ABSTRACT

Golden lion tamarins are small, arboreal primates endemic to lowland Atlantic coastal rainforest of Rio de Janeiro State, Brazil. About 600 individuals are found in 14 forest fragments, the largest of which is Poço das Antas Reserve. This reserve is a forest island surrounded by cattle pasture and contains about 347 tamarins. The authors monitored the behaviour and demography of about 110 individuals in 20 breeding groups for 13 years in this reserve. All individuals in the study population were individually marked and habituated to the presence of human observers. Dates and locations of all births, deaths, emigrations and immigrations and the identities of dam and probable sire for all offspring were recorded. Analysis of these data was used to test for the presence of inbreeding and inbreeding depression in this population. A total of 481 offspring were born during the study, and 47 of these were classified as inbred. Mortality of inbred offspring was significantly greater than that of non-inbred offspring (3.4 lethal equivalents per individual). Although the effects of inbreeding depression were most acute during the first six months of life, survivorship of inbred tamarins remained low relative to that of non-inbred individuals for at least the first two years of life. Inbreeding was thought to result when a daughter failed to disperse and bred with a close relative in her natal group or when an individual dispersed into another group and mated with a relative therein. The frequency of the latter type of inbreeding suggests that tamarins do not recognise relatives outside their natal group or do not reject them as mates.