Sosenski, Paula , Fornoni, Juan , Molina Freaner, Francisco , Weller, Stephen G. , Dominguez, César .
The evolution of flower morphology during the breakdown of tristyly, the combined effects of optimizing, density-dependent and frequency dependent selection in Oxalis alpina.
In this study, we estimated the strength and direction of natural and both density- and frequency-dependent selection, operating on the flower morphology of three populations of Oxalis alpina representing the evolutionary transition from tristyly to distyly. The breakdown of tristyly in this species is characterized by the loss of the mid morph and increased compatibility between formerly illegitimate crosses. For this study, we choose one tristylous isoplethic population without incompatibility modifications (Mariquita) representing the ancestral tristylous condition and two populations showing strong modifications in the incompatibility system but differing in the frequency of the mid morph. Morse Canyon is an intermediate population with a relatively low frequency of the mid morph, while Pinery Canyon has lost this floral morph. Because the Mariquita population fulfills the theoretical conditions for tristyly to be in equilibrium, and Pinery Canyon has reached (or is near to) a new floral adaptive peak, we hypothesize that stabilizing natural selection on the floral phenotype of each floral morph should be evident in these populations. In contrast, given that plants in the Morse Canyon population seem to be evolving toward the distylous condition, we expect an opposite effect of selection (disruptive) on the floral phenotype of long- and short-styled plants. Additionally, we measured the effects of density and frequency dependent selection on maternal fitness in all the three populations. We predict that density-dependent, but not frequency dependent selection should be present in all populations. The anisoplethic, intermediate population, in contrast, must show the strongest effect of frequency dependent selection.
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1 - Instituto de Ecologia, UNAM, Departamento de Ecologia Evolutiva, Instituto de Ecologia, UNAM, Apartado Postal 70-275, Mexico, Distrito Federal, 04510, Mexico
2 - Instituto de Ecologia, UNAM, Departamento de Ecologia Evolutiva, Instituto de Ecologia, UNAM, Apartado Postal 1354, Hermosillo, Sonora, 83000, Mexico
3 - University of California Irvine, Department of Ecology and Evolutionary Biology, 321 Steinhaus Hall, Irvine, California, 92697-2525, USA
Presentation Type: Poster:Posters for Topics
Location: Ball Room & Party Room/SUB
Date: Monday, July 28th, 2008
Time: 12:30 PM