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I re-examine the phenomenon of delayed timing of emergence from the nest by hatchling turtles (known as overwintering in temperate climates) within the context of the original summary of the topic in an article by Gibbons and Nelson in 1978. I base the overview on cumulative data from research at the Savannah River Ecology Laboratory since 1968 and reports from other locations during the past 34 yr. Investigators have reported known or suspected delayed emergence of hatchling turtles for 43 species, 22 genera, and 8 families from 11 countries and 36 U.S. states and Canadian provinces. The following perspective suggests questions to address and provides recommendations for how herpetologists should proceed in further investigating the phenomenon of hatchling emergence in turtles. The topic is one on which answers must be forthcoming to address turtle conservation on a global scale. For freshwater turtles, which include the majority of the world's turtles, natural selection has favored hatchlings that enter the aquatic habitat at the most propitious season for survival and subsequent growth. Nesting in most species spans several weeks; therefore, at the end of incubation hatchlings must use proximal environmental cues to adjust their timing of departure from the nest and entry into the aquatic habitat. Because of its widespread prevalence, delayed hatchling emergence in a turtle species should be considered the default behavior until evidence to the contrary is provided. Specifically, many turtles emerge several months after hatching, and in temperate climates emergence delayed by up to a year (overwintering) is likely the norm even though conventional wisdom predicts late summer or fall emergence.
Reexaminé el fenómeno de emergencia retrasada del nido de las crías de tortugas recién nacidas (conocido como estadía invernal en el nido en climas templados) en el contexto del resumen original del tema en 1978. La revisión está basada en datos acumulativos de investigaciones en el Savannah River Ecology Laboratory desde 1968 e informes adicionales de otras localidades durante los últimos 34 años. Los investigadores han registrado emergencia retrasada de crías de tortuga, ya sea constatada o sospechada, para 39 especies en 22 géneros y 9 familias de 10 países. Lo siguiente brinda una perspectiva sobre el tema con sugerencias acerca de las preguntas más significativas a tratar y recomendaciones sobre cómo los herpetólogos deberían continuar investigando este fenómeno. Para las tortugas de agua dulce, que incluyen a la mayoría de las tortugas del mundo, la selección natural ha favorecido a las crías que entran en el hábitat acuático en la estación más propicia para la sobrevivencia y consecuente crecimiento. La anidación de las hembras de la mayoría de las especies se extiende por varias semanas y las hembras no pueden predecir con exactitud qué condiciones ambientales prevalecerán durante y al final de la incubación. Así, las mismas crías deben usar claves ambientales proximales para ajustar el momento de su salida del nido y su entrada en el hábitat acuático o para encontrar un sitio terrestre adecuado para pasar el invierno. Debido a la preponderancia de la emergencia retrasada de las crías entre las tortugas, los biólogos que se dedican al estudio de las tortugas deberían considerar este comportamiento como el mecanismo dado por omisión para una especie determinada, hasta que haya evidencia de lo contrario. Los biólogos que estudian a las tortugas deberían considerar a la estadía invernal en el nido en climas templados como la norma, en lugar de mantener la idea convencional que la emergencia temprana del nido (al final del verano o en otoño en climas templados) es la que predomina.
Complex and ritualized displays require an assemblage of structural, neuronal, and muscular adaptations, and habitat structure may affect the effectiveness of signals to convey information. Therefore, ornament exaggeration through sexual selection may be severely constrained by the costs imposed by natural selection. We investigated this compromise in the courtship behavior of Mediterranean Tortoises by assessing the variability of the acoustic and behavioral signals used among species, and the relationship between courtship and species body size. Marginated, Greek, and Hermann's Tortoises base their courtship on the same kinds of displays, and differences among species rely mainly on the relative importance of aggressive displays with respect to acoustic signals. We found that the divergence of courtship patterns among species was also related to body size. Greek Tortoises, intermediate in size between the other two species, showed an intermediate courtship aggression. Body size in Mediterranean Tortoises relates to different vegetation structure of their preferred habitat, smaller species being advantaged in denser vegetation. Therefore, the divergence of courtship patterns in the three species of European tortoises might have been promoted by the progressive adaptation of incipient species to habitats with different vegetation structures. Because courtship signals play a central role in species isolation, a link between morphology and courtship is of particular interest and might be one of the central mechanisms of tortoise diversification.
The Diamond-backed Terrapin (Malaclemys terrapin), endemic to the brackish marshes of the eastern and Gulf of Mexico coasts of the United States, is a threatened species in Massachusetts with populations suffering drastic declines in the late 19th and early 20th centuries. To assess the potential effects of population bottlenecks on contemporary levels of genetic variation, we analyzed 219 bp of a major histocompatibility complex class I gene region (MHCI) by direct sequencing and single-strand conformational polymorphism analysis and six microsatellite loci from three locations around Cape Cod, Massachusetts. No variation was found at the MHCI, despite finding appreciable levels of variation within and among populations at the microsatellite loci. We discuss alternative explanations for these results, and we propose that the lack of variation at the MHCI may be due to the effects of selection rather than demographic changes in terrapin populations.
Three adult-sized Loggerhead Turtles (Caretta caretta), captured incidentally by bottom trawlers, were tracked by satellite in the Mediterranean Sea for a substantial part of their annual cycle, including the period preceding nesting. The three turtles performed long-distance movements that were variable between individuals but shared common features such as seasonal migration. Very prolonged dives (up to over 300 min) were associated with temperature drops to below 18°C , likely an overwintering strategy. Our findings integrate recent tracking data on the postnesting migrations of Mediterranean Loggerhead Turtles, documenting the movement patterns made during the poorly known nonreproductive phase.
Podocnemis expansa is the largest freshwater turtle in South America and exhibits a complex reproductive behavior. Females lay eggs in sandy banks formed during the dry season. Nesting habitat can influence hatching success and sex determination. In some turtle species, female body size is crucial to determine reproductive parameters such as clutch size and shape. In this study, we investigate allometric relationships between female body size and their tracks, and clutch characteristics and nest shape in sandy beaches along the Javaés River, southern Brazilian Amazon. Our results indicate that female body size can be estimated based on tracks. Larger females leave larger foot tracks in the sand and have larger clutch sizes with larger clutch mass than smaller females. Female carapace width and body mass can be considered reliable variables to estimate clutch size and total clutch mass for the species. Larger females should be protected because they can be responsible for most annual clutch production.
Podocnemis expansa é o maior quelônio de água doce da América do Sul, apresentando um comportamento reprodutivo complexo. Essa espécie nidifica em bancos arenosos formados durante as vazantes dos rios da Amazônia. As características do ambiente de nidificação podem influenciar o sucesso reprodutivo e o sexo dos filhotes. Alguns trabalhos já demonstraram que o tamanho corporal da fêmea é determinante para as condições da ninhada (quantidade e tamanho dos ovos) e nas dimensões dos ninhos (profundidade e diâmetro) em algumas espécies de quelônios. O presente estudo investigou as relações alométricas entre o tamanho corpóreo da fêmea, seus rastros, as variáveis da ninhada e a forma dos ninhos em ambiente natural em uma praia do rio Javaés, na Amazônia Brasileira. Foi observado que o tamanho corpóreo da fêmea de P. expansa pode ser estimado em função do seu rastro. Fêmeas maiores deixam rastros maiores na areia, além de produzirem mais ovos (tamanho da ninhada) e com maior massa (massa da ninhada) do que fêmeas menores. A largura da carapaça e a massa da fêmea podem ser consideradas variáveis confiáveis para estimar o tamanho e a massa da ninhada dessa espécie. A proteção de fêmeas de maior tamanho deveria ser priorizada, já que podem ser responsáveis por grande parte da produção anual de ovos.
Radio-tracking studies of African tortoises have elucidated differences in spatial ecology in differing habitats. Our study aimed to demonstrate such patterns by radio tracking the Leopard Tortoise Stigmochelys pardalis in a subtropical savanna, northeast Swaziland. Activity of tracked tortoises was correlated with minimum temperatures and greater in the warm wet months compared with the cool, dry months. All tracked tortoises, however, remained active throughout the cool months, and none were observed entering a burrow or any other hibernaculum. The tortoises typically moved 0–89 m per day, with maximum daily movement of over 300 m. A dry river bed and game viewing road did not appear to obstruct the movement of the tortoises.
Golf courses represent a common type of anthropogenically modified habitat in suburban environments. Golf courses may provide suitable habitat for semi-aquatic animals in suburban areas, yet studies comparing animal abundances in golf course ponds with other pond types in suburban environments are somewhat limited. In this study, we compared turtle abundances in golf course ponds with ponds found in residential areas and ponds found in rural (farm) areas and examined the relationship between turtle abundance and residential land-cover within individual golf courses. We captured turtles in 10 golf course ponds, 5 ponds surrounded by residential development, and 5 ponds located on farms. We estimated abundance and the effects of pond area, pond type (i.e., residential, golf, farm) and percentage of residential development within golf course boundaries. Using binomial mixture models and Bayesian inference, we found that ponds surrounded by residential development had lower abundances of Painted Turtles (Chrysemys picta) and Sliders (Trachemys scripta) than ponds located on golf courses and farms. Additionally, golf courses that have a greater amount of residential development within course boundaries had fewer turtles than courses that contained minimal residential development. Our results suggest that golf courses can offer suitable habitat for semi-aquatic turtles in suburban areas. However, residential development within golf course boundaries appears to have a negative effect on local abundances. Thus, if golf courses are to be seen as reserves for wetland-dependent animals, golf courses with low housing density should be considered as a more preferable option than courses associated with extensive residential development.
Chelonia mydas (Green Turtle) foraging areas, where juveniles, subadults, and adults of diverse natal origins coalesce and spend a large portion of their lives, can be located thousands of kilometers from nesting beaches. Unfortunately, the natal origin of turtles in many foraging areas remains unknown. Resolution of this issue was recently listed among the conservation priorities for the species by a global panel of Green Turtle researchers. We examined the genetic diversity and natal origins of Green Turtles from a well-known foraging area in the western Gulf of Mexico. Bayesian mixed-stock analysis of mitochondrial DNA haplotypes was used to demonstrate that an overwhelming percentage (∼95%) of individuals in the western Gulf of Mexico foraging group likely originate in other Gulf of Mexico and northern Caribbean rookeries, with smaller contributions from the western and southern Caribbean, and potentially the Mediterranean Sea. Management of Green Turtles in the western Gulf of Mexico will be improved by linking conservation efforts aimed at this foraging group to turtle aggregates occurring in other critical habitats within the recently defined northwest Atlantic Green Turtle regional management unit.
Reptiles, supposedly, do not produce pheomelanin pigments. Because this claim is based on rather weak evidence, we measured the shell pheomelanin content in the Hermann's Tortoise (Eurotestudo boettgeri). In contrast to expectation, we detected a substantial amount of this pigment. Given the recent interest in the adaptive function of melanin-based color traits, our study opens new avenues of research in reptiles.
During gravidity lizards experience a striking decrease in lung volume as a result of lung compression by eggs growing within the body cavity. In order to understand the effect of this decrease in lung volume on the respiratory biology of gravid egg-laying lizards, we measured changes in total lung volume, resting and postexercise expired volume, minute volume, respiratory frequency, and carbon dioxide production rate during reproduction in the Collared Lizard, Crotaphytus collaris, and the Leopard Lizard, Gambelia wislizenii. We found that compression of the lungs by shelled eggs resulted in an average 48% (range: 26–70%) decrease in total lung volume compared to the same postlaying C. collaris females, and an average 38% (range: 29–46%) decrease in G. wislizenii. CO2 production rates were altered significantly during reproduction in female C. collaris and were 58% higher in females carrying late-stage follicles, compared to after laying. Despite the remarkable reduction in lung volume in both of these species and the increase in CO2 production rates in C. collaris, no ventilation parameters changed over the course of reproduction. The highly distensible body cavities of C. collaris and G. wislizenii appear to be able to accommodate both growing eggs and adequate lung volumes for normal respiratory function during gravidity.
Amphibians are in decline in many parts of the world. Understanding the population dynamics of amphibian species is an important prerequisite for developing effective conservation strategies. We used capture–mark–recapture and skeletochronological techniques to investigate population size, body size, and age structure of metamorphic and pedomorphic forms of Ommatotriton ophryticus between 2006 and 2009 in the northwestern Black Sea region of Turkey. Our findings showed that time-specific survival rate, constant capture probability, no temporary emigration, and time-specific population size were the most appropriate models for this population. According to the best model (Model 6), population size of metamorphic forms of O. ophryticus was estimated as 517 (95% confidence interval [CI] = 338–851) adults in 2006, 338 (95% CI = 282−421) adults in 2008, and 527 (95% CI = 443–646) adults in 2009. Average annual capture probability was estimated at 0.21, although average survival rate across years was 0.35. The mean body size and age structure of the pedomorphs and metamorphs was significantly different for both sexes. Also, body size of both forms of O. ophryticus showed positive significant correlations with age. In addition to this, both forms shared a common allometric slope of the snout–vent lengths vs. age, and older individuals had larger bodies. Moreover, age at first reproduction and longevity exhibited great differences between forms whereas the median age was 4 yr for each newt category, except for metamorphosed males, in which it was 5 yr. These results indicate that pedomorphs in this population show retardation of the somatic development and an earlier maturation.
Amphibians are the most threatened vertebrate group in the world. One of the conservation strategies most used to preserve threatened species is the establishment of protected areas. We used gap analysis to evaluate whether or not the protected area network of northeastern Brazil safeguards populations of threatened amphibians that occur in this region. Data on species geographical ranges were obtained from the International Union for the Conservation of Nature (IUCN) and were overlapped on the northeastern Brazilian protected area network using ArcGIS 9.3. The threatened amphibians found in northeastern Brazil were represented by remnant populations of Adelophryne baturitensis, Adelophryne maranguapensis, Allobates olfersioides, and Agalychnis granulosa. There are 174 protected areas in the protected area network in northeastern Brazil. The network is made up of 65 strict protection areas (IUCN categories I–II) and 109 sustainable use areas (IUCN categories III–VI). The network corresponds to more than 15 million ha, which equates to about 10% of the region's total area. However, the size of the protected areas along the geographical range of these species doesn't necessarily guarantee their persistence in the future. The main threat to these species is loss of habitat due to deforestation and agricultural expansion. Therefore, the viability of new reserves with a diversity of representative ecosystems in northeastern Brazil may be the best solution to avoid extinction processes in this region.
Batrachochytrium dendrobatidis(Bd), the fungus responsible for chytridiomycosis, grows on the keratinized parts of the body (i.e., the entire skin of juveniles and adults, and the oral disk of tadpoles). The fungus affects epidermal structures, generating an imbalance of the osmotic equilibrium through the skin that ultimately leads to death. Therefore, larvae are likely to be much more resistant compared with juveniles and adults, which may suffer high mortality. However, nothing is known about how susceptibility varies during the juvenile life stages (from the end of metamorphosis to sexual maturity). The coexistence of tolerant hosts (either tolerant species or unaffected developmental stages) with susceptible hosts is a major reason why chytridiomycosis has become an epidemic disease. The aim of this study was to analyze the interspecific and developmental variation in susceptibility to Bd in juveniles of three North American anurans. Leopard Frog (Lithobates pipiens) incurred no lethal effects at 104 Bd zoospores ml−1, regardless of the age at which they were exposed to the fungus. On the contrary, Bd infection was more severe for newly metamorphosed juveniles of American toads (Anaxyrus americanus) than for 4-week-old juveniles. When exposed to 104 Bd zoospores ml−1, newly metamorphosed juveniles of this species experienced mortality rates above 70%, whereas 4-week-old juveniles had mortality rates below 30%. Variations in structural characteristics of the skin or the antifungal efficiency of skin peptides are proposed as potential reasons to explain the observed developmental differences in susceptibility to Bd.
Batrachochytrium dendrobatidis (Bd), el hongo responsable de la quitridiomicosis, crece sobre las partes queratinizadas del cuerpo (i.e. la piel de juveniles y adultos y el disco oral de las larvas). El hongo afecta a las estructuras epidérmicas generando una alteración del equilibrio osmótico en la piel que termina produciendo la muerte. De este modo, las larvas suelen ser mucho más resistentes que los juveniles o los adultos, los cuales pueden sufrir elevadas mortalidades. Sin embargo, se desconoce cómo varía la susceptibilidad a lo largo de la etapa juvenil (desde el final de la metamorfosis hasta la adquisición de la madurez sexual). La coexistencia de hospedadores tolerantes (ya sean especies tolerantes o estadios de desarrollo que no se vean afectados) con hospedadores susceptibles es una de las principales razones por las que la quitridiomicosis se ha convertido en una epidemia. El objeto de este estudio fue analizar las variaciones interespecíficas y a lo largo del desarrollo en la susceptibilidad de tres especies de anuros de Norteamérica a Bd. Los juveniles de rana leopardo (Lithobates pipiens) no sufrieron efectos letales a 104 zoosporas de Bd mL−1, independientemente de la edad a la que fueron expuestos al hongo. Por el contrario, la infección por Bd resultó más severa para individuos recién metamorfoseados de sapo americano (Anaxyrus americanus) que para juveniles con cuatro semanas de vida. Al exponerlos a 104 zoosporas de Bd mL−1, los juveniles recién metamorfoseados experimentaron tasas de mortalidad por encima del 70%, mientras que los juveniles con cuatro semanas de edad sufrieron tasas de mortalidad inferiores al 30%. Las variaciones en las características estructurales de la piel y/o en la eficacia antifúngica de los péptidos cutáneos se proponen como razones potenciales para explicar las diferencias en la susceptibilidad a Bd observadas a lo largo del desarrollo.
Many studies indicate that various vertebrates and invertebrates use sensory cues to recognize predators and to evaluate predation risk. Lizards and birds frequently occupy the same habitats; consequently, avian predation on lizards has been implicated as an important selective pressure on lizard behavior. However, there are few studies on how lizards respond to nonvisual cues. The response of adult male Brown Anoles (Anolis sagrei) to calls of birds was studied to determine whether they use auditory cues as an indicator of predation risk from birds. Anoles responded significantly more often with head tilt (increased vigilance) during playback of predatory vocalizations (Kestrel and Red-tailed Hawk calls) compared with low-risk stimuli (nonpredatory bird calls and white noise). Responses to auditory cues suggest that male Brown Anoles are able to distinguish the calls of birds known to prey upon lizards from the calls of nonpredatory birds. More important, this study demonstrates that anoles, most of which are nonvocal, are able to obtain information about predation risk through the use of auditory cues and that the role of hearing in these lizards has been underappreciated.
Spadefoot Toads, Spea bombifrons and Spea multiplicata, are often the most abundant amphibian species in playa wetlands in the semi-arid Southern Great Plains. Tadpoles of these species are morphologically indistinguishable, but both can develop omnivore and carnivore morphotypes. We tested the influence of species and morphotype on body mass of premetamorphic Spea tadpoles and the influence of land use (cropland vs. native grassland) and desiccation stress (water depth and daily rate of water-depth loss) on body mass of S. bombifrons carnivores and omnivores and on body mass of S. multiplicata and S. bombifrons omnivores. Spea bombifrons carnivores were larger than omnivores only in relatively deep playas. A decrease in water depth resulted in less body mass for carnivores, but omnivore body mass did not change. Spea bombifrons omnivores had larger body mass than did S. multiplicata omnivores at low and average playa depth. Spea bombifrons omnivores did not alter body size, whereas S. multiplicata omnivores were smaller when depth decreased. Generally, in average and deep playas, tadpoles were larger in cropland than grassland playas, but in shallow waters, cropland and grassland tadpoles had similar, smaller body mass. Also, cropland tadpoles had reduced body size, whereas grassland tadpoles had similar body mass when depth decreased. Our study documents body size divergence within the same morph in the two sympatric Spea species and species divergence within the omnivore morph depending on desiccation stress. Future studies should investigate whether these species may be mediating competition through both morph development and body size.
The Prehensile-Tailed Skink (Corucia zebrata) (Scincidae) is endemic to the Solomon Archipelago, where it inhabits all major islands. The species is evolutionarily distinct and diverged from its nearest relatives during the Oligocene. To expand on the limited information available with respect to the life history and ecology of C. zebrata in the wild, we explored the species' prevalence to group living and the fine-scale genetic structure of a large and isolated population. Fifty-one lizards were sampled in a 900-ha study plot within a larger area of continuous rain forest on Ugi Island in the Solomon Islands, an area that represents approximately 20% of the C. zebrata habitat on the island. Using information from eight polymorphic DNA microsatellite loci, we conducted Bayesian assignment analysis and pairwise kinship estimates between individual lizards. No geographically induced subpopulation structure was detected. The majority of lizards were not found in immediate proximity of other individuals; however, pairwise kinship analysis showed that lizards located less than 150 m from each other were likely to share alleles identical by descent and, thus, were more related than by chance. Additionally, we found indications that individual lizards have moved several kilometers within the study area. We have uncovered information on dispersal and genetic structure in a large population of C. zebrata, a species whose natural habitat across the Solomon Archipelago is increasingly fragmented and degraded because of unsustainable logging.
We evaluated patterns of site preference for oviposition in Espadarana andina based on the identification and characterization of microhabitats during rainy and dry seasons. We also evaluated the presence of males and females at oviposition sites and the proximity of the adults to the clutches. An electivity index was used to determine which microhabitats were selected for oviposition and calling by males. Additionally, abiotic factors that might influence the oviposition site preference in this species were evaluated. Espadarana andina selected green leaves of Hedychium coronarium along the stream edge, at a height of 70–140 cm for both oviposition and calling sites. All the recorded clutches were found exclusively on leaves of H. coronarium, an invasive plant, suggesting that this plant offers advantages for the reproductive activity of E. andina over other plant species present along the stream border. There was no difference in site selection for calling, mating, and oviposition between dry and rainy seasons and among months. Males stood near clutches during the night, calling from the same plant. Although they were significantly closer to the clutches than females, they did not show any action to increase the survival of the embryos in the clutches. Therefore, we did not observe true egg attendance in E. andina; this observation fits with the absence of parental care behaviors described for the Centroleninae.
Evaluamos los patrones de preferencia de sitio para la oviposición en Espadarana andina basados en la identificación y caracterización de los microhábitats durante las estaciones de lluvia y sequía; también evaluamos la presencia de machos y hembras en los sitios de oviposición y la cercanía de los adultos a las posturas. Un índice de electividad fue usado para determinar cuáles microhábitats fueron seleccionados para la oviposición y llamado de los machos. Adicionalmente, fueron evaluados los factores abióticos que podrían influir en la preferencia por el sitio de oviposición en esta especie. Espadarana andina seleccionó hojas verdes de Hedychium coronarium a lo largo del borde de la quebrada, a un rango de altura de 70–140 cm tanto para la oviposición como para los sitos de canto. Todas las posturas registradas fueron exclusivamente encontradas sobre las hojas de H. coronarium, una planta invasiva, por lo tanto, esta planta parece ofrecer mejores ventajas para la actividad reproductiva de E. andina que otras especies de plantas presentes a lo largo del borde de la quebrada. No hubo diferencias en la selección de sitios para canto, apareamiento y oviposición entre las estaciones de lluvia y seca, ni entre meses. Los machos permanecieron cerca de las posturas durante la noche, cantando desde la misma planta. Aunque los machos estuvieron significativamente más cerca de las posturas que las hembras, ellos no mostraron ninguna actividad para incrementar la supervivencia de los embriones en las posturas. Así, una verdadera atención a los huevos en E. andina no fue establecida; esta observación coincide con la ausencia de comportamientos de cuidado parental descrita para los Centroleninae.
We examined variation in body size, head width, and head shape between males and females of two ecologically distinct species of plethodontid salamanders, Eurycea aquatica (Brownback Salamander) and Eurycea cirrigera (Southern Two-lined Salamander). Female-biased sexual dimorphism in body size occurred in E. cirrigera but not in E. aquatica. Male-biased sexual dimorphism in relative head width occurs in both species. Furthermore, male E. aquatica had larger heads than did male E. cirrigera. We also found significant differences in ventral and lateral head shape between male and female E. aquatica (sexual dimorphism in head shape), but male and female E. cirrigera did not differ in head shape. Males of the two species also significantly differed in both ventral and lateral head shape, while females of the two species differed in ventral head shape but not in lateral head shape. Because sexual dimorphism differed between the two species in different characteristics (body size, relative head width, and head shape), we concluded that these species experience dissimilar levels of sexual selection, ecological selection, or both, possibly as a result of their divergent habitat preferences. Our study represents one of the few reported examples of sexual shape dimorphism in salamanders.
We studied the diet of the Annulated Sea Snake (Hydrophis cyanocinctus) in the mangrove habitat of the Iranian Hara Protected Area. Prey items consumed by 34 individual snakes included four species of gobiid fish. Mudskippers (Periophthalmus waltoni, Boleophthalmus dussumieri, and Scartelaos tenuis) comprised the vast majority of the diet. All prey items were ingested head first. There was a positive correlation between snake SVL and total length of prey, but large snakes also ate small prey. Snake neck diameter was correlated positively with maximum prey diameter, and snakes did not consume prey items with a maximum diameter more than 1.2 times their neck diameter, a characteristic that may indicate gape limitation.
Larval, juvenile, and adult testes of Discoglossus pictus were examined to investigate how the extremely elongated sperm of this species, up to 2,500 μm, can be accommodated within the testicular tubules of the gonad. Seminiferous tubules in D. pictus are modest in number, of large diameter, and run straight from the posterior to the anterior ends of the testis. The modified testis structure originates in its unique development. The anterior part of the testis is composed of short and straight tubules forming the rete testis. The lumen of the seminiferous tubules is filled with bundles composed of sperm embedded in a periodic acid-Schiff stain (PAS)-positive matrix secreted by Sertoli cells. The formation of such extremely elongated spermatozoa is possible because of anatomical modifications including simplification of testis structure, enlargement of the diameter of testicular tubules, reduction in their number, assembly of rete testis tubules in the anterior part of the testis, reduction of the collecting system to a single duct, and the occurrence of sperm bundles embedded in secretion. Additionally, the secretion of a PAS-positive substance by Sertoli cells during spermatogenesis was described. Thus the urogenital system in D. pictus deviates dramatically from the typical structure of male gonads in other anurans.
We evaluated an automated telemetry system that can dramatically increase the amount of activity and spatial data collected for snakes. We developed methods for analyzing data from single automated receiving units (ARUs) and ARU arrays, compared results from ARUs with conventional hand tracking, and assessed previously untested assumptions used in conventional telemetry, using data from ratsnakes (Pantherophis spp.) in Texas and Illinois. ARU data indicated that ratsnakes spent most of their time in small home ranges (mean = 25 ha) but engaged in forays of up to 1.5 km from their core-use areas, suggesting this species may engage in central place foraging. Forays inflated home-range sizes greatly if areas were estimated using minimum convex polygons rather than 95% kernels. Large numbers of locations generated by ARUs produce more reliable home-range estimates than those from hand tracking. ARU data indicated that snakes moved in response to observers during hand tracking. Daily hand tracking produced reliable estimates of distances moved but underestimated distances by a factor of 4 when snakes were tracked every 5 days. Drawbacks of ARUs are that the error associated with individual locations exceeds that for hand-tracked locations and that the costs exceed those for hand tracking. Automated receivers can increase data greatly from radio-tracked snakes, providing novel insights unavailable from conventional hand tracking. There are drawbacks to this technology, some of which will vary among study species; therefore, researchers should evaluate the appropriateness of the technology for both the study species and the questions being asked.
We used an occupancy modeling framework to test the relative importance of upland habitat composition (proportion of different types of vegetation and development) and pond characteristics (water chemistry and vegetation) in determining the occurrence of two species of pond-breeding salamanders, the Marbled Salamander (Ambystoma opacum) and Mabee's Salamander (Ambystoma mabeei), in an urban nature reserve in southeastern Virginia, USA. Of 55 ponds surveyed in 2009, we found A. opacum larvae in 17 (30.9%) ponds and A. mabeei larvae in seven (12.7%) ponds. We found a strong positive relationship between A. opacum larval occupancy probability and pH; salamanders were more likely to occupy less acidic waters. Sampled ponds were highly acidic, with pH values ranging between 3.36 and 4.41, but A. opacum occupied only ponds with pH values >3.66. Ambystoma mabeei was more tolerant of the highly acidic conditions and was more likely to occupy larger ponds with fewer trees and scrubs. Landscape-level models were not well supported. Although pond acidification is generally dismissed as a cause of amphibian declines, our results suggest that pH can be an important, species-specific factor in determining occupancy of pond-breeding amphibians.
We evaluated the hypothesis that adjustments in call duration made by male Gray Treefrogs render their calls less easily masked in noise and so facilitate communication with females in choruses. We also tested whether shifts in male call duration and rate can be elicited through changes in the level of filtered background noise. We found that males increased the number of pulses in their calls while lowering call rate with elevations in noise level in a fashion similar to that reported during broadcasts of calls. In phonotaxis tests with females using unmodulated or modulated background noise and calls (10, 20, 30, or 40 pulses long) presented at either unequal or equal rates, we failed to find significant differences in noise levels at call recognition thresholds for calls of different duration. However, calls were detected more easily (i.e., noise levels at recognition thresholds were higher) when the noise background was modulated as compared to unmodulated. Our results and those of an earlier study by our laboratory indicate that changes in vocal behavior made by males of Hyla versicolor in response to changes in the calling of other males and background noise within choruses likely do not function to lessen the problems of signal detection or degradation due to interference. Accordingly, a small advantage accruing to males because of an inherent, albeit context-dependent, female preference for long calls (even at low call rates) may account for the dynamic calling behavior of male Gray Treefrogs.
Crawfish Frogs (Lithobates areolatus) are a North American ranid, considered near threatened globally with populations in decline throughout their range. We studied populations of Crawfish Frogs on local and regional scales at their northeastern range limit to (1) assess the level of genetic diversity within populations, (2) estimate fine-scale genetic structure, and (3) estimate genetic differentiation between populations at the regional level. We used 10 microsatellite loci to genotype frogs collected from three regional sites in Indiana separated by 50–172 km and at one of these sites within a network of three breeding ponds <1 km apart. Heterozygosity estimates revealed high levels of diversity within these populations (mean HO: 0.54–0.67 per site), which is encouraging for future management. The degree of population subdivision was low at the regional level (FST = 0.071 for sites within 172 km). Genetic differentiation was related to geographic distance between sampling sites, as predicted by an isolation-by-distance model. We observed no genetic differentiation between individuals sampled from ponds approximately 250 m apart and slight divergence of individuals from a pond approximately 750 m away. This suggests ponds within 1 km form a genetically distinct single breeding unit composed of multiple subpopulations. Finally, we observed high genetic differentiation between southwest and southeast Indiana sites indicating historical (rather than recent) isolation of these sites. These data will be applied to a regional management plan in an attempt to recover Crawfish Frogs along the northeastern extreme of their range.
Metabolic depression is a common strategy used during stressful environmental conditions, allowing animals to survive for prolonged periods on limited endogenous fuel stores; yet, the mechanisms involved in regulating metabolic depression are poorly understood. The endogenous opioid system (EOS) has been implicated in the regulation of metabolism during hibernation in vertebrates, and we hypothesized that opioids also may regulate metabolic rate during aestivation in the Green-Striped Burrowing Frog, Cyclorana (Litoria) alboguttata (Gunther, 1867). When incubated in the presence of opioid agonists, liver and muscle tissue slices from C. alboguttata underwent tissue- and agonist-specific metabolic depression, and the effect of opioid agonists on metabolism was more pronounced in tissue slices from aestivating animals. Gene transcript levels for the δ-opioid receptor remained constant in the brain and muscle of aestivating C. alboguttata compared with that of active frogs, as did brain transcript levels of the opioid receptor XOR1. The results of this study demonstrate that opioids can influence metabolic rate in isolated tissues from C. alboguttata. The maintenance of key opioid receptor gene transcript levels in tissues of aestivating frogs suggests that despite the energetic costs, maintenance of receptor abundance is important. We propose that the maintenance of opioid receptor abundance during aestivation in C. alboguttata is indicative of a role for the EOS in the regulation of metabolic rate during aestivation.
Variation in personality traits is observed commonly in many taxa but has been rarely studied in amphibians. We tested whether individual Bullfrog tadpoles exhibit personality, behaving consistently across multiple trials, and differently from conspecifics. From video footage of individual tadpoles in a familiar (home) environment and a novel environment (open field), we obtained measures of their level of activity, boldness, and exploration behavior over multiple trials. We found that activity level did not differ consistently between individuals. Boldness was moderately repeatable and exploration highly repeatable within individuals across trials, but only exploration varied significantly among individuals. These findings provide evidence of typical personality traits in tadpoles and support the value of Bullfrog tadpoles as model organisms in personality research.
We describe a new species of Phyllodactylus from a xerophytic forest in the Andes of southern Ecuador. The new species differs from other mainland species of Phyllodactylus from South America by the combination of the following characters: preanal scales similar in size to other ventral scales, well-defined longitudinal rows of tubercles dorsally, a medial longitudinal row of enlarged caudal scales ventrally, tubercles on dorsal surface of tibia present, enlarged postanal scale absent, tubercles on dorsal surface of forearm absent, interorbital scales homogeneous in size, enlarged scales on proximal one-fourth of tail absent, gular scales granular, and maximum snout–vent length of 55 mm. Even though morphological similarity suggests a close relationship between the new species and Phyllodactylus reissii, phylogenetic analyses of 10 nuclear and mitochondrial genes contradict this hypothesis. We also report the first records of Phyllodactylus kofordi for Ecuador.