Delesalle, Veronique , Mazer, Susan , Paz, Horacio .
Ontogenetic variation in the Pollen:Ovule ratios in Clarkia (Onagraceae) taxa with contrasting mating systems: Field populations.
Selfing and outcrossing sister taxa provide interesting systems to compare the magnitude and direction of ontogenetic changes in gamete production and gender allocation. Although resource availability over the flowering season will decline for both taxa, changes in mating opportunities will depend on mating system and will vary less in selfing taxa. Consequently, we predicted that the P:O ratio should vary less among and within selfing individuals than in closely related outcrossing taxa. To test these predictions, we measured ontogenetic changes in gamete production and gender in multiple field populations of two pairs of sister taxa in the annual flowering plant genus Clarkia (Onagraceae). In the outcrossing C. unguiculata and the selfing C. exilis, ovule production declined similarly from early to late buds in both taxa, while pollen production reamined constant or increased in the outcrosser but remained constant or decreased in the selfer. Consequently, the P:O ratio increased in both unguiculata populations but marginally increased or stayed constant in exilis populations. In all populations of the selfing C. xantiana spp. parviflora and the outcrossing C. x. spp. xantiana, late flowers produced fewer ovules and fewer pollen grains than early flowers. These declines in gamete production had different effects on the P:O ratio of each subspecies. The P:O ratio did not differ between early and late flowers in xantiana. This was not due to a lack of change in the P:O ratio of individual plants but rather to the fact that the direction of change of individual plants was equally balanced between increases and decreases within each xantiana population. In contrast, parviflora populations differed in the mean direction of temporal change, corresponding to differences observed among the individuals within them. We found little evidence to support our initial predictions that the P:O ratio of the selfing taxa should be more canalized.
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1 - Gettysburg College, Department of Biology, Box 392, Gettysburg, Pennsylvania, 17325, USA
2 - University of California Santa Barbara, Department of Ecology Evolution And Marine Biology, Santa Barbara, California, 93106-9610, USA
3 - Universidad Nacional Autónoma de México, Centro de Investigaciones en Ecosistemas, Apartado Postal 27-3, (Xangari), Morelia, Michoacán, 58089, Mexico
Presentation Type: Oral Paper:Papers for Sections
Location: Williford B/Hilton
Date: Tuesday, July 10th, 2007
Time: 4:00 PM