Journal Article

Tests of adaptation: functional studies of pollen removal and estimates of natural selection on anther position in wild radish

Jeffrey K. Conner, Heather F. Sahli and Keith Karoly

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 103, issue 9, pages 1547-1556
Published in print June 2009 | ISSN: 0305-7364
Published online March 2009 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcp071
Tests of adaptation: functional studies of pollen removal and estimates of natural selection on anther position in wild radish

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Background

There are a number of difficulties associated with the study of adaptation. One is a lack of variation in the trait, which is common in adaptations because past selection has removed unfit variants. This lack of variation makes it difficult to determine the relationship between trait variation and fitness. Another difficulty is proving causation in this trait–fitness relationship, because a correlated trait might be the actual adaptation. These difficulties can be ameliorated at least partially by combining studies of natural variation with studies of experimentally manipulated traits and traits whose variance has been augmented by artificial selection.

Scope

We review here a number of our studies on the adaptive value of two aspects of anther position in wild radish (Raphanus raphanistrum, Brassicaceae): anther exsertion, i.e. the degree to which anthers protrude from the mouth of the corolla tube, and anther height dimorphism, i.e. the difference in lengths of the filaments between the two short and four long stamens. We have used both functional analyses, in which the response variable is pollen removal, and measurements of selection, in which the response variable is lifetime male fitness estimated by molecular genetic paternity analyses. In these studies we use both the natural variation in populations as well as manipulated variation, the latter through both stamen removal and artificial selection, to re-create the ancestral trait conditions.

Conclusions

Our work provides convincing evidence that intermediate anther exsertion values are adaptive, and that this is probably an adaptation to a subset of the pollinator fauna, small bees. The picture for anther height dimorphism is much less clear, as the weight of current evidence suggests that current values of this trait might actually be maladaptive; however, if this is true it is difficult to understand how the dimorphism is maintained across the family Brassicaceae.

Keywords: Wild radish; Raphanus raphanistrum; adaptation; natural selection; anther position; pollination; pollen removal

Journal Article.  6398 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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