Cooperative Fish and Wildlife Research Units Program: Idaho
Education, Research and Technical Assistance for Managing Our Natural Resources

Males and female cooperative breeders can use different strategies to maximize reproduction and fitness over their lifetimes. Answering questions about the combined effects of mate selection, group size, and genetic diversity on lifetime reproductive success often requires long-term studies. Despite the potentially negative effects of mortality on group-living animals, many of the exemplary long-term studies on cooperative breeders have been conducted on species that are not harvested. Gray wolves (Canis lupus) are cooperative breeders that are hunted annually in Idaho, USA. I asked how breeding tenure, number of mates, and young produced varied over a lifetime as a function of the genetic diversity of breeders and their relatedness to helpers, group size, and sex of the breeder in a hunted population of gray wolves. Wolves who secured breeding positions generally bred for two seasons and had more than one partner if they were able to maintain their breeding position longer. The minimum lifetime reproductive output averaged approximately 9.5 pups for both males and females but varied greatly among individuals. The genetic relatedness between breeders and helpers in a group appeared to benefit lifetime reproductive output suggesting kin selection positively influences reproduction in wolves. Female wolves with above average lifetime reproductive output appeared to benefit from sharing breeding opportunities with other females in the group. Sharing breeding within a group may benefit a dominant breeder because it increases cooperation and may reduce the chance of being wholly overthrown by subordinate female(s). This may be particularly true when the individuals sharing breeding are genetically related, as found for wolves in my study. Sharing of breeding opportunities rarely lasted longer than one season, however, thus there may be limits to how much cooperation such sharing produces over the long-term.