engleski

Selective Constraints in Cold-Region Wild Boar may Defuse the Effects of Small Effective Population Size on Molecular Evolution of Mitogenomes

Spatial range expansion during population colonization is characterized by demographic events that may have significant effects on the efficiency of natural selection. Population genetics suggests that genetic drift brought by small effective population size (Ne) may undermine the efficiency of selection, leading to the faster accumulation of non-synonymous mutations. However, it is still unknown whether this effect might be balanced or even reversed by strong selective constraints. Here, we used wild boar and local domestic pigs from tropical (Vietnam) and subarctic region (Siberia) as animal model to evaluate the effects of functional constraints and genetic drift in shaping molecular evolution. The likelihood ratio test (LRT) revealed that Siberian clade evolves significantly different from Vietnamese clade. Different datasets consistently showed that Siberian wild boar have lower Ka/Ks ratios than Vietnamese samples. The potential role of positive selection for branches with higher Ka/Ks was evaluated using branch-site model comparison. No signal of positive selection was found for the higher Ka/Ks in Vietnamese clade, suggesting the inter-clade difference is mainly due to the reduction of Ka/Ks for Siberian samples. This conclusion was further confirmed by the result from the larger sample-size that wild boar from northern Asia (subarctic and nearby region) show lower Ka/Ks than those from southern Asia (temperate and tropical region). The lower Ka/Ks might be due to either stronger functional constraints, which prevent nonsynonymous mutations from accumulating in subarctic wild boar, or larger Ne in Siberian wild boar, which can boost the efficacy of purifying selection to remove functional mutations. The latter possibility was further ruled out by the Bayesian skyline plot analysis, which revealed that historical Ne of Siberia wild boar is smaller than that of Vietnam wild boar. All together, these results suggest stronger functional constraints acting on mitogenomes of subarctic wild boar, which may provide new insights into their local adaptation of cold resistance.

Sus scrofa, Ka/Ks ratio, purifying selection, selective constraints, mitogenomes

nije evidentirano