Taxonomic revision of Madagascan Rhantus (Coleoptera, Dytiscidae, Colymbetinae) with an emphasis on Manjakatompo as a conservation priority

We review the diving-beetle genus Rhantus Dejean of Madagascar (Coleoptera, Dytiscidae, Colymbetinae) based on museum collection holdings and recently collected expedition material. Both morphology and DNA is used to test species boundaries, in particular whether newly collected material from the Tsaratanana mountains in the north represent a new species or are conspecific with Rhantus manjakatompo Pederzani and Rocchi 2009, described based on a single male specimen from the central Ankaratra mountains. DNA of the holotype of R. manjakatompo was successfully extracted in a non-destructive way and sequenced. The general mixed Yule coalescent model applied to an ultrametric tree constructed from mitochondrial cytochrome c oxidase subunit I (COI) sequence data delimited three species. Morphological characters supported the same species unambiguously. We therefore recognise three species of Rhantus to occur in Madagascar: R. latus (Fairmaire, 1869), R. bouvieri Régimbart, 1900 and R. manjakatompo Pederzani and Rocchi, 2009. All three species are endemic to Madagascar and restricted to the highlands of the island. Rhantusstenonychus Régimbart, 1895, syn. n., is considered a junior synonym of R. latus. We designate lectotypes for R. bouvieri and R. goudoti Sharp, 1882, the latter a junior synonym of R. latus. We provide descriptions, a determination key, SEM-images of fine pronotal and elytral structures, distribution maps, habitus photos, and illustrations of male genitalia and pro- and mesotarsal claws. We discuss the role of the Manjakatompo forest as a refugium for Madagascan Rhantus diversity and other endemics of the montane central high plateau

In or Out-of-Madagascar?—Colonization Patterns for Large-Bodied Diving Beetles (Coleoptera: Dytiscidae)

<div><p>High species diversity and endemism within Madagascar is mainly the result of species radiations following colonization from nearby continents or islands. Most of the endemic taxa are thought to be descendants of a single or small number of colonizers that arrived from Africa sometime during the Cenozoic and gave rise to highly diverse groups. This pattern is largely based on vertebrates and a small number of invertebrate groups. Knowledge of the evolutionary history of aquatic beetles on Madagascar is lacking, even though this species-rich group is often a dominant part of invertebrate freshwater communities in both standing and running water. Here we focus on large bodied diving beetles of the tribes Hydaticini and Cybistrini. Our aims with this study were to answer the following questions 1) How many colonization events does the present Malagasy fauna originate from? 2) Did any colonization event lead to a species radiation? 3) Where did the colonizers come from—Africa or Asia—and has there been any out-of-Madagascar event? 4) When did these events occur and were they concentrated to any particular time interval? Our results suggest that neither in Hydaticini nor in Cybistrini was there a single case of two or more endemic species forming a monophyletic group. The biogeographical analysis indicated different colonization histories for the two tribes. Cybistrini required at least eight separate colonization events, including the non-endemic species, all comparatively recent except the only lotic (running water) living <i>Cybister operosus</i> with an inferred colonization at 29 Ma. In Hydaticini the Madagascan endemics were spread out across the tree, often occupying basal positions in different species groups. The biogeographical analyses therefore postulated the very bold hypothesis of a Madagascan origin at a very deep basal node within <i>Hydaticus</i> and multiple out-of-Madagascar dispersal events. This hypothesis needs to be tested with equally intense taxon sampling of mainland Africa as for Madagascar.</p></div

Timetree of Cybistrini.

<p>Time-calibrated Bayesian phylogeny obtained with BEAST. The numbers indicate estimated divergence time for each node/posterior probability support for the node. Maps represent zoogeographical areas used to obtain the ancestral distributions. Pie charts at internal nodes: a) Ancestral reconstruction obtained from the S-Diva methods, b) ancestral reconstruction obtained from the DEC method.</p

Collecting localities from four expeditions 2006–2012 across the island and known species of <i>Cybister</i> and <i>Hydaticus</i> on Madagascar.

<p>Species in frames represent species that are endemic to Madagascar. Photos by Harry Taylor and Johannes Bergsten.</p

Timetree of Hydaticini.

<p>Time-calibrated Bayesian phylogeny obtained with BEAST. The numbers indicate estimated divergence time for each node/posterior probability support for the node. Maps represent zoogeographical areas used to obtain the ancestral distributions. Pie charts at internal nodes: a) Ancestral reconstruction obtained from the S-Diva methods, b) ancestral reconstruction obtained from the DEC method.</p