Jamieson Ian G, Wallis Graham P, Briskie James V
Department of Zoology, University of Otago, P.O. Pox 56, Dunedin, New Zealand.
Conserv Biol. 2006 Feb;20(1):38-47. doi: 10.1111/j.1523-1739.2005.00282.x.
There is growing evidence that inbreeding can negatively affect small, isolated populations. This contrasts with the perception in New Zealand, where it has been claimed that native birds are less affected by inbreeding depression than threatened species from continental regions. It has been argued that New Zealand's terrestrial birds have had a long history of small population size with frequent inbreeding and that this has 'purged" deleterious alleles. The rapid recovery of many tiny and inbred populations after introduced predators have been controlled, and without input from more genetically diverse populations, has further supported the view that inbreeding is not a problem. This has led to a general neglect of inbreeding as a factor in recovery programs for highly endangered species such as the Black Robin (Petroica traversi) and Kakapo (Strigops habroptilis). We examined the reasons for this situation and review the New Zealand evidence for genetic purging. Complete purging of the genetic load and elimination of inbreeding depression are unlikely to occur in natural populations, although partial purging may be more likely where small populations have become inbred over an extended period of time, such as on small isolated islands. Recent molecular data are consistent with the view that island endemics, including New Zealand's threatened birds, have low genetic variation and hence have possibly gone through longer periods of inbreeding than threatened species from continental regions. Nevertheless, results from recent field studies in New Zealand indicate that, despite the opportunity for purging, inbreeding depression is evident in many threatened species. Although inbreeding depression has not prevented some populations from recovering from severe bottlenecks, the long-term consequences of inbreeding and small population size--the loss of genetic variation--are potentially much more insidious. The degrees to which genetic factors reduce population viability generally remain unquantified in New Zealand. Although minimizing ecological risks (e.g., preventing reinvasion of islands by mammalian predators) will continue to receive high priority in New Zealand because of their much larger impacts, we advocate that genetic considerations be better integrated into recovery plans.
越来越多的证据表明，近亲繁殖会对小型孤立种群产生负面影响。这与新西兰的看法形成了对比，在新西兰，有人声称本土鸟类受近亲繁殖衰退的影响比来自大陆地区的濒危物种要小。有人认为，新西兰的陆栖鸟类长期以来种群规模较小且频繁近亲繁殖，这已经“清除”了有害等位基因。在引入的捕食者得到控制后，许多微小的近亲繁殖种群迅速恢复，且没有更多基因多样化种群的输入，这进一步支持了近亲繁殖不是问题的观点。这导致在为诸如黑知更鸟（Petroica traversi）和鸮鹦鹉（Strigops habroptilis）等极度濒危物种制定恢复计划时，普遍忽视了近亲繁殖这一因素。我们研究了造成这种情况的原因，并回顾了新西兰有关基因清除的证据。在自然种群中，完全清除遗传负荷和消除近亲繁殖衰退不太可能发生，尽管在小型种群长期近亲繁殖的情况下，如在小的孤立岛屿上，部分清除可能更有可能。最近的分子数据与以下观点一致，即包括新西兰受威胁鸟类在内的岛屿特有物种遗传变异低，因此可能经历了比来自大陆地区的受威胁物种更长时间的近亲繁殖。然而，新西兰最近的实地研究结果表明，尽管有基因清除的机会，但近亲繁殖衰退在许多受威胁物种中依然明显。虽然近亲繁殖衰退并没有阻止一些种群从严重瓶颈中恢复过来，但近亲繁殖和小种群规模的长期后果——遗传变异的丧失——可能更具潜在危害。在新西兰，遗传因素降低种群生存力的程度通常仍未得到量化。尽管由于生态风险（如防止哺乳动物捕食者再次入侵岛屿）的影响更大，在新西兰将继续高度优先考虑降低这些风险，但我们主张将遗传因素更好地纳入恢复计划。
