Meeting Abstract

P1.69  Sunday, Jan. 4  Placental Calcium Provision in a Lizard with Prolonged Oviductal Egg Retention LINVILLE, B.J.*; STEWART, J.R.; ECAY, T.W.; HERBERT, J.F.; THOMPSON, M.B.; East TN State Univ; East TN State Univ; East TN State Univ; Univ Sydney; Univ Sydney zbjl22@goldmail.etsu.edu

An hypothesis to explain the evolution of viviparity and placentation in reptiles predicts that reduction in shell thickness and the advent of placentotrophy occur coincident with prolonged oviductal egg retention. Saiphos equalis is an Australian scincid lizard with a reproductive mode that is uncommon for squamates: 1) eggs are retained in the oviduct until late developmental stages, and 2) the embryonic stage at oviposition varies geographically. We studied calcium mobilization by embryos in two populations with different egg retention patterns to determine the relationship between shell thickness, pattern of nutritional provision of calcium and embryonic stage at oviposition. Females from one population oviposit eggs that hatch in 6 days, while eggs from a second population hatch within 2 days. Embryos of both populations mobilized calcium from yolk, shell and placenta. Yolk provided the highest proportion of calcium to hatchlings. Shells of the population with a shorter period of egg retention had twice the calcium content of the second population and embryonic uptake of shell calcium was higher in these eggs. Placental transfer accounted for more calcium in hatchlings than extraction from the shell in both populations. Pattern of calcium provision is similar in these two populations, yet they vary in relative contribution of each source to hatchling nutrition. Our results demonstrate that shell calcium content is correlated inversely with the length of egg retention in S. equalis. Our findings also support the hypothesis that the evolution of placentotrophy occurs concurrently with prolonged oviductal egg retention. Supported by a grant from the NSF (IOB-0615695).