Seasonal variation in reproductive effort and its effect on offspring sizein the lizard Sceloporus undulatus

Fence lizards, Sccloporus undulatus, reproduce multiple times per year. Sur vival of reproducing females drops dramatically between clutches from first tu final clutch of the year. Also, offspring from later clutches emerge wi th less time available for growth and storage prior to hibernation. Conside ring these two facts, life history theory predicts that (1) females should exhibit greater reproductive effort (RE) in the second clutch of the active season than in the first, and (2) that the increase in RE should be mediat ed by a greater allocation of energy per offspring. To test these hypothese s, we compared reproductive traits (RE, clutch size, and egg mass) of lizar ds from a New Jersey population laying their first and second clutches. Two different estimates of RE (relative clutch mass, and clutch mass adjusted for condition) were significantly lower for the second clutch than for the first clutch. The difference in RE was manifested primarily as a decrease i n clutch size. Clutch size was correlated with female body size and conditi on, but average egg mass was not correlated vith either variable. Egg mass varied twice as much among clutches as it did within clutches, In fact, the variation in average egg mass observed among clutches was almost as great as that which exists among populations of S. undulatus. Variation in eg mas s within and among clutches has consequences for offspring quality because egg mass was positively correlated with snout-vent length, body mass, and c ondition of hatchlings. Our data do not support the predictions of existing theories regarding the optimal allocation of RE among offspring.