gland secretion (tuataric acid) suggests chemicals may be used as social signals. Social discrimination of recognized Tuatara populations (i.e., Cook Strait and northern versus Brothers) via chemosensory means has yet to be determined. To explore whether Tuatara react to cloacal gland odors or respond differently to the odor of a different population, three response variables were measured within 60 cm and 30 cm of a scent source within a captive colony: 1) time of first approach; 2) total number of approaches; and 3) total time. Ten male Cook Strait Tuatara were sequentially presented with three treatments: control (distilled water); male North Brother odor; and male Cook Strait odor. Although no significant differences in response were detected across odors and the control, on average, cloacal gland secretions were investigated faster, more often, and for longer than the water control. Further, four of the 10 test subjects made physical contact with the treatment containers when they contained cloacal gland secretions—this never occurred under control conditions. Although preliminary, our study provides insight into the potential role of chemical signals in Tuatara.
Oviposition site selection by breeding amphibians determines larval habitat for their offspring. Many amphibians breed in temporary ponds, which vary in hydroperiod and levels of competition, predation, and resource abundance. Newly filled ponds have fewer competitors and predators and more periphyton and phytoplankton, which are more palatable food sources for anuran larvae. We tested for oviposition site preference between old and new water pools in Hyla chrysoscelis, a species known to have better larval performance in newly filled pools. Consistent with larval performance and the observation that anurans often breed in ponds immediately after they fill, H. chrysoscelis selectively oviposited in new pools. Conductivity was significantly lower and dissolved oxygen significantly higher in new versus old pools, and these may be cues of pond age and productivity, respectively. We demonstrate that adult oviposition site selection preferences in our study match larval performance differences seen in previous work and that this preference is not simply for newly filled ponds but for ponds with a recent influx of water. These results further suggest novel ways for land managers to increase amphibian populations. Draining ponds will increase their attractiveness to breeding females who simultaneously avoid fish and choose new water.
The distribution of the federally endangered Shenandoah Salamander (Plethodon shenandoah) is presumed to be limited by competition with the Red-backed Salamander (Plethodon cinereus). In particular, the current distribution of P. shenandoah is understood to be restricted to warmer and drier habitats because of interspecific interactions. These habitats may be particularly sensitive to climate change, though the influence of competition may also be affected by temperature and relative humidity. We investigated the response of P. shenandoah to competition with P. cinereus under four climate scenarios in 3-dimensional mesocosms. The results suggest that, although climate change may alleviate competitive pressure from P. cinereus, warmer temperatures may also significantly influence the persistence of the species across its known range.
Increasing evidence indicates that sex-determination mechanisms in reptiles (genotypic sex determination [GSD] and temperature-dependent sex determination [TSD]) are considerably labile and not mutually exclusive. Environmental factors can override GSD in some reptile species and some species shift from GSD to TSD at certain temperatures. We present data on the effects of incubation temperature on sex ratio in Collared Lizard (Crotaphytus collaris) hatchlings. Eggs were incubated at one of seven constant temperatures. More males were produced at both lower and higher temperatures and more females at intermediate temperatures. Although none of the seven treatments produced only females or only males (nor even differed significantly from an equal sex ratio), incubation at different constant temperatures influenced hatchling sex ratios and produced an overall statistically significant pattern, consistent with TSD pattern II but in an inverse way. Even with a lack of evidence, GSD has been suggested as the sex-determining mechanism in the species. Our results suggest that sex ratio is modified in a consistent pattern depending on incubation temperature; therefore, labeling this species GSD is premature. More research is needed, however, to conclude that C. collaris is a TSD species or a GSD species with temperature interacting with genetic factors.
Evidencia creciente señala que el mecanismo de determinación de sexo en los reptiles (GSD, determinación genética; y TSD, determinación sexual por temperatura) son considerablemente flexibles y no mutuamente excluyentes. Factores ambientales pueden anular GSD en algunas especies de reptiles y algunas especies cambian de GSD a TSD en ciertas temperaturas. Presentamos datos de los efectos de la temperatura de incubación en la proporción de sexos en recién eclosionados de la Lagartija de Collar (Crotaphytus collaris). Los huevos fueron incubados a una de siete temperaturas constantes. Mayor número de machos se produjeron en temperaturas bajas y altas, y mayor número de hembras en temperaturas intermedias. Aunque ninguno de los siete tratamientos produjo sólo hembras o sólo machos (tampoco difieren significativamente de una proporción de sexo igual), la incubación a temperaturas constantes diferentes influenció la proporción de sexos de recién eclosionados y produjo un patrón general significativo consistente con el patrón de determinación sexual por temperatura II pero de manera inversa. A pesar de la falta de evidencia, la determinación sexual cromosómica (GSD) ha sido sugerida como el mecanismo de determinación sexual en esta especie. Nuestros resultados sugieren que la proporción de sexo se modifica en un patrón consistente dependiendo de la temperatura de incubación, por lo tanto es prematuro etiquetar esta especie como GSD. Se requiere más investigación para concluir que C. collaris es una especie TSD o una especie GSD con temperatura interactuando con factores genéticos.
Previous studies observed the synthesis of an abundant glycoprotein secretion in the collecting duct tubules of ambystomatid and salamandrid salamanders. The synthesis and release of this secretion occurred during times of mating activity; therefore, researchers concluded that collecting ducts of the pelvic kidneys functioned as secondary sexual structures. The purpose of this study was to determine if any male plethodontids possess kidneys with similar secondary sexual function. We captured male and female Eurycea longicauda longicauda (Common Name) from every month possible and removed their urogenital organs, along with known male secondary sexual glands, for histological examination. The heights of collecting duct and known secondary sexual gland epithelia were measured every month as a proxy for secretory activity. We compared known secondary sexual gland seasonal secretory activity with that of the seasonal secretory activity of the collecting ducts. We then qualitatively compared these data with the seasonal spermatogenic cycle of the testes, seasonal sperm transport through male genital ducts, and seasonal sperm transfer from males to females. Known secondary sexual structures and pelvic kidney collecting ducts increase epithelial height directly prior to and during autumn months, concordant with the later stages of sperm development, transport of sperm through the genital ducts, and transfer of sperm from males to females; i.e., the mating season.
A major challenge in amphibian ecotoxicology is understanding the population-level implications of laboratory-based, dose-response studies. We contrasted habitat occupancy among five species of frogs and toads in two adjacent segments of the upper Hudson River—one heavily contaminated by polychlorinated biphenyls (PCBs, compounds reported to have adverse impacts on individual amphibians) and the other uncontaminated—while controlling for site and sampling covariates. Site occupancy was estimated via repeated night call surveys at 40 wetland sites during 2006 and 2007. Habitat occupancy varied strongly in response to whether breeding sites were hydrologically connected to the Hudson River but was independent of the degree of PCB contamination of a given river segment. The results highlight the uncertainties of extrapolating outcomes of laboratory-based, toxicological studies to wild amphibian populations.
Water snakes of the genus Helicops have different uses of food resources that can facilitate species coexistence. To assess diet and foraging habitat of water snakes in eastern Brazilian Amazonia, we used prey consumed by Helicops angulatus, Helicops hagmanni, and Helicops polylepis deposited in scientific collections to analyze variations in composition, breadth, and niche overlap on a regional scale. Among these prey, we used fish (main item) to calculate ecomorphological attributes that might indicate fish habitat and, consequently, the foraging habitat used by snakes. Our analyses indicate these three snake species have similar diet compositions but differ in the proportion in which each item is consumed. Helicops angulatus had the most generalized diet and H. hagmanni had the most specialized diet. Food niche overlap among the three species was moderate. All three species forage in the medium and upper strata of the water column in the lentic zone; however, H. polylepis feeds on prey with varied morphological features that may indicate foraging in many types of environments. The snakes have similar diets and foraging habitats; however, they use food items and space in different proportions.
We describe a new species of smooth-scaled anguid from arid northern foothills of the Sierra Madre Oriental in Nuevo León, México. This new species is similar to the other smooth-scaled gerrhonotines: Gerrhonotus lugoiMcCoy, 1970, from the Cuatrociénegas Basin of Coahuila; G. parvusKnight and Scudday, 1985, from the Sierra Madre Oriental in Nuevo León; and G. farriBryson and Graham, 2010, from the Sierra Madre Oriental in Tamaulipas. It differs from these species in several important morphological characters, including number of postrostral scales, postoculars, postmentals, sublabials, and dorsal and ventral scale rows. It also is the only known anguid to possess three postmentals and a novel azygous scale between the postmentals and the gular shields.
Although many non-native species negatively influence amphibian populations, non-native aquatic vegetation has been documented to have positive, negative, and neutral effects on anuran larvae. To evaluate the response of anurans to non-native plants, we exposed two frog species, Gray Treefrog (Hyla versicolor-chrysoscelis) and Southern Leopard Frog (Lithobates sphenocephalus), to detritus from either native hardwood trees, non-native purple loosestrife (Lythrum salicaria), or a mixture of both. Experiments were conducted in artificial ponds, and we recorded the survival, growth, and metamorphic size of larvae. Gray Treefrog survival was highest in tanks with native leaf litter. Developmental time did not differ among treatments, but tadpoles in tanks with purple loosestrife were significantly larger than those in tanks with native leaf litter. Southern Leopard Frog survival was lowest in the mixed vegetation treatment. As with Gray Treefrogs, developmental time was not influenced by treatment, but larvae from tanks with purple loosestrife were significantly larger than those from other treatments. Lower survival in the presence of purple loosestrife has been linked to secondary compounds in the plant, and the higher growth rates we observed are consistent with recent findings on response of anuran larvae to other non-native plants. Our results suggest the negative effects of purple loosestrife detritus on the species examined are manifest at the individual and (perhaps) population level. Because the fewer animals that did survive in tanks with purple loosestrife grew larger, overall ecosystem-level effects may not be present; however, larger scale experiments are needed to evaluate this hypothesis.
Climate change is expected to increase amphibian extinction rates; however, little is known about the physiological responses of amphibian populations to climate change projections for their region. For the Cascade Mountain Range of the U.S. Pacific Northwest, high-resolution climate models predict temperature increases during summer months. We evaluated phenotypic plasticity in larval growth and development in response to this projected increase in temperature in three co-occurring Anuran species: Cascades Frogs (Rana cascadae), Western Toads (Anaxyrus boreas), and Pacific Chorus Frogs (Pseudacris regilla). We exposed each species to two temperature regimes: the control treatment simulated the historical summer temperatures for the decade of 2001–11; the warmed treatment mirrored this seasonal trend but simulated a 4°C average increase in temperature. To quantify the magnitude of plasticity and any consequences to body size, we measured growth characteristics throughout larval development and metamorphosis. We found significant acceleration in larval developmental rates and increased larval body mass under the warmed temperature treatment for all three species. When compared across Gosner developmental stages, however, the perceived weight gain in the warmed treatment was largely because of the advancement in development triggered by warming. As a consequence of rapid development, we observed differential shifts in body size features. We further identified an optimal temperature range (22–25°C) within which all three species showed maximum weight gain and development rates and above which performance plateaued. We provide empirical evidence for species-specific thermal tolerances and the potential for individualistic responses to climate change among co-occurring amphibian species.
The gecko adhesive system has been subject to widespread investigation for many decades, but relatively few studies explore environmentally relevant conditions that geckos likely face in their natural habitat. Recent evidence suggests that after Gekko gecko take more than three steps on wet glass, their shear adhesion is significantly lower than adhesion on dry substrates. Such an observation is intriguing because many species of geckos are indigenous to the tropics and must commonly navigate wet substrates. Here we report the locomotor performance of two gecko species, G. gecko and Chondrodactylus bibronii, measured on wet vertical glass and acrylic substrates over a distance of 2 m. We found that neither water nor substrate type had a significant effect on the mean sprint velocity of either species. Mean sprint velocity was unaffected despite variation in frequencies of slipping between species, where C. bibronii slipped significantly more than did G. gecko. Interestingly, the substrate effect on the frequency of slipping was nonsignificant, but misted glass showed a general trend of producing more slips than did misted acrylic. Our results suggest that geckos can sustain adhesive locomotion for at least 2 m on wet substrates.
The Gray Fossil Site (GFS) of northeastern Tennessee is a late Hemphillian fossil locality in the southern Appalachian mountain region of eastern North America with a diverse vertebrate fauna. Snakes make up a substantial microfossil portion of the GFS herpetofauna, particularly the Colubridae, comprised of members of the Colubrinae and Natricinae. Seven colubrid taxa have been identified from the site so far, including three natricines (cf. Neonatrix, Nerodia, Thamnophis) and at least four colubrines (Coluber/Masticophis, Pantherophis, Pituophis, gen. et sp. nov.). Indeed, cf. Neonatrix and the new genus (and species) are the only extinct genera identified. Although Neonatrix is tentatively identified for the first time east of Nebraska, the new species represents a distinct taxon. In addition, the oldest reported definitive occurrence of Masticophis is presented herein. Some of the snakes suggest a pond or other aquatic habitat at GFS, particularly cf. Neonatrix and Nerodia, whereas others, such as Masticophis and Pituophis, tend to prefer more open forested habitats. The GFS represents a poorly understood region of North America at a crucial time period in snake evolution, and its study may help us further understand the modern snake fauna present today in midcontinental and eastern North America.
How do changes in the environment affect the brain? More specifically, how do different physical environments shape areas of the brain that facilitate the contextual perception of animals' surroundings? We evaluated the relationship between rapid habitat change and the volume of the medial, lateral, and dorsal cortices, in two populations of wild male and female Lesser Earless Lizards (Holbrookia maculata). These populations inhabit neighboring, but physically distinct, environments in southern New Mexico: White Sands and dark soil habitats. The White Sands habitat is a geologically recent environment that formed over the last 2,000–7,000 yr. There is a stark physical contrast between White Sands and the surrounding typical Chihuahuan desert habitat that is characterized by dark soil, denser vegetation, and higher competitor and predator species abundances. We observed differences in the volumes of the medial cortex, an important neuroanatomical structure for navigation, but not in those of the dorsal or lateral cortices, between lizards inhabiting the White Sands and dark soil habitats. Male and female lizards in the White Sands habitat had smaller medial cortices (relative to their overall brain size) compared to those in the dark soil environment. We also found sex differences in the volume of the medial cortex; in the dark soil habitat, males had larger medial cortices than females. In summary, we have uncovered differences in neuroanatomy between habitats and between sexes in a wild species of lizard, which may reflect neuroanatomical plasticity and/or rapid evolutionary change in response to a geologically recent environmental change.
Forest removal is a global threat to amphibian diversity. Declines occur within these areas, but many amphibians also avoid moving into or through disturbed areas. Understanding which cues result in avoidance may provide targets for preservation of amphibian occupancy and population connectivity. Negative phototaxis is known from many amphibians, but light can serve as a cue or as a proxy for other environmental cues like temperature. This study sought to evaluate whether larval salamander habitat selection was influenced most by light or temperature cues. Because some individuals choose to remain in deforested habitat, we also assessed whether differences in habitat selection existed between individuals from forested and deforested habitat. Using a laboratory experiment, we found that salamanders use both light and temperature cues for habitat selection. Although salamanders demonstrated larger responses to temperature, they were willing to move into warmer habitats to avoid light. Individuals from deforested regions preferred brighter and warmer areas than individuals from forested regions although plasticity was higher with respect to light relative to temperature. We also noted that salamander thermal preferences were lower than daytime temperatures in small (< 60 m) deforested regions. Overall, a combination of light and thermal cues following forest removal may contribute to avoidance of deforested regions, but more research is necessary to understand why some salamanders continue to occupy warm and bright-disturbed areas.
To determine whether the herbicide, atrazine, affects the stress hormone corticosterone, we exposed Osteopilus septentrionalis (Cuban Treefrog) tadpoles to four concentrations of atrazine and two controls (water and acetone) for three time durations (4, 28, and 100 h). Atrazine concentration, but not exposure duration, had significant nonlinear effects on whole-body corticosterone. Relative to controls, intermediate concentrations of atrazine (10.2 and 50.6 μg/L) tended to lower corticosterone, whereas the lowest (0.1 μg/L) and highest atrazine concentrations (102 μg/L) elevated corticosterone. These results indicate that atrazine exposure might dysregulate corticosterone, a hormone integral to vertebrate immunity, neurogenesis, and health.
Habitat loss and modification are causing declines in the abundance and distribution of plant and animal species, yet robust information on which to base management and regulatory decisions for these species frequently is not available. Thamnophis gigas (Giant Gartersnakes), a species listed as threatened under the U.S. and California Endangered Species Acts, is strongly associated with aquatic ecosystems in the Great Central Valley (California), yet many aspects of its ecology remain poorly understood. We evaluated relationships between environmental attributes and occupancy of T. gigas and predicted the species' occupancy across ∼300,000 ha in the northern Central Valley. We trapped T. gigas at 159 sites and characterized land cover, land use, and soil type at each site. Occupancy of T. gigas was strongly and negatively associated with elevation and strongly and positively associated with canal density and the proportion of rice and perennial wetland. We also found a strong and previously undescribed association between occupancy and soil order. Estimated occupancy was over five times greater at sites underlain by alfisols, molisols, and vertisols than at sites underlain by entisols and inceptisols. We used the statistical associations between environmental variables and occupancy to predict occupancy at a spatial resolution and extent consistent with management of both T. gigas and regional land and water use.