No evidence for immune-gene specific signals of selection in termites

It has been hypothesized that selection pressure from pathogens plays an important role in shaping social evolution. Social behaviour, in particular brood care, is associated with pathogen pressure in wood-dwelling “lower” termites. Yet, generally pathogen pressure is low in wood-dwelling termite species that never leave the nest except for the mating flight. In comparison, pathogen pressure is higher in species that leave the nest to forage, and thus constantly encounter a diversity of microbes from their environment. We hypothesized that such differences in pathogen pressure are also reflected by differences in the intensity of natural selection on immune genes. We tested this hypothesis in a phylogenetic framework, analyzing rates of non-synonymous and synonymous substitutions on single-copy immune genes. Therefore, we leveraged recent genomic and transcriptomic data from eight termite species, representing wood-dwelling and foraging species as well as 14 additional species spanning the winged insects (Pterygota). Our results provide no evidence for a role of pathogen pressure in selection intensity on single-copy immune genes. Instead, we found evidence for a genome-wide pattern of relaxed selection in termites. Life Science Identifiers (as available Zoobank) Ephemera danica : urn:lsid:zoobank.org:act:06633F75-4809-4BB3-BDCB-6270795368D5 Coptotermes sp. urn:lsid:zoobank.org:pub:D6724B7F-F27A-47DC-A4FC-12859ECA0C71 Blattella germanica : rn:lsid:zoobank.org:pub:1EA126BA-E9D2-4AA6-8202-26BA5B09B8AD Locusta migratoria urn:lsid:zoobank.org:pub:D792A09E-844A-412A-BFCA-5293F8388F8C Periplaneta americana (Blatta americana) : urn:lsid:zoobank.org:act:95113A55-4C6D-4DC7-A0E5-620BACADFFE5 Apis mellifera : urn:lsid:zoobank.org:act:9082C709-6347-4768-A0DC-27DC44400CB2 Bombyx mori (Phalæna (Bombyx) mori) urn:lsid:zoobank.org:act:215466E3-E77F-46E9-8097-372837D7A375 Drosophila melanogaster : urn:lsid:zoobank.org:act:5B39F0AA-270D-4AA8-B9A3-C36A3A265910