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Ecological and genetic perspectives on dispersal in European Shags (Phalacrocorax aristotelis)

Barlow, Emily J.. 2011 Ecological and genetic perspectives on dispersal in European Shags (Phalacrocorax aristotelis). University of Aberdeen, PhD Thesis, 205pp.

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Abstract/Summary

Dispersal is a fundamental ecological and evolutionary process that can create demographic and genetic linkage between neighbouring and distant locations, influencing the dynamics, structure and ultimately the persistence of populations. To understand observed population dynamics and structure and to predict future change, comprehensive data are required describing the patterns of dispersal and gene flow across all relevant spatial scales. However, this is a major empirical challenge, particularly for species that disperse across considerable distances; long-distance dispersal may be underestimated and gene flow can be difficult to infer from observed population genetic structure. In this thesis I aimed to obtain rigorous and comprehensive empirical data quantifying natal dispersal patterns and population genetic structure across multiple spatial scales using the European shag (Phalacrocorax aristotelis) as a model species. I used a combination of direct field observations of shags individually ringed on the Isle of May, Scotland and indirect molecular genetic techniques to accomplish these aims. By locating adult shags that had been ringed as chicks on the Isle of May at their breeding locations across eastern Scotland, I demonstrated divergent dispersal distributions at small versus large spatial scales. Specifically, >99% of shags dispersed within the Isle of May but only c.10% dispersed from it. Furthermore, long-distance dispersal from the Isle of May was directional but did not mirror that observed at the within-population scale. Large-scale observations of ringed shags at non-breeding locations provided an independent means to validate breeding season estimates and suggested that the probability of detecting a ringed breeding adult was high (98%). Using both mitochondrial DNA markers and a newly developed set of microsatellite markers designed specifically for shags, I quantified population genetic structure and variation across 20 populations at a pan-European scale, covering two subspecies. I found weak population genetic structure across both molecular markers suggesting a role for occasional effective long-distance dispersal. Genetic variation across this large spatial scale also pointed to a potential role for historical gene flow and population dynamics. Furthermore, only one private mitochondrial haplotype was found among 5 subspecies, suggesting that this current taxonomic subdivision may not be mirrored by genetic isolation. However, a suite of evolutionary forces besides gene flow can create observed population genetic structure. Therefore, I quantified population genetic structure across populations in eastern Scotland, and quantitatively linked this indirect estimate of gene flow with my direct field observations of dispersal. This allowed me to gain insights into the processes underlying observed population genetic structure and the reliability of gene flow inference from field observations. I achieved this by simulating genotypes based on observed dispersal rates and distributions and testing whether the pattern and magnitude of gene flow inferred from observed dispersal alone was sufficient to quantitatively predict observed population genetic structure. Dispersal parameters derived explicitly from field observations and the spatial organisation of populations were shown to strongly influence observed population genetic structure. Overall, these data demonstrate the need to utilise both field observations and genetic methods to comprehensively estimate the extent and effectiveness of dispersal. Furthermore, these data provide current and accurate estimates of long-distance dispersal, which is difficult to achieve but urgently needed in order to understand and predict the long-term consequences of environmental change.

Item Type: Publication - Thesis (PhD)
Programmes: CEH Topics & Objectives 2009 onwards > Biodiversity
CEH Sections: Watt
Additional Keywords: Phalacrocorax aristotelis, population genetics, dispersal, microsatellites, Shag, phylogeography
NORA Subject Terms: Ecology and Environment
Date made live: 30 Jan 2012 12:25
URI: http://nora.nerc.ac.uk/id/eprint/16537

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