DISSERTATION RESEARCH: Linking functional evolution of odorant receptors to behavioral adaptations and the emergence of herbivory in drosophilids

本研究探讨了近缘种蝇类从以微生物为食转变为以植物为食过程中嗅觉的感觉适应所起的作用。食草动物是最多样化的动物群体，包括所有已命名物种的四分之一。然而，对于昆虫如何进化到以其他类型的植物为食，或者昆虫如何进化到以特定种类的植物为食，人们知之甚少。该项目将研究这些果蝇的嗅觉受体和潜在基因在进化过程中如何随着它们的饮食从酵母转向植物而发生变化。它将决定嗅觉感受器的变化，使其能够转换到新的饮食，以及潜在的基因如何转变为针对新的寄主植物。这种对嗅觉进化的进一步理解将使我们对生态相互作用的变化有一个大致的了解。这项研究可能进一步为操纵昆虫的食物选择提供见解。因此，它有可能通过应用于农业（昆虫是主要的作物害虫）和人类健康（因为昆虫经常传播疾病），对社会产生广泛影响。本研究将通过比较黄菖蒲（Scaptomyza flava）和苍白菖蒲（Scaptomyza pallida）的嗅觉系统，探讨生态位变化后嗅觉系统的进化。这两种蝇类亲缘关系很近，但食性不同。黄葡萄球菌是一种真正的食草动物，以芥菜植物为食，而苍白葡萄球菌则保留了更古老的微生物饮食。气相色谱(GC) -天线电图检测（EAD）将用于区分苍蝇可以检测到宿主物种叶子产生的挥发性化合物（气味）。这种技术将一股叶子挥发物分成两股相同的流。一个流被送入气相色谱检测器，通过人工嗅闻化合物进行识别。另一种是针对苍蝇的，EAD将通过确定该化合物是否触发单个神经细胞的反应来确定该化合物是否可以自然检测到。因此，草食性苍蝇检测到的叶子挥发物将被识别并与以微生物为食的苍蝇检测到的挥发物进行比较。气相色谱- ead鉴定的可区分两种植物的挥发物将被用作嗅觉试验的诱饵，其中四种含有不同挥发物的校准气流被送入正方形竞技场的角落。然后测量对每种植物挥发物的吸引力，以确定该物种的行为是否与它们的检测剖面相匹配。最后，在区分这两个物种中似乎很重要的基因将被设计成一种模式生物果蝇，以测试基因对食物选择的影响是否被完全理解。

This research investigates the role of sensory adaptation of smell in closely related species of flies in transitions from feeding on microbes to feeding on plants. Plant-feeding are the most diverse group of animals, including a quarter of all named species. Yet little is known about how insects evolve to feed on plants from other types of diets, or how insects evolve to target specific kinds of plants. This project will study how the smell receptors and underlying genetics of these flies have changed over evolutionary time as their diet switches from yeast to plants. It will determine the changes in smell receptors that allow the switch to new diets and how the underlying genetics shifts to target new host plants. This increased understanding of the evolution of the sense of smell will inform our general understanding of changes in ecological interactions. This research may furthermore provide insights that allow manipulation of insect food choice. It therefore has the potential to broadly impact society through applications to agriculture, where insects are major crop pests, and human health since insects frequently spread disease.This study will investigate the evolution of olfaction (sense of smell) after a niche change by comparing the olfactory systems of Scaptomyza flava and Scaptomyza pallida. These two fly species are closely related but differ in diet. S. flava is a true herbivore feeding on mustard plants, while S. pallida retains the more ancestral diet of microbes. Gas chromatography (GC) -electroantennographic detection (EAD) will be used to differentiate which volatile compounds (smells) produced by leaves of host species the flies can detect. This technique divides a stream of leaf volatiles into two identical streams. One stream is sent into a GC detector for identification by essentially artificially smelling the compound. The other stream is aimed at a fly where EAD will determine if the compound is detectable naturally by determining if the compound triggers a response in single nerve cell. Leaf volatiles that are detected by herbivorous flies will thereby be identified and compared to those detected by flies that feed on microbes. The volatiles identified by GC-EAD as differentiating the two species will then be used as baits in olfactory assays where four calibrated airstreams containing different volatiles are fed into the corners of a square arena. The attraction to each plant volatile will then measured to determine if the species behavior matches their detection profile. Finally, genes that appear to be important in differentiating these two species will be engineered into a model organism Drosophila melanogaster to test if the genes effect on food choice is fully understood.