Origin and dispersal of <i>Homalictus</i> (Apoidea: Halictidae) across Australia, Papua New Guinea and Pacific

The halictine bee genus <i>Homalictus</i> (Apoidea: Halictidae) is distributed broadly across south east Asia, Indonesia, Australia and the archipelagos of the Pacific. The group is well represented in the bee faunas of Australia and Papua New Guinea, but <i>Homalictus</i> is particularly important in the Pacific where it plays a keystone pollination role as the only endemic bee group in many islands. Understanding the origin and radiation of this genus is therefore important for understanding plant-bee co-evolution, not only in the Pacific, but the greater Oceania region. Previous studies have suggested that <i>Homalictus</i> has an Australian origin, and then dispersed northwards, but this is yet to be phylogenetically examined. Here we combine DNA sequences from the mitochondrial COI gene from <i>Homalictus</i> species from Papua New Guinea, the Pacific and Australia to infer the geographical and climatic origins of this group and subsequent dispersal events. Our results indicate a tropical origin for <i>Homalictus</i> in Australia, followed by multiple dispersals into the Pacific and subtropical, temperate and arid Australia. A tropical origin for <i>Homalictus</i> not only indicates the likely dispersal corridors for the ancestor of the group but has important implications for understanding social evolution in halictine bees.