Beetles

Loxomerus nebrioides

Beetles comprise the largest group of invertebrates known in the world and, likewise, are dominant in a number of species over most arthropod groups in the subantarctic islands, with well over 100 species recorded to date (Gressitt & Wise 1971). Though the weevils, the most diverse of the beetles, have been described thoroughly by Kuschel (1964, 1971), there are many species and records that need to be formally published (or confirmed) so that the evolution and ecology of the beetles can be fully appreciated.

The arthropod fauna of Campbell Island was documented last century, (see Gressitt 1964) and this island is perhaps the best studied and surveyed among New Zealand's subantarctic islands. It was discovered recently, however, that there was a new species of pselaphine rove beetle (Staphylinidae) among fresh and older material, and information on this species will be published soon (Carlton & Leschen, submitted), taking the number of species on this island to 44. In a recent survey of the remote Antipodes Islands (2100 hectares), Marris (2000), reports 25 species and at least 7 new species of Carabidae, Cerambycidae, Salpingidae, and Staphylinidae. By extrapolation, we may expect that the Auckland Islands (51 000 hectares), the largest and least known of the subantarctic islands with at least 57 species known thus far (Marris 2000), may have over 100 species, though work is necessary to document in detail the beetle diversity on this and Snares Islands. The beetle fauna of the Bounty Islands (135 hectares), with nine species, is currently under study by John Marris (Lincoln University), and Australia's Macquarie Island, about 200 kilometres south of Campbell Island, has eight species (Greenslade 1990).

Based on survey work on Campbell Island, we determined that only two genera (Holopsis (Corylophidae) and Melanophthalma (Latridiidae), Figs 1 & 2) are associated with microfungi, two are saprophagous and may be facultatively mycophagous (Meropathus (Hydraenidae) and Paracatops Leiodidae), and a single species feeds on lichen and other plant material (Pseudhelops (Tenebrionidae)). We estimate a higher diversity of mycophagous species in the Auckland Islands that include an additional six families compared with Campbell Island, including undescribed taxa from mycophagous families Cryptophagidae (nr. Thortus) and Phloeostichidae (nr. Priasilpha). We also observed Lepidoptera damage on Xylariaceae on Auckland Islands, and it is likely that this is another important mycophagous group in the subantarctic.

The beetles are providing suprising and important insights towards understanding the origin of the subantarctic fauna. Why, for example, do some Campbell Island beetle species that may be closely related occur in more or less exactly the same microhabitats throughout the island? Carlton & Leschen (submitted) suggest that the two species of Pselaphotheseus, members of the predatory group Pselaphinae (Staphylinidae), may have undergone sympatric speciation (evolution without geographic isolation). Though sympatric evolution has been evoked as a speciation mechanism for many taxa present on other islands such Hawaii and the Galapagos (see Otte & Endler 1989), this mode of speciation remains controversial. Detailed cladistic analyses of insular organisms (see Wagner & Funk 1995) reveal more complex patterns of evolution that include dispersal (movement from one landmass to another), radiation (speciation within a single area), and vicariance (speciation facilitated by the formation of [usually] geographic barriers between ancestral populations). Therefore, the hypothesis that the two species of Campbell Island Pselaphotheseus evolved in sympatry requires additional research. It is likely that this genus is also present on the Auckland Islands.

The organismal affinities of the Campbell Plateau are tied primarily with mainland New Zealand (see Gressitt et al. 1964) and to a lesser extent to other south temperate and subantarctic areas (Morrone 1998; Marris 2000). Based on distribution data and cladistic information, Leschen et al. (submitted) reveals that members of two unrelated groups of intertidal and wingless beetles (Staphylinidae and Salpingidae) present on the Campbell Plateau are either Gondwanan relicts of groups that were much more widespread, or are sister taxa to northern Pacific relatives 9000 km away. The species Baeostethus chiltoni Broun (Fig. 3), a member of liparocephaline Staphylinidae, is closely related to members of the genus Liparocephalus distributed in on the coasts of North America and northern Asia. These data add a third biogeographic component to the Campbell Plateau biota, which includes lineages that predate the separation of Gondwana from Laurasia and are present (and widespread) in northern Holarctic areas and restricted to New Zealand's subantarctic islands. This pattern is also seen in one terrestrial group of beetles, the gymnusine Aleocharinae (Hammond 1975; Klimaszewski 1979), with the remarkable species Stylogymnusa subantarctica Hammond present only on the Auckland Islands. This is one of the few beetles in the world that has piercing-sucking mouthparts reminiscent of similar structures present in other insect groups both living and extinct.

Does the level of mycophagy increase as a function of latitude or vegetative diversity and is the Campbell Plateau a mosaic of disharmonic species or is it a separate piece of Gondwana distinct from New Zealand? Our on-going systematic, inventory, and evolutionary work will focus on these basic questions.

Literature Cited

Greenslade, P. 1990: Notes on the biogeography of the free-living terrestrial invertebrate fauna of Macquarie Island with an annotated checklist. Papers and Proceedings of the Royal Society of Tasmania 124: 35-50.
Gressitt, J.L. et al. 1964: Insects of Campbell Island. Pacific Insects Monograph 7:1-663.
Gressitt, J.L., & Wise, K.A.J. 1971: Entomology of the Aucklands and other islands south of New Zealand: Introduction. Pacific Insects Monograph 27: 1-45.
Hammond, P.M. 1975: The phylogeny of a remarkable new genus and species of gymnusine staphylinid (Coleoptera) from the Auckland Islands. Journal of Entomology (B) 44: 153173.
Klimaszewski, J. 1979: A revision of the Gymnusini and Deinopsini of the world (Coleoptera: Staphylinidae, Aleocharinae). Agriculture Canada Monograph 25: 1169.
Kuschel, G. 1964: Insects of Campbell Island. Coleoptera: Curculionidae of the subantarctic islands of New Zealand. Pacific Insects Monograph 7: 416-493.
Kuschel, G. 1971: Entomology of the Aucklands and other islands south of New Zealand. Coleoptera: Curculionidae. Pacific Insects Monograph 27: 225-259.
Marris, J.W.M. 2000: The beetle fauna (Coleoptera) fauna of the Antipodes Islands,with comments on the impact of mice; and an annotated checklist of the insect and arachnid fauna. Journal of the Royal Society of New Zealand 30: 169-195.
Morrone, J.J. 1998: On Uvardy's Insulantarctica province: a test from weevils (Coleoptera: Curculionoidea). Journal of Biogeography 25: 947-955.
Otte, D.; J. A. Endler (eds). 1989: Speciation and its consequences. Sinauer Associates, Sunderland, MA.
Wagner, W. L.; Funk, V.A.(eds). 1995: Hawaiian Biogeography: Evolution on a hot spot archipelago. Smithsonian Institution Press.