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Natural Selection on Bill Characters in the Two Bill Morphs of the African Finch Pyrenestes ostrinus

Thomas Bates Smith
Evolution
Vol. 44, No. 4 (Jul., 1990), pp. 832-842
DOI: 10.2307/2409549
Stable URL: http://www.jstor.org/stable/2409549
Page Count: 11
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Natural Selection on Bill Characters in the Two Bill Morphs of the African Finch Pyrenestes ostrinus
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Abstract

Evidence for natural selection on seven bill and body characters is examined in the two bill morphs of the African estrildid finch Pyrenestes ostrinus. Two regression methods are used in examining natural selection in association with survivorship: a parametric (Lande and Arnold, 1983) and a non-parametric (Schluter, 1988) method. Selection was estimated in adult males, females and juveniles over a four-year period in a population in south-central Cameroon. Selection was common among groups but patterns differed and depended on the method used in detecting selection. The non-parametric method revealed evidence for disruptive selection occurring on bill width and is explained within the context of known feeding efficiencies and the hardness of important seeds in finch diets. Directional selection was common on bill characters in all groups, but infrequent on other characters. There was no evidence of selection on generalized size or shape characters. Selection on bill characters was common across groups despite low annual variation in rainfall. This contrasts with studies of Galapagos finches in which selection is frequently associated with dramatic changes in food supply caused by high variance in annual rainfall. Patterns of selection on bill traits in P. ostrinus also differ from those in song sparrows and Galapagos finches by exhibiting evidence for natural selection on all bill dimensions.

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