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.

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Nonnative Brook Trout Salvelinus fontinalis were introduced throughout western North America in the early and mid 1900s, resulting in populations that are difficult to eradicate and that often threaten native salmonids. Male YY Brook Trout (MYY), created in the hatchery by feminizing XY males and then crossing them with normal XY males, comprise a novel approach to eradicating undesirable Brook Trout populations. If stocked MYY Brook Trout survive and reproduce with wild females, it could eventually drive the wild population sex ratio to 100% males, at which point the population would be unable to reproduce and would be eradicated after stocking ceased. In this study, we stocked the limited number of catchable‐size (mean TL = 229 mm) MYY hatchery Brook Trout available from an established MYY broodstock into four streams. In two streams, the wild Brook Trout population was suppressed via electrofishing prior to stocking to determine whether diminished competition with wild fish would increase the survival of hatchery MYY fish. We used genetic assignment testing to identify the successful reproduction of stocked MYY fish. Apparent survival of MYY Brook Trout averaged 18% in streams with wild population suppression (mean suppression, 17%) and 9% in streams without suppression, suggesting that suppression of the wild population before stocking increased MYY survival poststocking. Hatchery MYY Brook Trout comprised an estimated 3.1% of all adult Brook Trout during spawning. Genetic assignment tests identified successful reproduction of MYY fish in all streams in which they were stocked, with an average of 3.7% of fry being the progeny of MYY fish. Our results confirm that hatchery MYY fish stocked in streams can survive and spawn successfully with wild fish and produce all‐male progeny. Despite the slightly reduced fitness of MYY Brook Trout, this technology may be a viable method for eradicating undesirable nonnative Brook Trout populations.

Twenty-five populations of westslope cutthroat trout from throughout their native range were genotyped at 20 microsatellite loci to describe the genetic structure of westslope cutthroat trout. The most genetic diversity (heterozygosity, allelic richness, and private alleles) existed in populations from the Snake River drainage, while populations from the Missouri River drainage had the least. Neighbor-joining trees grouped populations according to major river drainages. A great amount of genetic differentiation was present among and within all drainages. Based on Nei's D S , populations in the Snake River were the most differentiated, while populations in the Missouri River were the least. This pattern of differentiation is consistent with a history of sequential founding events through which westslope cutthroat trout may have experienced a genetic bottleneck as they colonized each river basin from the Snake to the Clark Fork to the Missouri river. These data should serve as a starting point for a discussion on management units and possible distinct population segments. Given the current threats to the persistence of westslope cutthroat trout, and the substantial genetic differentiation between populations, these topics warrant attention.

We describe 12 diagnostic single nucleotide polymorphism (SNP) assays for use in species identification among rainbow and cutthroat trout: five of these loci have alleles unique to rainbow trout (Oncorhynchus mykiss), three unique to westslope cutthroat trout (O. clarkii lewisi) and four unique to Yellowstone cutthroat trout (O. clarkii bouvieri). These diagnostic assays were identified using a total of 489 individuals from 26 populations and five fish hatchery strains.