Behavioral Basis of Shared Paternity in the Striped-backed Wren

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A successful animal (in the evolutionary sense) is one that behaves so as to maximize the representation of its genes in future generations. Therefore, an animal can be successful either by raising its own offspring, as usually occurs, or by helping to raise offspring that are closely related to itself, as occurs in most "cooperative breeders." For example, adult helpers at the nests of mated pairs of birds are often helping their parents raise offspring that are their own full siblings. In the stripe-backed wren of Venezuela, males and females raised in a given social group become helpers in the same group when they mature. Since the mortality rate is high and dominant females that die are replaced by immigrant females unrelated to the group, helpers often help raise juveniles that are their half siblings. Thus, the death of a dominant female and her replacement by an immigrant is a significant event for a male helper. His mother's death (1) suddenly decreases the genetic benefit he enjoys by helping to raise offspring of the dominant pair (since the female is no longer his mother) and (2) creates an opportunity for him to reproduce non-incestuously by mating with the new dominant female. Recent behavioral research revealed that male helpers routinely pursue and attempt to court dominant females unrelated to them and are only kept from mating with dominant females by dominant males. DNA fingerprinting, a molecular technique used to assign parentage, has shown that 15% of all juveniles from groups that contain male helpers unrelated to the dominant female are offspring of male helpers and dominant females. The remaining 85% are offspring of the dominant pair. Dr. Piper's research project will compare in more detail the behavior of male helpers that are sons of the dominant female and those that are unrelated to her. Specifically, he will examine the tendency of male helpers to associate with dominant females, the treatment of male helpers by dominant males, and the amount of parental care given by male helpers. This study will increase our understanding of helping behavior and incest avoidance in cooperatively breeding animals and, more generally, will give insight into the evolution of helping behavior.