Abstract
An important goal in the study of evolution is to determine the occurrence, causes and possible micro-evolutionary consequences of selection in natural populations1–3. Darwin's finches (Geospizinae) are suitable organisms for investigation because their morphological traits are highly heritable4, and they live in a climatically variable environment (Galápagos Islands)5,6. It has been suggested that selection fluctuates in direction and intensity, favouring different morphological optima in different years7, because strong annual variation in rainfall causes changes in food supply composition7,8. This suggestion has been supported in part by studies of the medium ground finch, Geospiza forth, on the island of Daphne Major, which have shown that large adult size is favoured under drought conditions, when the overall food supply is low and large hard seeds are disproportionately abundant8,9. Here we document a reversal in the direction of selection following the opposite climatic extreme, and demonstrate the connection between oscillating selection and fluctuations in food supply.
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References
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Gibbs, H., Grant, P. Oscillating selection on Darwin's finches. Nature 327, 511–513 (1987). https://doi.org/10.1038/327511a0
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DOI: https://doi.org/10.1038/327511a0
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