09/05/2011
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Galápagos frigatebird gain

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This female Magnificent Frigatebird photographed in Antigua should be well within the genetic mainstream of its species. Photo: Charlesjsharp (commons.wikimedia.org).
This female Magnificent Frigatebird photographed in Antigua should be well within the genetic mainstream of its species. Photo: Charlesjsharp (commons.wikimedia.org).

Swarovski Optik

The island isolation so important in the speciation of tubenoses now appears to be playing a greater role than thought in the evolution of another seabird group, the frigatebirds.

With the Fregatidae already having two endemic island species in Ascension and Christmas Island Frigatebird, the population of Magnificent Frigatebird on the Galápagos archipelago has now come under the scrutiny of molecular biologists.

To test the effectiveness of the islands' isolation in providing the conditions necessary for evolutionary divergence, an American team from the Smithsonian Institute in Washington DC sampled the mitochondrial DNA of 232 individuals from nine populations across the Atlantic and eastern Pacific, essentially bookending the Panama isthmus.

Being a highly dispersive species and being so widely distributed across the southern oceans, the species would hypothetically have rather a lot of gene flow between each population. However, the specimens revealed a clear and deep split between two separate lineages, though gene flow was indeed extensive between individuals of all areas except the Galápagos .

Therefore the extensive dispersal of the species seems to be maintaining its monotypic status in the majority of its range, even between Pacific and Atlantic colonies. Galápagos individuals appear to have been isolated there for several hundred years at least, even though birds identified from that source have been noted as vagrants in Central America.

While not declared a separate taxon from other Magnificent Frigatebirds, the genetic divergence is also underlined by the birds' biometrics - at least 80 per cent of individuals can be identified by these alone. A formal name for Galápagos Magnificent Frigatebird is unforthcoming at present, but the population is certainly distinctive enough for the authors of the paper to recommend the special conservation status that so many other forms on the islands enjoy.

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