Phylogenetic Analysis of the Hawaiian Damselfly Genus Megalagrion (Odonata: Coenagrionidae): Implications for Biogeography, Ecology, and Conservation Biology

Abstract

A phylogeny of the 22 species currently recognized in the genus Megalagrion, endemic to the Hawaiian Islands, is presented based on an analysis of 23 morphological and ecological characters. After the exclusion ofM. williamsoni, known from only a single male, and inclusion of subspecies within their nominate taxa, a single resolved tree of length 85 was obtained; this tree has a consistency index of 0.56 and a retention index of 0.72. Based on this phylogeny, it appears that the major clades within Megalagrion differentiated on Kaua'i or an antecedent high island. These clades subsequently colonized the younger islands in the chain in an independent and sequential fashion. The phylogeny also implies an ecological progression from ancestral breeding sites in ponds or slow stream pools to breeding on seeps, with the latter habitat having given rise on one hand to a clade of species breeding in phytotelmata or terrestrially, and on the other hand to a clade breeding in rushing midstream waters. The latter ecological progression also indicates a transformation series in larval gill structure from foliate to saccate and eventually to lanceolate. Most species of current conservation concern are shown to be clustered in particular clades, indicating an inherent phylogenetic vulnerability of certain taxon clusters to novel ecological perturbations; the additional species at risk not present in the above clades are endemics confined to the island of O'ahu and have declined because of their geographic provenance.