Michael Braun

I. Hybrid zones and speciation assesses the origin, structure and maintenance of avian hybrid zones within the conceptual framework of speciation. Because they are rich in genetic variation, such zones offer special opportunities to observe how microevolutionary processes produce patterns of geographic diversification. Three case studies are currently underway on manakins, chickadees, and marsh wrens. In the manakin case, sexual selection may be driving introgression of colorful male plumage traits across the zone (Parsons et al. 1993). In chickadees, selection against hybrids and tight ecological coupling seem to be structuring the zone. In marsh wrens, the distinctive song repertoires of males appears to provide a basis for assortative mating, which may be enhanced by character displacement in song types.

II. Genetic structure and diversity of avian populations examines variation within and among avian populations in relation to biogeographic history, environmental change and life history parameters. One project has examined the loss of genetic diversity in Whooping Cranes, as this species went through a drastic population bottleneck to become critically endangered. DNA derived from museum skins was used to assess variability in historical populations before the bottleneck. Another project is looking at population structure and diversity of two North American songbirds - Swainson's Warbler and Black-throated Blue Warbler - that migrate to the Neotropics, but whose populations are in decline.

III. Phylogenetic studies of birds and mammals - Three systematic studies are in progress: 1) development of the nuclear oncogene c-myc into a new model system for molecular phylogenetics as well as to gain insight into the radiation of modern birds; 2) systematics of caprimulgiform birds using cytochrome b and c-myc gene sequences to assess relationships and age within this poorly known group. Results to date indicate that the group is very old and diverse; 3) phylogeny of Marmota - Cytochrome b sequence data have been collected on all species of this Holarctic group. The phylogeny is expected to help us understand how often this group has crossed the Bering land bridge, and in what direction.

• In Press. Harshman, J., C. J. Huddleston, J. P. Bollback, T. J. Parsons, and M. J. Braun. True and false gharials: a nuclear gene phylogeny of Crocodylia. Systematic Biology.
• In Press. Bronson, C. L., T. C. Grubb, Jr., and M. J. Braun. Endogenous selection in a narrow hybrid zone: a manipulative experiment. Evolution.
• In Press. Braun, M. J., M. B. Robbins, C. M. Milensky, B. J. O'Shea, B. R. Barber, W. Hinds and W. S. Prince. New birds for Guyana from Mts. Roraima and Ayanganna. Bull. Brit. Orn. Club.
• In Press. Bronson, C. L., T. C. Grubb, Jr., G. D. Sattler and M. J. Braun. Mate choice: A possible causal mechanism for a moving hybrid zone. Animal Behaviour.
• 2001 Brumfield, R. T., R. W. Jernigan and M. J. Braun. Evolutionary implications of divergent clines in a manakin (Manacus; Aves) hybrid zone. Evolution 55: 2070-2087.
• 2001 McDonald, D. B., R. P. Clay, R. T. Brumfield and M. J. Braun. Sexual selection on plumage and behavior in an avian hybrid zone: experimental tests of male-male interactions. Evolution 55:1443--1451.
• 2001 Brumfield, R. T. and M. J. Braun. Phylogenetic relationships in bearded manakins (Pipridae:Manacus ) indicate that male plumage color is a misleading taxonomic marker. Condor 103:248-258.

Ph.D., Louisiana State University Medical Center, 1983.

Molecular approaches to evolutionary biology; recovering genetic information from ancient DNA; avian hybrid zones.