The genetics and genomics of adaptive sex ratio behaviour

我们将研究性比行为的遗传基础的寄生蜂Nasonia vitripennis。女性N.丽蝇蛹集茧蜂改变子代性比符合汉密尔顿的局部交配竞争（LMC）理论。LMC由相关雄性（例如兄弟）之间的配偶竞争引起，并且可以在局部群体中发生交配时发生，例如亲属群体之间。当LMC强烈时（例如，如果所有男性都是兄弟），最佳性别比例是女性偏向的。这种偏好减少了儿子之间的竞争，增加了这些儿子的配偶数量。随着LMC下降，预测的性别比例偏差也会下降。LMC的程度取决于有多少雌性在一片宿主上产卵（以及它们产了多少卵）。在过去的十年中，我们已经探索了女性纳索尼亚在LMC下分配性别时使用的线索。有了一个强大的理论框架，我们现在有一个非常好的了解兼性分配下LMC在表型水平在纳索尼亚。然而，我们对性别比的遗传学的理解更为初步，特别是在性别分配机制方面。到目前为止，我们对纳索尼亚的性别比例的数量遗传学有了一些了解（遗传力的估计，新突变的输入，以及四个数量性状基因座或QTL的鉴定）。我们也开始探索产卵过程中表达的基因。在本研究中，我们将在此基础上，利用三种互补的方法，探索Nasonia的性比变异和控制的遗传基础。首先，我们将首先使用限制性位点相关DNA测序（“RAD-seq”）方法，对我们最近的QTL研究进行跟踪，并重复来自同一自然群体的高和低性比品系之间的杂交。RAD-seq可以在基因组中生成数千个标记，从而实现更小规模的QTL作图项目。我们还将使用我们产生的数据来测试窝卵数变异QTL，测试多效性影响性别比和窝卵数的位点。其次，我们将跟踪我们最近的基因表达工作，探索与暴露于不同LMC环境和LMC线索的不同组合相关的基因表达变化。早在2004年，Shuker和West的实验表明，雌性Nasonia vitripennis对“宿主”和“社会”LMC线索的反应不同。我们将遵循类似的方案，在Illumina平台上使用RNA-seq测定焦点女性的转录组。我们的目的是看看我们是否可以将基因表达模式与我们所知道的对性别比例表型有很大影响的微妙环境差异联系起来。第三，我们将测试DNA的表观遗传修饰（特别是DNA甲基化）是否与性别比例行为的调节有关。基因表达的表观遗传控制在多大程度上影响行为，是目前人们非常感兴趣的焦点，不仅在人类和其他脊椎动物中，而且在昆虫中也越来越多。首先，我们将寻找模式的差异甲基化与交配（女性从交配搜索切换到主机搜索）和/或与LMC线索的相互作用，而产卵。第二，我们将破坏DNA甲基化并寻找性别分配的变化。如果DNA甲基化有助于调节与性别比例行为相关的基因网络，那么我们将在第一个实验中看到不同处理之间的差异甲基化模式，并在第二个实验中看到不同处理之间性别分配的变化。综上所述，这些方法将解决性别比例变异的遗传结构以及与性别分配相关的基因和基因通路，以及这些通路的调节是否涉及DNA甲基化。它们将提供互补的候选基因集，使功能基因组/分子进化研究能够充分实现基因型-表型联系。

We will examine the genetic basis of sex ratio behaviour in the parasitoid wasp Nasonia vitripennis. Female N. vitripennis facultatively change their offspring sex ratios in line with Hamilton's theory of Local Mate Competition (LMC). LMC arises from competition between related males (e.g. brothers) for mates, and can occur when mating occurs in localised groups, for instance amongst groups of kin. When LMC is intense (e.g. if all males are brothers), the optimal sex ratio is a female-biased one. This bias reduces competition amongst sons and increases the number of mates for those sons. As LMC declines, so does the predicted sex ratio bias. The degree of LMC depends on how many females lay eggs on a patch of hosts (and how many eggs they lay). Over the last decade, we have explored the cues female Nasonia use when allocating sex under LMC. With a robust theoretical framework, we now have a remarkably good understanding of facultative sex allocation under LMC at the phenotypic level in Nasonia. However, our understanding of the genetics of sex ratio is more rudimentary, especially in terms of the mechanism of sex allocation. Thus far, we have some picture of the quantitative genetics of sex ratio in Nasonia (estimates of heritability, input of new mutations, and the identification of four Quantitative Trait Loci, or QTL). We have also begun to explore what genes are expressed during oviposition. In this proposal, we will build on this work to explore the genetic basis of sex ratio variation and control in Nasonia, using three complementary approaches.First, we will first follow-up our recent QTL study using a Restriction Site Associated DNA sequencing ("RAD-seq") approach and a repeat of the cross between High and Low sex ratio lines drawn from the same natural population. RAD-seq can generate thousands of markers across a genome enabling finer-scale QTL mapping projects. We will also use the data we generate to test for clutch size variation QTL, testing for loci pleiotropically influencing both sex ratio and clutch size.Second, we will follow-up our recent gene expression work to explore changes in gene expression associated with exposure to different LMC environments and different combinations of LMC cues. Back in 2004, Shuker & West experimentally showed that female Nasonia vitripennis responded differentially to "host" versus "social" LMC cues. We will follow a similar protocol, assaying the transcriptomes of the focal females using RNA-seq on the Illumina platform. Our aim is to see whether we can link patterns of gene expression to subtle environmental differences which we know have a big effect on the sex ratio phenotype.Third, we will test whether or not epigenetic modifications of DNA (specifically DNA methylation) are associated with the regulation of sex ratio behaviour. The extent to which epigenetic control of gene expression influences behaviour is currently the focus of much interest, both in humans and other vertebrates, but also increasingly in insects. First, we will look for patterns of differential methylation associated with either mating (as females switch from mate-searching to host-searching) and/or interactions with LMC cues whilst ovipositing. Second, we will disrupt DNA methylation and look for changes in sex allocation. If DNA methylation helps regulate gene networks associated with sex ratio behaviour, then we will see patterns of differential methylation across the treatments in the first experiment and changes in sex allocation across the treatments in the second.Taken together, these approaches will address both the genetic architecture of sex ratio variation and also the genes and gene pathways associated with sex allocation, and whether or not the regulation of those pathways involves DNA methylation. They will provide complementary sets of candidate genes, enabling the functional genomic/molecular evolution studies required to fully realise the genotype-phenotype link.