Demographic Change and Reproductive Skew in Cooperative Breeding Primates (resubmit)

University Of Maryland, College Park, College Park MD

Investigators

Abstract

Although rare relative to other social systems, cooperative breeding species present unique opportunities to examine hypotheses explaining the evolution of cooperation and competition in kin-based societies. Early studies focused on the adaptive significance of alloparental care. Specifically, why did mature adults remain in their natal groups helping to raise offspring not their own? For various species of birds and a few mammals, substantial progress has been made in addressing the original question of why helpers help. By staying at home, alloparents often improve their chances of finding a breeding opportunity and receive gains in indirect fitness. Early research on callitrichid primates (marmosets, tamarins and lion tamarins) in captivity suggested that social and genetic monogamy was the norm for the family but recent reports from the wild and in captive settings suggested that callitrichid social organization is highly flexible, both within populations and across taxa. This variability provides fertile ground for testing hypotheses concerning the basis of reproductive skew and delayed dispersal. Dietz, Baker and colleagues propose a 3-year continuation of behavioral and demographic research on golden lion tamarin monkeys in Poco das Antas Reserve, Brazil. This 17-year study is unique in terms of its ability to address questions at the population level and in its scope, maintaining an integrated set of databases including behavior, demography, kinship, morphology, reproduction, use of space, group dynamics, food habits and samples of blood, hair and feces. During the first 13 years of this research, lion tamarin territories occupied all suitable habitat in the reserve, most groups contained several helpers and population growth was limited by high mortality during dispersal from natal groups. In the past three years a novel form of predation, decimation of complete groups while in den sites, resulted in profound changes in the social, experiential and demographic context of individuals surviving in the study population. Population density, group size and number of helpers decreased, and the rate of group extinction/recolonization increased. In effect, this pulse of increased predation resulted in a unique natural experiment. Relative to conditions before increased predation, Poco das Antas now contains more breeding opportunities for dispersing individuals, less competition to fill those slots and fewer alloparents to care for group offspring. By comparing patterns of dispersal and reproductive sharing before and after increased predation, and by integrating molecular genetic and endocrine techniques with field data, these investigators propose to determine if tamarins are assessing the availability and quality of reproductive opportunities outside the natal group, the extent to which ecological constraints affect dispersal and reproductive sharing, the effects of genetic relatedness on subordinate breeding, the relative effects of inbreeding avoidance and age on reproductive skew, and the circumstances and mechanisms by which dominants control reproduction of subordinates. Finally, the presence of this NSF-sponsored project provides resources, prestige and incentive to the Brazilian government agency managing the reserve and serves as a platform for training Brazilian and American biologists at all professional levels. Results of this research form the scientific basis for management of all four taxa of lion tamarins and were used to justify the creation of a new biological reserve and to inform and implement local projects including reforestation, planting of forest corridors, conservation education, reintroduction and translocation.