Joined: Jan. 2006
I just came across this study:
Evolution (OnlineEarly Articles).
SPATIAL DIFFERENTIATION FOR FLOWER COLOR IN THE DESERT ANNUAL LINANTHUS PARRYAE: WAS WRIGHT RIGHT?
Douglas W. Schemske and Paulette Bierzychudek
|Understanding the evolutionary mechanisms that contribute to the local genetic differentiation of populations is a major goal of evolutionary biology, and debate continues regarding the relative importance of natural selection and random genetic drift to population differentiation. The desert plant Linanthus parryae has played a prominent role in these debates, with nearly six decades of empirical and theoretical work into the causes of spatial differentiation for flower color. Plants produce either blue or white flowers, and local populations often differ greatly in the frequencies of the two color morphs. Sewall Wright first applied his model of "isolation by distance" to investigate spatial patterns of flower color in Linanthus. He concluded that the distribution of flower color morphs was due to random genetic drift, and that Linanthus provided an example of his shifting balance theory of evolution. Our results from comprehensive field studies do not support this view. We studied an area in which flower color changed abruptly from all-blue to all-white across a shallow ravine. Allozyme markers sampled across these regions showed no evidence of spatial differentiation, reciprocal transplant experiments revealed natural selection favoring the resident morph, and soils and the dominant members of the plant community differed between regions. These results support the hypothesis that local differences in flower color are due to natural selection, not due to genetic drift.|
I know it's partially off-topic (coloration in plants, not animals), but this study is one among many showing that selection can favor different colors in flowers.
EDIT: In that case, pollinators, which are the usual suspected factors of color selection, show no preference for either coloration. That didn't prevent researchers to test and verify the hypothesis of local selection. Have you learnt anything, Martin?
There are also those interesting examples of mimicry between plants. Morph frequencies in the field are very well explained by (gasp!) natural selection.