Surveying a Rugged Landscape

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Science  11 Jul 2003:
Vol. 301, Issue 5630, pp. 143
DOI: 10.1126/science.301.5630.143a

Adaptive radiation is the evolutionary process by which populations of organisms diverge and ultimately form new species. These radiations can be mapped as fitness surfaces that contain peaks of adaptation, occupied by populations or species, separated by unoccupied valleys and plains. In theory, these surfaces capture how natural selection contributes to the process of radiation. In practice, however, it has proved difficult to construct such surfaces with accuracy due to the numbers of confounding variables and the obstacles to obtaining enough information about all of the relevant species.

Benkman has quantified how natural selection acts on red crossbills in Idaho. These birds are a model system for studying radiation because of the clearcut link between their bill morphologies and conifer cones (their food resource), and because the divergence in the populations is recent. Fitness in these birds closely matches feeding efficiency, which in turn is a function of the precision of the match between bill shape and cone shape. The results provide a detailed adaptive surface for crossbills and give strong support to the theory of adaptive radiation via specialization on alternative resources. — AMS

Evolution 57, 1176 (2003).

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