Grant Peter R, Grant B Rosemary, Keller Lukas F, Markert Jeffrey A, Petren Kenneth
Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey 08544-1003, USA.
Evolution. 2003 Dec;57(12):2911-6. doi: 10.1111/j.0014-3820.2003.tb01532.x.
Studies of inbreeding and interspecific hybridization are generally pursued separately with different metrics. There is a need to integrate them because they have the common goal of seeking an understanding of the genetic and ecological basis of fitness variation in populations. We use mean expected heterozygosity as an axis of variation on which to compare the fitness of inbreeding and hybridizing Darwin's finches (Geospiza scandens and G. fortis) relative to the fitness of matched outbred controls. We find that relative fitness of inbred finches is less than one in the 1991 cohorts of both species. Inbreeding depression is stronger in the species (G. scandens) with the lower genetically effective population size. Relative fitness of hybrids (backcrosses) in the same cohort of G. scandens is greater than one. Evidence of heterosis in G. fortis is mixed. Thus the two interbreeding species displayed somewhat different fitness patterns under the same set of environmental conditions. Hybridization may enhance fitness to different degrees by counteracting the effects of inbreeding depression, by other additive and nonadditive genetic effects, and by producing phenotypes well suited to exploit particular ecological conditions.
近亲繁殖和种间杂交的研究通常是分别采用不同的指标进行的。有必要将它们整合起来，因为它们有着共同的目标，即寻求对种群适应性变异的遗传和生态基础的理解。我们使用平均预期杂合度作为一个变异轴，在这个轴上比较近亲繁殖和杂交的达尔文雀（勇地雀和大嘴地雀）相对于匹配的远交对照的适应性。我们发现，在这两个物种1991年的种群中，近亲繁殖的雀类的相对适应性小于1。在遗传有效种群数量较低的物种（勇地雀）中，近亲繁殖衰退更为明显。在同一批大嘴地雀种群中，杂交种（回交）的相对适应性大于1。在强地雀中杂种优势的证据并不明确。因此，在相同的环境条件下，这两个杂交物种表现出了 somewhat 不同的适应性模式。杂交可能通过抵消近亲繁殖衰退的影响、其他加性和非加性遗传效应以及产生非常适合利用特定生态条件的表型，在不同程度上提高适应性。
