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Abstract
Marmosets are cooperative breeding primates that produce fraternal twins whose placentas fuse during embryonic development allowing genetic exchange via blood flow between the twins. This genetic exchange causes infants to be chimeras, having tissues made up of cells which are derived from self and sibling lineages. The degree of genetic exchange and the tissues affected have not been well studied in this group. For this study five microsatellite markers were used to assess the extent and distribution of genetic exchange in Callithrix kuhlii between thirty-six sets of twins with known parentage. The inheritance of markers was traced across twin sets and throughout the tissues. All of the tissue types sampled were found to be chimeric in a number of individuals. Tissues derived from the hematopoietic system including liver, blood and spleen were found to differ significantly in their rate of chimerism from all other tissues. However, the ratio of chimeric cells within each tissue type varied greatly between individuals. Five of the fifteen family groups analyzed were found to have at least one parent that transmitted their sibling alleles to their offspring. Further, while other female mammalian chimeras have been shown to exhibit sterility as a result of chimerism, chimeric female marmosets were shown to not only maintain fertility, but also exhibit similar rates of chimerism as males in the population. The presence of genetic chimerism and the influence of genetic conflict on the evolution of cooperative breeding in callitrichids were also explored. The presence of sibling alleles throughout the body including the germ-line cells increased values of relatedness between alloparents and between multiply sired offspring and their fathers. The study of this unique system provides insights into genomic conflict in a vertebrate, the evolution of alloparental care in callitrichids, and provides the first analysis of the influences of genetic chimerism on the sociality of a vertebrate species.
