Order of oviposition and egg size in the red-eared slider turtle (Trachemys scripta elegans)

Abstract

We studied intraclutch variation in egg size and shape among 432 eggs from 35 clutches of the red-eared slider turtle (Trachemys scripta elegans) from west-central Illinois. Egg shape varied systematically with respect to oviposition order. The first two and last two eggs laid were slightly but significantly longer than eggs laid between the first two and last two eggs. The last two eggs laid were slightly but significantly narrower than other eggs in a clutch. In contrast, egg mass did not vary systematically with oviposition order. Mean egg mass of the first two eggs laid was slightly but insignificantly greater than that of the last two eggs laid and that of eggs laid between the first two and last two eggs. In this species, follicles are apparently fairly uniform in mass when they are ovulated. Consequently, reproductive output can be adjusted by either ovulating more equal-sized follicles or adding material uniformly to all follicles ovulated in a particular reproductive bout. We suggest an adaptive explanation of differences between intraclutch variation in T. s. elegans and that reported in previous studies of intraclutch variation in sea turtles.