Abstract:
Among mammals, several lineages have independently adapted to a subterranean niche and possess similar phenotypic
traits for burrowing (e.g., cylindrical bodies, short limbs, and absent pinnae). Previous research on mole-rats has revealed
molecular adaptations for coping with reduced oxygen, elevated carbon dioxide, and the absence of light. In contrast,
almost nothing is known regarding molecular adaptations in other subterranean lineages (e.g., true moles and golden
moles). Therefore, the extent to which the recurrent phenotypic adaptations of divergent subterranean taxa have arisen
via parallel routes of molecular evolution remains untested. To address these issues, we analyzed 8,000 loci in 15
representative subterranean taxa of four independent transitions to an underground niche for signatures of positive
selection and convergent amino acid substitutions. Complementary analyses were performed in nonsubterranean
“control” taxa to assess the biological significance of results. We found comparable numbers of positively selected genes
in each of the four subterranean groups; however, correspondence in terms of gene identity between gene sets was low.
Furthermore, we did not detect evidence of more convergent amino acids among subterranean species pairs compared
with levels found between nonsubterranean controls. Comparisons with nonsubterranean taxa also revealed loci either
under positive selection or with convergent substitutions, with similar functional enrichment (e.g., cell adhesion, immune
response, and coagulation). Given the limited indication that positive selection and convergence occurred in the same
loci, we conclude that selectionmay have acted on different loci across subterraneanmammal lineages to produce similar
phenotypes.
