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A wide variety of agricultural chemicals with potential to affect amphibian health are released into the environment daily. Most of these chemicals are xenobiotic compounds that are highly toxic to embryos, tadpoles, and terrestrial stages. Other substances that occur in pristine environments at harmless concentrations, such as inorganic nitrogenous compounds, may reach potentially toxic levels as a consequence of certain human activities, including the application of fertilizers. Most of the studies that analyze the effects of inorganic nitrogen on amphibian embryos are conducted with anurans, whereas little information exists regarding urodeles. Embryos of newts and salamanders usually exhibit longer times to hatch than frogs and toads. A longer hatching time results in a longer exposure of embryos to diffuse environmental pollution and therefore a higher risk of suffering toxic effects during the embryonic stage. We demonstrate that ammonium nitrate, a widely used nitrogenous fertilizer, at concentrations used in areas of high agricultural intensity, affects embryonic development of the Iberian newt (Lissotriton boscai). Although ammonium nitrate did not have significant lethal effects, it reduced the growth rate of exposed embryos, which were 9.6% smaller than controls. Hatching synchrony remained similar across treatments, and hatching date was not affected by ammonium nitrate, indicating that the effect on growth was not time-dependent. Researchers have demonstrated fitness costs in smaller than average tadpoles, suggesting that ammonium nitrate exposure could have long-term negative consequences for the Iberian newt.
Knowledge of life history and population demography of threatened amphibians is poor. I used skeletochronology in conjunction with mark–recapture data to examine growth rates, age at maturity, and longevity of the spotted tree frog, Litoria spenceri, a critically endangered Australian species. Ages were reliably determined for 578 individuals across two populations at 335- and 1110-m elevation. Females attained larger body sizes than males and took longer to reach sexual maturity, consistent with most anurans. Males matured at 2 yr and females at 3–4 yr at lower elevations, whereas at higher elevations, males matured at 3–4 yr and females took up to 6 yr to mature, which is slow compared with most anurans. Overall, L. spenceri is long-lived, with a maximum confirmed age of 14 yr. These life history attributes have implications for population dynamics of L. spenceri, which may have markedly different demographic responses to certain threatening processes compared with faster growing, shorter lived species. This study highlights the value and need for more life history and demographic data on threatened species. Generalizations about population demography and dynamics across environmental gradients should be made cautiously.
Atrazine (2-chloro-4-ethythlamino-6-isopropylamine-1,3,5-tiazine) is a widely used preemergent herbicide for controlling broadleaf plants. Because atrazine (a known endocrine-disrupting chemical) is applied in the late spring and early summer, its incidental effects on species exposed to runoff from terrestrial sources in this time period are of special interest. To examine the possible secondary impact of atrazine, we obtained eggs from 10 nests of two map turtle species, Graptemys ouachitensis and G. pseudogeographica, that nest on riverine sandbars. We incubated two eggs from each nest in sand containing one of four initial concentrations of atrazine (control and 0.1, 10, and 100 µg/L) based on levels measured in the river at the site where eggs were collected. We recorded hatching success, incubation time, external morphological abnormalities, gonadal sex, three measures of body size, righting time, and swimming time for all turtles. We reared a subset of the original neonates individually for 11 mo, during which time nest escape behavior, time to first foraging event, time to capture prey, growth, and survival were evaluated. None of the variables recorded at hatching was significantly affected by atrazine treatment, although abnormalities declined as atrazine levels increased. However, turtles deriving from the lowest atrazine-treated eggs had inhibited nest escape behavior and reduced posthatching survival. These findings reveal persistent fitness-reducing impacts on neonatal turtles resulting from atrazine exposure during embryonic development.
Insular lizards usually consume a large proportion of plant material compared to mainland ones, which is frequently attributed to a low prey availability on islands. In the present study, we analyze the diets of six populations (three insular and three continental) of the omnivorous lizard Tropidurus torquatus on the eastern Brazilian coast, to assess the extent which the insular and continental lizards differ in feeding habits, especially in the consumption of plant material. The degree of plant consumption varied greatly among areas, with the volumetric proportion of plant food in lizard diets ranging from 5% to 67%, but there was no tendency for insular lizards to consume more plant food than mainland ones. Moreover, insular lizards tended to eat more and larger prey items than those of the mainland, and estimated prey availability was not reduced on the islands compared to the mainland. The results of this study suggest that plant ingestion by T. torquatus is not related directly to insularity, but may be related to prey availability in the habitat. Therefore, the idea that populations of omnivorous lizards invariably tend to consume more plant food on islands than on the mainland must consider whether animal food is limited on a particular island.
Difference in growth pattern is one of the proximate causes of geographic variation in body size. Such a difference in growth pattern could be explained by two extremes such as genetically determined outcome and phenotypic plasticity or by a combination of these. The Japanese four-lined snake (Elaphe quadrivirgata) on Yakushima Island, Japan, has small body size compared with snakes on the main islands. To examine whether the dwarfism of Yakushima snakes is a consequence of genetic modification or a direct phenotypic response to immediate environmental conditions, E. quadrivirgata from Yakushima and a main island (Shiga Prefecture in Honshu Island), were reared from hatching in a laboratory environment. Data of field surveys were used to examine feeding habits and growth in the wild. Free-ranging snakes on Yakushima had significantly smaller body size and lower growth rate than those in Shiga. Yakushima snakes consumed almost exclusively lizards, whereas frogs were the main prey for Shiga snakes. The proportion of snakes that contained food in their stomach was lower in Yakushima than in Shiga. Available information suggests that the dwarfism of Yakushima snakes cannot be explained by lower survivorship. At hatching, Yakushima snakes of both sexes were larger than Shiga snakes. However, Yakushima and Shiga snakes reached similar body size after approximately 1 year. Captive-reared snakes from the insular dwarf population can reach comparable size to those from the main island, indicating that the growth rate, and hence body size, of E. quadrivirgata is obviously highly plastic. Based on these results, I consider that the dwarfism of Yakushima snakes is attributable to a direct phenotypic response, presumably to food limitation, rather than to microevolutionary changes.
The effect of temperature on sperm dynamic parameters in ectotherms in general, and reptiles in particular, remains poorly understood due to the lack of consistent evidence. As a group, snakes show considerable variability regarding mating systems, male reproductive behavior, thermoregulatory behavior, and preferred temperatures. Additionally, snakes present significant variability in sperm competition levels, which is determined by the species mating system. Because sperm longevity, motility, and velocity are positively related to reproductive success in both competitive and noncompetitive conditions, the sperm physiology of ectothermic organisms may functional optimally at ecologically relevant temperatures. The objective of this work was to analyze the effect of an ecologically plausible range of temperatures on sperm dynamic parameters of two species of snakes with contrasting mating systems and sperm competition levels: Boa constrictor occidentalis and Waglerophis merremii. To accomplish this, an in vitro incubation approach was used: sperm dynamic parameters (i.e., motility and velocity) were measured on sperm solution aliquots incubated at 25°C, 30°C, and 37°C for up to 10 h by means of a phase contrast video microscopy system. Results suggested that although an increase in temperature has a general negative impact on sperm motility and velocity, the two species studied present different degrees of sensitivity to high incubation temperatures. Moreover, these differences can be explained by the dissimilar thermal conditions that the sperm of the two species would experience during their reproductive seasons, which are a consequence of the differences in their reproductive behavior. In conclusion, sperm motility and swimming velocity respond mainly to environmental conditions imposed by mating systems rather than to selection by sperm competition.
We investigated the spatial ecology of the eastern massasauga (Sistrurus c. catenatus) at a study site unique in that it was near the northern extent of the species' geographic range and had a sandy substrate and extensive mixed coniferous forest. Forty-six individuals were radiotracked for at least one complete season between 2002 and 2004 or 2006 and 2007. Males had larger home ranges and core areas, range lengths, and movement rates than nongravid females, which in turn had larger movement parameters than those of gravid females. Movement rates and distances were not constant throughout the activity season, with males making greater movements as the activity season progressed and gravid females making the longest movements immediately following parturition. Total area used during the activity season was intermediate relative to that used by massasaugas at other sites, with minimum convex polygons around outermost observations during the active season averaging 16.7 ha. Movement indices at our site were much larger than reported indices from study sites in the central or southern portions of the massasauga's geographic range and more similar to those from Ontario and New York. The trend for increased movements at northern latitudes may have implications for managers attempting to provide sufficient habitat for viable populations and minimize interactions between snakes and roads or other anthropogenic disturbances.
A new species of Scinax is described from open formations of the coastal plains (Restingas) within the Tropical Atlantic Domain in northeastern Brazil. The new species most resembles S. auratus (Wied-Neuwied) and S. juncae Nunes and Pombal, and is diagnosed by the dorsal pattern of dorsolateral white stripes in dark-brown background, interocular white transversal stripe, and small scattered white blotches; snout rounded in dorsal view and profile; dorsal skin smooth; vocal sac smooth; presence of a few tubercles in a longitudinal way from the internal metatarsal tubercle to the heel; advertisement call with 7–8 notes; call dominant frequency 1.38 kHz. This new species can be easily distinguished from S. auratus and S. juncae by the different dorsal pattern, morphological traits, and advertisement call.
We describe a distinctively patterned new species of cascade stream frog from the mountains of Nueva Vizcaya and Aurora provinces, Luzon Island. The new species belongs to the genus Sanguirana, the definition of which we expand to include all Philippine species previously referred to the Rana (Hylarana) everetti complex. The new species is distinguished from other members of the genus by its possession of a bright yellow-green dorsum with conspicuous orange flower-shaped spots in females, bright white, postaxial dermal flanges on the limbs, green-to-purple flank transition, and a highly tuberculate, white venter, in addition to the absence of a dark canthal stripe. The new species is known only from high-gradient, cascading mountain streams between elevations of 750 and 1450 m in mature secondary forest and minimally disturbed primary forests. The discovery of such a distinctive new species emphasizes the relatively high degree to which endemic anuran diversity in the Philippines is still underestimated and underappreciated.