Female investment in offspring size and number shifts seasonally in a lizard with single-egg clutches

Abstract

The timing of reproduction strongly influences reproductive success in many organisms. For species with extended reproductive seasons, the quality of the environment may change throughout the season in ways that impact offspring survival, and, accordingly, aspects of reproductive strategies may shift to maximize fitness. Life-history theory predicts that if offspring environments deteriorate through the season, females should shift from producing more, smaller offspring early in the season to fewer, higher quality offspring later in the season. We leverage multiple iterations of anole breeding colonies, which control for temperature, moisture, and food availability, to identify seasonal changes in reproduction. These breeding colonies varied only by the capture date of the adult animals from the field. We show that seasonal cohorts exhibit variation in key reproductive traits such as inter-clutch interval, egg size and hatchling size consistent with seasonal shifts in reproductive effort. Overall, reproductive effort was highest early in the season due to a relatively high rate of egg production. Later season cohorts produced fewer, but larger offspring. We infer that these results indicate a strategy for differential allocation of resources through the season. Females maximize offspring quantity when environments are favorable, and maximize offspring quality when environments are poor for those offspring. Our study also highlights that subtle differences in methodology (such as capture date of study animals) may influence the interpretation of results. Researchers interested in reproduction must be conscious of how their organism’s reproductive patterns may shift through the season when designing experiments or comparing results across studies.