Evolution of diet breadth in Melissodes Latreille based on their phylogeny

The degree of specialization of pollinators has long interested entomologists. The traditional view holds that specialization is a derived condition that results from the selective pressures imposed by competition for floral resources and/or niche partitioning. It is now recognized that tight reciprocal evolution of bees and their hosts is an extremely rare event. Most specialist bees are pollinators of generalist flowers and most specialist flowers have generalist bees. This is explained by a conflict of interest between pollinators and their host plants. Within this theoretical framework, the evolution of generalization from specialization in bees is not only viable, it could be common. In the modern era of phylogenetic research, these hypotheses can be tested by mapping host-plant diet breadth or associations onto a phylogeny using ancestral character state reconstruction. We can investigate the frequency of host switching, possible co-evolutionary relationships, and determine the direction of the evolution of host breadth. The genus Melissodes is the second largest genus in the tribe Eucerini (Apidae) with 130 species. In a preliminary study, host data was compiled from museum labels for all species. Forty-four percent appear to be generalists (polylectic), 22% are specialists (oligolectic) on Asteraceae, 6% are oligolectic on something other than Asteraceae, and 28% of the species have no available data. The current study will use pollen samples collected directly from the scopae of the female bees to establish diet breadth and these data will be mapped onto a phylogeny based on molecular and morphological data.