Crested gibbons, genus Nomascus, are endemic to the Indochinese bioregion and occur only in Vietnam, Laos, Cambodia, and southern China. However, knowledge about the number of species to be recognized and their exact geographical distributions is still limited. To further elucidate the evolutionary history of crested gibbon species and to settle their distribution ranges, we analyzed the complete mitochondrial cytochrome b gene from 79 crested gibbon individuals from known locations. Based on our findings, crested gibbons should be classified into seven species. Within N. concolor, we recognize two subspecies, N. concolor concolor and N. concolor lu. Phylogenetic reconstructions indicate that the northernmost species, N. hainanus, N. nasutus, and N. concolor branched off first, suggesting that the genus originated in the north and successively migrated to the south. The most recent splits within Nomascus occurred between N. leucogenys and N. siki, and between Nomascus sp. and N. gabriellae. Based on our data, the currently postulated distributions of the latter four species have to be revised. Our study shows that molecular methods are a useful tool to elucidate phylogenetic relationships among crested gibbons and to determine species boundaries.
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