Polygynandry in a red fox population: implications for the evolution of group living in canids?

Abstract

Canid social groups are typically thought to consist of extended families, that is, a dominant breeding pair and related nonbreeding subordinates, that principally obtain indirect fitness benefits from helping to raise the offspring of the dominant pair. Consequently, the monogamous pair has been viewed as the basic fundamental unit of canid social organization. However, there have been few genetic studies that have tested this assumption. We analyzed the parentage of red foxes (Vulpes vulpes) in a high-density (19.6–27.7 adult foxes/km2) population in Bristol, UK, to determine (1) whether groups typically produced a single litter of cubs annually and (2) whether male and female foxes exhibited monogamous mating strategies. Social monogamy (the production of one litter in a social group) was observed or assumed in 54% of breeding attempts (N = 13 group-years). However, polyandrous and polygynous patterns of mating were common. Multiple paternity was confirmed in 38% of litters (N = 16) containing offspring with resolved maternity and paternity (N = 30 cubs); when including cubs with unresolved paternity (N = 20), multiple-paternity may have occurred in 69% of litters. Litters were sired by an average of 1.6 identified males (range = 1–4); when including cubs with unresolved paternity, litters may have been sired by up to seven males. Only 20% (6/30) of cubs with resolved maternity and paternity were sired by males within the social group. Within groups, dominant females did not breed with subordinate males; dominant males did breed with subordinate females. Dominant and subordinate females both produced cubs with dominant and subordinate males from other social groups. Mean adult relatedness in groups typically ranged from 0.15–0.35, indicative of second-order rather than first-order relatives.