Experimental niche evolution in seed beetles: Simulating responses to climate change in a currently evolving global crop pest

目前气候正在以前所未有的速度变化，许多生物正在以剧烈的范围变化来应对这些变化，其中包括进化反应。受气候变化影响最严重的生物是昆虫等小型放热动物，它们可以迅速进化并迅速分散到可用的生态位，往往对粮食安全（作为作物或储存食品害虫）、人类和动物福利（作为疾病媒介）构成新的威胁，并影响整个生态系统功能在快速变化的气候下，进化和范围转移的机制仍然知之甚少。其中一个问题与性状分化的顺序有关，这对生物多样性如何受到环境变化的影响有着重要的影响。在种群分化的a生态位优先模型中，生物首先进化出与其群落内生态位（即a生态位）相关的特征，如资源利用的替代模式、物种相互作用和微生境利用。与当地栖息地相互作用的新方法可以通过提供新的方法来克服先前的地理限制，从而促进范围的扩大。相反，在b生态位优先的情况下，环境变化导致范围转移（即对新生境和新地点的适应）先于或取代局部a生态位分化这些可供选择的情景都对生物如何长期应对气候变化具有重要意义。b优先级意味着精细尺度的局部适应范围有限，这可能会限制那些在气候变化中无处可去的生物的成功，而a优先级表明气候变化可能引发成功的入侵和适应性辐射。在各种自然系统中都发现了上述每种情况，但目前尚不清楚每种进化途径的一般条件。在这个博士项目中，学生将在一个圈养的种子甲虫（鞘翅目：Bruchidae）实验室群体中，利用准自然选择下的实验进化，研究这些替代生态位进化场景可能发生的条件。种子甲虫是世界范围内储存的豆类和谷物的主要害虫，并已被证明在应对气候变化的过程中进化出当地寄主-植物转移（栖息地利用，a生态位成分）和与进化的热耐受性相关的范围转移（b生态位成分）Jörgen Ripa（隆德大学）开发的动态模型表明，a生态位与b生态位进化的优先级取决于栖息地转移与替代资源利用所施加的进化权衡的相对优势，也取决于扩散能力。该学生将在具有连通性的两个栖息地场景中进行复制谱系的实验进化，其中栖息地的特征是不同的热状态。在每个栖息地内，个体也将有机会适应新的资源（即新的种子类型）。栖息地内的气候变化速率、种群密度、栖息地之间的扩散速率以及初始谱系的先前适应将被独立操纵。Jörgen Ripa开发的生态位进化路径的动态模型将为实验提供信息，我们的实验结果将完善和参数化未来的模型。对所得到的世系进行控制杂交试验，将揭示生境和资源利用轴上生态位分化的定量遗传基础，为观察到的格局提供机制解释。该项目还可以进一步发展，纳入基因组方法，以了解生态位进化的机制。该项目的产出将进一步发展进化理论，特别是在生态位进化领域，并将为虫害管理决策提供信息。

Climates are currently changing at an unprecedented rate, and many organisms are responding to these changes with dramatic range shifts involving evolutionary responses. Among the organisms most strongly affected by changing climates are small, exothermic animals such as insects, which can evolve rapidly and quickly disperse into available niches, often posing new threats to food security (as crop or stored-food pests), human and animal welfare (as disease vectors), and affecting overall ecosystem function.1 The mechanisms of evolution and range shift under rapidly changing climates remain poorly understood. One question relates to the order of trait divergence, which has important consequences for how biodiversity is affected by environmental change. In a model of a-niche priority for population divergence, organisms first evolve traits related to their within-community niche (i.e., the a-niche), such as alternative patterns of resource-utilization, species-interaction, and microhabitat use. New ways of interacting with their local habitat may then facilitate range expansion by providing new ways to overcome prior geographic limitations. Conversely, under b-niche priority, environmental change induces range shifts (i.e., adaptation to novel habitats and locales, the b-niche) prior to or in lieu of local, a-niche differentiation.2 These alternative scenarios each have important implications for how organisms respond to changing climates over the long term. b-priority implies limited scope for fine-scale local adaptation, which may limit the success of organisms that have nowhere suitable to go as climates change, while a-priority suggests that climate change may trigger successful invasions and adaptive radiations. Each of these scenarios has been found to occur in a variety of natural systems, but the general conditions favouring each evolutionary pathway are currently unknown. In this PhD project, the student will investigate conditions under which these alternative niche evolution scenarios may occur, using experimental evolution under quasi-natural selection in a captive lab colony of seed beetles (Coleoptera: Bruchidae). Seed beetles are major pests on stored legumes and grains worldwide, and have been shown to evolve local host-plant shifts (habitat utilization, an a-niche component) and range shifts associated with evolving thermal tolerances (a b-niche component) in response to changing climates.3 Dynamic models developed by Jörgen Ripa (Lund University) suggest that the priority of a- vs. b-niche evolution depends on the relative strengths of evolutionary trade-offs imposed by habitat shifts vs. alternative resource use, and also by dispersal capacities. The student will conduct experimental evolution of replicate lineages in a two-habitat scenario with connectivity, where habitats are characterized by alternative thermal regimes. Within each habitat, individuals will also have the opportunity to adapt to new resources (i.e., new seed types). Rates of climate change within habitats, population densities, dispersal rates between habitats, and prior adaptations of initial lineages will be independently manipulated. Dynamic models of niche evolution pathways developed by Jörgen Ripa will inform experiments, and our experimental results will refine and parameterize future models. Controlled crossing experiments of resulting lineages will indicate the quantitative genetic basis of niche divergence along habitat and resource utilization axes, providing a mechanistic explanation for observed patterns. The project can also be further developed to incorporate genomic methods for understanding the mechanisms of niche evolution. The outputs of this project will further evolutionary theory, particularly in the area of niche evolution, and will inform pest management decisions.