ST. JULIANA, J. R. ; JANZEN, F.J.: Behavioral and physiological maternal effects and temperature-dependent sex determination in common snapping turtles

In organisms exhibiting temperature dependent sex determination (TSD), offspring sex is determined primarily by the nest temperature. Recent work suggest that egg yolk hormones may also influence embryonic sex determination. Thus, both behavioral (i.e. nest-site choice) and physiological (i.e. yolk allocation) maternal effects may play important roles in determining the fundamental phenotypic characteristic of sex in species with TSD. Behavioral investment in common snapping turtles (Chelydra serpentina), a species with TSD, was evaluated by measuring a variety of nest microclimate variables (particularly overstory canopy cover) and exploring their relationship to nest temperature and offspring sex ratio (n=14 nests). The concordant physiological investment of these same, plus 12 additional, females was determined in the laboratory by incubating a subset of eggs at ~28 C, which should produce a 1:1 sex ratio across clutches (26 families, n=260). Significant deviations from the 1:1 sex ratio would suggest a physiological investment in the eggs affecting offspring sex. Yolk hormones in eggs at oviposition will be assayed to test the potential mechanism underlying among-clutch variation in sex ratio observed in the lab. Of particular interest is whether these behavioral and physiological investments are significantly correlated. The implications (or lack) of such a correlation will greatly assist our understanding of issues concerning female “control” of offspring sex, as well as the mechanisms maintaining TSD.