Search

Quantifying demographic parameters of freshwater turtle populations at the local scale is necessary in order to understand their natural history and assess their status. To examine whether maritime forest populations display different demographic traits compared to other populations, we studied the freshwater turtle assemblage at Nags Head Woods Ecological Preserve (NHWEP), located on a barrier island of North Carolina. We determined specific demographic traits such as abundance, sex ratio, size distribution, somatic growth, annual survival, and population growth rate of Snapping Turtles (Chelydra serpentina), Yellow-bellied Sliders (Trachemys scripta), Chicken Turtles (Deirochelys reticularia), and Northern Red-bellied Cooters (Pseudemys rubriventris). We determined that most demographic traits of freshwater turtle populations at NHWEP are structured similarly to other populations studied. We found that the population growth rates for three out of the four species analyzed are increasing, indicating expanding populations (with the exception of T. scripta). The annual survivorship rate for D. reticularia was similar to that of many semiaquatic turtles, contradicting previous studies for this species that have reported low annual survival because of reduced longevity. Analyzing multiple demographic traits of different freshwater turtle species within a maritime forest assemblage on a barrier island provides an important baseline on freshwater turtle demographics in unique habitats that are subject to intense environmental stochasticity. [ABSTRACT FROM AUTHOR]

Nesting in sea turtles involves a series of behavioral stages in which females ascend a coastal beach, move sand to bury and conceal eggs, and return to the sea. We created a partial ethogram of nesting stages in Green Sea Turtles (Chelonia mydas) from a central Florida Atlantic beach. We documented nesting stages through both in-person data collection and use of night-vision video-recording equipment for coding behaviors at a later date. The video-recorded footage allowed precise measurement of stage durations and descriptions of action patterns without observer effects. Using these methods, we recorded nesting behavior in 14 Green Sea Turtles, from which we measured limb and body movements, described nine modal action patterns, and identified seven distinct nesting stages—ascent, body pitting, digging, egg laying, covering, camouflaging, and descent. During body pitting and camouflaging stages, we found an inverse relationship between front flipper and rear flipper stroke rates. In body pitting, front flipper stroke rate decreased from start to finish, whereas rear flipper stroke rate increased over the duration of the stage. The inverse of this stroke rate pattern occurred during the camouflaging stage. Our work adds new detail to previous descriptions of Green Sea Turtles' nesting behavior, including a distinct transition between body pitting and digging. We compared our ethogram to previous studies on Green Sea Turtles' nesting behavior and propose these descriptions as a way to inform studies that test hypotheses concerning behavioral differences that might exist among populations, within populations over time, or between groups exposed to human disturbance or varied anthropogenic factors. [ABSTRACT FROM AUTHOR]

Ultrastructures of chelonian eggshells show wide interspecific variation, which might, in part, reflect requirements to protect embryos in various incubation environments. Relationships between eggshell ultrastructures and incubation environments are poorly understood. Using scanning electron microscopy, we examined ultrastructures of eggshells from wild and captive Speckled Dwarf Tortoises (Chersobius signatus), including shells from hatched and undeveloped eggs. Speckled Dwarf Tortoises produce multiple single-egg clutches during a short breeding season in spring, and bury their eggs in shallow nests that experience high temperatures and low water potentials. In light of this harsh incubation environment, we expected thick calcareous layers to minimize water loss during incubation. However, wild and captive eggshells had thin calcareous layers (mean values ranging from 125.1 to 148.3 µm) that lacked the multiple crystallite layers and cuticles found in several other tortoise species. We hypothesize that thin calcareous layers in eggshells of Speckled Dwarf Tortoises might be related to the production of multiple clutches within a short breeding season, leaving little time for the calcification of each eggshell. The benefits of producing multiple clutches might outweigh the benefits of a thick eggshell. Hatched eggshells had porous crystallite cores, and the shell membrane of hatched eggshells was usually separated from the calcareous layer. These characteristics are consistent with calcium absorption from the eggshell by developing embryos, resulting in shorter crystallite heights in shells of captive hatched compared to undeveloped eggs. [ABSTRACT FROM AUTHOR]

Over 9000 articles have been published on turtles and tortoises (excluding sea turtles) since 1950 according to the Web of Science, including over 8000 contained in a personal bibliography that we analyze in this paper. Research had a slow start from 1900 to 1950, with mostly anecdotal additions to our knowledge until the contributions of F. Cagle and A. Carr took turtle research to new levels as the cofathers of turtle ecology in the middle of the last century. Books written in 1939, 1952, and 1972 that compiled existing literature on turtles in the United States and Canada set the stage for growing interest in turtles. The first global compilation of turtle species did not become available until 1961. Publication frequency increased in the 1960s and especially the 1970s as interest in turtles grew, and a wave of turtle biologists emerged from doctoral degree programs. We briefly review the contributions of scientists who published extensively on turtle ecology in those and later decades up to the present. We also review advances in our knowledge of various topics, including the global distribution of turtle research efforts; changes in our perceptions of turtle species diversity over time; turtle community ecology; sex ratios, sex-determination, and climate change; overwintering behavior; sexual size dimorphism and sexual dichromatism; analyses of population genetics; turtles and vocalization; and the emergence of turtle conservation biology efforts. We conclude with a discussion of future opportunities and challenges for working with turtles. [ABSTRACT FROM AUTHOR]

Diamond-Backed Terrapins ( Malaclemys terrapin) are emydid turtles found in estuarine systems along the Gulf and Atlantic coasts of the United States between Texas and Massachusetts, and in Bermuda. Reductions in many terrapin populations have been documented throughout the species' range in association with habitat loss, overharvesting for consumption, bycatch in commercial and recreational fishing gear, and collection for the pet trade. Information on populations within Louisiana is limited, with survey efforts being performed only recently throughout the state's coastal zone. From 2012 through 2014, we sought to determine the distribution of Diamond-Backed Terrapins within the Deltaic Plain region of Louisiana, describe sex ratios and size class structure within select management basins, and establish marked populations to promote continued study of the species. Of the 27 terrapin sampling sites initially selected, 24 were chosen for further evaluation; a subset of these same locations were sampled more intensively in 2014. In all years, we utilized unbaited fyke nets. The presence of Diamond-Backed Terrapins was associated with a variety of coastal marsh vegetative communities (e.g., intermediate, brackish, and saline). Basin-specific analyses revealed variation in mean size, and sex ratios skewed toward males within all basins indicating higher female mortality rates or male-biased recruitment. These efforts confirm the presence of Diamond-Backed Terrapins across the Deltaic Plain region of the Louisiana coastline, and inform future examinations of the regional and range-wide abundance and population dynamics of the species. [ABSTRACT FROM AUTHOR]

Turtles in the Kinosternidae are well-known to have unique shell shapes and shell constructions, including hinged plastrons in many species. Members of this group also live in a wide range of habitats. Despite this variability, and the likely importance of shell shape in determining fitness across this clade's range, no studies have comprehensively surveyed the variation in shell shape in this clade, nor the allometric or ecomorphological patterns possible among these species. This study used geometric morphometric methods to quantify shape in the shells of 25 of the 26 species in Kinosternidae. We assessed carapace strength using finite element modeling and calculated several morphometric measures that are correlated with the ability of turtles to right themselves when overturned. These morphological and functional data were used to describe patterns of morphological and functional evolution, and to test hypotheses about the ecological or functional morphology within this group. No patterns in ecomorphology were identified. A relationship between posterior plastral kinesis and shell morphology and strength was found, however, indicating that different mechanisms of defense exert a stronger influence on shell shape than environmental pressures. Such mechanisms are likely important for turtles that cannot rely solely on shell strength for defense as a result of their small size. In addition, morphological proxies for righting performance indicate that kinosternids are unexceptional among turtles regarding this function. This is the first large-scale study of functional and ecological morphology in this clade, but much opportunity remains for discovering finer scale patterns of variation and unique functional characteristics associated with the unique shell shapes of this group. [ABSTRACT FROM AUTHOR]

The costs of an aquatic life are likely to be strongly influenced by an animal's buoyancy, which can be measured as specific gravity (SG). The shells of chelonians are negatively buoyant, and the tendency to sink is opposed by air in the lungs. Turtles can therefore regulate buoyancy by adjusting residual lung volume, but must do so within the constraint of a relatively fixed body volume set by the rigid shell. Emydids have been reported to effect changes in lung volume with reciprocal changes in the volume of water stored in the urinary bladder and, perhaps, for rapid short-term adjustments, the cloacal bursae. We examined buoyancy control in two species, the eastern painted turtle Chrysemys picta (Emydidae), which has well-developed cloacal bursae, and the common musk turtle Sternotherus odoratus (Kinosternidae), which lacks bursae. We measured SG in captive turtles, then manipulated SG by attaching either weights or floats, and measured SG again at 4 h and 24 h after attachment. Initial SG was consistently and significantly higher in bottom-walking Sternotherus (1.03) than in more free-swimming Chrysemys (1.01). Both species compensated nearly completely for weights up to 6% of body mass by decreasing weight in water (reflecting higher lung volumes); compensation in both species was mostly complete at 4 h. Both species also compensated for attached floats (buoyant forces equivalent to up to 4% of body mass in Sternotherus and at least 7% in Chrysemys) by decreasing lung volume. Lung volume changes (gauged by underwater weight) were not matched by changes in stored water volume (gauged by body mass in air) in Sternotherus and only partially matched in Chrysemys. Changes in lung volume did not affect surfacing frequency. Small differences in buoyancy regulation between species reflect differences in natural history and, presumably, morphology, but neither the mechanisms of chronic lung-volume maintenance nor the function of cloacal bursae are clear. [ABSTRACT FROM AUTHOR]

Most animals forage under the risk of predation. An animal may balance the benefits gained from obtaining adequate nutritious forage with the risk of falling prey to a predator by employing alternative, adaptive foraging tactics. We examined the foraging tactics employed by a central place forager, Gopherus polyphemus, as it foraged away from a refuge. We directly observed foraging paths of juvenile G. polyphemus and analyzed them using correlated random walk models. We also compared the sinuosity of foraging paths to the sinuosity of an optimal central place forager. Observed net squared displacement was greater than expected for outbound foraging paths and inbound return paths, but these paths could not be distinguished statistically from a correlated random walk. Sinuosity was less than expected for an optimal central place forager. Juvenile tortoises direct movement away from their burrows while foraging. Juveniles may give up the security of remaining near their burrows to forage until satiation. [ABSTRACT FROM AUTHOR]

The sex of young sea turtles is difficult to determine because they lack externally dimorphic characteristics and heteromorphic sex chromosomes, yet internal dimorphic morphology is defined at hatching. We tested the reliability of nine internal gonad and accessory duct characteristics to identify the sex of 558 posthatchling loggerhead sea turtles accurately. We modified existing laparoscopic procedures, previously used to classify the sex of larger sea turtles and other turtle species, for use in posthatchlings. Here we describe our approach and quantify the reliability of our morphological criteria. Sex was verified by histological examination of gonadal biopsies from a subset of the turtles. We noted seasonal shifts in early gonadal structure so that some characters which were reliable in the summer and fall were not reliable other times of the year. Thus, we confined the analysis to the six characters that were reliable year round: gonad shape, paramesonephric duct size, gonad size, paramesonephric duct lumen presence, paramesonephric duct mobility, and gonad attachment. Using discriminant analyses of the biopsy and morphological data, we found high correlations between sex from tissue biopsies and these six morphological characters; this analysis misclassified just 2% of the animals with histological verification. Applying the classification functions to animals without histology and comparing those results to our visual classification resulted in 2% reclassification. The analysis reclassified animals that we or the histology, correctly identified that had both female-like and male-like characters. Our method provided accurate identification of sex in very young sea turtles. This methodology enables sex ratio assessments in early life stages, which are critical to species recovery efforts. Additionally, sex assignment data are basic to our understanding of patterns and processes directing dimorphic changes of the gonads and their ducts. [ABSTRACT FROM AUTHOR]