Day B. Ligon

Temperature Effects During Early Life Stages of the Alligator Snapping Turtle (Macrochelys temminckii)

Abstract Alligator snapping turtle (Macrochelys temminckii) populations have declined across much of the southeastern United States in recent decades, due at least in part to overcollection. Recently, however, legal protection from large-scale harvesting has been granted to the species in all states where it is native, thereby drastically reducing one of the greatest threats to its survival. There is growing interest in captive propagation of alligator snapping turtles for reintroduction where populations have been decimated. In conjunction with one such effort, we analyzed the physiological effects of temperature on embryonic and posthatching development. Results indicate that extreme high and low incubation temperatures negatively affected embryo survival, and high incubation temperatures corresponded with shorter incubation time but also produced smaller hatchlings. The effects of temperature on gonadal differentiation indicated that the upper pivotal temperature was approximately 27.5°C. Posthatching growth was faster at warmer water temperatures, and there was little to no acclimation of metabolic rate to exposure to either incubation or water temperature. We conclude that intermediate (27.5°–28.5°C) incubation temperatures produce a female-biased mixed sex ratio and maximize hatching success and hatchling size while increasing incubation duration only slightly over that at the higher temperatures. In addition, posthatching growth was positively influenced by hatchling body temperature; therefore, warmer water temperatures (∼30°C) decreased the time required to rear turtles to a size suitable for reintroduction.

Distribution and management of Alligator snapping turtles, Macrochelys temminckii, in Kansas and Oklahoma

Abstract The Alligator snapping turtle, Macrochelys temminckii, historically occurred in the Arkansas, Caney, Verdigris, Neosho, and Spring river drainages of northern Oklahoma and southern Kansas. High harvest rates in Oklahoma and river impoundments in both states have greatly reduced populations by decimating populations and impeding dispersal routes. Populations of M. temminckii are poorly studied in both states, but particularly so in Kansas. Management efforts for M. temminckii were initiated in Oklahoma in 1997 with the collection of information on distribution, habitat use, and population structure, and establishment of a captive breeding/headstart program. Management efforts in Oklahoma could have positive repercussions for M. temminckii in Kansas. We outline current knowledge of the species in both states, provide information on management efforts for the species in Oklahoma, and provide recommendations for interstate collaboration for managing the species in Kansas.

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.

Temporal changes in an alligator snapping turtle (Macrochelys temminckii) population

Abstract Context. Monitoring populations of long-lived species requires continuous long-term efforts. This is especially applicable for species that have experienced declines range-wide. Aims. Our study assessed the current status of a population of wild Macrochelys temminckii and compared the present results to those from a survey conducted nearly a decade ago. Methods. Trapping in 2010–2011 was conducted on two creeks within the refuge, during the months of May–July. Capture data were compared with data collected by similar methods in 1997–2001. Key results. The population structure of M. temminckii was dominated by juveniles, with few large adults or small juveniles detected and a missing size class was evident. Retrospective analysis of 1997–2001 data revealed that the population was likely to be in decline even then, despite high capture rates. Conclusions. The M. temminckii population showed significant declines that indicated that the population had experienced stressors of unknown origin. The status of M. temminckii at the refuge is concerning, given the protection afforded this remnant population. Implications. Short-term data from 1997–2001 indicated a healthy M. temminckii population, whereas longer-term data showed that the population has declined, resulting in significant demographic changes. Continued monitoring will be necessary to develop management recommendations and track the impact of implemented management practices. Longer-term monitoring of long-lived vertebrates is required to identify population trends.

Activity Patterns of Ornate Box Turtles (Terrapene ornata) in Northwestern Illinois

Activity patterns of ectothermic animals are affected by weather, time of day, and season, but quantifying these effects can be logistically challenging. We used an automated radio telemetry system to quantify Ornate Box Turtle (Terrapene ornata) activity patterns for two years in northern Illinois. Continuously collected activity data were paired with meteorological data collected from the site to determine factors influencing turtle behavior. Temperature, relative humidity, rain, year, month, time of day, and reproductive status affected activity levels. Increased activity levels corresponded with rain events, and males were generally more active than females, especially during spring and late summer. Overall, turtles were less active during an uncharacteristically warm and dry year compared to a year with conditions that were closer to the long-term average. Bimodal daily activity patterns have been reported in more southerly populations, and we found similar patterns near the species’ northern range limit, indicating that thermal constraints may limit activity of this species across its range. Activity comparisons between a year with normal meteorological conditions and an abnormally warm and dry year provide insight to the effect that further onset of climate change may have on the activity of Ornate Box Turtles.

Comparison of Diet Among Reintroduced and Wild Juvenile Alligator Snapping Turtles (Macrochelys temminckii) and Adult Female Ouachita Map Turtles (Graptemys ouachitensis)

Abstract Reintroductions are increasingly utilized in conservation, but the experiences and environments to which animals are exposed prior to release can significantly impact the success of such efforts. We investigated differences in the diet of reintroduced juvenile alligator snapping turtles (Macrochelys temminckii) relative to juveniles from a wild population. In addition, we compared the diet of adult female Ouachita map turtles (Graptemys ouachitensis) to reintroduced M. temminckii with whom co-occurrence was recently reestablished and wild juvenile M. temminckii in a river system where the species have enjoyed long-term sympatry. There were differences in diversity and richness of the diet of M. temminckii at the two study sites that could be due to dissimilarity in foraging experience. There was greater overlap in diet of M. temminckii and G. ouachitensis at the site of reintroduction than at the site of long-term sympatry that corresponded to variation in composition of diet. Such a difference could indicate that partitioning of food resources has not taken place at the site of reintroduction to the degree that it has at the site with long-term sympatry.

Interspecific Variation in Temperature Effects on Embryonic Metabolism and Development in Turtles

We measured temperature-induced differences in metabolic rates and growth by embryos of three turtle species, Macrochelys temminckii, Trachemys scripta, and Apalone spinifera, at different, constant, temperatures. Oxygen consumption rate (VO2) was measured during development and used to characterize changes in metabolism and calculate total O2 consumption. Results from eggs incubated at different temperatures were used to calculate Q10s at different stages of development and to look for evidence of metabolic compensation. Total O2 consumption over the course of incubation was lowest at high incubation temperatures, and late-term metabolic rate Q10s were <2 in all three species. Both results were consistent with positive metabolic compensation. However, incubation temperature effects on egg mass-corrected hatchling size varied among species. Apalone spinifera hatchling mass was unaffected by temperature, whereas T. scripta mass was greatest at high temperatures and M. temminckii mass was lowest at high temperatures. Hatchling mass : length relationships tended to correlate negatively with temperature in all three species. Although we cannot reject positive metabolic compensation as a contributor to the observed VO2 patterns, there is precedence for drawing the more parsimonious conclusion that differences in yolk-free size alone produced the observed incubation temperature differences without energetic canalization by temperature acclimation during incubation.

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.

The Spring–Summer Nesting and Activity Patterns of the Western Chicken Turtle (Deirochelys reticularia miaria)

The Eastern and Florida Chicken Turtle subspecies (Deirochelys reticularia reticularia and D. r. chrysea) exhibit nesting cycles that are atypical for aquatic North American turtles, with nesting occurring in the fall, winter, and early spring. The reproductive cycles of the western subspecies (D. r. miaria), however, have not been studied. Therefore, we monitored the reproductive status of female D. r. miaria in 2012 and 2013. In our populations, both male and female D. r. miaria were inactive on land from mid-July to mid-March. This differs from the activity patterns of the other subspecies in which females typically remain active into the fall and sometimes winter. Also, in contrast to the nesting patterns of D. r. reticularia and D. r. chrysea, female D. r. miaria developed follicles in the spring and summer (March–July) and contained eggs in the summer (May–July). Therefore, we conclude that the Western Chicken Turtle exhibits a nesting pattern that is more similar to that of other sympatric species in the family Emydidae than it is to other subspecies of D. reticularia.

Nest-site selection among reintroduced Macrochelys temminckii

Abstract We evaluated nest-site selection in a reintroduced population of Macrochelys temminckii at two locations in southeastern Oklahoma by comparing mean values of variables characterizing microhabitat at nest-sites and random sites. We also analyzed the spatial distribution of nests using a computer randomization procedure. The spatial distribution of nests did not differ significantly from random. However, females nested in areas with significantly greater water depths 2 m from the shoreline and significantly less ground cover compared to random sites. Areas with little ground cover might indicate sites with thermal characteristics appropriate for incubation of eggs laid by M. temminckii, and greater water depth may provide cover for females prior to nesting. The discovery of nest-sites at the same location in consecutive years suggests that some female M. temminckii might return to the same place to nest repeatedly, but further study is required to confirm whether this species exhibits nest-site fidelity.