The Effect of Egg Size and Incubation Temperature on Growth in the Turtle, Malaclemys terrapin

Abstract

We conducted an incubation and rearing experiment to test the effects of incubation tem- perature and egg size on hatchling size and growth of the emydid turtle, Malaclemys terrapin. Eggs from four clutches were assigned randomly to two incubation temperatures, 26 C and 32 C. Half of the hatchlings were sacrificed and sexed after five months and the remainder were raised for three years in a common environment. Similar to other studies of emydid turtles, low and high temperature treatments produced exclusively males and females, respectively. Egg size was more variable among the four clutches than within each clutch. Egg mass accounted for 96% and 97% of the variance in hatchling mass for females and males, respectively. Both clutch and incubation temperature influenced post-hatching growth. The clutch effect was due to both differences in egg mass among clutches and the effects of egg size on hatchling size. Egg mass explained 59% of the variation in size among 3 year old females, but did not explain size variation among 3 year old males. Differences in female growth attributable to egg size could result in as much as a three year difference in age at first reproduction based on the growth trajectories of terrapins from a natural population.