Additive genetic effects in interacting species jointly determine the outcome of caterpillar herbivory

Plant-insect interactions are common and important in basic and applied biology. Trait and genetic variation can affect the outcome and evolution of these interactions, but the relative contributions of plant and insect genetic variation and how these interact remain unclear and are rarely subject to assessment in the same experimental context. Here we address this knowledge gap using a recent host range expansion onto alfalfa by the Melissa blue butterfly. Common garden rearing experiments and genomic data show that caterpillar performance depends on plant and insect genetic variation, with insect genetics contributing to performance earlier in development and plant genetics later. Our models of performance based on caterpillar genetics retained predictive power when applied to a second common garden. Much of the plant genetic effect could be explained by heritable variation in plant phytochemicals, especially saponins, peptides, and phosphatidyl cholines, providing a possible mechanis..., Neonate caterpillar was carefully transferred to a Petri dish with a sprig of fresh plant material (a few leaflets) with the stem of the plant tissue wrapped in a damp Kimwipe. We verified each caterpillar was alive and uninjured after transfer. The Petri dish containing the caterpillar was then returned to the incubator. Caterpillars were given fresh leaf tissue ad libitum and were checked daily for survival, pupation and eclosion as adults.
As metrics of performance, we measured 8-day and 14-day caterpillar weight, and weight at pupation using a Mettler Toledo XPE105 analytical microbalance (Mettler Toledo). Weights were recorded to the nearest 0.01 mg, and we took the mean of two independent weight measurements. We then considered the following nine performances metrics: 8-day caterpillar weight (mg), 14-day caterpillar weight (mg), weight at pupation (mg), survival to 8 days (binary), survival to 14 days (binary), survival to pupation (binary), survival to adult (binary), total surv..., All data files are ASCII text and can be opened with any text editor.