CHANDLER, C. H.*; PHILLIPS, P. C.; JANZEN, F. J.; Iowa State University; University of Oregon; Iowa State University: Characterization of thermal reaction norms for sex ratio in two mutant lines of Caenorhabditis elegans

A great variety of sex-determining mechanisms exists in the animal kingdom, from genotypic sex determination (GSD) by sex chromosomes, additive effects spread across multiple genes, and haplodiploidy, to environmental sex determination, including temperature-dependent sex determination (TSD). A number of hypotheses have been proposed to explain the occurrence and adaptive significance of TSD. Unfortunately, TSD is most common in reptiles such as lizards and turtles, most of which have long generation times and relatively little background data on their development and genetics, rendering direct support for these hypotheses difficult to obtain. Previous research, therefore, has focused on testing these hypotheses indirectly by examining their assumptions or predictions. While some models have been discredited using this approach, support for the remaining hypotheses would be strengthened greatly by direct tests in a more tractable model system. In this spirit, we have characterized two mutant lines of Caenorhabditis elegans that exhibit TSD. The thermal reaction norms of sex ratio in these two strains closely mirror type Ia and type Ib patterns of TSD in reptiles. The similarity in pattern between these C. elegans strains and reptiles, combined with the short generation times and the wealth of developmental and genetic data on C. elegans, makes this an attractive model system for directly testing hypotheses about the evolution and adaptive significance of mechanisms of environmental sex determination as well as exploring questions regarding sex-ratio evolution.