DISSERTATION RESEARCH: The Lost Herbivores: Phylogeny and Floral Host Preferences of Callandrena Bees (Hymenoptera: Andrenidae: Andrena)

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9902301Simpson and Larkin Callandrena is a New World subgenus of ca. 80 species in Andrena, the largest genus of bees, with over 1200 described species worldwide. Preliminary analysis of DNA sequence data casts doubt on the current understanding of the subgenus; species relationships are different from what was previously thought based on morphology, and members of other subgenera are apparently nested within the phylogeny of Callandrena itself. Graduate student Leah Larkin, under the direction of Dr. Beryl Simpson at the University of Texas, will be studying the phylogeny of this group of bees, emphasizing mitochondrial and nuclear gene sequences as primary sources of data, sampled from as many species as can be collected from field work in Mexico and the U.S. The estimate of evolutionary relationships (phylogeny) which results will provide a better understanding of a large group of North American bees, and will contribute to a phylogeny, currently lacking, of Andrena as a whole. From the phylogeny, one can infer which morphological characters are too variable for classification purposes, information which may be applicable to the study of other bee groups. Additionally, the phylogeny will permit further studies of behavior and adaptation, including seasonal activity, nest architecture, and nest parasites. The subgenus Callandrena has also served as a model system for the study of the evolution of bee diet choice in pollen foraging, but the evolutionary changes in these behaviors have not been amenable to analysis without a robust phylogeny to guide interpretation of host shifts and direction of change. Bees collect pollen from flowers to provision their nests, and in so doing exhibit a range of hostplant specificity from generalist (numerous and different plant species, called polylectic) to specialist (few species, usually within a single plant family, called oligolectic) to rare cases of monolecty (use of a single plant species). While this behavior is analogous to hostplant choice in herbivorous insects in general, its evolution is poorly understood. Pollen choice in numerous species of Callandrena will be studied in the field in Mexico and the U.S., and will be inferred from analysis of pollen loads in museum specimens of bees maintained in major collections. This study will be the first to evaluate thoroughly pollen host choice in an evolutionary context in bees. The study will improve understanding of the evolution of bee behavior and the evolution of herbivory in general.