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

自然和人为引起的物种分布变化导致了物种之间新的相互作用，并增加了密切相关物种之间杂交的机会。杂交可能对物种的命运有深远的影响，尽管两个物种在二次接触时是否会融合、分裂或细分还很难预测。两个物种是否会进行杂交，在很大程度上取决于这两个物种是否承认彼此为配偶。感官线索，如求爱歌曲和信息素在一个性别中产生，以及异性对这些线索的感知和偏好促进了(物种内)的分类交配。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，目前人们对这些基因如何塑造物种边界知之甚少，这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。拟人鱼和塞切利亚人是兄弟物种，大约25万年前在印度洋的交替岛屿上分叉开来。我们的同事最近发现了D-Simans-D。这为研究配偶分选基因将如何影响杂交结果提供了一个机会。行为障碍阻止了雄性拟南针吸虫和雌性拟南针吸虫之间的交配，但异形吸虫雄性更有可能与雌性拟南针吸虫交配，比例为2：1。我们的长期目标是了解决定配偶选择的基因将如何影响杂交结果。我们在这项提议中朝着这个目标迈出了重要的一步，通过识别控制拟单胞藻和双胞藻之间的配偶选择的基因。我们的初步工作发现，雄性基因组中的两个主效位点和雌性基因组中的两个主效位点影响着是否会与异性异种果蝇发生交配。我们已经成功地验证了两个基因的作用，这两个基因可以产生物种特有的信息素7，11-庚二烯(7，11-HD)，我们的图谱数据表明第二种信息素是在男性身上产生的。我们认为，在D.sechellia-D.Simans物种对中的分类交配是由一组交替的等位基因决定的，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，这些信息素等位基因的特定组合将促进或减少杂交。在我们的第一个活动中，我们将CRISPR辅助的精细定位与分子遗传学相结合，揭示了赋予Sechellia雄性的吸引力或D的雄性的厌恶对7，11-HD的交替等位基因。接下来，我们将分离可能产生一种未知信息素的基因，并研究候选信息素受体的替代等位基因在赋予雌性对雄性信息素反应的差异中的作用。在最后的目标中，我们将重新组合同一基因组中的交替等位基因，以测试我们是否可以以与物种形成相关的方式改变分类交配。从本质上讲，我们是在模仿塞舌尔杂交区中发生的拟单胞藻和单胞藻之间的重组效应。一旦我们在实验室了解了信息素传输/接收等位基因是如何影响杂交的，我们就能够对该领域的基因流动方向做出预测。在这笔赠款完成后，未来的研究将追踪随着杂交的进展，塞舌尔野生种群中等位基因的命运。

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.