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Ecology of Hatchling Sex Ratio in Map Turtles
- Vogt, R. C., Bull, J. J.
- Ecology 1984 v.65 no.2 pp. 582-587
- Chrysemys picta, Graptemys, beaches, females, males, nesting, nesting sites, nests, sand, sex ratio, temperature, turtles, vegetation, Wisconsin
- 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.