Search

Genes acquired by horizontal transfer are increasingly being found in animal genomes. Understanding their origin and evolution requires knowledge about the phylogenetic relationships from both source and recipient organisms. We used RNASeq data and respective assembled transcript libraries to trace the evolutionary history of polygalacturonase (pectinase) genes in stick insects (Phasmatodea). By mapping the distribution of pectinase genes on a Polyneoptera phylogeny, we identified the transfer of pectinase genes from known phasmatodean gut microbes into the genome of an early euphasmatodean ancestor that took place between 60 and 100 million years ago. This transfer preceded the rapid diversification of the suborder, enabling symbiont-free pectinase production that would increase the insects' digestive efficiency and reduce dependence on microbes. Bacteria-to-insect gene transfer was thought to be uncommon, however the increasing availability of large-scale genomic data may change this prevailing notion.

In a few insect groups, males pierce the female's integument with their penis during copulation to transfer sperm. This so-called traumatic insemination was previously confirmed for Strepsiptera but only in species with free-living females. The more derived endoparasitic groups (Stylopidia) were suggested to exhibit brood canal mating. Further, it was assumed that females mate once and that pheromone production ceases immediately thereafter. Here we examined Stylops ovinae to provide details of the mating behaviour within Stylopidia. By using μCT imaging of Stylops in copula, we observed traumatic insemination and not, as previously suggested, brood canal mating. The penis is inserted in an invagination of the female cephalothorax and perforates its cuticle. Further we show that female Stylops are polyandrous and that males detect the mating status of the females. Compared to other strepsipterans the copulation is distinctly prolonged. This may reduce the competition between sperm of the first mating male with sperm from others. We describe a novel paragenital organ of Stylops females, the cephalothoracic invagination, which we suggest to reduce the cost of injuries. In contrast to previous interpretations we postulate that the original mode of traumatic insemination was maintained after the transition from free-living to endoparasitic strepsipteran females.