Department of Biology, Hamilton College, Clinton, New York.
Cornell University Laboratory of Ornithology, Ithaca, New York.
Mol Ecol. 2019 Mar;28(5):1116-1126. doi: 10.1111/mec.14866. Epub 2019 Feb 4.
Although matings between relatives can have negative effects on offspring fitness, apparent inbreeding preference has been reported in a growing number of systems, including those with documented inbreeding depression. Here, we examined evidence for inbreeding depression and inbreeding preference in two populations (Clinton, New York, and Davis, California, USA) of the cooperatively breeding American crow (Corvus brachyrhynchos). We then compared observed inbreeding strategies with theoretical expectations for optimal, adaptive levels of inbreeding, given the inclusive fitness benefits and population-specific magnitude of inbreeding depression. We found that low heterozygosity at a panel of 33 microsatellite markers was associated with low survival probability (fledging success) and low white blood cell counts among offspring in both populations. Despite these costs, our data were more consistent with inbreeding preference than avoidance: The observed heterozygosity among 396 sampled crow offspring was significantly lower than expected if local adults were mating by random chance. This pattern was consistent across a range of spatial scales in both populations. Adaptive levels of inbreeding, given the magnitude of inbreeding depression, were predicted to be very low in the California population, whereas complete disassortative mating was predicted in the New York population. Sexual conflict might have contributed to the apparent absence of inbreeding avoidance in crows. These data add to an increasing number of examples of an "inbreeding paradox," where inbreeding appears to be preferred despite inbreeding depression.
尽管亲属之间的交配会对后代的适应性产生负面影响，但越来越多的系统都报告了明显的近交偏好，包括那些已经证实存在近交衰退的系统。在这里，我们研究了两种具有合作繁殖行为的美洲乌鸦（Corvus brachyrhynchos）种群（美国纽约州克林顿和加利福尼亚州戴维斯）中近交衰退和近交偏好的证据。然后，我们将观察到的近交策略与给定适合度收益和种群特定近交衰退程度下的最优、适应性近交水平的理论预期进行了比较。我们发现，在两个种群中，33 个微卫星标记面板上的低杂合性与后代的低存活率（育雏成功率）和低白细胞计数相关。尽管存在这些成本，但我们的数据更符合近交偏好而不是回避：在 396 只被抽样的乌鸦后代中观察到的杂合性明显低于如果当地成年个体随机交配的预期。这种模式在两个种群的一系列空间尺度上都是一致的。考虑到近交衰退的程度，加利福尼亚种群的适应性近交水平预计非常低，而纽约种群则预计会出现完全的非随机交配。性冲突可能导致了乌鸦中明显缺乏近交回避的现象。这些数据增加了越来越多的“近交悖论”的例子，即尽管存在近交衰退，但近交似乎仍然受到偏好。
