Experimental evolutionary genomics of herbivorous insects on multiple host plant species
Authors: Diler Haji 1; Andrew Gloss 2; Noah Whiteman 1
Affiliations: 1) University of California, Berkeley; 2) University of Chicago
Keywords: Experimental evolution
Despite decades of progress, a major question in evolutionary biology is how so much functional genetic variation within species is segregating when genetic drift and both positive and negative selection should drive its loss. Balancing selection may explain how much of this variation is maintained. In the broadest sense, balancing selection can act through a variety of mechanisms including spatially- and temporally varying selection (STVS). In 1953, Howard Levene proposed a compelling model of STVS that has largely been untested. In this model, viability selection across niches in a randomly mating diploid population ensures the maintenance of alternative alleles without heterozygous advantage. This mode of balancing selection is particularly relevant to insect herbivores – plant parasites that feed on an assortment of different host plants containing varying chemical defenses (i.e., host “chemo-niches”). We tested the Levene model by experimentally evolving the herbivorous leaf-mining drosophilid fly Scaptomyza flava for 11 generations on monocultures or mixtures of two natural and chemically divergent mustard host plants, Barbarea vulgaris and Turritis glabra, and then compared our experimental findings with wild-caught populations from both host plants. We found that S. flava evolved to become strongly local adapted to each monoculture. Using a pooled genome sequencing approach, we found preliminary evidence that evolution on monocultures led to a stronger reduction in genetic diversity genome-wide than evolution on mixtures in some monoculture populations. We compare these results to wild samples of S. flava reared from their two natural host plant species. These results suggest that STVS may contribute to the maintenance of functional genetic diversity directly as a result of biotic interactions at the plant-herbivore interface.