Dissertation Research: Hybridization between the Western Gull (Larus occidentalis) and the Glaucous-winged Gull (L. glaucescens)

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Douglas Bell, a doctoral student working under the direction of Dr. Ned Johnson at the University of California..Berkeley, is working on an ambitious study of geographic variation in the Western and Glaucous.winged Gulls and a hybrid zone between the two. The Western Gull is an important coastal species ranging from the Baja Peninsula north along the Pacific coast to southern Washington where it gives way to the Glaucous.winged Gull which ranges northward to the western most Aleutian Islands; the hybrid populations occur from northern Oregon through Washington. Although hybridization among gull species (genus >Larus>) is often cited as an example of the process of species formation, the actual extent, nature and origin of hybridization among the gulls is poorly known. Bell proposes to address three conceptual foci: 1) geographical variation in the parental species, 2) the type of hybrid zone (is the hybrid zone stable, are hybrids selected against, are hybrids favored by selection in an ecologically intermediate area of overlap?), and 3) the origin of the hybrid zone in a historical context. The study will involve field work to collect specimens, to collect data on reproductive success in hybrid and non.hybrid pairings, on assortative mating and on vocalizations, and to make field observations on behavior. Characterizations of geographic variation will be made on hybrid index scores based on plumage color variation and other "soft" part color variation (iris color, leg color, etc.), on statistical analysis of skeletal measurements and at the molecular level. The study of species that are so closely related that they still hybridize (albeit on a limited basis) provide opportunities for dissecting the genetics and evolutionary processes that lead to the origin of species.