Evolution

Alone, But Not Lonely

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Science  22 Oct 2010:
Vol. 330, Issue 6003, pp. 428
DOI: 10.1126/science.330.6003.428-d
CREDIT: ROBERT C. FLEISCHER

Darwin's On the Origin of Species was shaped by his visits to the Galapagos Islands; in particular, he noted the prevalence of species, from land tortoises to finches, which were not found elsewhere. Since that time, it has been hypothesized that the remote location and singular environment of the Galapagos have shaped wayward migrants through in situ radiations into their myriad endemic and unusual forms. On the other hand, species that can travel long distances would be expected to be less likely to become lonely; instead, they would maintain gene flow with their mainland counterparts and thus limit the adaptive divergence observed in more sedentary species.

Darwin suggested that marine birds should display less endemism than other species, but recent work by Hailer et al. on the highly vagile magnificent frigate bird (Fregata magnificens) suggests that the power of the Galapagos to facilitate divergence is not due solely to its isolation. Specifically, by looking for divergence across a suite of genetic markers and proxies for body size in populations throughout the western hemisphere, they show not only that the Galapagos population is unique, but also that it is unique in its uniqueness. F. magnificens from other locations, extending from Mexico to the Virgin Islands, are genetically and phenotypically indistinguishable despite being separated by, in some cases, thousands of kilometers and the Panamanian Isthmus. So if geographic isolation is not driving divergence in Galapagos frigate birds, what is? The authors hypothesize that the drivers could be ecological or behavioral.

Proc. R. Soc. London Ser. B 277, 10.1098/rspb.2010.1342 (2010).

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