Aenetus Herrich-Schäffer 1855

(2) Aenetus in the Southwest Pacific

The principal diversity of Aenetus is in Australia (18 species) and New Guinea (9 species). Outside this range there is a single species each in northern Sumatra (Grehan, Witt & Ignatyev in prep.), Maluku (Moluccas), New Caledonia and New Zealand (Fig. 8a). The New Zealand and New Caledonian species do not appear to be sister taxa, as the male genitalia of the latter show greater, specialized similarities with species from Australia and New Guinea (cf. Grehan 1983; Dugdale 1994; Simonsen 2018). The New Zealand species A. virescens (Doubleday, 1843) occurs only in the North Island and its offshore islands where it occupies low- to mid-elevation forests (Grehan 1987; Dugdale 1994). Several features, including a unique valve configuration of the male genitalia, suggest that it is the sister taxon to all other species of Aenetus (Dugdale 1994, JRG pers. obs.). This relationship is compatible with vicariance rather than being derived by dispersal from a particular species or group of species in eastern Australia. This vicariance may not be simply the result of the Tasman Sea basin separating the ancestor as this would not explain the apparent lack of a close relationship with the New Caledonian A. cohici (Viette, 1961) (Dugdale (1994). It is possible that an earlier vicariance separated A. virescens before New Zealand and New Caledonia both became geographically isolated from Australia. The Maluku archipelago is part of the Philippine Sea Plate arc that collided with the northern edge of New Guinea at ̴25 Ma and moved westwards to its present position. Ongoing examination of Aenetus specimens from the Lesser Sunda indicates the possible presence of several undescribed species that may be endemic to individual islands (Grehan & Mielke in prep). It would not be surprising to find Aenetus in Sulawesi given that some eastern sections are made up of Australian plate-derived terranes (Hall 2000).

Several biological and morphological similarities suggest a close affinity and perhaps a sister group relationship between Aenetus (and a new genus in eastern Australia, Simonsen 2018) and Endoclita although the current evidence is inconclusive (Dugdale 1994, Grehan and Rawlins 2003). The distribution of Endoclita encompasses much of eastern Asia as well as India (Fig. 8b) and current records suggest a southeastern Philippines-Borneo-Bali boundary for the group (Grehan 2011b; Grehan and Ismavel 2016). This lies close to the northwestern limits of the Australian continental margin which collided with the Asian fore-arc at ̴4 Ma and now forms part of the outer Banda Arc islands (Malaku, Ambon, Aru, Tanimbar, and Timor) (Audely-Charles 2011). Until very recently the allopatry of Endoclita and Aenetus appeared to be substantial even with uncertainties about the distributional limits of both genera in the vicinity of Sulawesi, the western Lesser Sunda, and southern Philippines (Fig. 8b). Discovery of a new species of Aenetus (Grehan, Witt & Ignatyev in prep.) in northern Sumatra indicates a greater degree of sympatry and the possibility that undiscovered populations are present over a wider region, at least along the Greater Sunda (Fig. 8b) suggesting a more extensive tectonic history for Aenetus that includes both South East Asia and the Southwest Pacific as documented for many other plant and animal taxa.