FOLTZ, D.W.*; HRINCEVICH, A.W.; ROCHA-OLIVARES, A.; Louisiana State University, Baton Rouge; Louisiana State University, Baton Rouge; CICESE, Ensenada, Mexico: Substitution Patterns for Mitochondrial Genes Vary with Mode of Reproduction in Marine Invertebrate Species

Under a nearly-neutral model in which most amino acid substitutions are slightly deleterious, variation in life history traits among closely-related species can potentially modify the effective population size or the selective regime, leading to differences in the rate of nonsynonymous substitution. We studied substitution patterns for two mitochondrial protein coding genes in several genera of echinoderms and gastropod molluscs. Ratios of nonsynonymous to synonymous substitutions (d_N /d_S) between species were analyzed in a sea star genus (Patiriella) and a molluscan genus (Littorina), each containing multiple lineages with pelagic and non-pelagic larvae. In both genera, lineages with non-pelagic larvae had significantly higher d_N /d_S ratios than lineages with pelagic larvae. The hypothesis that the elevated d_N /d_S ratios in species with non-pelagic larvae was due to reduced effective population size was tested by comparing nucleotide diversities in three genera of gastropod molluscs (Littorina, Crepidula and Hydrobia), each with several modes of reproduction. Overall, there was a significant (P<0.05) reduction in nucleotide diversity in species with non-pelagic larvae, compared to species with pelagic larvae. Similar results were obtained when substitution patterns and nucleotide diversities for the cytochrome oxidase subunit I (COI) gene were analyzed in a sea star genus (Leptasterias spp.) with an obligate brood-protecting mode of reproduction and genetically-subdivided populations and compared to available COI sequences in eight other genera of echinoderms with pelagic planktotrophic larvae. Leptasterias had significantly greater d_N/d_S ratios between and within species, and a significantly smaller transition/transversion rate ratio, than did the non-brooding genera. These results highlight the potential influence of reproductive traits and other life history attributes on patterns of nucleotide substitution within and between species.