Research Article

Adaptive Evolution of Pelvic Reduction in Sticklebacks by Recurrent Deletion of a Pitx1 Enhancer

Science  15 Jan 2010:
Vol. 327, Issue 5963, pp. 302-305
DOI: 10.1126/science.1182213

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Adaptive Girdle Loss in Sticklebacks

How do molecular changes give rise to phenotypic adaptation exemplified by the repeated reduction in the pelvic girdle observed in separate populations of sticklebacks? Now Chan et al. (p. 302, published online 10 December) have identified the specific DNA changes that control this major skeletal adaptation. The key locus controlling pelvic phenotypes mapped to a noncoding regulatory region upstream of the Pituitary homeobox transcription factor 1 gene, which drives a tissue-specific pelvic enhancer. Multiple populations showed independent deletions in this region and enhancer function was inactivated. Reintroduction of the enhancer restored pelvic development in a pelvic-reduced stickleback.


The molecular mechanisms underlying major phenotypic changes that have evolved repeatedly in nature are generally unknown. Pelvic loss in different natural populations of threespine stickleback fish has occurred through regulatory mutations deleting a tissue-specific enhancer of the Pituitary homeobox transcription factor 1 (Pitx1) gene. The high prevalence of deletion mutations at Pitx1 may be influenced by inherent structural features of the locus. Although Pitx1 null mutations are lethal in laboratory animals, Pitx1 regulatory mutations show molecular signatures of positive selection in pelvic-reduced populations. These studies illustrate how major expression and morphological changes can arise from single mutational leaps in natural populations, producing new adaptive alleles via recurrent regulatory alterations in a key developmental control gene.

  • * Present address: Max Planck Institute for Evolutionary Biology, 24306 Plön, Germany.

  • Present address: University of Chicago, Chicago, IL 60637, USA.

  • Present address: Harvard Medical School, Boston, MA 02115, USA.

  • § Present address: University of Utah, Salt Lake City, UT 84112, USA.

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