Social evolution in termites reduces natural selection efficacy

In eusocial species, reproduction is monopolized by a few reproductive individuals. From the perspective of population genetics, this implies that the effective population size (Ne) of these organisms is likely to be smaller compared to solitary species, as has been proposed in the literature for eusocial Hymenoptera. In this study, we investigate the genomic consequences of eusociality in termites (Isoptera) across two different timescales. First, by analyzing transcriptome data from 66 Blattodea species, we focus on the ratio of nonsynonymous to synonymous mutations (dN/dS) as a marker of natural selection efficiency and effective population size. Our results demonstrate an elevated dN/dS ratio in termites compared to other Blattodea members, which further generalizes the idea that convergent evolution toward eusociality strongly reduces effective population size and genome-wide efficiency of natural selection. Then, by comparing 68 termite transcriptomes, we show that this decrease in natural selection efficiency is even more pronounced in termites displaying high levels of social complexity. This study contributes to understanding the complex interplay between social structures and natural selection patterns, highlighting the genetic footprint of eusociality in shaping termite evolution.