Seasonal changes in reproduction have been described for many taxa. As reproductive seasons progress, females often shift from greater energetic investment in many small offspring towards investing less total energy into fewer, better provisioned (i.e. larger) offspring. The underlying causes of this pattern have not been assessed in many systems. Two primary hypotheses have been proposed to explain these patterns. The first is an adaptive hypothesis from life-history theory: early offspring have a survival advantage over those produced later. Accordingly, selection favours females that invest in offspring quantity early in the season and offspring quality later. The second hypothesis suggests these patterns are not intrinsic but result from passive responses to seasonal changes in the environment experienced by reproducing females (i.e. maternal environment). To disentangle the causes underlying this pattern, which has been reported in brown anole lizards (Anolis sagrei), we performed complementary field and laboratory studies. The laboratory study carefully controlled maternal environments and quantified reproductive patterns throughout the reproductive season for each female. The field study measured similar metrics from free ranging lizards across an entire reproductive season. In the laboratory, females increased relative effort per offspring as the reproductive season progressed; smaller eggs were laid earlier, larger eggs were laid later. Moreover, we observed significant among-individual variation in seasonal changes in reproduction, which is necessary for traits to evolve via natural selection. Because these patterns consistently emerge under controlled laboratory conditions, they likely represent an intrinsic and potentially adaptive adjustment of reproductive effort as predicted by life-history theory. The field study revealed similar trends, further suggesting that intrinsic patterns observed in the laboratory are strong enough to persist despite the environmental variability that characterizes natural habitats. The observed patterns are indicative of an adaptive seasonal shift in parental investment in response to a deteriorating offspring environment: allocating greater resources to late-produced offspring likely enhances maternal fitness.
Bibliographical noteFunding Information:
We thank A. Hulbert, D. Quinn, R. Weesner, C. Reali, K. Wilson for help with animal care, M. Wolak for statistical advice and C. Mothes and H. Howell for assistance with animal collection. The research was approved by IACUC # 2015-2785 and funded by the National Science Foundation (DEB-1564563 to D.A.W., DBI-1402202 to T.S.M., and PRFB 1711564 to C.J.T.). This is contribution #893 of the Auburn University Museum of Natural History. The authors declare they have no conflict of interest.
- egg size
- life-history evolution
- parental investment
- seasonal fitness decline
PubMed: MeSH publication types
- Journal Article
- Research Support, U.S. Gov't, Non-P.H.S.