Adaptational Glories

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Science  07 Jul 2000:
Vol. 289, Issue 5476, pp. 13
DOI: 10.1126/science.289.5476.13d

Adaptation can be studied at various scales of biological organization, from molecular to ecological, but in practice there are few organisms or characters of organisms that lend themselves to such analysis. An exception is flower color, a phenotypic character with links directly to ecology (via pollinators) and to molecular biology and genetics (via biosynthetic pathways for floral pigments).

Clegg and Durbin survey 25 years of research by many workers on the genetics and ecology of flower color polymorphisms in the morning glory in Mexico and the southeastern United States, and paint an equally colorful picture of the complexities of floral adaptation. They find that most of the mutations that lead to phenotypic differences in flower color are the result of insertions of transposable elements (for more on transposition, see Davies et al., Research Article, this issue, p. 77). The levels of color polymorphism are high in the southeastern US (where the morning glory has been introduced, and flower colors possibly selected, by humans) and low in its native Mexican highlands; but the patterns of molecular variation are the reverse—high in Mexico, low in the US. Bee pollinators discriminate against white phenotypes compared to other color morphs. This discrimination leads to an increased level of self-fertilization among white flowers; but other disadvantages of the white phenotype combine to hold its frequency at about 10% of the population throughout its range. Hence, even such superficially simple systems contain surprises and unanticipated levels of complexity, but to merge so many levels of biology promises rich rewards for evolutionary studies. — AMS

Proc. Natl. Acad. Sci. U.S.A. 97, 6941 (2000).

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