Maternal Condition and Nest Site Choice: An Alternative for the Maintenance of Environmental Sex Determination?

SYNOPSIS. Egg size and nest site selection are two potentialeffects that can have a persistent influence on the phenotypeof offspring. In this paper, I develop the maternal condition-dependentchoice hypothesis for the maintenance of environmental sex determination.The hypothesis stipulates three conditions: 1) there must bevariation in the maternal effect, 2) the variation in the maternaleffect must influence fitness of the offspring differently betweenthe sexes, and 3) female reproductive behavior is determinedby her condition or how her condition will influence her offspring'sfitness. Females with the ability to recognize environmentsthat have a higher probability of producing the sex that wouldbenefit the most from maternal condition will have an advantage.Using egg size as a maternal effect, I test this hypothesisin the diamondback terrapin, an emydid turtle with temperature-dependentsex determination. Terrapins have large variation in egg sizeamong clutches and little variation within clutches. Egg massis the primary determinant of hatchling mass and can resultin as much as a three year difference in reaching minimum sizeof first reproduction in females, but may not affect age orsize of first reproduction in males. Finally, terrapins selectopen nesting sites with warmer incubation conditions and placelarger eggs there. Females place smaller eggs in cooler sites.Terrapin reproduction is consistent with the prediction of thematernal condition-dependent nest site choice hypothesis. Themodel and supporting data demonstrate how maternal effects canbe an important factor to consider in studies of environmentalsex determination.