Cladistic analysis, phylogeny and biogeography of the Hawaiian Platynini (Coleoptera: Carabidae)

Abstract

The 128 known native Hawaiian species of the tribe Platynini are analysed cladistically. Cladistic analysis is based on 206 unit‐coded morphological characters, and also includes forty‐one outgroup taxa from around the Pacific Rim. Strict consensus of the multiple equally parsimonious cladograms supports the monophyly of the entire species swarm. The closest outgroup appears to be the south‐east Asian‐Pacific genus Lorostema Motschulsky, whose species are distributed from India and Sri Lanka to Tahiti, supporting derivation of the Hawaiian platynines from a source in the western or south‐western Pacific. The biogeographic relationships of the Hawaiian taxa are analysed using tree mapping, wherein items of error are minimized. The area cladogram found to be most congruent with the phylogenetic relationships, and most defensible based on underlying character data is {Kauai[Oahu(Hawaii{Lanai[East Maui(West Maui + Molokai)]})]}. This progressive vicariant pattern incorporates progressive colonization from Kauai, and vicariance of the former Maui Nui into the present islands of Molokai, Lanai, West Maui and East Maui. The evolution of flightlessness, tarsal structure, pronotal setation and bursal asymmetry are evaluated in the context of the cladogram. Brachyptery is a derived condition for which reversal is not mandated by the cladogram, although repeated evolution of reduced flight wings is required. Tarsal structure supports Sharp's (1903) recognition of Division 1 as a monophyletic assemblage, but exposes his Division 2 as a paraphyletic group requiring removal of the genus Colpocaccus Sharp. Pronotal setation is exceedingly homoplastic, and is not useful for delimiting natural groups. Left‐right asymmetry of the bursa copulatrix reversed twice independently, resulting in mirror‐image bursal configurations in B. rupicola and Prodisenochus terebratus of East Maui. The amount of character divergence is greater among species comprising Division 1 than among species of its sister group, the redefined Division 2. Based on superior fit of Division 1 relationships to the general biogeographic pattern, a greater speciation rate coupled with more extensive extinction is rejected as the cause for this greater divergence. Intrinsic differentiation in the processes underlying cuticular evolution appears to be more consistent with the observed biogeographic and morphological patterns.