Phylogeny of sea skaters, Halobates Eschscholtz (Hemiptera, Gerridae), based on mtDNA sequence and morphology

We examined phylogenetic relationships among halobatine water striders (Hem iptera, Gerridae) using molecular and morphological data. The molecular dat a set was 780 bp DNA sequence data from the 3' half of the mitochondrial ge ne encoding cytochrome oxidase subunit I from 19 species of sea skaters, Ha lobates, and one species from each of three related genera, Asclepios annan dalei, Austrobates rivularis, and Eurymetra natalensis. The morphological d ata set was a slightly modified version of a previously published data set. Unweighted parsimony analyses of the molecular data set gave one tree with weak support for most branches. Maximum likelihood analysis of the same da ta set gave a tree with slightly different topology, but reveiled many of t he clades found in parsimony analyses of the morphological data set. Parsim ony analyses of the combined molecular + morphology data sets gave a better resolved and better supported tree than did analyses of any single data se t. The phylogeny of Halobates presented here allows a more rigorous evaluat ion of several prior hypothese about evolutionary processes in marine water striders. In particular, it supports the hypothesis of at least two separa te transitions from coastal to oceanic environments. (C) 2000 The Linnean S ociety of London.