Danush Vasan Viswanathan, Ph.D. candidate

Specificity of induced plant responses to multiple herbivore species: Consequences for patterns of herbivore abundance in the field

    I started in the Thaler lab in the fall of 2000.  Generally, I’m examining specificity of induced plant responses to the different herbivore species that share Solanum dulcamara (bittersweet nightshade) as a host plant.  The particular questions I’m addressing include:

1.      Can specificity of induced plant responses affect herbivore abundance in the field?  Different herbivore species can elicit different phenotypic responses in a given host plant.  In addition, herbivore preference and performance can vary with host phenotype.  Hence, priority of herbivore colonization and damage in the field may influence the subsequent abundances of herbivores on a plant over the course of a growing season.  Using manipulative and observational field experiments with different initial damagers in a patch of plants, I’ve found both short-term and long-term within-season priority effects on the abundance of multiple herbivore species.  These effects have been consistent across field seasons.

2.      Can specificity of induced plant responses influence herbivore population dynamics?  In the previous study, priority effects on herbivore abundance occurred within a patch of plants.  At a larger spatial scale, where birth, death, immigration and emigration create local populations, whole plant patches with different histories of damage may produce differently sized herbivore populations over time.  I’ll be addressing this possibility with a manipulative field experiment this coming summer.

3.      Does specificity of plant response to herbivore damage affect rates of predation by the natural enemies of herbivores?  A field experiment in collaboration with Cesar Rodriguez-Saona (a post-doc in the Thaler lab) has suggested that generalist predators do not discriminate between herbivores found on different induced plant phenotypes.  Future field experiments will examine rates of attraction of specialist parasitoids to plants with different histories of damage.

4.      Since herbivores often share more than one host plant species, can the relative herbivore performance be affected by which of the plants has received damage, and the identity of the initial damager?  I’m currently developing this idea with Tara Nicholls, an undergraduate honours thesis student.

Email: danush@botany.utoronto.ca