Anthropogenic Macaque Hybridization and Genetic Pollution of a Threatened Population

Abstract

Interspecific matings between one released male pig-tailed macaque and female rhesus macaques were observed in a small isolated semi-wild troop of rhesus macaques in northeastern Thailand. Two of three juvenile males suspected to be hybrids based on their appearance, were caught and examined morphologically and genetically. Both suspected hybrids had a dark brown and anteriorly narrow crown patch and thinly haired tails as are common in pig-tailed macaques, and tail-lengths in the range of rhesus macaque. Male no. 19 showed neither cheek hair whorl nor the bipartite pattern of pelage color characteristics of rhesus macaque, whereas male no. 14 displayed both of these characters. We could not determine whether they were truly hybrids based on our morphological assessments and so both animals were also examined genetically. Study of variation at the Y-chromosome linked TSPY locus showed that although monkey no. 19 was sired by the pig-tailed macaque, monkey no. 14 was sired by a rhesus macaque. A mtDNA analysis indicated that both suspected hybrids were sons of rhesus mothers. Electrophoretic examination of blood hemoglobin-α protein confirmed that only monkey no. 19 was truly a hybrid. Although only one individual was confirmed to be hybrid in this troop, the hybridization could become a severe threat to the genetic integrity of the native troop and may hinder the tracing of the evolutionary history of the population. It is especially true in the rhesus populations which are now very rare in Thailand.