Testing the effectiveness and repeatability of genetic rescue from inbreeding depression in Tribolium castaneum

背景：当种群枯竭或孤立时，减少的遗传变异会通过近亲交配衰退导致种群适合度降低。导致这种情况的环境环境在未来只可能增加，基因变异现在被世界自然保护联盟列为保护优先事项。因此，迫切需要解决保护遗传学中的研究问题，最近的一项影响很大的审查确定了优先事项，以了解近亲繁殖衰退的主要表型途径，以及是否可以通过从相关个体引入新的遗传变异来拯救近亲繁殖群体。这篇综述指出的问题是：(A)野生研究通常无法控制已知的影响适合度的潜在环境混乱；(B)对于许多系统来说，近亲繁殖抑制的具体表型途径仍未得到证实，因此需要更广泛的更详细的生殖特征测量；以及(C)由于破坏局部适应而可能发生的近亲繁殖抑制是一个重要的考虑因素，因此需要对F2代及以后(当非连锁基因开始重组时)进行评估。该项目旨在使用受控、多代和可重复的实验方法来克服这些弱点。模型：粉甲虫已经成功地被用作回答进化论和生态学问题的实验室系统。我们最近通过NERC项目使用这一系统的经验意味着我们对测量一系列生殖健康特征有了详细的熟悉。我们还在UEA建立了50个菌株的系统发育图，因此我们可以客观地识别具有越来越远的遗传背景的种群，并评估它们对遗传拯救的相对影响。重要的是，与相似繁殖的对照相比，我们对20个重复的近交种群的生殖输出存在一致的近交抑制。方法：我们有两个总体目标：(1)对一些潜在的生殖适合性进行详细的测量，以确定哪些是近亲繁殖衰退的原因；(2)测量在不同但可控的条件下‘基因拯救’的一致性和有效性。(1)近亲交配抑制的大多数例子都是通过干扰生殖而发生的。我们计划使用20个近交复制群体和10个非近交对照，通过4个递增的近交系数来确定不同的生殖特征是否更容易受到近亲繁殖抑制的影响。对15个已确立的生殖健康特征(从精子质量和竞争力到雌性卵子产量和幼虫孵化)的详细和重复测量将使人们能够评估导致抑郁症的特定生殖表型。(2)即使是很少数量的“移民”，基因拯救也是可能的。我们将评估我们已建立的近交系(和非近交系对照)中的遗传拯救，方法是导入先前项目中已知的遗传相关的4个不同群体。使用五倍范围的移民，再加上使用表型标记测量的基因传播的监测，我们将能够确定多少导入可以拯救近亲繁殖的种群，以及不同的遗传背景如何发挥作用。重要的是，我们将对三代人进行监测，以确定第二代可能发生的局部适应基因丢失可能导致的异种繁殖抑郁的可能作用。结论：我们的结果将通过(1)允许对易感性状进行有针对性的筛选，以及(2)是否应该根据移民基因的选择和近亲繁殖抑制的风险来发起遗传挽救，从而为关注近亲繁殖的保护管理计划提供参考。我们的实验材料将免费用于进一步的基因组分析。

BACKGROUND: When populations become depleted or isolated, reduced genetic variation can lead to reduced population fitness through inbreeding depression. The environmental circumstances leading to this situation are only likely to increase in the future, and genetic variation is now recognised by the IUCN as a conservation priority. There is therefore a pressing requirement to address research questions in conservation genetics, with a recent high-impact review identifying priorities for understanding the primary phenotypic routes to inbreeding depression, and whether inbred populations can be 'rescued' through the introduction of new genetic variation from related individuals. Problems identified by this review were: (a) wild studies usually failed to control for potential environmental confounds known to influence fitness; (b) for many systems, the specific phenotypic routes to inbreeding depression within 'fecundity' remain unconfirmed, so a wider range of more detailed reproductive trait measures are required; and (c) the potential for outbreeding depression via disruption of local adaptation is an important consideration and therefore assessment to the F2 generation and beyond (when unlinked genes begin recombining) is required. This project aims to overcome these weaknesses using a controlled, multi-generational and replicated experimental approach. THE MODEL: The flour beetle Tribolium castaneum has been successfully employed as a laboratory system for answering questions in evolution and ecology. Our recent experience with this system through a recent NERC project mean we have detailed familiarity with measuring a range of reproductive fitness traits. We also have an established phylogeny for 50 strains at UEA, so we can objectively identify populations with increasingly-distant genetic backgrounds, and assess their relative impact on genetic rescue. Importantly, we have consistent inbreeding depression of reproductive output for 20 replicate inbred populations, by comparison with similarly-bred controls. METHODS: We have two general aims: (1) conduct detailed measurement of a number of potential reproductive fitness traits to identify which are responsible for inbreeding depression, and (2) measurement of the consistency and effectiveness of 'genetic rescue' under different but controlled conditions. (1) Most examples of inbreeding depression occur via disruption to reproduction. We plan to determine whether different reproductive traits are more susceptible to inbreeding depression using 20 inbred replicate populations and 10 non-inbred controls, across 4 increasing inbreeding coefficients. Detailed and replicated measurement of 15 established reproductive fitness traits (from sperm quality and competitiveness to female egg output and larval hatch) will allow assessment of the specific reproductive phenotypes responsible for depression. (2) Genetic rescue might be possible with even small numbers of 'immigrants'. We will assess genetic rescue in our established inbred lines (and non-inbred controls) using introgression of 4 different populations of known genetic relatedness from a previous project. Using a five-fold range of immigration, coupled with monitoring of genotypic spread measured using phenotypic markers, we will be able to establish how much introgression can rescue an inbred population, and how different genetic backgrounds play a role. Importantly, we will monitor across 3 generations, to determine the likely role of outbreeding depression through loss of local adaptation genes that might occur in the second generation. CONCLUSIONS: Our results will inform conservation management programs concerned about inbreeding by (1) allowing targeted screening of susceptible traits, and (2) whether genetic rescue should be instigated according to the choice of immigrant genes and the risk of outbreeding depression. Material from our experiments will be freely available for further genomic analyses.