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.

译文

:我们测试了一个假设,即性别偏向的出生扩散会减少美洲黑熊的近亲繁殖,美国黑熊是一种近距离完整的男性传播和雌性传的单亲物种。利用微卫星DNA和来自繁殖成熟熊(>或= 4岁)的空间数据,我们研究了1993年至2000年新墨西哥州两个不同种群的空间遗传结构。如所预测的,亲缘关系(r)和紧密关系的频率(双亲或全兄弟姐妹)随着雌性二元组间距离的增加而减少,而男性或异性二元组间的变化很小。邻近的女性比邻近的男性更亲密。近交的可能性很低。多数生活在足够近距离以促进交配的异性对之间是无关的,很少是近亲。我们没有发现证据表明熊会积极避免从附近的池塘中选择近亲,因为潜在配对和实际配对之间的均值r和关系频率没有差异(由亲子关系分析确定)。尽管密度相差近两倍,但在两个研究领域中这些基本模式都是显而易见的。但是,根据附近有雄性和雌性亲属的熊的比例,在低密度地区的性别分散倾向不太明显。该结果表明,雄性熊可能通过降低其传播速度或传播距离来应对竞争的减少。有证据支持这样的假说:近亲回避是通过男性偏向的散布来实现的,但也表明竞争(对配偶或资源)的竞争改变了散布的方式。

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