Date of Award:

5-1-2001

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Committee Chair(s)

Paul G. Wolf

Committee

Paul G. Wolf

Committee

Carol D. von Dohlen

Committee

Vincent J. Tepedino

Committee

Jon Seger

Committee

Mary E. Barkworth

Abstract

I examined the phylogenetic relationships, taxonomy, and evolution of host choice in Diadasia, a genus of New World bees. Diadasia species are particularly interesting because they are considered pollen specialists. Females of each species are believed to provision their nests with pollen from only a few closely related plant taxa. At the same time, the choice of floral hosts within the genus is diverse, and includes five distantly related plant families: Malvaceae, Onagraceae, Convolvulaceae, Asteraceae, and Cactaceae. To estimate phylogenetic relationships within this group, I sequenced ~ 2 kb of the mitochondrial genes CO I and II and tRNA leu, and ~ 1 kb of the nuclear gene EF1-α for 28 Diadasia species and five outgroup genera. A parsimony analysis produced a well-resolved phylogeny supporting the monophyly of Diadasia, but not that of traditional subgenera: Diadasia subgenus Diadasia was paraphyletic. With one exception, North and South American species formed separate clades, supporting previous hypotheses of two dispersals from South to North America. I presented a new taxonomic key for 30 North and Central American Diadasia species, and described three new species from Mexico. I used molecular markers to verify and refine my understanding of morphological characters used to distinguish similar species. Finally, I examined levels of pollen host specificity and the evolution of host choice in North American Diadasia. I analyzed the scopal pollen loads of 25 of the 30 species of North American Diadasia. Each Diadasia species showed a preference for one of five plant families. However, the 25 species varied in their level of host specificity: In 17 of the 25 species all or most specimens examined contained pure loads of one host taxon, while in eight species, some individuals carried pure loads of an unrelated, alternative host taxon. Mapping host preferences onto a phylogenetic tree indicated that Malvaceae is the ancestral host for the genus, and use of other hosts can be explained by a single switch to each of the other four host plant families. This study serves as a framework for examining putative adaptive characteristics for host use within Emphorini, the tribe to which Diadasia belongs.

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