WALGUARNERY, J.W.; University of Tennessee, Knoxville: Nonrandom patterns of sex determination in Anolis lizards

Despite the general selective advantage afforded parents investing equally in sons and daughters, deviations from random sex determination do occur and can provide important insight into reproductive adaptation. Recently it was discovered that individuals of the lizard, Anolis carolinensis, a taxon widely described as a model in reproductive behavior and ecology, sequentially alternate the sex of successive offspring, a pattern not previously known to occur in any species. Of female lizards collected from a population in Columbia County, Georgia, a majority alternated the sex of consecutive offspring, significantly more so than expected by chance. However, my own research on A. carolinensis collected in Duval County, Florida indicated no deviation from randomness in sex of consecutive offspring and conclusively rejected the hypothesis of even a weak tendency to alternate sex. Since neither the physiological mechanism of sex alternation nor a selective advantage of this unique pattern is yet known, it had not been possible to determine from existing data whether this disparity was due to unmeasured differences in the environment and condition of the animals or whether it indicated a genetically constrained reproductive strategy of limited geographic range. As a preliminary study of the geographic and phylogenetic distribution of this novel pattern, I simultaneously examined additional series of offspring produced by female A. carolinensis from populations in Georgia and Florida as well as series of offspring produced by a congener, A. sagrei. The results of these data indicate that a pattern of sequential alternation of offspring sex is not characteristic of the genus Anolis, nor even inherent to the reproduction of A. carolinensis, and suggest a need for further research into the conditions leading to nonrandom sex determination.