Ecological contexts of balancing selection in nature
Presented by: Dr Lauren Carley
November 5th at 12:30pm EST
How genetic variation is maintained in the face of persistent natural selection is a central question in evolutionary biology. Neutral models of mutation-selection balance are possible, but do not explain intermediate-frequency polymorphisms that have been observed in many populations and species. An alternative explanation is balancing selection, in which natural selection actively maintains polymorphisms at higher than neutral levels over space and/or time. This phenomenon is frequently invoked, but rigorous tests demonstrating balancing selection operating in nature are scarce, particularly on complex traits, which frequently display high levels of variation. Moreover, balancing selection is an evolutionary process that may be generated by a variety of mechanisms, including overdominance, spatial and temporal variation in selection, frequency-dependent selection, and antagonistic pleiotropy, which may result from diffuse and/or multivariate ecological interactions.
Focusing on a biochemical polymorphism in the wildflower Boechera stricta (Brassicaceae), we use tractable genetic tools in field and greenhouse experiments to elucidate the molecular underpinnings of ecological plant-herbivore interactions and fitness in nature. Further, we use population modeling to investigate the role of ecological variation and covariance in determining lifetime fitness. Together, these approaches suggest that variation in secondary metabolic profiles in B. stricta may persist at present due to balancing selection, and may continue to persist in the future under a range of varying environmental scenarios, offering an integrated perspective on the forces contributing to the maintenance of natural variation.