Meeting Abstract
S11-1.1 Monday, Jan. 7 Williams’s Paradox and the role of phenotypic plasticity in sexual systems LEONARD, J.L.; Univ, of California-Santa Cruz jlleonar@ucsc.edu
As George Williams pointed out in 1975, although evolutionary explanations, based on selection acting on individuals, have been developed for the advantages of simultaneous hermaphroditism, sequential hermaphroditism and gonochorism, none of these evolutionary explanations adequately explains the current distribution of these sexual systems in the Metazoa (Williams’s Paradox). As Williams further pointed out, the current distribution of sexual systems is explained largely by phylogeny. Since 1975 we have made a great dealof empirical and theoretical progress in understanding sexual systems. However we still lack a theory that explains the current distribution of sexual systems in animals nor do we understand the evolutionary transitions between hermaphroditism and gonochorism.Empirical data collected over the last 40 years, demonstrate that gender may have more phenotypic plasticity than was previously realized. We know that not only sequential but also simultaneous hermaphrodites use phenotypic plasticity to vary their sex allocation in response to social and environmental conditions. A focus on phenotypic plasticity suggests that one sees a continuum in animals between genetically determined gonochorism on the one hand and simultaneous hermaphroditism on the other, with various types of sequential hermaphroditism and environmental sex determination as points along the spectrum. Here I suggest that perhaps we have been unable to resolve Williams’s Paradox because the problem was not correctly framed. Perhaps the question we need to ask is what selective forces favor increased vs. reduced phenotypic plasticity in gender expression. With this symposium we hope to begin to look at the question of sexual system as one of understanding the timing and degree of phenotypic plasticity in gender expression in the life history in terms of selection acting on a continuum, rather than a set of discrete sexual systems.
