Abstract
We examine reproductive options for parents and offspring in cooperatively breeding golden jackals (Canis aureus) and how these may change with relatedness and ecological constraints. Golden jackals are obligatory monogamous breeders with long-term pair bonds. Both members of the pair jointly defend their territory, normally produce 1 litter per year and raise their offspring together, with successive litters probably being full siblings. Some pups remain on the natal territory and help care for next year's litter as reproductively suppressed subordinates before they disperse. Why did older offspring stay and help as subordinates, rather than disperse and breed elsewhere, and why did parents allow older offspring to stay on the natal territory? Under the reproductive skew concession model, such helping is expected if ecological constraints are intense and dispersal chances are low but should be less likely if ecological constraints are relaxed. We tested this idea by analyzing data from golden jackals on the Serengeti short-grass plains from 1977 to 1990 when the intensity of ecological constraints changed 3-fold. We collected data on the annual reproductive success of dominant breeders with and without support from helpers, the tenure of territorial breeders, and the number of breeding slots accessible to subordinates elsewhere, and used these to assess the fitness consequences of different reproductive roles and the likelihood of reproductive conflict. Between 1977 and 1984, the quantitative analysis of territorial tenureship showed that subordinates faced the difficulty of acquiring a breeding slot elsewhere as a major ecological constraint, with their best option either to help or, theoretically, to breed on the natal territory. After the arrival of parvovirus in 1985-an exotic pathogen lethal to pups-the number of available breeding slots rose strongly, relaxing ecological constraints. However, some subordinates continued to help, thus losing the reproductive conflict with dominants over their optimal breeding role. In golden jackals, the frequent observation of helping may therefore reflect resolution of the potential reproductive conflict in favor of the dominant breeder, as selection pressure on the dominant to recruit subordinates as helpers is stronger than the selection pressure of subordinates to resist. The theoretical exploration of fitness benefits of different reproductive tactics under different levels of ecological constraints calibrated with empirical fitness benefits illuminated why polygamy and/or multiple monogamy is rare or nonexistent in Serengeti golden jackals.