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

摘要

A phylogeny of the 22 species currently recognized in the genusMegalagrion, endemic to the Hawaiian Islands, is presented based on an analysisof 23 morphological and ecological characters. After the exclusion ofM. williamsoni,known from only a single male, and inclusion of subspecies within their nominatetaxa, a single resolved tree of length 85 was obtained; this tree has a consistencyindex of 0.56 and a retention index of 0.72. Based on this phylogeny, it appearsthat the major clades within Megalagrion differentiated on Kaua'i or an antecedenthigh island. These clades subsequently colonized the younger islands in the chainin an independent and sequential fashion. The phylogeny also implies an ecologicalprogression from ancestral breeding sites in ponds or slow stream pools to breedingon seeps, with the latter habitat having given rise on one hand to a clade of speciesbreeding in phytotelmata or terrestrially, and on the other hand to a clade breedingin rushing midstream waters. The latter ecological progression also indicates atransformation series in larval gill structure from foliate to saccate and eventuallyto lanceolate. Most species of current conservation concern are shown to be clusteredin particular clades, indicating an inherent phylogenetic vulnerability of certaintaxon clusters to novel ecological perturbations; the additional species at risk notpresent in the above clades are endemics confined to the island of O'ahu and havedeclined because of their geographic provenance.