High diversity of Cetiocyon beetles (Coleoptera: Hydrophilidae) along an elevational gradient on Mt. Wilhelm, New Guinea, with new records from the Bird's Head Peninsula

A major component of the "Our Planet Reviewed – Papua New Guinea" project was to evaluate insect diversity along an elevational gradient on Mt. Wilhelm (Madang Province, Papua New Guinea), the fourth highest peak in New Guinea. Flight intercept traps were installed at eight sites separated by approximately 500 m in elevation from 200 m a.s.l. to 3700 m a.s.l. Here we focus on the water scavenger beetle genus Cetiocyon (Coleoptera: Hydrophilidae) collected as part of this project. Cetiocyon species are uniform in much of their external morphology, but diagnostic characters are found in the male genitalia. Our aim was to test the hypothesis that local species diversity was high, and that Cetiocyon species diversity is elevationally structured. A small amount of additional material from western New Guinea (Bird's Head Peninsula: Arfak Mts.) was also examined. Ten new species are described, seven from Mt. Wilhelm Cetiocyon paweli sp.n., C. depilis sp.n., C. onyx sp.n., C. augai sp.n., C. ibiscanus sp.n., C. mogianus sp.n., and C. gemellus sp.n., and three from the Arfak Mountains: C. jakli sp.n., C. colossus sp.n., and C. hamifer sp.n.. Twelve Cetiocyon species were found on the slopes of Mt. Wilhelm, most of which were only found at one or two neighboring elevations. The largest diversity of species was found at intermediate elevations (1200 – 1700 m). We successfully sequenced the 3' end of mitochondrial cox1 gene for 10 species, which we used along with morphological characteristics to infer a species level phylogeny and examine the effect of elevation on species diversity. Interspecific genetic distances were significantly lower at higher elevations on Mt. Wilhelm, and our phylogenetic reconstruction suggests that Cetiocyon ancestrally inhabited low or intermediate elevations. As the result of recent research eighteen Cetiocyon species are currently known form New Guinea. An updated identification key to all New Guinean species is included, along with photographs and illustrations of relevant morphological characters