Chimeras vs genetically homogeneous individuals: potential fitness costs and benefits

Colonies of the compound tunicate Botryllus schlosseri show the capacity for colony specificity resulting either in vascular fusion or in rejection between genetically distinct colonies. Cosettlement of kin colonies increases the probability of fusion between allogeneic colonies, but fusion terminates in the resorption of one partner, and raises the threat of somatic/germ cell parasitism. The authors tested the suggestion that colony fusion between relatives may be beneficial to one or both members of a chimera by increasing the size, the fecundity and/or survivorship. Results show that these parameters were not augmented in chimeras when compared to isolated colonies or when compared to rejecting pairs of kin and non-kin colonies. Costs in fitness incurred by fusion, the possible resorption of the less vigorous colony, and the threat of germ cell parasitism are more beneficial than other costs incurred by alternative processes of intraspecific competition for settlement space. -from Authors