Meeting Abstract

P3.32  Jan. 6  Constant versus fluctuating incubation regimes differentially affect offspring phenotype LES, Heather L; PAITZ, Ryan T; BOWDEN, Rachel M*; Illinois State Univ; Illinois State Univ; Illinois State Univ rmbowde@ilstu.edu

In the painted turtle (Chrysemys picta) and red-eared slider (Trachemys scripta), the temperature that eggs are exposed to during incubation determines the sex of the developing embryo. Constant temperature incubation experiments have shown that for each of these species there is a pivotal temperature that produces a 1:1 sex ratio; higher temperatures bias sex ratios towards females, and lower temperatures towards males. Few studies have examined how fluctuating temperatures, as would be experienced in natural nests, affect sex determination. A model by Georges et al. (1989) predicts that under fluctuating temperatures, sex determination depends on the proportion of development that occurs above or below the pivotal temperature. We tested the effect of fluctuating versus constant temperature incubation regimes on sex ratios of both painted and red-eared slider turtles. Eggs were divided into two treatments with half of the eggs from each species incubated at a constant intermediate temperature, 28.5˚C, and the other half incubated under temperatures that fluctuated 3˚C above and below 28.5˚C. Using the Georges model, we converted the fluctuating temperature data into a constant temperature equivalent (CTE) so that we could directly compare constant and fluctuating incubation regimes. The CTE for the fluctuating regime for both species was higher than the constant temperature, which would predict an increase in the production of females. The fluctuating regime did produce a higher proportion of females, but also resulted in increased developmental time and increased hatchling mass, indicating that fluctuating temperatures produce complex effects on hatchling phenotype.