Genetic relatedness of mates does not predict patterns of parentage in North American red squirrels

Abstract

Previously limited to laboratory studies, the deleterious effects of inbreeding are now being revealed in a number of wild systems. Female North American red squirrels, Tamiasciurus hudsonicus, show high levels of multimale mating and little to no overt precopulatory mate selection. We hypothesized that the negative repercussions of inbreeding should select for a female's ability to select sperm from more distantly related males. Consequently, successful sires should be less genetically related to the female than are unsuccessful males. We tested this hypothesis using both an analysis of absolute success among all copulating males and also relative success of sires within multiply sired litters. Pairwise genetic relatedness and paternity were determined through molecular analysis of tissue samples collected from reproductive females, copulating males and resultant offspring. In contrast to other systems, we found no evidence that the genetic similarity of mates predicts patterns of parentage in red squirrels. Genetic relatedness did not predict whether a copulating male would sire any offspring, and relative success of sires within multiply sired litters was unrelated to their relatedness to the dam of the litter. Furthermore, selection for inbreeding avoidance mechanisms may be minimal, as there were no observable negative fitness repercussions to inbreeding. We detected no relationship between the genetic relatedness of an offspring's parents and its neonatal mass, growth rate or survival to reproductive age. In red squirrels, we found no evidence of parentage patterns based on genetic similarity of mates, and this phenomenon may be less universal than previously thought.