Marmosets are New World monkeys of the family Callitrichidae that form large cooperative breeding groups in which many individuals care for the offspring of the breeding pair. In order to explain this behavior based on indirect fitness benefits for the help providers, it is necessary to determine the true genetic relationship among individuals. This is not easy to do for marmosets because of their unique reproductive system. Marmosets produce fraternal twins, whose placentas fuse during early embryonic development, resulting in genetic exchange through the blood flowing between the twins. This genetic exchange causes the infants to be genetic chimeras, having tissues with mixtures of cells with their own DNA and cells with the DNA of their twin. Little is known about the extent of genetic exchange and what tissues are affected. The proposed study will use microsatellite genetic markers to assess the extent and distribution of genetic exchange between twins during development. At least ten types of tissues from twin sets of known female-male pairings of Callithrix kuhlii will be assayed, using specimens archived from a breeding colony. Further studies will assess genetic paternity in the breeding groups that contained multiple males, in order to determine whether it is possible that multiple males are siring a single set of twins. Documentation of horizontal genetic exchange may drastically affect calculations of indirect fitness due to an increase in shared alleles between individuals. The study of this unique system will provide insights into the mechanisms affecting alloparental care, kin recognition, and kin selection and may alter current views of the evolution of social behavior.
