More functional V1R genes occur in nest-living and nocturnal terricolous mammals

Abstract

Size of the vomeronasal type 1 receptor (V1R) gene repertoire may be a good indicator for examining the relationship between animal genomes and their environmental niche specialization, especially the relationship between ecological factors and the molecular evolutionary history of the sensory system. Recently, Young et al. (Young JM, Massa HF, Hsu L, Trask BJ. 2009. Extreme variability among mammalian V1R gene families. Genome Res.) concluded that no single ecological factor could explain the extreme variability of the V1R gene repertoire in mammalian genomes. In contrast, we found a significant positive correlation between the size and percentage of intact V1R genes in 32 species that represent the phylogenetic diversity of terricolous mammals and two ecological factors: spatial activity and rhythm activity. Nest-living species possessed a greater number of intact V1R genes than open-living species, and nocturnal terricolous mammals tended to possess more intact V1R genes than did diurnal species. Moreover, our analysis reveals that the evolutionary mechanisms underlying these observations likely resulted from the rapid gene birth and accelerated amino acid substitutions in nest-living and nocturnal mammals, likely a functional requirement for exploiting narrow, dark environments. Taken together, these results reveal how adaptation to divergent circadian rhythms and spatial activity were manifested at the genomic scale. Size of the V1R gene family might have indicated how this gene family adapts to ecological factors.

FIG. 1.—

Ecological factors influence the size of the intact V1RGR among 32 terricolous mammals. Octagons represent spatial activities: nest-living behavior (green) and open-living behavior (gold). The circles represent rhythm activities: diurnal behavior (yellow) and nocturnal behavior (blue). Gray and white shading differentiate species by order. The phylogenetic relationships of mammals shown to the left is taken from Ensembl (http://www.ensembl.org/).

FIG. 2.—

Box plots of the number of intact V1Rs in 32 mammalian species that have different ecological factors. Rectangles represent different ecological factors including open-living behavior, nest-living behavior, diurnal activity, cathemeral activity, and nocturnal activity as labeled below each box. Error bars show the standard error of the mean. (A) Box plots showing the size of the intact V1Rs in 32 mammalian species. Median value and range of intact V1R gene numbers are shown. (B) Box plots showing the percentage of intact V1Rs in 32 mammalian species. Median value and range of the percentage of intact V1Rs are shown. Statistical significant differences are indicated by ** for P < 0.01 and *** for P < 0.001. R represents the Pearson product-moment correlation coefficient.