Functional divergence of the pigmentation gene melanocortin-1 receptor (MC1R) in six endemic Macaca species on Sulawesi Island.

Coat color is often highly variable within and between animal taxa. Among hundreds of pigmentation-related genes, melanocortin-1 receptor (MC1R) plays key roles in regulating the synthesis of the dark eumelanin and the red-yellow pheomelanin. The six species of macaques that inhabit Sulawesi Island diverged rapidly from their common ancestor, M. nemestrina. Unlike most macaques, Sulawesi macaques commonly have a dark coat color, with divergence in shade and color pattern. To clarify the genetic and evolutionary basis for coat color in Sulawesi macaques, we investigated the MC1R sequences and functional properties, including basal cAMP production and α-MSH-induced activity in vitro. We found fixed non-synonymous substitutions in MC1R in each species. Furthermore, we found that six species-specific variants corresponded with variation in agonist-induced and basal activity of MC1R. Inconsistent with the dark coat color, four substitutions independently caused decreases in the basal activity of MC1R in M. hecki, M. nigra, M. tonkeana, and M. ochreata. Selective analysis suggested MC1R of M. nigra and M. nigrescens underwent purifying selection. Overall, our results suggest that fixed differences in MC1R resulted in different functional characteristics and might contribute to divergence in color among the six Sulawesi macaque species.

Functional divergence of the bitter receptor TAS2R38 in Sulawesi macaques.

ABSTRACT: Bitter perception is mediated by G protein-coupled receptors TAS2Rs and plays an important role in avoiding the ingestion of toxins by inducing innate avoidance behavior in mammals. One of the best-studied TAS2Rs is TAS2R38, which mediates the perception of the bitterness of synthetic phenylthiocarbamide (PTC). Previous studies of TAS2R38 have suggested that geographical separation enabled the independent divergence of bitter taste perception. The functional divergence of TAS2R38 in allopatric species has not been evaluated. We characterized the function of TAS2R38 in four allopatric species of Sulawesi macaques on Sulawesi Island. We found variation in PTC taste perception both within and across species. In most cases, TAS2R38 was sensitive to PTC, with functional divergence among species. We observed different truncated TAS2R38s that were not responsive to PTC in each species of Macaca nigra and M. nigrescens due to premature stop codons. Some variants of intact TAS2R38 with an amino acid substitution showed low sensitivity to PTC in M. tonkeana. Similarly, this intact TAS2R38 with PTC-low sensitivity has also been found in humans. We detected a shared haplotype in all four Sulawesi macaques, which may be the ancestral haplotype of Sulawesi macaques. In addition to shared haplotypes among Sulawesi macaques, other TAS2R38 haplotypes were species-specific. These results implied that the variation in TAS2R38 might be shaped by geographical patterns and local adaptation. OPEN RESEARCH BADGES: This article has earned an Open Data Badge for making publicly available the digitally-shareable data necessary to reproduce the reported results. The data is available at https://doi.org/10.5061/dryad.908jf3r.