PT - JOURNAL ARTICLE AU - Erin R. Siracusa AU - Stan Boutin AU - Ben Dantzer AU - Jeffrey E. Lane AU - David W. Coltman AU - Andrew G. McAdam TI - Familiar neighbors, but not relatives, enhance fitness in a territorial mammal AID - 10.1101/589002 DP - 2019 Jan 01 TA - bioRxiv PG - 589002 4099 - http://biorxiv.org/content/early/2019/03/26/589002.short 4100 - http://biorxiv.org/content/early/2019/03/26/589002.full AB - Resolving conflict amongst solitary adversaries provides the first steps toward the evolution of sociality. Kin selection and mutually beneficial interactions among unrelated individuals are two important pathways to conflict resolution, but the relative importance of these mechanisms has been difficult to assess in the wild. Using 22 years of data from North American red squirrels, we assessed how kinship and familiarity with neighbors affected fitness in this solitary, territorial species. While living near kin did not enhance fitness, social familiarity increased survival by up to 17% and annual reproductive success by at least 40%. These fitness benefits were strong enough to compensate for the effects of aging later in life, with potential consequences for the evolution of senescence. Mutually beneficial interactions stemming from social familiarity can, therefore, provide the opportunity for the evolution of cooperation between adversarial neighbors, even in the absence of kin benefits.One Sentence Summary Stable social relationships increase reproductive success and survival in solitary red squirrels and can offset the negative effects of aging.