Intricate interactions: investigating plant defence strategies to deal with multi-herbivore attack and their fitness consequences in Brassicaceae.

Plants are subjected to a plethora of herbivorous insects which can exert opposing selective pressures on plant traits. In a multi-herbivore environment, individual plants induce their defence after herbivore attack but also have to anticipate future attacks to ensure reproductive success. Relatively little is known about how variation in plastic (defence) traits corresponds with temporal assembly of insect communities on individual plants. Therefore, the aim is to investigate the drivers of multiherbivore community assembly on plants and the effects on plant fitness, by 1) synthetizing and quantifying current knowledge about the effects of multi-herbivore attack on plant defence; 2) establishing which plant defence strategies are conserved across Brassicaceae plants by studying altered susceptibility after attack by different feeding guilds of insect herbivores; 3) elucidating how variation in plant defence strategies corresponds with temporal assembly of insect communities on individual plants across Brassicaceae; 4) investigating which (a)biotic factors contribute to temporal variations in insect community structure on Brassica nigra; 5) demonstrating how a single herbivore species may alter assembly of insect communities and Brassica nigra fitness. The methods to study both intra- and interspecific variation in plant defence are common garden experiments using the Brassicaceae plant family as model system. Also, in- and exclusion treatments will be used for herbivorous insects to investigate priority effects in community assembly. Additionally, a greenhouse experiment will be performed to assess the interspecific variation in plant defence to attack by different feeding guilds.