The eucnemidae of South-East Asia and the Western Pacific — a biogeographical study

Abstract

Eighty-nine eucnemid genera occur in the region from South-east Asia to the south-west Pacific. The phylogenies of 84 of these were used together with the present-day distributions of the species to analyse the biogeographical history of the area. Fifty-seven genera shared a pattern coinciding with the traditional model of Laurasia–Gondwana break-up. Six genera showed a pattern contradicting the model. The remaining 21 genera neither supported nor refuted the model. Twenty-five genera were observed to include an Indomalesian clade younger than the South America–Australia connection. This biogeographical unit consisted of present-day South-east Asia and the Sunda islands, but did not include the Philippine Islands and Sulawesi. In addition to this Indomalesian clade, three separate clades involving northern Australia or New Guinea were observed, New Guinea–Australia, New Guinea–Philippines–Sulawesi and New Guinea–Fiji. The possible presence of four separate areas in the general region of New Guinea–north Australia as the result of the Cretaceous geological events is suggested. Three of these, in the area of present-day New Guinea, originally sharing sister-groups with the north-eastern Australian isolate, are regarded as the sources of the New Guinea–Indomalesia, New Guinea–Philippines and New Guinea–Fiji faunas after northward drifting of the Australian continent. During the Oligocene–Miocene these source areas were flooded and their original fauna lost. When the present-day New Guinea emerged, it was invaded from the north-eastern Australian region. This invasion created new New Guinea–Australia connections and brought in the sister-groups of the old New Guinea source areas as well.

The eucnemids of Vanuatu, Samoa and Tonga are regarded as having originated in connection with dispersal from Fiji.

The New Zealand fauna has strong, old connections with that of south-eastern Australia, but other complex connections are indicated.

The Eocene Baltic Amber fauna agrees well with the results obtained from extant species. The species belonging to five fossil genera belong to Gondwanan groups that seem to have invaded the Holarctic via Central America. Four other fossil genera showing discordant patterns belong to the group of six genera exhibiting these aberrant patterns even today. The eucnemid fauna of the region is of Gondwanic origin. Only six Laurasian genera have invaded the area, all of them apparently quite recently.