Fox Charles W, Scheibly Kristy L, Reed David H
Department of Entomology, University of Kentucky, Lexington, Kentucky 40546, USA.
Evolution. 2008 Sep;62(9):2236-49. doi: 10.1111/j.1558-5646.2008.00441.x. Epub 2008 Jun 28.
The degree to which, and rapidity with which, inbreeding depression can be purged from a population has important implications for conservation biology, captive breeding practices, and invasive species biology. The degree and rate of purging also informs us regarding the genetic mechanisms underlying inbreeding depression. We examine the evolution of mean survival and inbreeding depression in survival following serial inbreeding in a seed-feeding beetle, Stator limbatus, which shows substantial inbreeding depression at all stages of development. We created two replicate serially inbred populations perpetuated by full-sib matings and paired with outbred controls. The genetic load for the probability that an egg produces an adult was purged at approximately 0.45-0.50 lethal equivalents/generation, a reduction of more than half after only three generations of sib-mating. After serial inbreeding we outcrossed all beetles then measured (1) larval survival of outcrossed beetles and (2) inbreeding depression. Survival of outcrossed beetles evolved to be higher in the serially inbred populations for all periods of development. Inbreeding depression and the genetic load were significantly lower in the serially inbred than control populations. Inbreeding depression affecting larval survival of S. limbatus is largely due to recessive deleterious alleles of large effect that can be rapidly purged from a population by serial sib-mating. However, the effectiveness of purging varied among the periods of egg/larval survival and likely varies among other unstudied fitness components. This study presents novel results showing rapid and extensive purging of the genetic load, specifically a reduction of as much as 72% in only three generations of sib-mating. However, the high rate of extinction of inbred lines, despite the lines being reared in a benign laboratory environment, indicates that intentional purging of the genetic load of captive endangered species will not be practical due to high rates of subpopulation extinction.
近亲繁殖衰退从种群中被清除的程度以及清除的速度，对保护生物学、圈养繁殖实践和入侵物种生物学具有重要意义。清除的程度和速率还能让我们了解近亲繁殖衰退背后的遗传机制。我们研究了以种子为食的甲虫——缘纹豆象（Stator limbatus）在连续近亲繁殖后平均存活率的进化以及存活方面的近亲繁殖衰退情况，该甲虫在发育的各个阶段都表现出显著的近亲繁殖衰退。我们通过全同胞交配创建了两个重复的连续近亲繁殖种群，并与远交对照组配对。卵发育为成虫的概率的遗传负荷以大约0.45 - 0.50个致死当量/代的速度被清除，仅经过三代同胞交配后就减少了一半以上。连续近亲繁殖后，我们让所有甲虫进行远交，然后测量（1）远交甲虫的幼虫存活率和（2）近亲繁殖衰退情况。在连续近亲繁殖的种群中，远交甲虫在所有发育阶段的存活率都进化得更高。连续近亲繁殖种群中的近亲繁殖衰退和遗传负荷显著低于对照组种群。影响缘纹豆象幼虫存活的近亲繁殖衰退主要是由于具有较大效应的隐性有害等位基因，这些等位基因可以通过连续同胞交配迅速从种群中被清除。然而，清除的有效性在卵/幼虫存活阶段有所不同，并且在其他未研究的适合度成分中可能也有所不同。这项研究呈现了新的结果，表明遗传负荷能够快速且广泛地被清除，特别是仅经过三代同胞交配就减少了多达72%。然而，尽管近交系是在良好的实验室环境中饲养的，但近交系的高灭绝率表明，由于亚种群灭绝率高，有意清除圈养濒危物种的遗传负荷将不切实际。
