Investigating the dual role of mate choice genes in behavioural isolation and hybridization

物种分布的自然和人为变化导致物种之间的新的相互作用，并增加了密切相关的物种之间杂交的机会。杂交可能会对物种的命运产生深远的影响，尽管两个物种是否会在二次接触后融合，分裂或细分很难预测。两个物种是否会杂交，在很大程度上取决于物种是否承认对方是配偶。感官线索，如求爱歌曲和信息素，是在一个性别，和感知和偏好，这些线索在异性促进自愿（物种内）交配。决定配偶选择的基因的遗传控制和功能将促进或限制物种之间的杂交。然而，目前对这些基因如何塑造物种边界知之甚少，主要是因为大多数物种间杂交的研究都是在非模式生物中进行的，对这些生物来说，遗传操作是具有挑战性的。D. simulans和D. sechellia是大约25万年前在印度洋的交替岛屿上分歧的兄弟物种。我们的同事最近发现了D。simulans-D. sechellia杂交在塞舌尔群岛，这提供了一个机会，研究如何交配排序基因将塑造杂交的结果。行为障碍阻止了D. simulans male和D. sechellia雌性，而D. sechellia雄性更倾向于与D. simulans女性比女性从自己的物种由2：1的保证金。我们的长期目标是了解赋予配偶选择的基因如何塑造杂交的结果。在这个提议中，我们朝着这个目标迈出了重要的一步，确定了控制D。simulans和D. sechellia。我们的初步工作发现，雄性基因组中的两个主要效应位点和雌性基因组中的两个主要效应位点影响是否会发生交配与异性果蝇。我们已经成功地验证了赋予物种特异性信息素7，11-二十七碳二烯（7，11-HD）产生的两个基因的作用，并且我们的作图数据暗示了在雄性中产生的第二种信息素。我们认为，在D. sechellia-山核桃D. simulans物种配对是由一组交替的等位基因赋予的，这些等位基因决定了两种不同信息素的感知和产生的差异，并且这些信息素等位基因的特定组合将促进或减少杂交。在我们的第一项活动中，我们将联合收割机CRISPR辅助的精细作图与分子遗传学相结合，以揭示赋予D. sechellia males，或D. simulans雄性，至7，11-HD。接下来，我们将分离出可能产生D. sechellia男性，并研究候选信息素受体的交替等位基因在赋予女性对男性信息素的反应差异中的作用。在最终目标中，我们将重组同一基因组中的替代等位基因，以测试我们是否可以以与物种形成相关的方式改变选型交配。从本质上讲，我们是在模仿D。simulans和D. sechellia，出现在塞舌尔混合区。一旦我们了解了信息素传输/接收等位基因如何影响实验室中的杂交，我们将能够预测该领域的基因流动方向。未来的研究，将在完成这项赠款，将跟踪在塞舌尔野生种群的等位基因的命运杂交的进展。

Natural and human-induced changes in species' distributions lead to novel interactions between species and increase the opportunity for interbreeding between closely related species (hybridization). Hybridization may have a profound effect on the fate of species, although whether two species will fuse, divide or subdivide upon secondary contact is difficult to predict. Whether two species will interbreed depends, in large part, upon whether the species recognize each other as mates. Sensory cues, such as courtship songs and pheromones that are produced in one sex, and perception and preferences for these cues in the opposite sex promote assortative (within species) mating. The genetic control and function of the genes that determine mate choice will either facilitate or constrain hybridization between species. Yet little is currently known of how such genes shape species boundaries, largely because most studies of hybridization between species have been conducted in non-model organisms for which genetic manipulation is challenging. D. simulans and D. sechellia are sibling species that diverged on alternate islands in the Indian Ocean about 250,000 years ago. Our colleagues recently discovered D. simulans-D. sechellia hybrids in the Seychelles Archipelago, and this provides an opportunity to study how mate sorting genes will shape the outcomes of hybridization. Behavioral barriers prevent mating between D. simulans males and D. sechellia females, but D. sechellia males are more likely to mate with D. simulans females than with females from their own species by a margin of 2:1. Our long-term goal is to understand how the genes that confer mate choice will shape the outcome of hybridization. We take an important step toward that goal in this proposal by identifying genes that govern mate choice between D. simulans and D. sechellia. Our preliminary work finds two major effect loci in the male genome and two major effect loci in the female genome influence whether copulation will occur with heterospecific flies of the opposite sex. We have successfully verified the role of two genes that confer production of a species- specific pheromone, 7,11-heptacosadiene (7,11-HD), and our mapping data implicates a second pheromone that is produced in males. We propose that assortative mating in the D. sechellia - D. simulans species pair is conferred by a set of alternate alleles that determine differences in the perception and production of two distinct pheromones, and that particular combinations of these pheromone alleles will promote or reduce hybridization. In our first activity we combine CRISPR-assisted fine mapping with molecular genetics to reveal the alternate alleles that confer attraction in D. sechellia males, or aversion in D. simulans males, to 7,11-HD. Next, we will isolate the genes that likely confer production of an uncharacterized pheromone produced in D. sechellia males, and investigate the role of alternate alleles of a candidate pheromone receptor in conferring differences in female response to the male pheromone. In the final objective, we will recombine alternate alleles in the same genome to test whether we can alter assortative mating in ways that are relevant to speciation. Essentially, we are mimicking the effects of recombination between D. simulans and D. sechellia that occur in the Seychelles hybrid zone. Once we understand how pheromone transmission/reception alleles affect hybridization in the lab, we will be able to make predictions about the direction of gene flow in the field. Future studies, that will follow completion of this grant, will track the fate of the alleles in wild populations in the Seychelles as hybridization progresses.