Consequences of extended egg retention in the Eastern Fence Lizard (Sceloporus undulatus)

Egg retention beyond the normal time of oviposition occurs frequently in oviparous squamate reptiles and is thought to be a response to unfavorable nesting conditions. During studies of the Eastern Fence Lizard (Sceloporus undulatus), we obtained data on the effects of extended egg retention on embryonic development, hatchling phenotypes, and posthatching survival under natural field conditions. Females that retained eggs beyond the normal time of oviposition produced heavier eggs with embryos more advanced (by one stage unit) at the time of oviposition than females that did not retain eggs for extended periods. Egg retention did not affect any hatchling phenotype (i.e, body size, thermal preference, running speed, desiccation rate, growth rate) but had a significant positive effect on posthatching survival in the field. However, the mechanism by which extended egg retention affects posthatching survival remains unclear. Our results have implications for the evolution of viviparity, but carefully designed experiments are needed to further understand the causes and consequences of extended egg retention.