Biogeography and diversification of the Pacific ant genus Lordomyrma Emery (Hymenoptera: Formicidae)

The Fijian archipelago hosts a diverse terrestrial biota more typical of a mature continental ecosystem than a collection of small islands isolated in the remote reaches of the southwestern Pacific. We take a phylogenetic approach to investigating the biogeographic origin of a genus of ants (Hymenoptera: Formicidae) largely confined to the Pacific Islands. This study uses evidence inferred from molecular data to examine alternative hypotheses regarding the biogeographic origin of the Fijian endemics in the genus Lordomyrma Emery (subfamily Myrmicinae). Specifically, we address three questions: (1) are the Fijian Lordomyrma derived from one or multiple colonization events, (2) where did the lineage originate and (3) Where do the closest extant relatives of the Fijian species occur? Fragments of four nuclear genes (28S, argK, LW Rh, CAD), comprising ~2.5 kb of sequence, were obtained from ants in the genus Lordomyrma, collected from Pacific islands, Melanesia and China. These sequences were used to reconstruct phylogeny and estimate dates of divergence within this lineage. The biogeographic history of Lordomyrma is examined in the context of current hypotheses regarding colonization of the Fijian archipelago. The Fijian Lordomyrma are found to be monophyletic, with a New Guinean lineage emerging as their closest living relatives. Diversification of the Fijian taxa is estimated to have occurred approximately 8.8 million years ago, congruent with Miocene fragmentation of the Vitiaz Arc and Pliocene emergence of Vanua Levu within the Fijian archipelago.