My research focuses on multi-trophic interactions between plants, herbivores, and natural enemies. Specific avenues of study include: (1) patterns of infection in insects and causal mechansisms (2) ecoimmunology and the evolution of diet breadth in insect herbivores (3) chemical ecology of the insect immune response (4) evolution and maintenance of diversity in tropical communities.
Patterns of infection
Insect-pathogen interactions are a critical component of community interactions. Using the Junonia coena densovirus (JcDV) we have explored how biotic (host plants, immunity), and abiotic (temperature, seasonality)affect patterns of infection for a number of different lepidopteran species. We are also exploring the extent to which this pathogen occurs in natural systems, investigating the geographical range including tropical montane and lowland forests in Costa Rica and Ecuador.
Ecoimmunology and diet breadth
Ecoimmunology is a relatively recent field of study that highlights questions in ecology that can be addressed by understanding the immunology of the study organism. My lab seeks to understand the evolution of diet breath by investigating the role that diet plays in determining the strength of the immune response. Recent work in the lab has focused on the interaction between plant chemistry, egg microbes, and an insect virus on the immune response of a specialist caterpillar. Results from this work show that caterpillars are better protected from the virus when feeding on host plants with high concentrations of a natural product (iridoid glycosides) and when they have a full compliment of microbes from their egg casing. The protective role of chemistry and microbes show a benefit to feeding on particular host plants.
Chemical ecology and the immune response
Recent publications from my research program elucidate the effects of plant chemistry on caterpillar resistance to parasitism. In particular, I and collaborators have shown that specialist buckeye caterpillars exhibit a decrease in immune function due to sequestration of plant secondary metabolites, making them more susceptible to parasitism and pathogens. In contrast, my research with dietary generalist caterpillars (woolly bears) indicates that plant chemistry can help to defend from parasitism. These two very different effects of plant chemistry on herbivore resistance are a result of the unique adaptations of specialist versus generalist herbivores. While generalist herbivores can choose plants according to physiological needs, specialist herbivores are more constrained to a particular diet. These two foraging strategies are likely the evolutionary result of a suite of different community variables, with natural enemies undoubtedly standing out as an extremely important source of selection pressure.
A central goal of ecology is to understand the origin and maintenance of biodiversity. In particular, understanding the enormous diversity in tropical communities has been a serious challenge. Our research group addresses this challenge by using a well-studied tropical system composed of plants (Piper), specialist caterpillars (Eois) feeding exclusively on this group plants, and a group of specialist wasps (Microgastrines) that attack the caterpillars. The diversity within each of these groups is enormous (>2,000 species), and our goal for this project is to better understand the evolution of biodiversity by testing specific hypotheses addressing patterns of plant chemical evolution and the role of plant chemistry in biodiversity. To address these hypotheses, our collaborative group consists of two chemists (Chris Jeffrey for synthesis and Craig Dodson for natural products) to elucidate the plant chemistry, one molecular ecologist to reconstruct the evolutionary history of Eois (Matt Forister), and three systematists to identify and describe Piper plants (Eric Tepe and Alejandra Jaramillo) and Microgastrine wasps (Jim Whitfield), and three chemical ecologists (Lee Dyer, Lora Richards, me) to describe the interaction between each group.
The hypothesis that the evolution of one organismal group (i.e. plants) can affect the evolution of another interacting group (i.e. caterpillars) is not a new idea; however, our approach to address this hypothesis is novel, as we focus on multiple trophic levels (plants, caterpillars, wasps), which has rarely been undertaken. In addition, our diverse collaborative team allows us to thoroughly explore all aspects of this system to yield high explanatory power for the question addressed.