Chelonian Conservation and Biology最新文献

With the exception of the savanna side-necked turtle (Podocnemis vogli) and the red-headed river turtle (Podocnemis erythrocephala), the species within the pleurodire genus Podocnemis have been relatively well-characterized in terms of their temperature-dependent sex determination (TSD) parameters. In this study, we incubated 4 nests of P. vogli (46 eggs) under controlled laboratory incubation conditions to determine whether this species also presents a TSD Ia pattern where males are produced at lower temperatures, characterize the constant temperature producing a 1:1 sex ratio (T_piv), and document the transitional range of temperatures (TRT) that produces both sexes. The incubation temperatures employed were 29°, 31°, and 33°C (± 0.15°C). Our results were consistent with the conclusion that P. vogli exhibits a TSD Ia pattern, but it was not possible to document the T_piv or the superior TRT, because the 29° and 31°C conditions produced all males and even the 33°C condition produced male-biased sex ratios, suggesting a high pivotal temperature for this species. We also documented maternal effects in initial size of the hatchlings, with the female that laid larger eggs producing hatchlings that were larger. Incubation periods of P. vogli were notably longer than those of its congeners incubated under comparable constant temperature and soil moisture conditions. In species of this genus, the TSD Ia pattern suggests that besides the threats these species face from overexploitation and habitat degradation, they also are highly vulnerable to the effects of global warming.

Burrowing organisms augment the availability of important resources for other species. The gopher tortoise (Gopherus polyphemus) is a keystone excavator in open canopy pine-forest ecosystems in the southeastern United States because its burrows are utilized by over 360 species. Across its range, the gopher tortoise is declining, which is thought to negatively affect burrow-associated species and ecosystem functionality. The nine-banded armadillo (Dasypus novemcinctus) is another burrower of similar size that has become syntopically distributed with the gopher tortoise as a result of range expansion. Recent studies have documented vertebrates utilizing armadillo burrows, linking armadillo burrowing to support of local biodiversity similar to the gopher tortoise. We sought to determine the potential for ecological redundancy between gopher tortoises and armadillos and test quantitatively for differences in associate events at their burrows in a mixed-pine–hardwood forest where they co-occur. Using motion activated game cameras to monitor burrows, we compared metrics of vertebrate occurrence between armadillo and tortoise burrows and examined the effects of environmental variables using a series of regression models. A total of 40 vertebrate taxa were observed visiting burrows between October 2019 and December 2020. Richness, diversity, and community composition were not significantly different between the two burrow types. However, associate event counts were significantly greater at tortoise burrows. Burrow and microhabitat variables had varying effects on associate event counts, with consistently positive effects for tortoise burrows, active burrows, and increased richness of tree species, while negative effects were detected for increased canopy cover as well as increased proportions of hardwood trees. Our study provides a framework for testing redundancy of function between syntopic ecosystem engineers, adds to the growing body of work on the ecological significance of armadillo range expansion, and identifies aspects of the habitat that cause fluctuations in the importance of burrows for associate species.

Effective management of a species requires that resource managers know critical aspects of its ecology, including information on home range and habitat use. We conducted the first telemetry study on the Suwannee alligator snapping turtle (Macrochelys suwanniensis), and we examined movements at an upper river (UR) site and a lower river (LR) site in the Suwannee River in Florida, USA. We estimated home range size with kernel density estimates (KDE) using the FishTracker GIS toolbox, and we examined potential differences in KDEs with Generalized Linear Models (GLMs). We also used GLMs (family = binomial) to examine habitat selection for M. suwanniensis. We used an information-theoretic approach to rank and select the most parsimonious models. Overall, our models revealed that M. suwanniensis possessed larger 90% KDEs in the LR site than the UR site, and in both sites, turtles moved into the floodplain during flooded conditions. Remarkably, these movements continued even after water levels receded and the aquatic links were severed. Interestingly, M. suwanniensis selected shallow water with some type of subsurface cover, especially large woody debris (LWD). Instream LWD is likely extremely important, especially during low water levels when undercut banks and other bank habitats are unavailable, so the removal of LWD, including deadhead logs, could negatively affect the species. Minimum flows have been established in the drainage, but river water levels have declined an estimated 40% since human settlement, partly because of groundwater withdrawal outside the drainage, potentially imperiling this state Threatened species.

Variation in sand composition at the individual beach level is an important factor for hatching success and hatchling phenotype that does not appear to have been previously investigated. We studied variation in intrabeach substrate composition in an important loggerhead turtle (Caretta caretta) nesting colony on the island of Maio, Cabo Verde, and examined its relationship with embryonic development success, hatchling phenotype, and hatchling vitality. Thirty-two nests from different females were studied under experimental conditions, controlling for beach position, depth, humidity, and temperature in a randomized block design. Two sand treatments corresponding to 2 types of sand from the same beach were used. While nesting females selected nesting sites indiscriminately between substrate types, their nests differed significantly in all variables measured for reproductive success (hatching success, hatchling size, and hatchling agility) between the 2 sand types. Therefore, the intrabeach observations of substrate phenotype of progeny found here could differentially affect offspring survival. The effects of choosing different nesting sites will generally act to spread the probability of selective pressures on embryos. Variation in reproductive success was due to differences between substrate types within the beach rather than the location of nests within the beach. The importance of determining sand types with the highest hatching success, even within the same beach, should be greatest in colonies or populations highly threatened with extinction, where the hatching success of each nest becomes of utmost importance.

Infestation of Ornate Box Turtles (Terrapene ornata) by sarcophagid botflies was studied over 38 yrs in western Nebraska. At least 2% of captured individuals were infected, primarily in late spring following warm temperatures in the previous September. Botflies may be a significant cause of mortality in box turtles in some years.

The Central American river turtle (Dermatemys mawii) is one of the of the most critically endangered turtle species worldwide, as a result of habitat loss and heavy hunting for consumption. Research on D. mawii becomes more challenging as wild populations are disappearing, while basic ecological data are still required to inform conservation efforts. In this study, our aim was to analyze the diet of D. mawii based on sex, and compare the information provided by stomach flushing and fecal samples. We examined both types of samples from individuals captured in 2017 and 2018 in a lentic system in the Lacantun River Basin, Chiapas, Mexico. We identified 3 broad categories (aquatic macrophytes, riparian resources and invertebrates) and 12 different food items, of which four are new reports of vascular plants for the diet of this turtle. The principal items consumed by D. mawii were Pistia stratiotes (a free-floating macrophyte) and Ludwigia sp. (a riparian plant). A low index of relative importance (≤ 0.5) for invertebrates suggests that they may be ingested accidentally when feeding on plants. We did not detect significant sex differences in the relative contribution of food items between the two sampling methods; additionally, we found a large dietary overlap (Cλ ≥ 0.89) between sexes that indicates a similar use of resources in this lentic system. We found all 3 broad food categories in stomach flushing samples and only one (riparian resources) in fecal samples; however, we did not find significant differences in the number of food items. The use of both postingestion sampling methods provided a more comprehensive view of the diet of this herbivorous freshwater turtle.

All monitoring programs on the west coast of Australia have trialed a new mark–recapture protocol to address tag loss in individual flatback turtles (Natator depressus) during recent nesting seasons (2020, 2021, 2022). This protocol aligns with ethical considerations for the tagging of marine megafauna. In addition to increasing retention rate of identification tags, this new protocol is expected to decrease the potential long-term health impacts of tagging on this species.

The map turtles and sawbacks (Graptemys) sort by female head width into narrow-headed (microcephalic) females of 5 species that eat few mollusks, moderately broad-headed (mesocephalic) females of 4 species that eat moderately high amounts of mollusks, and broad-headed (megacephalic) females of 5 species that eat mollusks almost exclusively. The microcephalic species include a clade of 3 sawbacks, Graptemys nigrinoda, Graptemys flavimaculata, and Graptemys oculifera. The first 2 are sponge specialists, but 2 previous dietary studies of G. oculifera did not report sponges; both also lacked comparisons between the sexes. Both of the other sawbacks also feed on brackish-water mussels near the coast, but this phenomenon has not been examined for G. oculifera. Increased body sizes occur in coastal populations of both other sawbacks as well. We examined G. oculifera diets using fecal samples and found that contrary to the earlier results, they also fed primarily on sponges, as well as insects. Females also consumed algae, Asian clams, and, in a coastal population, mussels. In low-gradient river reaches near the coast, G. oculifera achieved large body sizes compared to populations inhabiting sandbar-dominated inland reaches; they were also large at the confluences of the Pearl River and a tributary creek with the Ross Barnett Reservoir. The fact that G. oculifera at the 2 confluences with a large inland reservoir showed the same trend in body size as they did at the coastal sites suggests that the primary reason for large body size may be thermal stability and/or slowing current that promotes biological production, rather than consumption of brackish-water mussels in coastal populations, as the mussels were absent near the reservoir. In addition, high predation by alligators may also occur at the reservoir confluence and coastal sites and select for large body sizes. Overall, the 3 allopatric sawbacks show a pattern of vicariant divergence as ecological analogues, consistent with findings for other allopatric sets of related species.

Most studies on wild ornate box turtles (Terrapene ornata) estimate maximum age in the 30s with some data suggesting that individuals may live beyond 50. We present data from a 29-yr study of 374 marked turtles in which at least 44% lived into their 30s and at least 3.5% survived into their 40s. Females may survive longer than males. Older turtles can affect reproductive potential of the population; therefore, conservation and management for this state-threatened species should account for longer lifespans than previously assumed.

Eastern box turtles (Terrapene carolina) are becoming increasingly threatened by the rate of urbanization and habitat fragmentation. The high population density and heavy urbanization of Long Island, New York, provide an ideal system to examine possible drivers of differences in eastern box turtle shell damage and health in an urban landscape, as well as possible differences in sex and stage ratios. Over the course of our 2-yr study, we captured a total of 189 unique individual eastern box turtles across 20 sites on Long Island. Shell damage was evaluated according to a 5-level ranking system based on the amount and type of damage an individual turtle exhibited. To study eastern box turtle health, we calculated a body condition index using each turtle’s body weight and straight-line carapace width. All damage and health data were compared by site, sex, and life stage using generalized linear models. These relationships were also analyzed against a set of land cover and land use variables. Across all comparative analyses performed, only the US Geological Survey land cover variable Dryland Cropland and Pasture showed a significant relationship to shell damage. Additionally, Long Island’s eastern box turtles appear to exhibit greater rates of shell damage when compared with turtles in more rural parts of their range. We found male-biased sex ratios across the island; however, no definitive driver was identified. Our study underscores the need for future work on the long-term viability of eastern box turtle populations, specifically those inhabiting areas of high human population density.