Understanding temperature adaptation in tropical insects

如果我们希望了解和减轻气候变化的影响，了解热适应是一个优先事项。生物体目前的耐受性及其适应或迁移到新地区的能力将决定它们是否能在变暖的环境中生存下来。与温带物种相比，目前关于热带地区热适应的数据相对较少。热带昆虫占地球生物多样性的很大比例，但目前人们对它们应对气候变化的能力知之甚少。我们建议使用一组被充分研究的热带外温带蝴蝶来评估海拔梯度上的热适应，确定遗传和环境变异对这些特征的贡献，并确定潜在的遗传基因座。在赫利尼乌斯内部，有几个亚种的例子也显示了按海拔的结构。利用群体基因组序列数据和H.Melpomene的参考基因组，我们最近发现，H.Melpomene和H.Erato的三个亚种对在基因组中包含热适应候选基因的区域表现出差异，如代谢酶和热休克蛋白。我们将通过描述种群和物种之间发现的生理差异来表征这些物种的生态生理学。在厄瓜多尔境内，这些物种在安第斯山脉的东西两侧有平行的海拔斜坡，这使我们能够评估我们确定的任何趋势的可复制性。温度也可能是划定生态位的重要因素，因此也是推动多样性和物种形成的重要因素。对赫利尼乌斯系统的研究主要集中在颜色模式在推动种群和物种之间差异方面的作用，但也存在生境差异，并被认为是导致差异的原因。例如，安第斯山脉西侧的物种对H.Melpomene和H.cydno已经成为物种形成研究的经典系统，它们显示出不同的海拔范围。导致栖息地利用差异的表型差异还有待研究，但生理上对温度的适应似乎很有可能。因此，我们将在实验中测试姊妹分支H.Melpomene和H.cydno/timareta之间的热适应差异，以评估温度在决定这些物种的海拔范围和物种分布方面的重要性。我们将利用Helconius可用的大量基因组资源进行基因组扫描和详细的关联图谱分析，以确定H.Melpomene内负责热适应的基因座。识别这些基因座将使我们能够解决这样一个问题，即参与温度适应的基因是否显示出物种之间存在渐入选择或分化选择的证据。物种间温度适应基因的共享可以使物种快速适应新的环境，而差异则表明热适应在维持物种特性方面是重要的。近年来，关于赫利柯斯的研究蓬勃发展，导致了对基因组差异和物种形成过程的许多见解。然而，所研究的生态特征在很大程度上仍局限于颜色格局。该项目将是朝着建立更全面的生态遗传学模式系统的方向迈出的重要一步，利用该系统中现有的知识、基因组资源和技术来研究热带地区更广泛的生态问题。

Understanding thermal adaptation is a priority if we wish to understand and mitigate the impacts of climate change. Organisms' current tolerances and their ability to adapt or move to new areas will determine whether they survive warming environments or not. There is currently a relative paucity of data on thermal adaptation in tropical as compared to temperate species. Tropical insects make up a large proportion of the Earth's biodiversity, but little is currently known about their ability to respond to climate change. We propose to use a well-studied group of tropical ectotherms, the Heliconius butterflies, to assess thermal adaptation across altitudinal gradients, to determine the contributions of genetic and environmental variation to these traits, and to identify the underlying genetic loci. Within Heliconius there are several instances of subspecies that also show structuring by altitude. Using population genomic sequence data and the reference genome for H. melpomene we recently showed that three subspecies pairs of H. melpomene and H. erato across altitudinal gradients exhibit divergence in regions of the genome that contain candidate genes for thermal adaptation such as metabolic enzymes and heat shock proteins. We will characterise the ecophysiology of these species, through characterisation of the physiological differences found between populations and species. Within Ecuador these species have parallel altitudinal clines on the east and west side of the Andes allowing us to assess the replicability of any trends we identify.Temperature can also be an important factor in delimiting the ecological niche and so in driving divergence and speciation. Research on the Heliconius system has largely focussed on the role of colour patterns in driving divergence between populations and species, but habitat differences are also present and thought to contribute to divergence. For example, the species pair H. melpomene and H. cydno on the western side of the Andes, which have become a classic system in speciation research, show divergent altitudinal ranges. The phenotypic differences driving divergence in habitat use have yet to be investigated, but physiological adaptations to temperature seem highly likely. Therefore, we will experimentally test for thermal adaptation differences between the sister clades H. melpomene and H. cydno/timareta, to assess the importance of temperature in determining altitudinal range and species distributions in these species.We will use the extensive genomic resources available for Heliconius to perform genome scans and detailed association mapping analyses to identify loci responsible for thermal adaptation within H. melpomene. Identifying these loci will then allow us to address the question of whether genes involved in temperature adaptation show evidence for either introgression or divergent selection between species. Sharing of temperature adaptation genes between species could allow rapid adaptation to novel environments, while divergence would suggest thermal adaptation is important in maintaining species identities.Research on Heliconius has flourished in recent years leading to many insights into the process of divergence and speciation in the genome. However, the ecological characters investigated have remained largely restricted to colour pattern. This project will be a major step towards establishing Heliconius as a more comprehensive model system for ecological genetics, making use of the existing knowledge, genomic resources and techniques available in this system to investigate broader ecological issues in the tropics.