Morphology of adults and larvae and integrative taxonomy of southern hemisphere genera Tormus and Afrotormus (Coleoptera: Hydrophilidae)

Abstract: Adult morphology of the genera Tormus Sharp, 1884 and Afrotormus Hansen, 1999, endemics of New Zealand and South Africa respectively, is examined and illustrated. The larval morphology of Tormus is also reviewed. Both adult and larval morphology supports the hypothesis of close relationship between these genera and Paracymus Thomson, 1867 of the tribe Laccobiini as shown by molecular data. The principal adult characters supporting this hypothesis are the presence of an organized stridulatory file on abdominal laterosternite 3 and the morphology of the mesofurca. The larva of Tormus is very similar to that of Paracymus, with the exception of the absence of the ligula and the presence of dense pubescence on antenna, maxilla and labium which are possible adaptations to a terrestrial lifestyle. The sister relationship of Tormus and Afrotormus seems quite probable based on several unique or rarely occurring character states shared by both genera, but needs to be confirmed by a formal phylogenetic analysis. Tormus inhabits moss on forest floor and Afrotormus was collected from under stones, and both genera hence represent previously unrecognized independent ecological transitions to terrestrial environment within Hydrophilidae. Genital morphology of Tormus indicated two well-defined groups treated as species: Tormus helmsi Sharp, 1884 (= Tormus nitidus Broun, 1893a, syn. nov., = Stygnohydrus nitidus Broun, 1893b, syn. nov., = Stygnohydrus femoralis Broun, 1910, syn. nov. = Stygnohydrus basalis Orchymont, 1937, syn. nov.) and Tormus posticalis (Broun, 1917), stat. restit. Genetic data from cox1 mitochondrial gene indicated five haplotype lineages, of which the Fiordland group is equivalent to T. posticalis. The more derived T. helmsi clade, distributed west and north of the Alpine Fault, consists of four haplotype groups that may be cryptic species with variable male genitalia. Though based on a single gene and limited sampling, our data suggest a South Island origin for Tormus. Evidence for isolation by distance was weak and while haplotype lineages of T. helmsi form a grade south to north with a monophyletic haplogroup in the North Island, environmental barriers may explain the population structure.

Key words: Coleoptera, Hydrophilidae, Laccobiini, Tormissini, Tormus, Afrotormus, Paracymus, adult morphology, larval morphology, chaetotaxy, integrative taxonomy, cox1, cryptic species, New Zealand, South Africa