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Sex Determining Temperatures in Turtles: A Geographic Comparison

J. J. Bull, R. C. Vogt and C. J. McCoy
Evolution
Vol. 36, No. 2 (Mar., 1982), pp. 326-332
DOI: 10.2307/2408051
Stable URL: http://www.jstor.org/stable/2408051
Page Count: 7
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Sex Determining Temperatures in Turtles: A Geographic Comparison
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Abstract

In many turtles the hatchling's sex is determined by the incubation temperature of the egg, warm temperatures causing femaleness and cool temperatures maleness. Consequently, the population sex ratio depends upon the interaction of (i) environmental temperature, (ii) maternal choice of nest site, and (iii) embryonic control of sex determination. If environmental temperature differs between populations, then sex ratio selection is expected to adjust either maternal behavior or embryonic temperature-sensitivity to yield nearly the same sex ratio in the different populations. To test this hypothesis in part, we have compared sex determining temperatures among embryos of emydid turtles in the northern and southern U.S. We predicted that embryos of southern populations should develop as male at higher temperatures than those of northern populations. The data offer no support for this prediction among the many possible comparisons between northern and southern species. The data actually refute the prediction in both of the North-South intraspecific comparisons. Further study is needed, in particular, of nest temperatures in the different populations.

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