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Heritability of Sex Ratio in Turtles with Environmental Sex Determination

J. J. Bull, R. C. Vogt and M. G. Bulmer
Evolution
Vol. 36, No. 2 (Mar., 1982), pp. 333-341
DOI: 10.2307/2408052
Stable URL: http://www.jstor.org/stable/2408052
Page Count: 9
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Heritability of Sex Ratio in Turtles with Environmental Sex Determination
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Abstract

In several turtles the incubation temperature of the egg determines the sex of the hatchling. This paper investigates whether there are possibly weak genetic effects on sex determination in these species as well as the temperature effects. Sex ratios are compared among families of turtle eggs incubated at the same constant temperature, 29.2 C. The sex ratios are significantly more heterogeneous than would be expected if all differences were due to sampling variability, and we interpret this as evidence of heritable differences in the primary sex ratio (sex determination). The results are quantified in terms of a threshold model of polygenic sex determination and yield an estimate of 0.82, with a 95% confidence interval of 0.31 to 1, for the heritability of the postulated sex determining character. In natural populations, variation in temperature between nests reduces the genetic influences on sex determination, so that the rate of evolution of this sex determining character is much less than expected from such a high heritability.

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