Reproductive cycles of alligator snapping turtles (Macrochelys temminckii).

The alligator snapping turtle (Macrochelys temminckii) is a species for which captive propagation and reintroduction programs are well established; however, little is known about its reproductive behavior and physiology. In this study, we measured monthly plasma sex steroid hormone concentrations of androgen (T + DHT) estradiol-17B (E2), and progesterone (P4), and used ultrasonography to monitor annual reproductive cycles of a captive population of alligator snapping turtles that is maintained under semi-natural conditions in southeastern Oklahoma. Concurrently, we used automated radio telemetry to measure the relative activity levels of male and female alligator snapping turtles and examine these activity patterns in the context of their reproductive cycles. We also measured monthly concentrations of the glucocorticoid (GC) corticosterone (CORT). Seasonal variation was only detected for T in males, but was observed for T, E2, and P4 in females. Vitellogenesis began in August and ended in April and coincided with elevated E2. Ovulation took place 10-29 April and the nesting period lasted from 11 May - 3 June. Males exhibited greater relative activity levels than females in the fall, winter, and early spring, which coincided with the period when mature sperm would be available for mating. Females were more active than males during the peri-nesting period in the spring. Seasonal changes in CORT were detected and did not differ between males and females. CORT concentrations were elevated in the late spring and summer, coincident with the foraging season, and depressed in the fall, and winter, and at their nadir in the early spring.

Correcting for unequal catchability in sex ratio and population size estimates.

Wildlife populations often exhibit unequal catchability between subgroups such as males and females. This heterogeneity of capture probabilities can bias both population size and sex ratio estimates. Several authors have suggested that this problem can be overcome by treating males and females as separate populations and calculating a population estimate for each of them. However, this suggestion has received little testing, and many researchers do not implement it. Therefore, we used two simulations to test the utility of this method. One simulated a closed population, while the other simulated an open population and used the robust design to calculate population sizes. We tested both simulations with multiple levels of heterogeneity, and we used a third simulation to test several methods for detecting heterogeneity of capture probabilities. We found that treating males and females as separate populations produced more accurate population and sex ratio estimates. The benefits of this method were particularly pronounced for sex ratio estimates. When males and females were included as a single population, the sex ratio estimates became inaccurate when even slight heterogeneity was present, but when males and females were treated separately, the estimates were accurate even when large biases were present. Nevertheless, treating males and females separately reduced precision, and this method may not be appropriate when capture and recapture rates are low. None of the methods for detecting heterogeneity were robust, and we do not recommend that researchers rely on them. Rather, we suggest separating populations by sex, age, or other subgroups whenever sample sizes permit.

Effects of life-history requirements on the distribution of a threatened reptile.

Survival and reproduction are the two primary life-history traits essential for species' persistence; however, the environmental conditions that support each of these traits may not be the same. Despite this, reproductive requirements are seldom considered when estimating species' potential distributions. We sought to examine potentially limiting environmental factors influencing the distribution of an oviparous reptile of conservation concern with respect to the species' survival and reproduction and to assess the implications of the species' predicted climatic constraints on current conservation practices. We used ecological niche modeling to predict the probability of environmental suitability for the alligator snapping turtle (Macrochelys temminckii). We built an annual climate model to examine survival and a nesting climate model to examine reproduction. We combined incubation temperature requirements, products of modeled soil temperature data, and our estimated distributions to determine whether embryonic development constrained the northern distribution of the species. Low annual precipitation constrained the western distribution of alligator snapping turtles, whereas the northern distribution was constrained by thermal requirements during embryonic development. Only a portion of the geographic range predicted to have a high probability of suitability for alligator snapping turtle survival was estimated to be capable of supporting successful embryonic development. Historic occurrence records suggest adult alligator snapping turtles can survive in regions with colder climes than those associated with consistent and successful production of offspring. Estimated egg-incubation requirements indicated that current reintroductions at the northern edge of the species' range are within reproductively viable environmental conditions. Our results highlight the importance of considering survival and reproduction when estimating species' ecological niches, implicating conservation plans, and benefits of incorporating physiological data when evaluating species' distributions.

Acute and persistent effects of pre- and posthatching thermal environments on growth and metabolism in the red-eared slider turtle, Trachemys scripta elegans.

Many ectotherms possess the capacity to survive a wide range of thermal conditions. Long-term exposure to temperature can induce acclimational and/or organizational effects, and the developmental stage at which temperature exposure occurs may affect the type, degree, and persistence of these effects. We incubated red-eared slider turtle embryos at three different constant temperatures (T(inc); 26.5, 28.5, 30.5°C), then divided the resulting hatchlings between two water temperatures (T(water); 25, 30°C). We calculated growth rates to assess the short- and long-term effects of thermal experience on this metabolically costly process. We also measured resting metabolic rate (RMR) at three body temperatures (T(body;) 26.5, 28.5, 30.5°C) shortly after hatching and 6 months posthatching to characterize the degree and persistence of acclimation to T(inc) and T(water) . Hatchling RMRs were affected by T(body) and T(inc) , and fit a pattern consistent with positive but incomplete metabolic compensation to T(inc) . Average growth rates over the first 11 weeks posthatching were strongly affected by T(water) but only marginally influenced by T(inc) , and only at T(water) = 30°C. Six-month RMRs exhibited strong acclimation to T(water) consistent with positive metabolic compensation. However, within each T(water) treatment, RMR fit patterns indicative of inverse metabolic compensation to T(inc) , opposite of the pattern observed in hatchlings. Average growth rates calculated over 6 months continued to show a strong effect of T(water) , and the previously weak effect of T(inc) observed within the 30°C T(water) treatment became more pronounced. Our results suggest that metabolic compensation was reversible regardless of the life stage during which exposure occurred, and therefore is more appropriately considered acclimational than organizational.

Physiological and behavioral variation in estivation among mud turtles (Kinosternon spp.).

Kinosternid mud turtles, a primarily aquatic group, exhibit variable degrees of terrestrial activity in the Sonoran and Chihuahuan Deserts. We compared behavioral and physiological responses to dry conditions in four populations representing three species, Kinosternon sonoriense, Kinosternon flavescens, and Kinosternon hirtipes. All four groups were subjected to simulated dry season conditions in the laboratory, during which activity was monitored and physiological responses (blood chemistry and rates of resting metabolism and evaporative water loss) were measured. Kinosternon flavescens and K. hirtipes represented extremes in apparent ability to estivate, based on activity and rate of increase of plasma osmolality. Two populations of K. sonoriense exhibited intraspecific differences in behavioral and physiological measures that were related to extant environmental conditions. Large numbers of K. sonoriense from Arizona and K. hirtipes, the poorest estivators, had to be rehydrated after only 30 d out of water. Kinosteron flavescens had the lowest metabolic rates, but no evidence of metabolic depression during dehydration was found for any of the four populations. We conclude that the differences in capacity for estivation among populations are primarily linked to variable behavioral responses to dry conditions, though high rates of evaporative water loss in K. hirtipes represent a probable physiological constraint.