A revision of the genus Mecodema Blanchard 1853 (Coleoptera: Carabidae: Broscini) from the North Island, New Zealand, and biogeographical interpretations of the subtribe Nothobroscina

Abstract

goal of this thesis is to revise the North Island species of the endemic ground beetle genus Mecodema (Coleoptera: Carabidae: Broscini), which is one of six Nothobroscina genera in New Zealand. However, to revise Mecodema it was necessary to look at all the New Zealand genera in context, and then expand to include the rest of the Gondwanan distributed nothobroscine genera. The genus Mecodema is unique amongst the other eleven genera in that it is very specious and widely distributed throughout New Zealand and some offshore islands. Because the genus is so diverse, the North Island offered a natural geographical boundary to work to, as only four species were known to have ranges across both islands. Prior to this study there were a total of 70 described Mecodema species, of which 25 were found in the North Island and only six species in the Northland region. In fact, many North Island regions were species poor, but habitat rich, e.g., Hawke’s Bay, Auckland, Coromandel, etc.). I borrowed all of the North Island specimens from Institutional Collections (e.g., Auckland Museum) and private collections (e.g., John Nunn). I conducted a pitfall trap survey of a large number of the North Island native forest habitats, targeting entomological regions with low diversity (e.g., East Cape). Examination of all North Island specimens revealed 24 new species, many of which were found in Northland, Auckland and the Hawke’s Bay. Inclusion of the New Zealand genera resulted in the synonymies of the monotypic Brullea and the three species of Metaglymma within Mecodema. These results increased the described diversity of Mecodema to 102 species. In previous studies, the diversity rich Mecodema has been divided into seven informal species groups based on morphology and to a lesser extent distribution. During the revision process, a morphological matrix of 128 multistate characters for 66 taxa was produced using Mesquite. I tested the monophyly and taxonomic viability of the informal species groups proposed in previous revisions and taxa descriptions. Phylogenies showed that only two (curvidens, infimate) groups are monophyletic and that the other five (alternans, costellum, ducale, laterale, spiniferum) groups are paraphyletic. However, the inclusion of more species representing each group may result in more monophyly of these species groups. Nothobroscina genera are found on all of the southern hemisphere Gondwanan countries, e.g., Australia, New Caledonia, New Zealand and southern South America. Each country has genera that are endemic, except the very disjunct geographical distribution of Percosoma between Tasmania and New Caledonia. The cladistic analyses supported a new genus of nothobroscine endemic to New Caledonia, Monteremita to house the former Percosoma asymetrica. The placement of the other nothobroscine genera on the phylogenies was similar to prior research. The biogeography and evolution of the subtribe and the derived New Zealand genus Mecodema has been reconstructed using phylogenetic analyses of the combined CO1 and 28S genes. Not all of the species represented in the morphological analyses were present in the molecular phylogenies, yet the general placement of taxa was very similar. Deep divergence between Mecodema and its sister taxon Percosoma suggested speciation due to vicariance, rather than long-distance dispersal via New Caledonia and the Norfolk—Reinga Ridge. I propose alternative hypotheses for the evolution of Mecodema, which have led to high diversity within a unique New Zealand genus.