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Although most of the unique ways that frogs reproduce were described in the 1800s and 1900s, additional modes are still being discovered in the 21st Century. The concept of reproductive mode has evolved from descriptive natural history to an integration of developmental biology, genetics, systematics, evolution, ecology, behavior, and physiology that frames our thinking about the transition of vertebrates from water to land and about anuran reproductive adaptations to diverse environments today. We have classified reproductive modes, examined quantitative parameters, searched for geographical and ecological patterns, and described variability. We have speculated about selective pressures guiding the evolution of terrestrial reproduction and argued about the usefulness of reproductive mode as a character to construct phylogenies. In the past, researchers assumed that the reproductive modes exhibited by living frogs represented stages in an incomplete, linear sequence of steps toward greater independence from open water, with direct development at the end of the spectrum. Newly proposed phylogenies based on molecular data allow us to re-think the evolution of anuran reproductive modes. On another level, we are increasingly realizing the value of incorporating life history information (aquatic larvae or terrestrial development) in setting priorities to formulate more effective and ecologically relevant conservation strategies. The next decade is certain to witness significant advances in our understanding of anuran reproductive modes.
Numerous studies have explored environmental factors that drive the distributions of anuran larvae. However, the causal links between physical or chemical factors and tadpole distributions often remain untested. The Río Salado is an intermittent, naturally saline river in Puebla, Mexico, that is increasingly being impacted by removal of water for commercial salt production. Using tadpoles of Exerodonta xera (Hylidae; Puebla Treefrog) and Incilius occidentalis (Bufonidae; Pine Toad), we experimentally examined the hypothesis that the distribution of tadpoles along the Río Salado results from the effects of salinity on tadpole survivorship, growth, and metamorphosis. We also examined the effect of tadpole density and the interaction of tadpole density and salinity, because pool size likely affects tadpole density. Increased salinity did not affect survivorship in I. occidentalis but reduced survivorship in E. xera by approximately 20% at both 0.4 parts per thousand (ppt) (0.4 g L−1) and 0.8 ppt (0.8 g L−1). Higher salinities delayed metamorphosis by up to 9 wk in E. xera and by 3 or 4 d in I. occidentalis. Tadpole density had a nonlinear effect on survivorship in E. xera, and higher densities delayed metamorphosis in I. occidentalis. There were no significant interactions between salinity and tadpole density in either species. Our results suggest that even though they can be found in pools averaging 0.8 ppt, tadpoles may not emerge from such pools because of delayed metamorphosis at salinities around 0.8 ppt. Decreasing pool volume and increasing tadpole density may further delay emergence of I. occidentalis. The removal of water from the Río Salado to produce salt may threaten amphibians that use the river for breeding.
Numerosos estudios han examinado los factores ambientales que influyen en la distribución de renacuajos; sin embargo, los vínculos entre factores físicos o químicos y la distribución de renacuajos frecuentemente permanecen sin probarse. El Río Salado es un río salino localizado en Puebla, México que está siendo muy impactado por la extracción de agua para la producción comercial de sal. Utilizando renacuajos de Exerodonta xera e Incilius occidentalis, experimentalmente examinamos la hipótesis que la distribución de los renacuajos a lo largo del Río Salado es el resultado de los efectos de la salinidad sobre la sobrevivencia, crecimiento y metamorfosis de los renacuajos. También examinamos el efecto de la densidad de renacuajo y la interacción de la densidad de renacuajos y la salinidad, ya que el tamaño de las pozas probablemente afecta la densidad de los renacuajos. El incremento de la salinidad no afecto la supervivencia de I. occidentalis pero redujo la sobrevivencia de E. xera en aproximadamente 20% tanto en tratamientos de 0.4 como de 0.8 partes por mil (ppm). Salinidades más altas retrasaron la metamorfosis hasta por nueve semanas en E. xera y por tres o cuatro días en I. occidentalis. La densidad de renacuajos tuvo un efecto no lineal sobre la supervivencia en E. xera y las densidades más altas retrasaron la metamorfosis en I. occidentalis. No hubo interacciones significativas entre la salinidad y densidad de renacuajos en ninguna de las dos especies. Nuestros resultados sugieren que aunque estas especies pueden ocupar pozas con un promedio de 0.8 ppm, los renacuajos podrían no salir de estas pozas que se están secando debido al retraso en la metamorfosis en salinidades de alrededor 0.8 ppm. Disminuyendo el volumen de las pozas e incrementando la densidad de los renacuajos puede retrasar la transformación de renacuajos de I. occidentalis. La extracción de agua del Río Salado para producir sal puede amenazar la habilidad de los anfibios que utilizan el Río Salado para reproducirse.
Currently there is limited information on the population dynamics of tadpoles, particularly in the Neotropical region. Because of this dearth of information, studies on the temporal distribution of different tadpole developmental stages are important for understanding the dynamics of these organisms in their aquatic environment. We studied the temporal distribution of the Torrent Frog Hylodes uai tadpoles, and their relationship with rainfall, in an Atlantic Rainforest–Cerrado ecotone in Southeastern Brazil. There is no previous information on population dynamics for this tadpole species. We sampled 42 m along a forest stream between April 2003 and March 2005. Tadpoles occurred during all months. Tadpoles in initial developmental stages (up to Gosner stage 25) represented 66.7% of sampled individuals and occurred throughout year, suggesting continuous and prolonged reproductive activity. Body length in tadpoles varied between seasons and among developmental stages. Overall tadpole density varied from 0.024 to 0.67 tadpoles/m of stream and was higher in the dry season, which may be an adaptation to target their metamorphosis to the rainy season. The main microhabitat used by tadpoles was under stones, and there was a tendency for tadpoles with smaller body size to occupy shallower stream portions. Our study contributes to the understanding of tadpole dynamics in tropical forest streams and adds information on the ecology of a stream-dwelling amphibian.
In the case of contaminants that are commercially available and introduced by humans, understanding where and how often a product is used is critical in assessing its ecological impact. By contextualizing a product's ecotoxicological impact with details regarding its application, we can provide a more complete characterization of the product's environmental risk than is possible with ecotoxicological data alone. We conducted an ecotoxicology experiment to examine the interaction between predator-induced stress and one of three common mosquito insecticide formulations (Mosquito Dunks, Mosquito Bits, and Mosquito Torpedoes) on the performance of Gray Treefrog (Hyla versicolor) tadpoles and changes in aquatic communities in pond mesocosms. Then, to describe the extent to which each product was applied in the region surrounding our study area, we conducted a survey of mosquito insecticide practices by individuals who owned or managed property within U.S. Environmental Protection Agency region seven. When applied in the presence of predators, Mosquito Torpedo use resulted in the lowest tadpole survival rates. Mosquito Dunks also reduced tadpole survival when applied in the context of predators (P = 0.06), and Mosquito Bits had no effect on tadpole survival. Of land managers who applied a mosquito insecticide, 5% used Mosquito Bits, 5% used Mosquito Torpedoes, and 81% used Mosquito Dunks. Despite the fact that Mosquito Torpedoes appear to have more severe negative effects on tadpole survival than do Mosquito Dunks, the widespread use of Mosquito Dunks by individuals in our survey leads us to recommend that future research efforts be directed toward Mosquito Dunks.
Tropical frogs show extensive variation in timing of breeding, reproductive strategies, and spatial patterns of calling males and nest sites. Over 2 yrs I studied a poorly known species of frog that exhibits maternal care. I report results from behavioral observations, breeding monitoring, and mark–recapture, describing the temporal and spatial distribution of males and foam nests in relation to pond depth and rainfall. I found that Leptodactylus insularum is a prolonged, episodic breeder with an average temporal lag of 12 d between breeding events. Although more nests were laid on nights following days with more rain, not every heavy rain triggered oviposition and there does not seem to be an absolute threshold in cubic millimeters of rain for laying eggs. Frogs laid their nests in shallow areas (15–115 mm) of the marsh and distributed nests in a spatially clumped pattern. Individual males were not recaptured in the same area of the marsh, which, combined with behavioral observations, suggests that they are not territorial. I recaptured 41% of 182 adult frogs tagged within a season, but did not recapture any adults across seasons, suggesting high mortality rates and a functionally semelparous life-history strategy. I found that juveniles reach sexual maturity in the following breeding season. I discuss the breeding strategies of L. insularum in relation to environmental factors and in comparison with related species and unrelated frogs with similar breeding patterns.
Las ranas tropicales varían extensamente en cuanto a sus temporadas de cría, estrategias reproductivas, y patrones espaciales de sitios de canto en machos y colocación de nidos. Durante dos años, estudié una especie de rana poco conocida que provee cuidado maternal a sus renacuajos. Reporto resultados de observaciones de comportamiento, monitoreo reproductivo, y captura-recaptura, describiendo la distribución espacio-temporal de los machos y de los nidos de espuma en relación a la profundidad del estanque y la cantidad de lluvia. Encontré que Leptodactylus insularum muestra una estrategia reproductiva episódica y prolongada, con un periodo promedio de 12 días entre eventos de cría. Aunque las hembras pusieron más nidos en noches de días con más lluvia, no todas las lluvias fuertes incitaron oviposición y no parece haber un umbral absoluto en milímetros cúbicos de lluvia para que las hembras pongan huevos. Las ranas pusieron sus nidos en las áreas poco profundas (15–115 mm) del pantano y presentaron un patrón de distribución aglomerada. Las recapturas de cada macho no se concentraron en áreas particulares del pantano, lo que, combinado con observaciones comportamentales, sugiere que los machos no son territoriales. Recapturé el 41% de 182 ranas adultas marcadas en una misma temporada, pero no recapturé ningún adulto de una temporada reproductiva a la siguiente, lo que sugiere altas tazas de mortalidad y una historia de vida funcionalmente semélpara. Hallé que los juveniles alcanzan la madurez sexual en la siguiente temporada de cría. Discuto las estrategias reproductivas de L. insularum en relación a factores ambientales y en comparación a especies relacionadas, y además comparo mis resultados con estudios en ranas no relacionadas pero con patrones de cría similares.
Male Hypsiboas punctatus emit seven different types of calls: three consist of repeated trains of notes, and four are single-note calls with frequency modulation. Behavioral observations allowed assigning the calls to specific functions: (1) and (2) advertisement calls (short and long duration), (3) territorial signaling, (4) courtship interactions, (5)–(7) aggressive interactions (aggressive, fighting, and release calls). All calls consist of a single note and possess harmonic structure. The harmonic structure from the advertisement call suggests a missing fundamental frequency. Advertisement calls exhibit inter- and intraindividual variation in the dominant frequency. Our results indicate that previous comparisons among vocalizations of H. punctatus were based on different types of calls.
We describe the vocal repertoire of Melanophryniscus cupreuscapularis, a bufonid toad of the Melanophryniscus stelzneri species group, which has been recently listed as “Vulnerable” by the Asociación Herpetológica Argentina. Recordings were obtained in “Paraje El Perichón,” a relict of Schinopsis balansae “quebracho” forest near Corrientes City, Argentina, in September 2007. We provide data on the structure and frequency of three kinds of vocalization: the advertisement, the encounter, and the release calls. We found that the advertisement call is formed by two distinct sections: a first segment consisting of short emissions, usually grouped, and a fast trill. We found that the encounter call is also composed of two segments but that the number of simple emissions in the first segment is greater and more variable (6–60) than in the advertisement call, and the emissions are ungrouped. Although the dominant frequency was similar to the advertisement call, the encounter call frequency was 2,184 Hz (range: 1,832–2,482). The release call is composed of isolated emissions emitted at a lower frequency (1,798 Hz, range: 1,712–1,926) than are the other calls. The structure of the advertisement call was similar to that of other species of the stelzneri group.
Se describe el repertorio vocal de Melanophryniscus cupreuscapularis, un bufónido que pertenece al grupo stelzneri recientemente categorizada como “vulnerable” por especialistas de la Asociación Herpetológica Argentina (AHA). Las grabaciones fueron obtenidas en septiembre de 2007 en el Paraje “El Perichón,” un relicto de bosque de quebracho colorado, Schinopsis balansae, cercano a la ciudad de Corrientes, Argentina. Proveemos información sobre el análisis estructural y de frecuencia de tres tipos de vocalizaciones: canto de advertencia, de encuentro y de rechazo. M. cupreuscapularis emite un canto de advertencia formado por dos secciones diferentes: un primer segmento compuesto de emisiones aisladas, generalmente agrupadas, seguidas por un rápido vibrato. El canto de encuentro está compuesto también por dos segmentos, pero en este caso el número de emisiones simples del primer segmento es mayor y más variable (6–60) que en el canto de advertencia y se presentan desagrupadas. Si bien la frecuencia dominante es similar a la del canto de advertencia, en el canto de encuentro estas ocurren aproximadamente a 2,184 Hz (1,832–2,482). Finalmente, el canto de rechazo es una vocalización conformada por emisiones aisladas emitidas a menor frecuencia (1,798 Hz, range: 1,712–1,926) que en los otros dos casos. Nosotros encontramos similitudes entre la estructura del canto de esta especie con la de otros miembros del grupo stelzneri.
We used nightly surveys to monitor the status of building-dwelling gecko species on the southern Caribbean island, Curaçao. Two gecko species were detected in 10 counts across five nights from 18 sites. We recorded the nonnative Wood Slave, Hemidactylus mabouia (81%, 369/455 observations), native Dutch Leaf-Toed Gecko, Phyllodactylus martini (11%, 50/455 observations), and unidentified geckos (8%, 36/455 observations) on the island. The Dutch Leaf-Toed Gecko was most common near the forest and rare elsewhere. Wood Slave abundance was not influenced by forest proximity. Wood Slaves commonly perched near lights that provided heat and attracted insect prey. In contrast, the Dutch Leaf-Toed Gecko perched away from lights. Similar to gecko species in Florida, Wood Slaves displaced Dutch Leaf-Toed Geckos. The Dutch Leaf-Toed Gecko was syntopic with the Wood Slave on buildings near the forest when resources were not limiting or if other gecko populations were not self-sustaining. As Wood Slave populations grew, they excluded Dutch Leaf-Toed Geckos, and possibly Antilles Geckos, Gonatodes antillensis, from these buildings. This exclusion adds novel obstacles to the continued survival of the Dutch Leaf-Toed Gecko on Curaçao. A similar situation may be present on Bonaire, and for a congeneric species on Aruba, where the Wood Slave is a more-recent colonist.
Few examples of mesopredator release, whereby subordinate predators increase in abundance in response to a reduction in dominant predators, have been demonstrated from reptile communities despite the important ecological role of large varanids and snakes. We tested the hypothesis that trophic cascades attributable to mesopredator release of varanids could explain the apparently perverse decline of some small reptiles following removal of exotic mammalian predators in a landscape-scale reserve in arid South Australia. We used counts of Sand Goanna (Varanus gouldii) tracks and diggings as a surrogate activity index in paddock-scale treatments with different assemblages of feral predators and reintroduced mammals. Varanus gouldii activity was five times higher in regions where cats and foxes were removed than where they were present. We hypothesize that the suppression of mammalian predators can have complex effects that extend to reptile communities and should inform conservation management decisions in environments with large reptile predators.
Flooding and predation are the two major causes for the decline in hatching rate and hatchling survival in crocodilian species. Recently, Solenopsis invicta (Red Fire Ant) has been recognized as a formidable invasive species, causing changes in wild populations of reptiles. Because of the elevated densities of Red Fire Ants present in Caiman latirostris (Broad-Snouted Caiman) nests during the breeding season, experiments in captivity and in the wild were performed to verify if the presence of S. invicta affects nest success or care of eggs and the hatching-assistance behavior of C. latirostris females. Hatchling survival from eggs incubated in a lab setting in the presence of Red Fire Ants decreased by approximately 10% compared to nests without ants. In a second experiment performed in the wild, the presence of Red Fire Ant resulted in a 43% reduction in nest success including direct (14.5%) and indirect (28.5%) effects. Our study confirmed that Red Fire Ants negatively affect C. latirostris nest success, directly because Red Fire Ants attack and cause the hatchling's death after pipping and indirectly by preventing females from caring for eggs, providing hatching assistance, and maintaining nests.
Las inundaciones y la depredación son las dos principales causas de la disminución en la tasa de eclosión y supervivencia de las crías en especies de cocodrilos. Recientemente, Solenopsis invicta (Hormiga Colorada) ha sido reconocida como una formidable especie invasora, provocando cambios en las poblaciones silvestres de reptiles. Debido a las altas densidades de Hormigas Coloradas presentes en los nidos de Caiman latirostris (yacaré overo) durante la época reproductiva, se realizaron experimentos en cautiverio y en la naturaleza para comprobar si la presencia de S. invicta afecta el éxito de eclosión, el cuidado de los huevos y el comportamiento de asistencia durante la eclosión por parte de las hembras de C. latirostris. La supervivencia de neonatos de los huevos incubados en condiciones de laboratorio en presencia de Hormigas Coloradas disminuyó aproximadamente un 10% comparado a los nidos sin presencia de hormigas. En un segundo experimento realizado en la naturaleza la presencia de Hormigas Coloradas produjo una reducción del 43% en el éxito de eclosión, incluyendo los efectos directos (28,5%) e indirectos (14,5%). Nuestro estudio confirmó que las Hormigas Coloradas afectan negativamente la tasa de eclosión de C. latirostris, directamente cuando las Hormigas Coloradas atacan causando la muerte de las crías producto de sus picaduras, e indirectamente mediante el impedimento del cuidado de los huevos, la asistencia durante la eclosión, y el mantenimiento de los nidos por parte de las hembras.
Can the loss of forest habitat cause changes in local communities? The results of our study of anuran assemblages in the southern Amazon indicate that the conversion of forest into open environments results in the substitution of species and the reduction of beta diversity. The increasing loss of tropical forests to agricultural development, especially in the Amazon, has resulted in the extensive modification of the natural landscape, transforming once-continuous forests into a mosaic of modified habitats. Our data indicate that this process resulted in the substitution of forest species by generalists, which are more typical of open environments. Also, this process has a homogenizing effect, making different areas more similar to one another, resulting in a decrease in beta diversity. This substitution–homogenization process may become increasingly common through the ongoing advance of agricultural frontiers, resulting in the local extinction of an important component of the biodiversity of tropical forests.
Stream microhabitats are strongly influenced by adjacent terrestrial land use and other anthropogenic disturbances. Therefore, sensitive stream fauna can be highly imperiled. We investigated relative susceptibility of stream-associated salamanders to riparian land use by studying species-specific responses that influence community assembly. The Piedmont and Blue Ridge ecoregions of the southeastern United States have high aquatic biodiversity, centuries of land use, and increasingly extensive urbanization. We surveyed low-order streams in these regions for salamanders across four riparian land uses (forests, agricultural, residential, and urban) and assessed 15 habitat variables at each sampling site. We found that forested streams were more diverse compared to streams affected by riparian land uses. Our study showed two distinct assemblages of salamanders in response to riparian land use: forest-dependent, large-bodied, long-lived species sensitive to riparian land uses (disturbance avoiders) and cosmopolitan, small-bodied, short-lived species that are relatively resistant to impacts of riparian land uses (disturbance tolerants). These assemblages varied in composition between the ecoregions, with Blue Ridge harboring more land-use–intolerant species. Results indicated that multiple habitat features of the riparian zone (canopy cover, canopy height, leaf litter cover), and stream geomorphology (bank complexity, streambed heterogeneity, sedimentation) are dramatically altered by riparian land uses, and influence the assemblage structure of salamanders. Riparian buffers in both ecoregions are largely unprotected (70% in Blue Ridge, 96% in Piedmont) and are possibly threatened with anthropocentric land uses. Results suggested that conservation of stream salamander communities should be strengthened with protection and restoration of riparian forests, connectivity among riparian forests, and soil-conservation practices.
We studied nesting of Cuvier's Dwarf Caiman, Paleosuchus palpebrosus, in flooded forest around the Amazon River, and streams draining into the Brazilian Pantanal. Nests were located by searching on foot. Eighty nests were located in the Amazonian sites between 2001 and 2010, and 35 nests were found in the Serra das Araras Ecological Station and streams draining Urucum Mountain on the periphery of the Pantanal between 2006 and 2011. Sizes of embryos indicated that nesting occurs in the Amazonian sites during the dry season and coincides with falling water levels. Although nesting coincides with the warmest and wettest months in the streams around the Pantanal, the streams are not subject to long-term floods. Clutch size varied from eight to 21 eggs, was correlated with female size, and the mean clutch size did not differ between the Amazonian sites and those around the Pantanal.
Understanding growth patterns is critical for determining age and size at sexual maturity and longevity in species that are severely threatened by over-collection and habitat loss, particularly in poorly understood species in tropical East Asia. Using data collected during a 9-year mark–recapture study, we fit the von Bertalanffy and logistic growth models to examine growth patterns of the endangered Big-headed Turtle (Platysternon megacephalum). Growth rate of P. megacephalum was best described by the von Bertalanffy model. Mean age at maturation for female and male P. megacephalum was 8 and 13 years. At maturity for female and male P. megacephalum, mean carapace length was 100 mm and 130 mm, respectively. We determined that counting growth rings on the carapace and plastron was not a reliable method for estimating ages. The long time to maturation in P. megacephalum may be costly in harvested populations, with individuals potentially being removed from populations prior to first reproduction. The growth patterns we have documented, and associated information on body size and age at sexual maturity, yield metrics that may be used to assess the effects of harvesting in populations and may contribute to conservation efforts for this endangered species.
We examined the diet of New Mexico Ridge-nosed Rattlesnakes (Crotalus willardi obscurus) from the Sierra San Luis and the Sierra Pan Duro in the northern Sierra Madre Occidental, México. All snakes included in this study were encountered during August, September, and October in 2003 and 2004. Including recaptures of previously captured individuals, 107 of 199 snakes contained at least one prey item. We examined 103 prey items from 92 of these snakes; some snakes contained multiple prey items. Approximately two-thirds of prey items were ectotherms (54.4% lizards and 13.6% scolopendromorph centipedes); birds (21.4%) and mammals (10.7%) were also taken. The diet of juvenile snakes (n = 32) consisted primarily of lizards (62.5%) and centipedes (25.8%), although large juveniles also consumed mammals (6.3%) and passerine birds (6.3%). Adult snakes (n = 71) fed primarily on lizards (50.7%) and passerine birds (28.2%) but also consumed mammals (12.7%) and centipedes (8.4%). Crotalus willardi in the Sierra San Luis and Sierra Pan Duro consumed more birds than has been reported from C. willardi in nearby populations and continued to consume centipedes as adults.
Examinamos la dieta de la New Mexico Ridge-nosed Rattlesnake (Crotalus willardi obscurus) en la Sierra San Luis y la Sierra Pan Duro en el norte de la Sierra Madre Occidental, México, de serpientes colectadas en los meses de agosto, septiembre y octubre en 2003 y 2004. Capturamos 199 serpientes contando capturas y recapturas. Y de ellas 107 contenían restos de por lo menos una presa. Examinamos 103 restos de presas provenientes de 92 serpientes; algunas serpientes presentaban restos de múltiples presas. Aproximadamente dos tercios de las presas fueron ectotermos (54.4% lagartijas y 13.6% ciempiés); también fueron consumidas aves (21.4%) y mamíferos (10.7%). La dieta de las serpientes juveniles (n = 32) consistió principalmente de lagartijas (62.5%) y ciempiés (25.8%), aunque los juveniles grandes también consumieron mamíferos (6.3%) y aves paseriformes (6.3%). Las serpientes adultas (n = 71) se alimentan principalmente de lagartijas (50.7%) y aves paseriformes (28.2%), aunque también consumieron mamíferos (12.7%) y ciempiés (8.4%). Las serpientes en la Sierra San Luis y la Sierra Pan Duro consumieron más aves de lo que ha sido reportado para las poblaciones cercanas y los adultos continúan alimentándose de ciempiés.
Bachia bicolor is a small serpentiform lizard distributed from central to northern Colombia and western Venezuela; until now ecological and reproductive data are unknown for this species. We studied some ecological and reproductive aspects of a population of B. bicolor that inhabits urban areas from a Colombian city. Lizards are found in house gardens and public parks, living underground in organic-rich soils and feeding on small arthropods such as termites, insect larvae, coleopterans, and terrestrial isopods, among others. Males and females of B. bicolor reach sexual maturity with a similar body size and a similar body form; however, males have larger heads than do females. Males and females were found to be reproductively active throughout the year without differences in gonadal morphometric variables between months or seasons. Neither the amount of ingested food nor the abdominal fat body masses varied among months or seasons. These observations, together with the presence of juveniles in most months, suggest continuous reproductive activity and continuous feeding in this population. Our results show that B. bicolor lives and feeds underground as do other fossorial gymnophthalmids, and its diet clearly differs from those of semi-fossorial and surface-dweller gymnophthalmid lizards. Given its lifestyle and the favorable conditions offered by these urban systems, the ecological and reproductive characteristics of this population may be the result of either phylogenetic constraints (related to fossoriality) or a high resource availability, or a combination of both.
Bachia bicolor es un pequeño lagarto serpentiforme que se encuentra distribuido desde el centro hasta el norte de Colombia, y en el oeste de Venezuela; hasta el momento los datos ecológicos y reproductivos de esta especie son desconocidos. En este trabajo estudiamos algunos aspectos ecológicos y reproductivos de una población de B. bicolor que habita en el área urbana de una ciudad Colombiana. Estos lagartos se encuentran en los jardines de las casas y parques públicos viviendo bajo tierra en suelos ricos en material orgánico y alimentándose de pequeños artrópodos como termitas, larvas de insectos, coleópteros, e isópodos terrestres entre otros. Los machos y las hembras alcanzan la madurez sexual con un tamaño corporal similar y la forma del cuerpo es también igual para ambos sexos; sin embargo, los machos tienen cabezas significativamente más grandes que las hembras. Tanto machos como hembras son reproductivamente activos a lo largo del año, sin diferencias en las variables morfométricas gonadales entre meses o estaciones. La cantidad de alimento consumido y la masa de los cuerpos grasos abdominales tampoco variaron entre los meses o estaciones. Estas observaciones, junto con la presencia de juveniles en la mayoría de los meses, sugieren una actividad reproductiva y una alimentación continua en esta población. Nuestros resultados muestran que B. bicolor vive y se alimenta bajo tierra al igual que otros gymnophthalmidos fosoriales, y su dieta claramente difiere de gymnophthalmidos semi-fosoriales y de superficie. Debido a su estilo de vida y las condiciones ofrecidas por estos sistemas urbanos, las características ecológicas y reproductivas de esta población pueden ser el resultado de limitaciones filogenéticas (relacionadas con la fosorialidad), una alta disponibilidad de recursos, o una combinación de las dos.
Among reptiles, reproduction in the absence of males is often assumed to result from long-term sperm storage. Through the application of molecular genetic tools, biologists are beginning to recognize that facultative parthenogenesis can also explain such reproductive events in snakes. We observed a Copperhead (Agkistrodon contortrix) give birth to a stillborn neonate and four infertile ova after 9 yr in isolation from male snakes. To test the hypothesis that the neonate was produced asexually, we screened a panel of 10 microsatellite loci to genotype the mother and her offspring, as well as wild-caught individuals in the mother's population of origin, to assess the probability of paternity. Confirming prior research on Copperheads that suggests parthenogenesis by terminal fusion automixis, we found that four heterozygous maternal loci were homozygous in the neonate. We calculated the probability of a random male from the population as a sire to the neonate to be 2.32 × 10−13 by using the population allele frequencies and the genotype of the neonate. These results further confirm that Copperheads are facultatively parthenogenetic and suggest that this reproductive mode may be general within the species.
Amphibian parasite communities are often suggested to be dependent on host size. However, age-related differences in parasite exposure and susceptibility could lead to differences in parasitism unaccounted for by host size. To address these hypotheses, we determined the ages of Wood Frogs (Lithobates sylvaticus) using skeletochronology and assessed the relationships of host age and size with helminth infections. Neither age nor size was significantly related to helminth species richness. Total infection intensity increased with female age and generally increased with age and size in males. However, these overall measures may mask more complex dynamics with individual helminth species. Although the intensity of Alaria spp. increased in males initially, both the intensity and prevalence of Alaria spp. ultimately decreased with male age. The prevalence of both Fibricola sp. and Echinoparyphium rubrum increased with female age. The abundance of Fibricola sp. also increased with female age, whereas Fibricola sp. prevalence and intensity increased with male size. Rhabdias bakeri abundance increased with female size, but decreased with female age. These results suggest age and size are both related to some aspects of Wood Frog infection dynamics. We hypothesize that the absence of trematode metacercariae in young female frogs may be a result of delayed maturity because female Wood Frogs generally avoid water until they are reproductively mature. In contrast, male parasite-specific relationships may be the result of host immune response, host mortality, or parasite mortality. Because males and females were sampled at different times of the season, differences in parasitism based on host sex alone should be interpreted with caution.
Prairie Rattlesnakes (Crotalus viridis) are a species of conservation concern in Canada because of suspected population declines. Data on the habitat selection of Prairie Rattlesnakes at northern range limits are essential to inform management strategies and implement recovery plans in Canada and other northern regions. We used radio-telemetry and generalized linear mixed models to create resource selection functions for Prairie Rattlesnakes (N = 23) in and around Grasslands National Park, Saskatchewan, Canada. Eight habitat variables were compared between used and available sites to quantify microhabitat selection. We found that Prairie Rattlesnakes select for specific sites (i.e., within 1 m) with shrub cover and burrows and avoid bare ground. Shrub cover was two-times higher at used sites compared to available ones, while bare ground showed the opposite trend. In addition, two-thirds of all snake location points were within 1 m of a burrow, which suggests that retreat sites are important. None of the habitat variables measured at 10 m from used points were significant predictors of rattlesnake habitat selection, indicating that rattlesnakes select habitat at a very fine level. Northern range limits present a thermally challenging environment in which burrows and shrubs are likely crucial for thermoregulation. In addition, these retreat sites likely provide a prey source, protection from predators, and suitable areas for reproduction. Retreat sites such as burrows and shrubs are therefore critical components of habitat for Prairie Rattlesnakes and should be included in management strategies for the species.
An isolated supraoccipital from the late Miocene of Chiapas, southern Mexico, can be referred to Caimaninae, a group including the living caimans and their closest extinct relatives. The specimen shares a polygonal shape, indicating lateral contact with the squamosals, with extant Caiman and Melanosuchus, but some extinct caimanine lineages had a similar morphology. This is the northernmost known caimanine occurrence during the Neogene, suggesting that members of this salt-intolerant lineage were present in North America possibly before the Isthmus of Panama was complete. It might also indicate that extant lineages within Caiman, including those found in Mesoamerica today, were distinct earlier than generally believed.
The Pratt Slide fossil site of Brown County, Nebraska has yielded a diverse frog fauna from the late Clarendonian North American Land Mammal Age (late Miocene; ca. 10.5–9.5 Ma). The fauna includes the extant genera Spea, Rana, Bufo, Hyla, and cf. Acris, the second record of the late Clarendonian genus Tregobatrachus, and a new, unique genus of frog. The fauna was dominated by Rana (at least 39 individuals). Overall, the taxonomic composition of the Pratt Slide frog fauna supports suggestions by others that the frog fauna of the Great Plains was predominantly modern at the generic level by ca. 10 Ma. Fossil evidence also suggests that the extinct toad Bufo pliocompactilis was common in the Great Plains during the late Miocene, and the extant genus Hyla occupied a larger Great Plains distribution during the late Miocene than today.
The Arizona Toad (Bufo [ = Anaxyrus] microscaphus) occupied the entire Agua Fria River drainage in central Arizona until relatively recently. By the 1980s, a close relative, Woodhouse's Toad (Bufo woodhousii), colonized the lower reaches of the Agua Fria and replaced B. microscaphus at some sites. We tested the hypothesis that habitat disturbance drives replacement of B. microscaphus by B. woodhousii, via hybridization, by examining shifts in the distribution of these toads following the expansion of the Waddell Dam on the lower Agua Fria River in the early 1990s. As of 2010, the high elevation headwaters of the Agua Fria River were still occupied by B. microscaphus, the lower reaches near the confluence with the Gila River were occupied by B. woodhousii, and along the middle reaches, hybridization between these two anurans occurred at the same three sites as documented in the early 1990s. Contrary to expectations, evidence of hybridization along middle reaches of the river is largely unchanged: B. microscaphus has not been replaced by B. woodhousii at any additional sites nor is there any evidence of introgression of woodhousii mtDNA into putatively “pure” microscaphus populations upstream of hybrid sites.
Cryptobranchus guildayi has been described as an extinct species of large salamander that is related closely to the modern Hellbender, Cryptobranchus alleganiensis. The validity of this extinct taxon has been questioned; thus, an expanded osteological sample of modern Hellbenders was compared to the C. guildayi fossil material. Based on our analysis of the fossil material, all morphological characters used to define C. guildayi can be observed in specimens of C. alleganiensis, or are based on misidentifications. Therefore, C. guildayi is considered to be conspecific with C. alleganiensis and taxonomically should be considered a junior synonym of the latter. The reassignment of the C. guildayi specimens to C. alleganiensis expands the prehistoric geographical range of the modern species to the Potomac River and its tributaries and also extends the age of the species into the Irvingtonian North American land mammal age.