2016-12-23T18:52:10

The sex of hatchling map turtles is determined by incubation temperature of eggs in the laboratory as well as in nature. Temperature controls sex differentiation rather than causing a differential mortality of sexes. Temperature has no effect on sex determination in a soft-shelled turtle.

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Turtles and tortoises (chelonians) have been integral components of global ecosystems for about 220 million years and have played important roles in human culture for at least 400,000 years. The chelonian shell is a remarkable evolutionary adaptation, facilitating success in terrestrial, freshwater and marine ecosystems. Today, more than half of the 360 living species and 482 total taxa (species and subspecies combined) are threatened with extinction. This places chelonians among the groups with the highest extinction risk of any sizeable vertebrate group. Turtle populations are declining rapidly due to habitat loss, consumption by humans for food and traditional medicines and collection for the international pet trade. Many taxa could become extinct in this century. Here, we examine survival threats to turtles and tortoises and discuss the interventions that will be needed to prevent widespread extinction in this group in coming decades.

In many turtles sex differentiation is controlled by the incubation temperature of the embryo, with low temperatures producing males, high temperatures producing females. This study investigates the developmental period of temperature-sensitivity in two species of emydid turtles, using different combinations of incubation at a male-determining temperature (25 degrees C) and at a female-determining temperature (31 degrees C). The sensitive period extends throughout much of the middle third of development. Sex is more readily influenced by 25 degrees than by 31 degrees, however, so that maleness can be determined much earlier in development than can femaleness. Comparison of these results with a previous study of snapping turtles indicates that the sensitive period occupies somewhat the same developmental interval in these different turtles. However, in snapping turtles, the female-determining temperature used (30 degrees) is more influential than the male-determining temperature (26 degrees), in contrast with these results from emydids.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Society for the Study of Amphibians and Reptiles is collaborating with JSTOR to digitize, preserve and extend access to Journal of Herpetology. IVERSON, J. B. 1982. Biomass in turtle populations: a neglected subject. Oecologia (Berlin) 55:69-76. MACFARLAND, C. G., J. VILLA, AND B. TORO. 1974. The Galapagos giant tortoises (Geochelone elephantopus) Part I: Status of the surviving populations. Biol. Conserv. 6:118-133. NICHOLS, J. D., B. R. NOON, S. L. STOKES, AND J. E. HINES. 1981. Remarks on the use of mark-recapture methodology in estimating avian population size. In R. A. Raitt and J. M Scott (eds.), Estimating Numbers of Terrestrial Birds. Studies in Avian Biology No. 6. Allen Press, Lawrence, Kansas. POLLOCK, K. H. 1981. Capture-recapture models: a review of current methods, assumptions, and experimental design. In R. A. Raitt and J. M. Scott (eds.), Estimating Numbers of Terrestrial Birds. Studies in Avian Biology No. 6. Allen Press, Lawrence, Kansas. IVERSON, J. B. 1982. Biomass in turtle populations: a neglected subject. Oecologia (Berlin) 55:69-76. MACFARLAND, C. G., J. VILLA, AND B. TORO. 1974. The Galapagos giant tortoises (Geochelone elephantopus) Part I: Status of the surviving populations. Biol. Conserv. 6:118-133. NICHOLS, J. D., B. R. NOON, S. L. STOKES, AND J. E. HINES. 1981. Remarks on the use of mark-recapture methodology in estimating avian population size. In R. A. Raitt and J. M Scott (eds.), Estimating Numbers of Terrestrial Birds. Studies in Avian Biology No. 6. Allen Press, Lawrence, Kansas. POLLOCK, K. H. 1981. Capture-recapture models: a review of current methods, assumptions, and experimental design. In R. A. Raitt and J. M. Scott (eds.), Estimating Numbers of Terrestrial Birds. Studies in Avian Biology No. 6. Allen Press, Lawrence, Kansas.ABSTRACT.-Influence of incubation temperature on sex determination, hatchling size, and residual yolk in Podocnemis unifilis were studied under natural and laboratory conditions. Nest temperatures and sex ratio were influenced by the sand texture of the nesting site. Switch experiments performed in the field revealed that the critical period is longer and covers more developmental stages than in other species of turtles developing under constant conditions. Mean and variance in incubation temperature and number of hours at or above the threshold temperature were the indices that best described sex ratio in nature.Hatchlings were heavier when incubated in nests with higher mean temperatures. Residual yolk weight was positively related to egg width.RESUMEN.-La influencia de la temperatura de incubacion sobre determinacion del sexo, tamano de cria, y yema residual en Podocnemis unifilis eran estudiado bajo condiciones na...

Incubation temperature is known to determine the sex of hatchlings in many species of turtles, including the map turtles. Graptemys ouachitensis, G. pseudogeographica, G. geographica, and painted turtle, Chrysemys picta. This paper presents a study of sex ratio and nest ecology in natural populations of these species in Wisconsin, but largely for G. ouachitensis and G. pseudogeographica. Nesting was monitored during June, and hatchlings were obtained from 236 nests during August and September 1980. The distribution of nest sex ratios samples of the two common species was bimodal, tending to be all—female or all—male within a nest, with an overall excess of females. Nests with males were located amid vegetation, with cool temperatures, and nests with females were located in open sand exposed to the sun, with high temperatures. The sex ratio differed significantly between nesting beaches, apparently because of differences in the availability of warm vs. cool nest sites. All—female nests hatched in less time than all—male nests, and the sex ratio of emerging hatchlings consequently changed from nearly all female early in August to all male in September. The data indicate major environmental influences on the hatchling sex ratio in map turtles.