Molecular ecology and phylogenetics of the water beetle genus Ochthebius revealed multiple independent shifts to marine rockpools lifestyle

Abstract

Trizzino, M. (2016) Molecular ecology and phylogenetics of the water beetle genus Ochthebius revealed multiple independent shifts to marine rockpools lifestyle -Zoologica Scripta, 45:175-186. Marine rockpools represent a dynamic ecosystem where inhabiting species usually suffer changeable conditions, with consequent phenomena of local populations' size expansions and reductions. Nevertheless, a few specialized insect groups are known to live in marine rockpools, and among them, several species belong to the water beetle family Hydraenidae. Three groups of Ochthebius sensu lato (s.l.) live in fact in marine rockpools: the putative subgenus Calobius, the former subgenus Cobalius (both mostly Mediterranean-Macaronesian) and two species of the O. capicola group from South Africa. In this work, we performed a molecular phylogeny of Ochthebius s.l., running molecular clocks, aiming to address the following questions: Are these three groups related? Which is their position within Ochthebius s.l.? How many different times and in how many lineages of Ochthebius s.l. a shift from inland waters to marine rockpools environments happened? Is the current taxonomic status of these three groups supported by genetics? We found that Calobius, Cobalius and the O. capicola group represent three distinct groups, with no sister relationships, suggesting that a shift from fresh/ brackish waters to marine rockpools happened independently at least three different times along the diversification of the genus. Cobalius represents an effective separate subgenus, whereas such a rank is not supported by molecular data for Calobius, which represents a monophyletic clade within the nominal subgenus Ochthebius sensu stricto (s.str.). However, as Calobius is monophyletic and characterized by strongly peculiar and distinguishing morphology, we suggest referring to this group as the 'Calobius' lineage. Three Mediterranean taxa within this lineage represent likely valid new species, to be described soon. In the same way, the taxonomy of Cobalius should be revised, with two previously formally recognized species found to be paraphyletic, and the possible presence of two additional cryptic species.

A molecular phylogeny of the tribe Ochthebiini (Coleoptera, Hydraenidae, Ochthebiinae)

“…Described as a subgenus of Ochthebius by Rey (), synonymized by Perkins () with Ochthebius s.s. and considered again as subgenus by Sabatelli et al . (). We recovered it here as a strongly supported monophyletic lineage clearly outside Ochthebius s.s., confirming its status as subgenus.…”

“…Sabatelli et al . () used these data to study the origin of species typical of rockpools, recovering basically the same relationships and establishing a new species group for the South African O. capicola Péringuey. In the same paper, the subgenus Cobalius was found to be outside Ochthebius s.s., but Calobius nested within it, referring to it as the ‘ Calobius ’ lineage.…”

“…A large number of species are tolerant to hypersaline waters, living in coastal rockpools (e.g. Cobalius Rey or Calobius Wollaston; Antonini et al, ; Sabatelli et al, ), coastal or inland saltpans or inland hypersaline streams (especially the O. notabilis group, but also many other species in different groups; Abellán et al, ; Millán et al, ).…”

Evolution of salinity tolerance in the diving beetle tribe Hygrotini (Coleoptera, Dytiscidae)

“…salinarius ) were grouped in the same monophyletic radiation. In other families of aquatic Coleoptera, species that were apparently not closely related were also found to have a common origin of their tolerance to salinity, as for example in the genera Ochthebius Leach, 1815 (Hydraenidae; see Sabatelli et al., ) and Enochrus Thomson, 1859 (Hydrophilidae; see Arribas et al., ).…”

“…Many species of Hydroporinae live in extreme or unusual environments for diving beetles, such as subterranean aquifers, forest litter or hypersaline waters. While the origin and evolution of subterranean and terrestrial lifestyles have received recent attention (e.g., Leys & Watts, ; Tierney et al., ; Toussaint, Hendrich, Escalona, Porch, & Balke, ), the origin of the species of diving beetles able to sustain extreme salt concentration has never been addressed in a phylogenetic context, whereas for other families of aquatic Coleoptera, such as Hydrophilidae or Hydraenidae, comparative studies on the evolution of saline tolerance are already available (Arribas et al., ; Sabatelli et al., ).…”