Data_Sheet_1_No Evidence for Single-Copy Immune-Gene Specific Signals of Selection in Termites.pdf

Selection pressures from pathogens appear to play an important role in shaping social evolution. Social behavior, in particular brood care, is associated with pathogen pressure in wood-dwelling “lower” termites. Yet, generally pathogen pressure is predicted to be low in wood-dwelling termite species that never leave the nest except for the mating flight. In comparison, pathogen pressure is predicted to be 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 predicted 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.

病原体施加的选择压力似乎在社会演化的塑造中发挥着重要作用。在栖木性“低等”白蚁中，社会行为（尤其是育幼行为）与病原体压力存在关联。然而，通常而言，除婚飞外从不离巢的栖木性白蚁物种，其预测的病原体压力较低。相比之下，离巢觅食、因而持续接触环境中多种微生物的物种，其预测的病原体压力更高。我们提出假说：预测的病原体压力差异，也会体现在免疫基因所受自然选择强度的差异上。我们在系统发育框架下验证了这一假说，分析了单拷贝免疫基因的非同义替换率与同义替换率。为此，我们利用了来自8个白蚁物种的最新基因组与转录组数据，这些物种涵盖了栖木性和觅食性类群，此外还纳入了覆盖有翅昆虫（翅亚纲Pterygota）的另外14个物种。我们的研究结果并未发现病原体压力对单拷贝免疫基因的选择强度存在影响的证据；相反，我们发现白蚁存在全基因组范围内的松弛选择模式。