09/06/2011
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Egyptian Vulture's rapid change

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Continental Egyptian Vultures like this bird are now quantifiably distinct from those of the Canary Islands. Photo: Kousik Nandy (commons.wikimedia.org)
Continental Egyptian Vultures like this bird are now quantifiably distinct from those of the Canary Islands. Photo: Kousik Nandy (commons.wikimedia.org)

Genetic analysis of Egyptian Vultures on the Canary Islands has potentially revealed just how rapidly a distinct form can evolve.

Egyptian Vultures are known to have probably established themselves on Spain's Canary Islands territories within the last 2,500 years, coinciding with the first arrival of colonists on the archipelago. A team from Seville, Spain, has examined the genetic structure of Egyptian Vultures from the islands, discovering that the species had changed quite significantly within an estimated 200 generations.

The arrival of just a few birds on the islands created a biased genetic sampling (technically a 'founder effect' created by a 'population bottleneck') within subsequent generations, causing the birds to rapidly change. Canarian Egyptian Vultures are now 16 per cent heavier and three per cent large than their mainland counterparts.

The island population also has far less genetic variation than the much larger mainland Iberian population, and the standardised mutation rates indicated an origin of about 2,500 years ago. There is also enough divergence for the form to be maintained as a distinct subspecies, which rarely hybridises with migrant nominate birds.   

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That migrants can continually reach the islands in small numbers implies that the actual colonisation of the archipelago by the species probably coincided with a change in habitat or food availability there. That change would have been the arrival of human beings, and the resultant environmental changes.

The study shows that evolution can follow an ecological time scale rather than a slower geological time scale, even on a relatively long-lived bird species,  and underlines the fact that anthropogenic ecological changes can affect the evolution of vertebrates far more dramatically than is often considered.

Reference
Agudo, R, Rico, C, Vilà, C, Hiraldo, F and Donázar, J A. 2010. The role of humans in the diversification of a threatened island raptor. BMC Evolutonary Biology 10: 384. http://www.biomedcentral.com/content...148-10-384.pdf