Evol Ecol Res 8: 1499-1510 (2006)     Full PDF if your library subscribes.

Monitoring juveniles across years reveals non-Fisherian sex ratios in a reptile with environmental sex determination

Steven Freedberg1* and David R. Bowne2

1Department of Biology, University of Virginia, Charlottesville, VA 22903 and  2Department of Biology, Franklin and Marshall College, PO Box 3003, Lancaster, PA 17604, USA

Author to whom all correspondence should be addressed.
e-mail: freedber@stolaf.edu


Question: Sampling biases influence the estimation of sex ratio in species with environmental sex determination (ESD). Are these biases the sole reason for the apparent sex ratio in such species?

Methods: Over a 6-year period, we studied maturing painted turtles (Chrysemys picta) through mark and recapture in a complex of ponds in northern Virginia. To avoid the biases associated with the measurement of primary and adult sex ratios, we monitored individuals over multiple years and measured sex-specific capture and survival rates.

Results: We observed a significant female bias that cannot be attributed to climatic variance or differential survival, capture, or age at maturity.

Conclusions: The observed female bias cannot be explained by existing evolutionary models and is consistent with a lag in evolutionary response to the loss of male-producing environments resulting from human influences on vegetation cover.

Keywords: environmental sex determination, mark–recapture, sex ratio, turtle.

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