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

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Abstract
SYNOPSIS. Egg size and nest site selection are two potential effects that can have a persistent influence on the phenotype of offspring. In this paper, I develop the maternal condition-dependent choice hypothesis for the maintenance of environmental sex determination. The hypothesis stipulates three conditions: 1) there must be variation in the maternal effect, 2) the variation in the maternal effect must influence fitness of the offspring differently between the sexes, and 3) female reproductive behavior is determined by her condition or how her condition will influence her offspring's fitness. Females with the ability to recognize environments that have a higher probability of producing the sex that would benefit the most from maternal condition will have an advantage. Using egg size as a maternal effect, I test this hypothesis in the diamondback terrapin, an emydid turtle with temperature-dependent sex determination. Terrapins have large variation in egg size among clutches and little variation within clutches. Egg mass is the primary determinant of hatchling mass and can result in as much as a three year difference in reaching minimum size of first reproduction in females, but may not affect age or size of first reproduction in males. Finally, terrapins select open nesting sites with warmer incubation conditions and place larger eggs there. Females place smaller eggs in cooler sites. Terrapin reproduction is consistent with the prediction of the maternal condition-dependent nest site choice hypothesis. The model and supporting data demonstrate how maternal effects can be an important factor to consider in studies of environmental sex determination.

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