Population differentiation and evolution among thick-billed (Uria lomvia) and common murres (U. aalge)

Birt-Friesen, V. L. (1992) Population differentiation and evolution among thick-billed (Uria lomvia) and common murres (U. aalge). Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The genetic structure of animal populations determines their potential for local adaptation and speciation. Most birds are highly mobile and accordingly have little genetic structuring, but some are strongly philopatric and exhibit substantial differentiation. In the present study, population differentiation and evolution were examined within two strongly philopatric seabird species, thick-billed (Uria lomvia) and common (U. ciat^e) murres, using morphometries, protein electrophoresis and nucleotide sequence analysis of amplified mitochondrial DNA (mtDNA). -- Four of five morphological measurements differed significantly both among three western Atlantic colonies of thick-billed murres, and between eastern and western Atlantic colonies. Electrophoretic analysis of 18 nuclear-encoded proteins indicated Utile genetic differentiation either among western Atlantic colonies, or across the Atlantic. Eighteen genotypes, defined by 16 variable nucleotide sites, were found within 253 base pairs (bp) of cytochrome b among 239 thick-billed murres from five Atlantic and two Pacific colonies. Significant genetic differentiation was found between Atlantic and Pacific thick-billed murres, concordant with geographic separation of the populations. Little genetic differentiation was found either among western Atlantic colonies, or across the Atlantic. The apparent genetic homogeneity of Atlantic colonies is inconsistent with evidence of strong natal philopatry and phenotypic differentiation of colonies, and may result from gene flow and/or recent colonizations by large founder populations. -- Common murres from Hornoya, Norway were significantly larger than those from Funk Island, Newfoundland in all of five dimensions. Ten genotypes, defined by 13 variable nucleotide sites, were found within 204 bp of cytochrome b among 142 common murres from four Atlantic and three Pacific colonies. Significant genetic differences were found between Atlantic and Pacific common murres, in accordance with their geographic separation. Genotype frequencies also varied clinally within the Atlantic. This cline is similar to a reported cline in the incidence of 'bridling' (a white sye ring and auricular grove) in common murres, and may have resulted from colonization of the Atlantic from two or more refugial centers following the Pleistocene glaciations. -- Little differentiation was found using morphometries or protein electrophoresis among thick-billed murres breeding at different sites within each of three colonies. However, cytochrome b genotype frequencies differed significantly both between two ledges in one area and among four areas at Hom0ya, Norway. Differentiation in mtDNA within Hornflya is consistent both with band returns, which indicate that murres often breed on their natal ledges, and with morphological evidence, which indicates that phenotypic differentiation exists within some colonies. -- Analyses of cytochrome b nucleotide sequences of six Atlantic alcid species, two gull species, two shorebird species and a dove revealed a preponderance of transitions over transversions, and of third position over first or second position substitutions. Saturation of transitions prevented phylogenetic analyses above the family level. Nonetheless, cladistic analysis of the alcid sequences supported previously suggested phytogenies in 1) grouping murre, razorbill (Alca torda) and dovekie (Alle alle) sequences, 2) clustering the black guillemot sequence with the murres, razorbill and dovekie, and 3) placing the Atlantic puffin (Fratercula arcticn) outside the other alcid sequences. The phylogenetic positions of the razorbill and dovekie relative to the murres could not be resolved. -- A review of mtDNA analyses indicated that genetic differentiation of populations and species is greater in freshwater and terrestrial species than in aerial or marine animals. This agrees with general dispersal capabilities, and probably relates to long-term effective population sizes. -- Key words: Alcidae; cytochrome b; morphometries; murrc; protein electrophoresis; polymerase chain reaction; review, Uria.

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