Research Interests
I would probably be best described as an "Evolutionary Ecological Entomologist."
I am generally interested in evolutionary biology and ecology, and in uniting these fields to study insect diversity, how it is organized, and how it has originated. Some of my more specific interests include the ecological organization of insect communities, processes of population differentiation and adaptive radiation, the evolution and ecological consequences of species interactions (especially tritrophic interactions), phylogenetic systematics of parasitoid insects, and the behavioral ecology of parasitoids. I am particularly fascinated by parasitoids and their ecological and evolutionary interactions with hosts. One such group that I have spent a number of years studying is the Tachinidae, a very diverse (10,000+ desc. spp.), abundant, and poorly known family of parasitoid flies that attack insects and other arthropods. I find the morphology, behavior, and ecology of several other parasitic/predaceous groups of Diptera such as Asilidae, Bombyliidae, intellectually and aesthetically fascinating was well. Plant-insect interactions, primarily dealing with caterpillars and Cecidomyiid gall midges, are another major area of interest that I have been pursuing with a number of collaborators (see below). Some of the primary areas of research that I am pursuing are described in more detail below.
Lespesia prob. datanarumAutomeris with tachinid egg
Speciation and coevolution between plants, herbivorous insects, and parasitoids
In my collaborative work with John Nason (Iowa State) and Steve heard (U. New Brunswick) I examined the process of host race formation of insect herbivores on two sympatric species of golden-rod. We gathered evidence that several herbivore species have differentiated into genetically distinct host races on these two plant species, supporting an important role for sympatric speciation in herbivorous insects. In addition, we found tantalizing evidence in two cases where the parasitoids of these herbivores appear to be following suit, suggesting the possibility of "cascading host-race formation". If this one model system is indicative of diversification processes and patterns in other host-parasite systems (both plant-herbivore and herbivore-parasitoid trophic interactions), it supports the view that much of the immense diversity of herbivorous and parasitoid insects may have arisen due via ecological speciation associated with tritrophic interactions. I continue to use population genetic and phylogeographic tools to explore population differentiation in insect herbivores and their parasitoids, and to reconstruct population level histories of parasitoid species that vary in geographically in host use.
Recently, Patrick Abbot (Vanderbilt U.) and I were awarded an NSF grant to study the adaptive radiation of another herbivore that feeds on goldenrods (Solidago sp.), gall midges in the genus Asteromyia. Although, taxonomically described as a single species, genetic data suggests that populations of these gall midges are undergoing a cryptic but extensive adaptive radiation on to different Solidago species. An especially interesting aspect of this adaptive radiation is that it is likely strongly influenced by a symbiotic fungus necessary for the formation of Asteromyia galls as well as a diverse suite of parasitoid wasp enemies.
Use of phylogenetic methods to explain the evolution of behavior, life histories, and ecological traits in parasitoids
My interest in phylogenetic biology is primarily driven by questions of how behavioral, morphological, and ecological characteristics evolve and how speciation proceeds in "parasitic" organisms. A phylogenetic study that I conducted on Tachinidae, represented the first large-scale phylogenetic analysis of the family and the first application of molecular data to understand evolutionary relationships within this group. In addition, it allowed me to examine the evolution of a number of ecologically important traits including the origination of host-piercers in females, ovovivipary and egg morphology, and associations with adult host stages. I plan to continue analyzing phylogenetic relationships in the Tachinidae using molecular and morphological data with the goals of reconstructing the evolution of reproductive strategies and understanding how they are associated with the range and character of hosts attacked.
Perhaps the most interesting result of these phylogenetic analyses was the finding that polyphagy evolved numerous times within the family and almost all reconstructed transitions indicate the evolution of generalists from more specialized ancestors. This result contradicts the traditional paradigm that specialized lineages are derived from more generalized ancestors and that it strictly limits future evolutionary opportunities.
Tritrophic interactions between parasitoids, host insects, and plants
I am broadly interested in multitrophic interactions between parasitoids and their hosts, and herbivores and their host plants over both ecological and evolutionary time scales. I find most intriguing the dynamic interplay between natural enemies, their herbivorous insect hosts, and the plants upon which these herbivores feed; particularly in how parasitoids may interact with host plants to shape herbivore niches and how herbivore niches influence parasitoid community structure. Attempts at explaining patterns of insect-plant associations, such as the high degree of specialization among herbivorous insects, have traditionally focused only upon the direct, usually physiological, interactions between herbivores and plants. It has now been realized for some time that natural enemies such as parasitoids may play a significant role in shaping herbivore niches, however, our understanding of how they do this and their importance relative to other factors is only in its infancy. Thus, I am interested in exploring questions such as: What is the role of enemy free space in structuring herbivore-plant associations? Does pressure from natural enemies influence the propensity for speciation in herbivorous insects? How do mechanisms of host location in parasitoids influence behavior and host plant use of their hosts? How do traits of hosts affect the character and size of their parasitoid assemblages?
Parasitoids represent a significant fraction of all insect species, they are often important in shaping population dynamics of other insects, and they likely represent strong selective forces in most terrestrial ecosystems. In order to understand how and why parasitoids have diversified taxonomically, morphologically, and physiologically, it is necessary to know how they interact with their hosts and with their hosts food plants. My previous explorations of ecological variation in tachinid parasitism and behavioral mechanisms of host location and selection, were designed to establish ecological patterns and investigate their mechanistic causes. These studies have led me to hypothesize that mechanisms of host location are instrumental in determining the types and breadth of hosts attacked, and may have important consequences for population dynamics and speciation of tachinid parasitoids.
"tri-trophic" photo by Mike Singer
Insect Behavioral Ecology
While studies of parasitoid behavior have flourished and made many important contributions to areas such as insect learning, behavioral ecology, and population ecology, almost all of this work has focused on a single clade of parasitoids, the parasitic wasps (Hymenoptera). However there are many other groups of insects (and other organisms) that share this parasitoid lifestyle and thus face similar ecological pressures. By working with one of these important yet understudied groups, I hope to provide insight into how parasitoids have converged on similar behavioral strategies to attack their hosts, as well as how they differ due to their disparate life histories, phylogenetic histories, morphologies and physiologies. I am particularly interested in how host ranges in insect parasitoids are determined at a both the proximate mechanistic level and the ultimate evolutionary level. Research that I have conducted regarding host location and selection in tachinid parasitoids and herbivorous insects suggests that many of large scale ecological patterns of host use in these organisms can be best understood by examining the behavior of individual females.
