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

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.