Fraser Dylan J
Department of Biology, Dalhousie University Halifax, NS, Canada.
Evol Appl. 2008 Nov;1(4):535-86. doi: 10.1111/j.1752-4571.2008.00036.x. Epub 2008 Jun 2.
Captive breeding programs are increasingly being initiated to prevent the imminent extinction of endangered species and/or populations. But how well can they conserve genetic diversity and fitness, or re-establish self-sustaining populations in the wild? A review of these complex questions and related issues in salmonid fishes reveals several insights and uncertainties. Most programs can maintain genetic diversity within populations over several generations, but available research suggests the loss of fitness in captivity can be rapid, its magnitude probably increasing with the duration in captivity. Over the long-term, there is likely tremendous variation between (i) programs in their capacity to maintain genetic diversity and fitness, and (ii) species or even intraspecific life-history types in both the severity and manner of fitness-costs accrued. Encouragingly, many new theoretical and methodological approaches now exist for current and future programs to potentially reduce these effects. Nevertheless, an unavoidable trade-off exists between conserving genetic diversity and fitness in certain instances, such as when captive-bred individuals are temporarily released into the wild. Owing to several confounding factors, there is also currently little evidence that captive-bred lines of salmonids can or cannot be reintroduced as self-sustaining populations. Most notably, the root causes of salmonid declines have not been mitigated where captive breeding programs exist. Little research has also addressed under what conditions an increase in population abundance due to captive-rearing might offset fitness reductions induced in captivity. Finally, more empirical investigation is needed to evaluate the genetic/fitness benefits and risks associated with (i) maintaining captive broodstocks as either single or multiple populations within one or more facilities, (ii) utilizing cryopreservation or surrogate broodstock technologies, and (iii) adopting other alternatives to captive-rearing such as translocations to new habitats. Management recommendations surrounding these issues are proposed, with the aim of facilitating meta-analyses and more general principles or guidelines for captive-breeding. These include the need for the following: (i) captive monitoring to involve, a priori, greater application of hypothesis testing through the use of well-designed experiments and (ii) improved documentation of procedures adopted by specific programs for reducing the loss of genetic diversity and fitness.
为防止濒危物种和/或种群即将灭绝，圈养繁殖计划越来越多地启动。但它们在保护遗传多样性和适应性方面能做得多好，或者在野外重新建立自我维持的种群呢？对鲑科鱼类中这些复杂问题及相关问题的综述揭示了一些见解和不确定性。大多数计划能够在几代人的时间内维持种群内的遗传多样性，但现有研究表明，圈养环境中适应性的丧失可能很快，其程度可能随着圈养时间的延长而增加。从长期来看，（i）不同计划在维持遗传多样性和适应性的能力方面，以及（ii）物种甚至种内生活史类型在适应性成本产生的严重程度和方式方面，可能存在巨大差异。令人鼓舞的是，现在有许多新的理论和方法可用于当前和未来的计划，以潜在地减少这些影响。然而，在某些情况下，例如将圈养繁殖的个体临时放归野外时，在保护遗传多样性和适应性之间存在不可避免的权衡。由于几个混杂因素，目前也几乎没有证据表明鲑科鱼类的圈养繁殖品系能否作为自我维持的种群重新引入。最值得注意的是，在存在圈养繁殖计划的地方，鲑科鱼类数量下降的根本原因并未得到缓解。也很少有研究探讨在何种条件下，圈养养殖导致的种群数量增加可能抵消圈养引起的适应性降低。最后，需要更多的实证研究来评估与以下方面相关的遗传/适应性益处和风险：（i）在一个或多个设施内将圈养亲鱼作为单一或多个种群进行维持，（ii）利用冷冻保存或替代亲鱼技术，以及（iii）采用圈养养殖的其他替代方法，如转移到新栖息地。围绕这些问题提出了管理建议，旨在促进荟萃分析以及制定圈养繁殖更通用的原则或指南。这些建议包括需要：（i）圈养监测事先更多地通过设计良好的实验应用假设检验，以及（ii）更好地记录特定计划为减少遗传多样性和适应性丧失而采用的程序。
