Department of Biological Sciences, Macquarie University, NSW 2109, Australia.
Conserv Biol. 2011 Jun;25(3):465-75. doi: 10.1111/j.1523-1739.2011.01662.x. Epub 2011 Apr 12.
Fragmentation of animal and plant populations typically leads to genetic erosion and increased probability of extirpation. Although these effects can usually be reversed by re-establishing gene flow between population fragments, managers sometimes fail to do so due to fears of outbreeding depression (OD). Rapid development of OD is due primarily to adaptive differentiation from selection or fixation of chromosomal variants. Fixed chromosomal variants can be detected empirically. We used an extended form of the breeders' equation to predict the probability of OD due to adaptive differentiation between recently isolated population fragments as a function of intensity of selection, genetic diversity, effective population sizes, and generations of isolation. Empirical data indicated that populations in similar environments had not developed OD even after thousands of generations of isolation. To predict the probability of OD, we developed a decision tree that was based on the four variables from the breeders' equation, taxonomic status, and gene flow within the last 500 years. The predicted probability of OD in crosses between two populations is elevated when the populations have at least one of the following characteristics: are distinct species, have fixed chromosomal differences, exchanged no genes in the last 500 years, or inhabit different environments. Conversely, the predicted probability of OD in crosses between two populations of the same species is low for populations with the same karyotype, isolated for <500 years, and that occupy similar environments. In the former case, we recommend crossing be avoided or tried on a limited, experimental basis. In the latter case, crossing can be carried out with low probability of OD. We used crosses with known results to test the decision tree and found that it correctly identified cases where OD occurred. Current concerns about OD in recently fragmented populations are almost certainly excessive.
动物和植物种群的碎片化通常会导致遗传侵蚀和灭绝的可能性增加。尽管通过在种群碎片之间重新建立基因流通常可以逆转这些影响，但由于担心杂交衰退（OD），管理者有时未能做到这一点。OD 的快速发展主要是由于适应性分化导致的，这种分化是由于选择或染色体变异的固定。固定的染色体变异可以通过经验来检测。我们使用了扩展形式的繁殖者方程来预测由于最近隔离的种群碎片之间的适应性分化而导致 OD 的概率，这取决于选择的强度、遗传多样性、有效种群大小和隔离的世代数。实证数据表明，即使在隔离了数千代之后，处于相似环境中的种群也没有发展出 OD。为了预测 OD 的概率，我们开发了一个决策树，该决策树基于繁殖者方程中的四个变量、分类地位和过去 500 年的基因流。当两个种群具有以下至少一个特征时，它们之间的杂交发生 OD 的预测概率就会升高：是不同的物种，具有固定的染色体差异，在过去 500 年内没有交换基因，或者栖息在不同的环境中。相反，对于同一物种的两个种群之间的杂交，当它们具有相同的核型、隔离时间<500 年且栖息地相似时，预测 OD 的概率就会降低。在前者的情况下，我们建议避免杂交，或在有限的、实验性的基础上尝试。在后一种情况下，具有低 OD 发生概率的杂交可以进行。我们使用具有已知结果的杂交来测试决策树，发现它正确地识别了发生 OD 的情况。目前对最近碎片化种群中 OD 的担忧几乎肯定是过度的。
