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

背景技术背景：当种群枯竭或孤立时，减少的遗传变异会通过近亲繁殖衰退导致种群适应度降低。导致这种情况的环境条件只会在未来增加，遗传变异现在被IUCN视为保护优先事项。因此，迫切需要解决保护遗传学的研究问题，最近的高影响力的审查确定优先事项，了解主要的表型途径近亲繁殖抑郁症，以及是否可以通过引进新的遗传变异从相关的个人“拯救”近交群体。本综述发现的问题是：（a）野生研究通常未能控制已知影响适合度的潜在环境干扰;（B）对于许多系统，在“繁殖力”内导致近交衰退的特定表型途径仍未得到证实，因此需要更广泛更详细的生殖性状测量;和（c）通过破坏局部适应而导致远系繁殖衰退的可能性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。该项目旨在利用一种受控的、多代的和可复制的实验方法来克服这些弱点。模型：面粉甲虫赤拟谷盗已成功地作为一个实验室系统，以回答问题的进化和生态学。通过最近的NERC项目，我们最近对这个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了解。我们还在UEA建立了50种菌株的遗传学，因此我们可以客观地识别具有越来越远的遗传背景的人群，并评估其对遗传拯救的相对影响。重要的是，我们有一致的近交抑郁症的繁殖输出20个重复的近交群体，与类似的繁殖控制。方法：我们有两个总体目标：（1）详细量度多项潜在的生殖适合性特质，以找出导致近亲繁殖衰退的原因;及（2）量度“基因拯救”在不同但受控制的条件下的一致性及成效。(1)大多数近亲繁殖衰退的例子是通过破坏繁殖而发生的。我们计划使用20个近交重复群体和10个非近交对照，在4个增加的近交系数，以确定是否不同的生殖性状更容易受到近交衰退。详细和重复测量15个已建立的生殖健康性状（从精子质量和竞争力，女性卵子产量和幼虫孵化）将允许评估负责抑郁症的特定生殖表型。(2)即使是少量的“移民”，基因拯救也是可能的。我们将使用来自先前项目的已知遗传相关性的4个不同群体的基因渗入来评估我们建立的近交系（和非近交对照）中的遗传拯救。使用五倍范围的移民，再加上监测的基因型传播使用表型标记测量，我们将能够建立多少基因渗入可以拯救近交群体，以及不同的遗传背景如何发挥作用。重要的是，我们将监测3代，以确定通过可能发生在第二代的局部适应基因的丢失而导致的远交抑郁症的可能作用。结论：我们的研究结果将通过（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远交抑郁症的风险来启动遗传拯救，为关注近亲繁殖的保护管理计划提供信息。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.