Comparative genomics provides insights into molecular adaptation to hypermetamorphosis and cantharidin metabolism in blister beetles (Coleoptera: Meloidae)

Blister beetles (Coleoptera: Meloidae) are currently subdivided into three subfamilies: Eleticinae (a basal group), Nemognathinae, and Meloinae. These are all characterized by the endogenous production of the defensive terpene cantharidin (CA), whereas the two most derived subfamilies show a hypermetamorphic larval development. Here, we provide novel draft genome assemblies of five species sampled across the three blister beetle subfamilies (Iselma pallidipennis, Stenodera caucasica, Zonitis immaculata, Lydus trimaculatus, and Mylabris variabilis) and performed a comparative analysis with other available Meloidae genomes and the closely-related canthariphilous species (Pyrochroa serraticornis) to disclose adaptations at a molecular level. Our results highlighted the expansion and selection of genes potentially responsible for CA production and metabolism, as well as its mobilization and vesicular compartmentalization. Furthermore, we observed adaptive selection patterns and gain of genes devoted to epigenetic regulation, development, and morphogenesis, possibly related to hypermetamorphosis. We hypothesize that most genetic adaptations occurred to support both CA biosynthesis and hypermetamorphosis, two crucial aspects of Meloidae biology that likely contributed to their evolutionary success.

Phylogenetics and population structure of the steppe species Hycleus polymorphus (Coleoptera: Meloidae: Mylabrini) reveal multiple refugia in Mediterranean mountain ranges

Many continental species distributed in the Eurasian steppe occur as relict populations in the mountains of Western Europe. Their biogeographical responses to Quaternary climate changes have been poorly studied; however, they could have responded as cold-adapted species. We investigated the biogeographic history of a steppe beetle, Hycleus polymorphus, using mitochondrial and nuclear DNA sequences (COI, CAD, ITS2), and species distribution modelling (SDM) under present and past bioclimatic envelopes. We first performed a phylogenetic assessment to define species boundaries within the H. polymorphus species group. Specimens previously treated as Hycleus humerosus on morphological grounds are assigned to H. polymorphus, and those identified as Hycleus zebraeus assigned to Hycleus atratus. ITS2 data analyses revealed a strong phylogeographical structure of H. polymorphus populations, with four haplogroups corresponding to the (i) Italian Alps, (ii) French Alps and Pyrenees, (iii) South Balkan and Pontic mountains, and (iv) North Dinaric Alps. Based on these analyses and the SDM, we propose that during a glacial period, following the spread of steppic habitat, H. polymorphus underwent a range expansion from Asia to South-West Europe. Within the Mediterranean area, during the last interglacial the climatic suitability for the species was limited to mountains that acted as refugia and prompted allopatric divergence into four main lineages.

Revision of the Hycleus sexmaculatus species group (Coleoptera: Meloidae, Mylabrini)

In this study, the blister beetles belonging to the Hycleus sexmaculatus species group are revised. Morphological characters are described and figured for each species and keys to both male and female are provided. Hycleus hayki new species from Southwest Iran is described and the following new synonymies are proposed: Mylabris triangulifera ab. reitterioides Mader 1929 = Hycleus bipunctatus (Olivier, 1811) new synonymy; Mylabris triangulifera ab. bushirensis Mader 1929 = Hycleus bipunctatus (Olivier, 1811) new synonymy; Mylabris javeti Marseul, 1870 = Hycleus colligatus (Redtenbacher, 1850) new synonymy; Mylabris javeti umbilicatus Kaszab, 1958 = Hycleus colligatus (Redtenbacher, 1850) new synonymy; Hycleus amrishi Makhan, 2012 = Hycleus cingulatus (Faldermann, 1837) new synonymy. Additional remarks which rectify previous errors in the identification of the species are provided. The taxonomic positions of Zonabris soumacovi Pic, 1930 and Zonabris sialanus Pic, 1929 are also discussed. Phylogenetic relationships of the species, based on a subset of available species inferred from molecular data are proposed, and some morphologically defined subgroups of species are distinguished with the molecular support. The geographic and ecological distributions of all the species are defined, and a detailed list of localities is provided. The ecological information including phenology, elevation and host plants of the species are summarized in a table. Based on literature records, collections and recently collected data, the distribution of the sexmaculatus species and their biogeographic characteristics are discussed.

Phylogeny, biogeography and systematics of the hyper-diverse blister beetle genus Hycleus (Coleoptera: Meloidae)

Hycleus is a hyper-diverse genus of blister beetles including ~500 species widely distributed in the Old World, currently divided into three "sections" and into 45 "phenetic" species groups according to morphological characters. Recently the monophyly of Hycleus was questioned pointing out its paraphyly with respect to the genera Ceroctis and Paractenodia. In this study, we built a time-calibrated phylogenetic tree based on DNA sequence data from mitochondrial and nuclear genes obtained from 125 species, to understand the phylogenetic relationships among the species of this genus, to infer the biogeographic processes behind their diversification, and to assess their taxonomy and classification. Our results identified four main lineages one of which included the species belonging to Ceroctis and Paractenodia; therefore, both taxa are now referred to Hycleus as new synonyms. The three described sections of Hycleus resulted polyphyletic and are rejected, whereas several species groups represented well supported clades. Hycleus likely originated in Africa during the Early Miocene (~20 Mya), and subsequently spread in Europe and western Asia. Later, in the Late Miocene (~6 Mya) a Saharo-Sindian group branched off from the Palaearctic lineage, whereas the Oriental Region was colonized following a dispersal event through the Arabian Peninsula from the Afrotropical Region (~5 Mya).