Reproduction in the Western Box Turtle, Terrapene ornata luteola

Abstract

Optimal egg size theory was tested using reproductive data from the western box turtle, Terrapene ornata luteola, obtained from 272 X-rays of 124 different turtles, 72 of which were gravid. Clutch size was positively correlated with maternal body size, but egg width was not related to either maternal length or width or clutch size but was related to maternal mass. Pelvic width was significantly correlated with egg width and maternal body size. Egg size varied little, as predicted by optimal egg size theory. Mean clutch size was 2.70 (n = 77) and mean egg width was 2.66 cm (n = 203); clutch size is smaller and egg width is larger than for T. o. ornata. During the three years of the study, two years had unusually wet springs, and egg production was high; one year had a dry spring, and a smaller proportion of females produced eggs; but mean clutch and egg sizes were not significantly different from other years. These data indicate that spring rains may increase the proportion of females laying eggs in the summer, and in years with dry springs, turtles may defer laying eggs completely, rather than reducing annual output.