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"A test of the 'flexible stem' model of evolution: ancestral plasticity, genetic accommodation, and morphological divergence in the threespine stickleback radiation" Matthew A. Wund, John A. Baker, Brendan Clancy, Justin L. Golub, and Susan A. Foster


Threespine stickleback (photograph by Anna Mazzarella)

When reared on macroinvertebrates, marine fish (ancestral) resembled benthic stickleback; when reared on zooplankton, marine fish resembled limnetic stickleback. This demonstrates that environmentally induced variation in head shape in ancestral stickleback resembles evolved variation in head shape in freshwater ecotypes—a key prediction of the “flexible stem” model. Furthermore, the derived, freshwater populations also exhibited changes in head shape when reared on alternative diets, indicating that plasticity of head shape has not been lost over evolutionary time.



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June 2008

Volume 171, Number 6
Am Nat 2008. Vol. 171, pp. 816–823
0003-0147/2008/17106-42875$15.00
DOI: 10.1086/587757
Natural History Note

Coevolution and Divergence in the Joshua Tree/Yucca Moth Mutualism

William Godsoe,*

Jeremy B. Yoder,

Christopher Irwin Smith, and

Olle Pellmyr§

Department of Biology, University of Idaho, Moscow, Idaho 83844

Abstract:

Theory suggests that coevolution drives diversification in obligate pollination mutualism, but it has been difficult to disentangle the effects of coevolution from other factors. We test the hypothesis that differential selection by two sister species of pollinating yucca moths (Tegeticula spp.) drove divergence between two varieties of the Joshua tree (Yucca brevifolia) by comparing measures of differentiation in floral and vegetative features. We show that floral features associated with pollination evolved more rapidly than vegetative features extrinsic to the interaction and that a key floral feature involved in the mutualism is more differentiated than any other and matches equivalent differences in the morphology of the pollinating moths. A phylogenetically based, ancestral states reconstruction shows that differences in moth morphology arose in the time since they first became associated with Joshua trees. These results suggest that coevolution, rather than extrinsic environmental factors, has driven divergence in this obligate pollination mutualism.

Submitted September 24, 2007; Accepted January 30, 2008; Electronically published April 4, 2008

Keywords:

coevolution, diversification, mutualism, pollination, Tegeticula, Yucca.

Natural History Editor: Henry M. Wilbur

Cited by

Christopher Irwin Smith, William K. W. Godsoe, Shantel Tank, Jeremy B. Yoder, Olle Pellmyr. (2008) DISTINGUISHING COEVOLUTION FROM COVICARIANCE IN AN OBLIGATE POLLINATION MUTUALISM: ASYNCHRONOUS DIVERGENCE IN JOSHUA TREE AND ITS POLLINATORS. Evolution 62:10, 2676-2687
Online publication date: 1-Nov-2008.
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