Weak large‐scale population genetic structure in a philopatric seabird, the European Shag Phalacrocorax aristotelis

Barlow, E.J., Daunt, F., Wanless, S., Alvarez, D., Reid, J.M. and Cavers, S., 2011. Weak large‐scale population genetic structure in a philopatric seabird, the European Shag Phalacrocorax aristotelis. Ibis, 153(4), pp.768-778.

Quantifying population genetic structure is fundamental to testing hypotheses regarding gene flow, population divergence and dynamics across large spatial scales. In species with highly mobile life-history stages, where it is unclear whether such movements translate into effective dispersal among discrete philopatric breeding populations, this approach can be particularly effective. We used seven nuclear microsatellite loci and mitochondrial DNA (ND2) markers to quantify population genetic structure and variation across 20 populations (447 individuals) of one such species, the European Shag, spanning a large geographical range. Despite high breeding philopatry, rare cross-sea movements and recognized subspecies, population genetic structure was weak across both microsatellites and mitochondrial markers. Furthermore, although isolation-by-distance was detected, microsatellite variation provided no evidence that open sea formed a complete barrier to effective dispersal. These data suggest that occasional long-distance, cross-sea movements translate into gene flow across a large spatial scale. Historical factors may also have shaped contemporary genetic structure: cluster analyses of microsatellite data identified three groups, comprising colonies at southern, mid- and northern latitudes, and similar structure was observed at mitochondrial loci. Only one private mitochondrial haplotype was found among subspecies, suggesting that this current taxonomic subdivision may not be mirrored by genetic isolation.

Multilocus population analysis of Gavia immer (Aves: Gaviidae) mtDNA reveals low genetic diversity and lack of differentiation across the species breeding range

Bartolomé, C., Maside, X., Camphuysen, K.C., Heubeck, M. & Bao, R., 2011. Multilocus population analysis of Gavia immer (Aves: Gaviidae) mtDNA reveals low genetic diversity and lack of differentiation across the species breeding range. Organisms Diversity & Evolution, 11(4), pp.307-316.


We analyzed the patterns of nucleotide sequence variation at three mitochondrial DNA loci, the noncoding mitochondrial control region and two genes (cytochrome b and cytochrome oxidase I) of Gavia immer in the largest collection of wintering individuals from Southern Europe to date. The sample consisted of 33 birds, oiled during the 2002/2003 Prestige tanker spill and washed ashore on the Galician coast (NW Iberian Peninsula). The aims of the study were to investigate the levels of standing genetic variation in the species, and to identify the geographic origin of these wintering birds. To do this, all available sequences of these loci, mostly from North American specimens collected from both the Atlantic and Pacific coasts, were retrieved from GenBank and included in the analysis. Overall, only 14 genetic variants were detected in the nearly 2 Kb surveyed, which reflects very low levels of nucleotide site diversity in this species. Interestingly, all variants were found at very low frequencies, and there was no indication of any clear subdivision in the G. immer population. This genetic profile is consistent with G. immer being a single panmictic population of small effective population size as compared with other seabirds. These circumstances preclude identification of the breeding regions of these wintering birds relying solely on genetic data. In the light of these results, possible causes, and the genetic and ecological consequences, of this demographic scenario are discussed.