Data from: Severe inbreeding depression and no evidence of purging in an extremely inbred wild species - the Chatham Island black robin

Although evidence of inbreeding depression in wild populations is well
established, the impact of genetic purging in the wild remains
controversial. The contrasting effects of inbreeding depression, fixation
of deleterious alleles by genetic drift and the purging of deleterious
alleles via natural selection mean that predicting fitness outcomes in
populations subjected to prolonged bottlenecks is not straightforward. We
report results from a long-term pedigree study of arguably the
world's most inbred wild species of bird: the Chatham Island black
robin Petroica traversi, in which conditions were ideal for purging to
occur. Contrary to expectations, black robins showed a strong, negative
relationship between inbreeding and juvenile survival, yielding lethal
equivalents (2B) of 6.85. We also determined that the negative
relationship between inbreeding and survival did not appear to be mediated
by levels of ancestral inbreeding and may be attributed in part to
un-purged lethal recessives. Although the black robin demographic history
provided ideal conditions for genetic purging, our results show no clear
evidence of purging in the major life-history trait of juvenile survival.
Our results also show no evidence of fixation of deleterious alleles in
juvenile survival, but do confirm that continued high levels of
contemporary inbreeding in a historically inbred population could lead to
additional severe inbreeding depression.

尽管野生种群中近交衰退（inbreeding depression）的证据已得到充分证实，但遗传清除（genetic purging）在野生环境中的影响仍颇具争议。近交衰退、遗传漂变（genetic drift）固定有害等位基因（deleterious alleles）以及自然选择（natural selection）清除有害等位基因这三者的效应相互对立，使得预测经历长期瓶颈效应（prolonged bottlenecks）的种群的适合度结果（fitness outcomes）并非易事。我们在此报告了一项长期谱系研究（pedigree study）的结果，该研究的对象堪称全球近交程度最高的野生鸟类——查塔姆岛黑知更鸟（Petroica traversi），其生存环境恰好为遗传清除提供了理想条件。与预期相悖的是，黑知更鸟呈现出近交程度与幼体存活率（juvenile survival）之间显著的负相关关系，致死当量（lethal equivalents, 2B）达6.85。我们还发现，近交与存活率之间的负相关关系似乎并非由祖先近交（ancestral inbreeding）水平介导，这一现象在一定程度上可归因于未被清除的隐性致死突变（un-purged lethal recessives）。尽管黑知更鸟的种群统计历史为遗传清除提供了理想条件，但我们的研究结果并未在幼体存活率这一核心生活史性状（life-history trait）中找到明确的遗传清除证据。此外，我们未发现幼体存活率存在有害等位基因固定的迹象，但确实验证了：在一个历史上已存在近交的种群中，持续高水平的当代近交仍可能引发额外严重的近交衰退。