Assessment of the Hybridization Between Rhesus (Macaca mulatta) and Long-Tailed Macaques (M. fascicularis) Based on Morphological Characters

Objectives: Hybridization between rhesus (Macaca mulatta) and long-tailed (M. fascicularis) macaques has become a focal point of interest. The majority of such studies have evaluated their genetics, but not their morphological characters. Materials and Methods: We analyzed morphological characters of eight free-ranging populations of Indochinese rhesus and long-tailed macaques distributed at the proposed hybrid zone (15.75-21.58 degrees N) in comparison with one population each of Chinese and Indian-derived rhesus macaques and three populations of Sundaic long-tailed macaques. Results: Chinese and Indian rhesus macaques had a heavier body mass, longer crown-rump length, shorter relative facial length and relative tail length, and a greater contrast of reddish and yellowish dorsal pelage color than the Sundaic long-tailed macaques for which the latter three parameters could be used to visually discriminate between the two species. Although the morphological characters of Indochinese rhesus and long-tailed macaques were intermediate between the Chinese/Indian rhesus and Sundaic long-tailed macaques, they were more similar to their respective conspecifics. The species-specific characters of a shorter tail (<70%) and a bipartite pelage color pattern were retained in the Indochinese rhesus macaques while the longer tail (>90%) and no bipartite pattern was found in the Indochinese long-tailed macaques. No morphological cline was observed across the species and the variations were abrupt to some extent. Discussion: The hybridization between rhesus and long-tailed macaques may be results of multiple contacts and isolations over a long period of time, thus their evolutionary history should not be drawn solely by genetic or morphological analysis. (C) 2015 Wiley Periodicals, Inc.