LB 25-267 - Herbivore behavior and morphology are influenced by pathogens and climate change: Implications for multi-species interactions.

Background/Question/Methods:

Species exist in an intricate web of interactions, and thus predicting the effects of climate change should incorporate how the target species interacts with others. For example, many insect host-pathogen interactions occur within tritrophic interactions, in which the plant is the food supply of the insect host and the insect provides resources for the pathogen. In such situations, climate-driven changes to the plant could elicit changes in the host-pathogen interaction. Conversely, exposure to pathogens could change plant-herbivore interactions. We explored how drought experienced by Passiflora caerulea, the larval food plant of the butterfly Agraulis vanillae, influences the dynamics of A. vanillae and its host-specific baculovirus. Larvae were reared on one of two diet treatments (drought-stressed or high-water Passiflora plants) and exposed to one of four doses of virus (n=295 larvae total). We then measured traits affecting this plant-insect-pathogen interaction, including larval diet and butterfly oviposition preferences, as well as butterfly morphological traits.

Results/Conclusions:

We found that butterflies reared with high-water Passiflora plants preferred low-water plants both as larval diet (F(1,124)= 4.39, p= 0.04) and for oviposition site (logistic regression, LR= 38.31, p< 0.001). Intriguingly, this effect was greatly strengthened by exposure to the pathogen, consistent with our finding that larvae reared with low-water plants exhibited lower disease-induced mortality. Thus, insects appear to be choosing plants that will increase their fitness in the presence of a highly prevalent virus. Moreover, female butterflies exposed to the virus and reared under the low-water diet exhibited a smaller wing length and higher fecundity relative to their body weight, suggesting more resources might be allocated to gonads and reproduction (F(1, 42)= 4.16, p= 0.05). The change in these tri-trophic interactions suggests that P. caerulea plants suffering from drought stress under climate change might also be more vulnerable to a specialist herbivore, increasing the potential impacts of climate change on these plant populations. Together, our results suggest that climate change can alter the magnitude and outcome of species interactions which can affect ecological and evolutionary processes.