Rapid evolution in an herbivore biological control agent: simultaneous adaptation to novel host and climate
Herbivores that are introduced for biological control of weeds are tested prior to release for their host specificity and tolerance of climatic conditions in the target area. However, the potential for rapid evolution in traits related to climate or host specificity makes introductions of biological control organisms less predictable and raises concerns about safety and effectiveness of biological control practices. While much is currently known about rapid adaptation to climate factors alone, the goals of this project were to assess how rapid adaptation of an herbivore biological control agent changes the effects of climate and host plant species. Specifically, we conducted a fully factorial, reciprocal transplant experiment along an elevational gradient to test how adaptation of the biological control agent Tyria jacobea to a novel mountain climate and non-target host affects range expansion.
We found that survival in the ancestral setting (ancestral host and valley climate) did not differ between mountain and valley genotypes, but survival in the mountain climate and on the novel host was significantly higher for the mountain compared to valley genotypes. This confirms rapid adaptation to both climate and novel host plant in populations undergoing range expansion.
In both environments, development time was significantly shorter for the mountain genotype than for valley genotype (reflecting the shorter growing season in mountain enviornments) and significantly longer on novel host plants (reflecting some intial level of maladpation to new hosts).
Our findings represent a rare case of rapid simultaneous adaptation to host plant and climate in populations undergoing range expansion. This means evolution should be incoporated in models of range expansion, biological invasion, and biotic responses to recent climate change. For biological control, this means potential for rapid adaptation in biological control organisms should be incorpoated into risk analyses assessed prior to release .