The Evolution and Maintenance of Mixed Mating Systems
Goodwillie, Carol .
Evolution in the timing of self-compatibility in Leptosiphon jepsonii.
Some theoretical models predict that mixed mating systems are transitional, with highly selfing or outcrossing species as evolutionarily stable endpoints. Conversely, mixed mating has been viewed as adaptive, especially in species with unreliable pollinator visitation. In particular, delayed selfing, which promotes mixed mating, is argued to be a “best of both worlds” mating strategy because it provides reproductive assurance through selfing without usurping ovules or pollen for outcrossing. The annual plant, Leptosiphon jepsonii, exhibits a floral-age-dependent form of self-incompatibility that confers delayed selfing. However, all populations studied contain some individuals that can self-fertilize early in anthesis. The frequency of early selfing varies among populations and is positively associated with the population selfing rate. The development of true breeding early and delayed selfing lines from three populations demonstrates that variation in the timing of self-compatibility is genetically based. Early and delayed selfing lines were crossed to create F1 and F2 progeny from each population, and the timing of self-compatibility was assayed by counting pollen tubes in self-pollinated flowers. Comparison of variance in pollen tube number in F1 and F2 progeny revealed that relatively few genes control this variation. In all populations, F1 progeny were found to produce few self pollen tubes, indicating that early selfing is largely recessive. When early selfing lines from the three populations were crossed in a complementation test, delayed selfing was restored in two of three crosses, indicating that two distinct genetic elements are responsible for early selfing in different populations. This finding is congruent with the results of a study of population genetic structure in L. jepsonii suggesting independent evolution of highly selfing populations within the species. Delayed selfing does not appear to be resistant to invasion by more selfing variants, which is interpreted in light of the controversy surrounding the stability of mixed mating.
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1 - East Carolina University, Department of Biology, Howell Science Complex, Greenville, North Carolina, 27858-4353, USA
mixed mating system.
Presentation Type: Symposium or Colloquium Presentation
Location: Stevens 5/Hilton
Date: Monday, July 9th, 2007
Time: 8:45 AM