The takin and muskox: A molecular and ecological evaluation of relationship

Abstract

This research clarifies the classification of and relationship between the takin (Budorcas taxicolor) and muskox (Ovibos moschatus). Although both are social ungulates of similar body size, takins live in dense mountainous habitats at temperate latitudes in Asia, and muskoxen live in open arctic habitats in Alaska, Canada and Greenland. Morphological, paleontological and chromosome comparisons have supported a close relationship between these species and their classification within the tribe Ovibovini in the subfamily Caprinae. Previous studies, however, have not defined the genetic relationship of the takin and muskox. This project used ecological and molecular comparisons to evaluate these proposed relationships. Ecological studies in Shaanxi, China showed takins are generalists in their use of habitat and forage, but live in dense habitat in groups, ostensibly to avoid predation. Likewise, muskoxen live in groups and are generalists, but inhabit open landscapes. Some ecological and behavioral similarities appear to support the hypothesis of close relationship. In contrast, molecular studies using cytochrome b sequences from mitochondrial DNA (mtDNA) clearly separate the takin and muskox into distinct clades. Takins are more closely related to sheep (Ovis spp.) and muskoxen to the Asian goral (Nemorhaedus caudatus). Similarities between the takin and muskox appear due to convergent evolution as an adaptation to large body size. A broader comparison of cytochrome b sequences from 11 species of Caprinae supported the separation of takins and muskoxen. Unequal rates of evolution among the species precluded complete resolution of Caprinae relationships. To define differences between muskox subspecies and populations, sequences of the highly variable control region of mtDNA from 37 muskoxen were compared. Delineation of muskox subspecies is a critical issue due to the potential for interbreeding of indigenous Canadian (O. m. moschatus) and introduced Alaskan (O. m. wardi) populations of muskoxen as range expansion occurs. Variability between these populations was so low differences could not be detected with this comparison. I suggest a history of genetic bottlenecks has reduced genetic variability of muskoxen to low levels and neither populations nor subspecies can be defined from control region sequences.