Reconstructing the evolutionary and ecological history of the sea skaters Halobates spp. (Heteroptera: Gerridae)

The genus Halobates includes the only five insect species that have been successful in a pelagic marine environment. Different scenarios of independent colonization events of that environment have been proposed, considering the appearance of pelagic distribution in several non-sister clades in the phylogeny of the genus. In this paper, we aim to update the phylogenetic hypothesis under the criterion of Bayesian inference, calibrate a molecular clock using the only fossil described in the genus and also analyze the diversity pattern of the lineage since its divergence. High support values were found in the phylogenetic reconstruction, which tend to decrease with an increase of the distances from the root. Low supports for the most derived clades or relatively recent divergences cast doubt on the delimitation of some species. Although the divergence time for Halobates was estimated at 42.01 mya (± 8.13) the emergence of the lineage probably happened a few million years before, so the estimated time of divergence probably also marked the start of diversification of the marine lineages of this genus. Since divergence, the richness of genus showed continuous linear growth for approximately 24.4 my, when the lineages began to diversify more quickly with a significantly lower extinction rate.The colonization of the pelagic environment which occurred nearly 42 mya, could also have been the starting point of the colonization of the marine pelagic environment when changes in their morphology, physiology and behaviour enabled them to exploit novel ecological niches. Ancestors of pelagic marine insects probably inhabited areas close to the seacoast more than 41 mya ago. The ecological history of Halobates was probably not limited to a pair of open water colonization events as indicated by earlier proposals. We hypothesize instead that at least three independent events of open water colonization by Halobates species have occurred. In this sense, the ecological character of coastal or pelagic distribution is considered to be a homoplasic character without direct implications on the net diversification of Halobates.