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

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.