Sex‐biased natal dispersal and inbreeding avoidance in American black bears as revealed by spatial genetic analyses

Abstract

We tested the hypothesis that sex-biased natal dispersal reduces close inbreeding in American black bears, a solitary species that exhibits nearly complete male dispersal and female philopatry. Using microsatellite DNA and spatial data from reproductively mature bears (>or= 4 years old), we examined the spatial genetic structure of two distinct populations in New Mexico from 1993 to 2000. As predicted, relatedness (r) and the frequency of close relationships (parent-offspring or full siblings) decreased with distance among female dyads, but little change was observed among male or opposite-sex dyads. Neighbouring females were more closely related than neighbouring males. The potential for inbreeding was low. Most opposite-sex pairs that lived sufficiently close to facilitate mating were unrelated, and few were close relatives. We found no evidence that bears actively avoided inbreeding in their selection of mates from this nearby pool, as mean r and relationship frequencies did not differ between potential and actual mating pairs (determined by parentage analysis). These basic patterns were apparent in both study areas despite a nearly two-fold difference in density. However, the sex bias in dispersal was less pronounced in the lower-density area, based on proportions of bears with male and female relatives residing nearby. This result suggests that male bears may respond to reduced competition by decreasing their rate or distance of dispersal. Evidence supports the hypothesis that inbreeding avoidance is achieved by means of male-biased dispersal but also indicates that competition (for mates or resources) modifies dispersal patterns.

Extirpation Risk of an Isolated Black Bear Population Under Different Management Scenarios

“…), suggesting that black bears may be at equilibrium, and hence we would expect genetic drift to have little impact on them compared to natural selection. Because our results do not support a panmictic structure in Ontario black bears and show discrepancies in differentiation levels between genetic markers, the most likely explanation is a combination of malemediated gene flow and female natal philopatry, which supports our prediction and previous studies that detected those patterns in black bears (Costello et al 2008;Onorato et al 2007;Rogers 1987).…”

Survival and divergence in a small group: The extraordinary genomic history of the endangered Apennine brown bear stragglers

“…This pattern was not observed in the nuclear genomes, and it implies a strong genetic barrier in Sweden and a strict affinity between Apennine and Alpine bears. The discrepancy between nuclear and mitochondrial data is likely explained by male-biased dispersal (43)(44)(45)(46), and the pattern of low genetic structure we observed at the Y-chromosome further supports this view (47, see SI Appendix, section S7) Until recent times, bear populations were geographically homogenized by males, but females philopatry resulted in some level of mtDNA structuring. Interestingly, habitat destruction and fragmentation has been suggested as a general factor that favors the increase of female philopatry (48,49).…”

Age-dependent genetic structure of arctic foxes in Svalbard

“…Often, however, the difference in likelihood between the most likely relationship and other relationships determined by this method is small, and the identification of relationships is not very accurate (Costello et al 2008). Therefore, we used a simplified classification and considered pairs of FS and PO born in the same year as potential siblings, originating from the same litter.…”