CRB: Predictability of Inbreeding Depression in Insular and Mainland Populations

在自然种群中，近亲交配通常会导致后代出现更频繁的出生缺陷、更高的死亡率、更慢的生长速度、更低的生育率、更弱的抗病能力和/或其他方面的健康状况下降。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在不同物种之间差别很大，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为小的、孤立的片段，近亲交配可能在剩余种群中变得普遍。种群是否能够适应这样的条件并恢复或将遭受不可避免的适合度下降，将取决于导致近亲繁殖衰退的基因的数量和性质尚不清楚。与大的中心种群相比，长期处于小而孤立状态的种群受近亲繁殖的影响可能较小，因为在过去的几次近亲交配中，自然选择可能已经消除了小种群中有害的隐性基因。然而，早期对Permyscus小鼠的一项研究未能发现近亲繁殖衰退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交配的反应是否可重复，并进一步测试种群对近亲交配的反应是否可以根据种群规模和遗传多样性的知识来预测。已经在小儿麻痹症小鼠的岛屿种群、外围种群和中心种群的样本中检测了遗传变异性；如果这些种群过去偶尔被迫近亲繁殖，那么岛屿种群的遗传变异性要小得多。莱西博士将从三个种群中收集老鼠(一个在岛上，一个在牧场边缘，一个在牧场中心)，并从每个种群中创建三个重复的实验室种群。在实验近交系和非近交系配对中，将监测繁殖成功、生长速度、幼体存活率和四肢骨骼不对称(生长过程中发育异常的敏感指标)。初步研究表明，来自密切相关群体的群体对近亲交配的反应存在惊人的差异。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差异是否源于野生种群之间近亲繁殖抑制的差异(对所有小种群的管理者来说都很重要)，或由于对可能更为同质的自然种群进行抽样而产生的差异(对于圈养种群的建立以及转移和重新引入的努力具有重要意义)。

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).