Phylogeny and the fossil record of the Helophoridae reveal Jurassic origin of extant hydrophiloid lineages (Coleoptera: Polyphaga)

Abstract

We performed a phylogenetic analysis focused on the hydrophiloid family Helophoridae (Coleoptera: Polyphaga) in order to test the phylogenetic position of selected Mesozoic fossils assigned to the Hydrophiloidea. The analysis is based on 92 characters of larvae and adults, and includes all extant subgenera of Helophorus and representatives of all other extant hydrophiloid families. Based on this analysis, we provide additional evidence for the monophyly of the helophorid lineage containing the families Helophoridae, Georissidae and Epimetopidae, as well as the first hypothesis on the phylogenetic relationships within Helophorus, revealing three main clades: Lihelophorus, Rhopalohelophorus and the clade of sculptured small subgenera; the subgenera Helophorus s.str., Gephelophorus, Trichohelophorus and Transithelophorus are recognized as paraphyletic or polyphyletic. Inclusion of fossil species in the analysis reveals the Mesozoic genera Hydrophilopsia Ponomarenko, Laetopsia Fikáček et al. (adult forms) and Cretotaenia Ponomarenko (larval form) as basal extinct clades of the helophorid lineage, the former genus Mesosperchus Ponomarenko as containing probable stem taxa of Helophorus and the former genus Mesohelophorus Ponomarenko as a member of the Helophorus clade containing extant sculptured subgenera. The extant subgenus Thaumhelophorussyn.nov. is synonymized with Rhopalohelophorus. Our results show that the family Helophoridae may be dated back to the late Jurassic (c. 150 Ma) and the extant clades of Helophorus back to the Early Cretaceous (c. 136 Ma). The basal groups of Helophorus and the supposed basal extinct lineages of the helophorid lineages are shown to be aquatic as adults. A single origin of trichobothria and ventral hydrophobic pubescence in the common ancestor of the Hydrophiloidea is hypothesized, indicating ancestral aquatic habits in the adult stage for the whole Hydrophiloidea.

Clade Age and Diversification Rate Variation Explain Disparity in Species Richness among Water Scavenger Beetle (Hydrophilidae) Lineages

“…Our molecular age estimates for Early-Middle Jurassic origins of most major hydrophilid clades are consistent with the fossil record because several modern hydrophiloid families were already well established by the Late Jurassic [21], [47] and Hydrophilidae was worldwide in distribution by the Late Jurassic [48]. Thus, our study provides the most robust temporal framework to date for interpreting the diversification of hydrophiloid water beetles.…”

Modern hydrophilid clades present and widespread in the Late Jurassic and Early Cretaceous (Coleoptera: Hydrophiloidea: Hydrophilidae)

“…Morphological terminology follows Komarek () and Lawrence et al . (); the term trichobothrium is used for ‘systematic puncture’ sensu Hansen (; see Fikáček et al ., 2012b for details).…”

“…Recent revision by Fikáček et al . (2012a) revealed that M. schultzi does not belong to Mesosperchus Ponomarenko, , which is now considered a formal subgenus of Helophorus (Hydrophiloidea: Helophoridae), comprising its Late Jurassic species (Fikáček et al ., 2012a,b). Instead, ‘ Mesosperchus ’ schultzi was shown to resemble modern Hydrophilidae by the shape of the head, presence of the large clypeus and distinct frontoclypeal suture (Fikáček et al ., 2012a).…”

“…Protochares gen. nov. may be reliably assigned to the superfamily Hydrophiloidea by the large clypeus and distinct frontoclypeal sutures reaching the lateral margin of the head closely before eyes. The presence of the triangular scutellar shield excludes all hydrophiloid families except Hydrophilidae and Spercheidae (Fikáček et al ., 2012b); from Spercheidae it differs in head not strongly constricted behind the eyes and the well‐sclerotized and largely exposed labrum. It may be therefore reliably assigned to the Hydrophilidae s.s.…”

“…The early evolution of the Hydrophilidae remained undocumented in the fossil, even though a Jurassic–Cretaceous minimum age was expected for the family based on the fact that other hydrophiloid families were already well established by the Late Jurassic. (Fikáček et al ., 2012b).…”