S8-1.2 Friday, Jan. 6 Relaxed selection on rates of molecular evolution: consequence or cause of phenotypic plasticity? LEICHTY, A. R.; PFENNIG, D. W.*; JONES, C. R.; PFENNIG, K. S.; University of Pennsylvania; University of North Carolina, Chapel Hill; University of North Carolina, Chapel Hill; University of North Carolina, Chapel Hill email@example.com
Phenotypic plasticity––the capacity of a single genotype to produce different phenotypes in response to varying environmental conditions––is ubiquitous. Yet, its contribution to evolutionary innovation and diversification remains controversial. Theory suggests that plasticity might foster evolution when genes involved in the production of alternative, environmentally induced phenotypes experience relaxed selection in non-inducing environments and thereby accumulate greater variation. Indeed, genes that are differentially expressed between environmentally induced phenotypes (morph-biased genes) typically accumulate variation more rapidly than genes that are not differentially expressed between phenotypes (unbiased genes). However, rather than arising as a consequence of plasticity, enhanced evolutionary rates of morph-biased genes might be associated with some other variable that is a precondition for plasticity’s evolution. To test these ideas, we characterized morph-biased and unbiased genes in two frog species with environmentally induced alternative phenotypes. We also characterized their orthologs in four species lacking such plasticity. Contrary to expectation, morph-biased genes did not evolve any faster in species with plasticity than in species without plasticity. Indeed, in all six species, biased genes evolved faster than unbiased genes. Moreover, morph-biased genes exhibited higher levels of expression variance than unbiased genes in all species. Thus, morph-biased genes are apparently under more relaxed genetic constraint than unbiased genes, which might explain why they were co-opted to become morph-biased genes.