Farrell Lab @ Harvard University

Chris Elzinga

[currently on leave]

Research Interests

A high proportion of host-plant specialists has been a common observation among phytophagous insects. Indeed, the diversity of phytophagous insects has long been supposed to be a result of specialized plant feeding, but the means by which specialization influences diversity remain controversial.

Specialization may strongly influence the likelihood of speciation, since genetic isolation is a necessary condition for speciation. In other words, similar forces (perhaps specialization) may be at work along a continuum from population differentiation to speciation. With this background, several questions come into focus:

1. What are the effects of niche-breadth change on the population dynamics of a given species?
2. Do these changes in dynamics lead to a change in the likelihood of speciation?
3. Can the direction of the shift be characterized for the particular group at hand (i.e. more often from generalist to specialist or from specialist to generalist, see Kelley and Farrell 1998)?

To address these questions, I have chosen to study the Cerambycid genus Crossidius in detail. Crossidius species vary in their diet breadth, ranging from those that feed on a subset of one plant species to those that feed on plants from as many as three genera. The genera of host plants for these insects are Chrysothamnus, Gutierrezia, Isocoma (formerly placed within "Haplopappus"), and Ericameria, a close relative of Chrysothamnus. All of these genera are within the tribe Astereae of the Asteraceae.

Multiple locales where both specialist(s) and generalist species have been sampled which may be the best way of comparing different species population genetics within the genus. Further efforts this year will hopefully provide a complete collection of the species in the genus.

In summary, collecting of all fourteen Nearctic Crossidius species with substantial geographic breadth for the sampled species across their Western North American range is underway. Numerous specific sites carry local Crossidius populations in abundance, and are providing the sampling depth necessary for rigorous investigations of population histories and dynamics. These investigations will include comparisons of population dynamics for specialist and more generalist Crossidius species, a molecular phylogeny of the genus, and a phylogeographic interpretation of the sampled populations.