Access

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

If You Use a Screen Reader

This content is available through Read Online (Free) program, which relies on page scans. Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.

The Dissolution of a Complex Genetic Polymorphism: The Evolution of Self-Fertilization in Tristylous Eichhornia paniculata (Pontederiaceae)

Spencer C. H. Barrett, Martin T. Morgan and Brian C. Husband
Evolution
Vol. 43, No. 7 (Nov., 1989), pp. 1398-1416
DOI: 10.2307/2409456
Stable URL: http://www.jstor.org/stable/2409456
Page Count: 19
  • Read Online (Free)
  • Download ($4.00)
  • Subscribe ($19.50)
  • Cite this Item
Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
The Dissolution of a Complex Genetic Polymorphism: The Evolution of Self-Fertilization in Tristylous Eichhornia paniculata (Pontederiaceae)
Preview not available

Abstract

Eichhornia paniculata (Pontederiaceae) displays a wide range of outcrossing levels as a result of the dissolution of the tristylous genetic polymorphism and the evolution of semihomostyly. Population surveys, comparison of fitness components of the style morphs, and computer simulations were used to investigate the breakdown of tristyly and the selective mechanisms responsible for the evolution of self-fertilization. Of 110 populations surveyed in northeast Brazil and Jamaica, 53% were trimorphic, 25% were dimorphic, and 22% were monomorphic for style morph. The short (S) morph was underrepresented in trimorphic populations and absent from nontrimorphic populations. The mid (M) morph predominated in dimorphic populations and was the only morph in monomorphic populations. Stamen modifications promoting selfing, associated with semihomostyle evolution, were largely confined to the M morph. They were rare in trimorphic populations, common in dimorphic populations, and often fixed in monomorphic populations. Stochastic simulations and comparisons of fruit set in natural populations indicate that founder events, population bottlenecks, and lowered fertility of the S morph due to an absence of long-tongued pollinators can each account for loss of the S morph from trimorphic populations. A reduced level of disassortative mating can accentuate the rate at which the S morph is lost by both random and deterministic processes. Nontrimorphic populations occur at the geographical margins of the region surveyed and tend to be smaller and less dense than trimorphic populations. These observations and the higher fruit set of the M morph relative to the L morph in dimorphic populations suggest that reproductive assurance, favoring selfing variants of the M morph under conditions of low pollinator service, has been of primary importance in the origin of most monomorphic populations. Where pollinator service is reliable, however, automatic selection of selfing genes, aided by mating asymmetries between the morphs, can cause the M morph to spread to fixation in dimorphic populations.

Page Thumbnails

  • Thumbnail: Page 
1398
    1398
  • Thumbnail: Page 
1399
    1399
  • Thumbnail: Page 
1400
    1400
  • Thumbnail: Page 
1401
    1401
  • Thumbnail: Page 
1402
    1402
  • Thumbnail: Page 
1403
    1403
  • Thumbnail: Page 
1404
    1404
  • Thumbnail: Page 
1405
    1405
  • Thumbnail: Page 
1406
    1406
  • Thumbnail: Page 
1407
    1407
  • Thumbnail: Page 
1408
    1408
  • Thumbnail: Page 
1409
    1409
  • Thumbnail: Page 
1410
    1410
  • Thumbnail: Page 
1411
    1411
  • Thumbnail: Page 
1412
    1412
  • Thumbnail: Page 
1413
    1413
  • Thumbnail: Page 
1414
    1414
  • Thumbnail: Page 
1415
    1415
  • Thumbnail: Page 
1416
    1416