The evolution of a pollen diet: Host choice and diet breadth of Andrena bees (Hymenoptera: Andrenidae)Leah L. Larkin1, 2, John L. Neff3 and Beryl B. Simpson1
1 Section of Integrative Biology, The University of Texas at Austin, Austin, Texas 78712, USA
2 Present address: Department of Biology and Museum of Southwestern Biology, MSC 03 2020, University of New Mexico, Albuquerque, NM 87131, USA
3 Central Texas Melittological Institute, Austin, TX 78731, USA
(Received 18 June 2007 - Revised 1 November 2007 - Accepted 14 November 2007 - Published online 12 February 2008)
Abstract - We investigate of two aspects of pollen diet of Andrena bees: the evolution of diet breadth within nearctic representatives of the genus, which includes both polylectic and oligolectic species; and host choice within an oligolectic clade of Andrena. We also evaluate phenology. Traits were mapped onto a molecular phylogeny to identify the ancestral character states. Overall, oligolecty appears to be the basal state within Andrena, and broader diets have evolved a number of times, suggesting that specialization is not a "dead end". Within the oligolectic clade studied, host shifts occur predominantly between members of the same plant tribe, indicating a phylogenetic constraint to host-usage; however, shifts to other tribes are not uncommon, and may lead to adaptive radiation. Additionally, some lineages retain the ability to use pollen from an ancestral host-plant tribe. Finally, we find a correlation between using host plants in the family Asteraceae and fall emergence.
Key words: Andrena / diet breadth / host choice / pollen / specialization
© INRA, DIB-AGIB, EDP Sciences 2008