| Summary: | Understanding how evolutionary forces shape population genetic structure is a principal goal of evolutionary geneticists. Guillemots (Aves: Charadriiformes: Alcidae: Cepphus) provide useful systems for investigating population genetic differentiation in a genus with a wide geographic range that disperses according to a one-dimensional stepping stone model. Guillemots may also be highly vulnerable to climate change in parts of their range. For this reason, identifying population genetic structure is important for their successful management and conservation. I used various genetic markers and methods to assess population genetic variation in pigeon guillemots (C. columba) and black guillemots (C. grylle). In both species, I found evidence of limited dispersal and restricted gene flow between distant populations. Genetic differentiation appeared to follow a pattern of isolation by distance in both species. In pigeon guillemots, evidence suggested that population genetic structure arose through a combination of both historical and contemporary processes. Based on my results, I recommend that pigeon guillemot subspecies be revised. I also suggest that pigeon guillemot populations in the Aleutian Islands be considered for designation as an evolutionarily significant unit (ESU) as their differentiation has been strongly influenced by historical processes. Population genetic structure in black guillemots did agree with current subspecies delineations. Based on the level of variation detected within the subspecies however, I would recommend that black guillemots be treated as management units. The results from this study hold promising insight into how patterns of gene flow can lead to different patterns of population genetic structure. M.Sc.
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