Phylogenetic analysis of molecular lineages in a species-rich subgenus of sea stars (Leptasterias subgenus Hexasterias)

Among diverse marine invertebrate taxa, the evolution of a non-planktotroph ic larva is often associated with increased rates of cladogenesis, compared to related taxa that retain the ancestral planktotrophic larval form, Mole cular phylogenetic analyses of non-planktotrophic land, presumably species- rich) clades of marine invertebrates are rare, Here we analyze 1542 base pa irs of mitochondrial DNA sequence comprising two gene regions, the cytochro me oxidase I gene and the putative control region and flanking sequences, f or 23 molecular lineages in the obligately brood-protecting asteroid genus Leptasterias, Using maximum likelihood, minimum evolution, and maximum pars imony methods, five major clades were identified that corresponded to five taxa (species or species complexes) in the subgenus Hexasterias, section ca mtschatica (following the taxonomy of Waiter K, Fisher). Two clades (L. aeq ualis complex and L. aleutica/L. camtschatica complex) were composed of num erous molecular lineages (7-8 lineages/clade), and several clades had multi ple shallow nodes, suggestive of recent radiations. Two of the clades (L. a leutica/L. camtschatica complex and L. hexactis complex), with geographic r anges restricted to latitudes higher than 48 degreesN, were lacking deep ph ylogenetic nodes, This pattern is consistent with the hypothesis that high- latitude taxa have high rates of extinction due to repeated climatic crises . A log-likelihood ratio test performed on the camtschatica section, includ ing a member (Leptasterias polaris) of the polaris section and using a repr esentative (L. mulleri) of Leptasterias subgenus Leptasterias as an outgrou p, demonstrated that the camtschatica section is monophyletic.