Genetic basis of species differentiation in Sulawesi macaques, Indonesia

概要

One of the greatest challenges faced by evolutionary biologists is to explain the world’ s enormous biodiversity. The group of Macaca spp. on Sulawesi Island have undergone rapid morphological and coat color changes from their closest common ancestor. By st udying Sulawesi macaques, the candidate aimed to explore: 1. What are the important t raits that have diversified, and what are the genes and gene combinations underlying th ose traits (Chapter 2), 2. How do gene functions change and how do they shape pheno typic differentiation (Chapter 3). In Chapter 2, the genome-wide sequencing between fiv e neighboring species were conducted to explore genetic variation contributing to specie s differentiation. Using the sequence capture library for exon regions, in total, four pair wise species comparisons were made between M. nigra vs M. nigrescens, M. nigrescens vs M. hecki, M. nigrescens vs M. tonkeana and M. tonkeana vs M. maurus with ~10 individuals in each species. It was found that hundreds of thousands of SNPs were co mpletely differentiated (Fst=1) between species. Further analysis showed that the genes categorized to pigmentation was significantly enriched in the differentiated genes. Sever al differentiated SNPs located in key pigmentation genes were predicted to cause functi onal consequence of the proteins. Specifically, a key pigmentation related gene, melano cortin-1 receptor (MC1R) was found to have differentiated SNPs in all four pairwise sp ecies comparisons. These results suggested that genes related to pigmentation largely di verged between species and contributed to species differentiation. To clarify the genetic and evolutionary basis for coat color variation in Sulawesi macaques, in chapter 3 the functional consequence of species-specific variants of MC1R was investigated using an in vitro expression system. cAMP production activities were compared between MC1R from six Sulawesi species M. nigra, M. nigrescens, M. hecki, M. tonkeana, M. maurus, M. ochreata, and outgroup M. nemestrina and corresponding mutants. Species specificall y fixed variants of MC1R showed different functional characteristics in the six species. Six species-specific variants corresponded with variation in agonist-induced and basal ac tivity. Inconsistent with the dark coat color, four substitutions independently caused dec reases in the basal activity of MC1R in four species, while M. maurus specific mutatio n caused an increase of activity. Fixed genes useful for genetic markers shaping specie s differentiation were detected. Because the pigmentation system of Sulawesi macaques should be related to conspecific mate recognition system, further study is expected to e lucidate the color patterning mechanism as well as MC1R functions. Sulawesi macaques are a good model for elucidating the genetic basis of speciation during a short period allopatric separation.