CRB: Predictability of Inbreeding Depression in Insular and Mainland Populations

在自然种群中，近亲繁殖通常会导致后代出生缺陷更频繁、死亡率更高、生长速度更慢、生育力更低、抗病能力更弱和/或其他方面适应性降低。这种现象被称为“近亲繁殖抑制”，几乎是普遍存在的，但近亲繁殖抑制的严重程度因物种而异，而且近亲繁殖抑制的原因仍然知之甚少。随着越来越多的自然种群减少到小的、孤立的片段，近亲繁殖可能在残余种群中变得普遍。种群能否适应这样的条件并恢复，还是将遭受不可避免的适应性下降，将取决于导致近亲繁殖衰退的基因的数量和性质，这些基因的数量和性质仍然未知。与大型的中心种群相比，长期处于小而孤立状态的种群受近亲繁殖的影响可能更小，因为自然选择可以在小种群过去的近亲繁殖中去除有害的隐性基因。然而，对Peromyscus小鼠的早期研究未能发现近亲繁殖抑郁症的严重程度与历史种群规模之间的联系。莱西博士建议确定种群对近亲繁殖的反应是否可重复，并进一步测试种群对近亲繁殖的反应是否可以通过种群规模和遗传多样性的知识来预测。遗传变异已在脊灰过裂肌小鼠岛、外围和中心种群样本中进行了检测；岛屿种群的遗传变异性要小得多，如果这些种群在过去偶尔被迫近亲繁殖，这是可以预料的。莱西博士将从三个种群（一个在岛上，一个在范围边缘，一个在范围中心）中收集老鼠，并从每个种群中复制三个实验室种群。繁殖成功率、生长率、幼崽存活率和肢骨不对称性（生长过程中发育异常的敏感指标）将在实验近交和非近交交配中进行监测。初步研究表明，在近亲繁殖的情况下，亲缘关系密切的种群之间存在着惊人的差异。通过统计分析三个不同种群的重复种群对近亲繁殖的反应，莱西博士将确定种群间的变异是否源于野生种群间近亲繁殖抑制的差异（这对所有小种群的管理者都很重要），或取样可能更加同质的自然种群所产生的差异（在建立圈养种群以及在迁移和重新引入努力中具有重要意义）。

In natural populations, inbreeding commonly results in offspring with more frequent birth defects, higher mortality, slower growth, lower fertility, lesser disease resistance, and/or other aspects of reduced fitness. This phenomenon, termed "inbreeding depression", is almost universal, but the severity of inbreeding depression varies widely among species and the causes of inbreeding depression are still poorly understood. As increasingly many natural populations are reduced to small, isolated fragments, inbreeding may become common in remnant populations. Whether populations can adapt to such conditions and recover or will suffer an inevitable decline in fitness will be determined by the still unknown number and nature of genes that contribute to inbreeding depression. Populations that have long been small and isolated may be affected less by inbreeding than are large, central populations, because natural selection could have removed deleterious, recessive genes during past episodes of inbreeding in the small populations. However, an earlier study of Peromyscus mice failed to find an association between the severity of inbreeding depression and the historical size of populations. Dr. Lacy proposes to determine whether responses to inbreeding by populations are repeatable, and to test further whether the response of a population to inbreeding can be predicted from knowledge of the population size and amount of genetic diversity it harbors. Genetic variability has been examined in samples of island, peripheral, and central populations of Peromyscus polionotus mice; island populations have much less genetic variability, as would be expected if those populations have been occasionally forced to inbreed in the past. Dr. Lacy will collect mice from three populations (one on an island, one at the range margin, and one in the central part of the range), and create three replicate laboratory stocks from each. Reproductive success, growth rate, juvenile survival, and asymmetry of limb bones (a sensitive measure of developmental abnormalities during growth) will be monitored in experimental inbred and non-inbred matings. Preliminary study demonstrated surprising variation among populations derived from closely related populations in response to inbreeding. By statistically analyzing responses to inbreeding in replicated stocks of three different populations, Dr. Lacy will determine whether the between-stock variation derived from differences in inbreeding depression among wild populations (of importance to all managers of small populations), or from differences arising from sampling possibly much more homogenous natural populations (of importance in establishment of captive stocks and in translocation and reintroduction efforts).