Stability of pollen–ovule ratios in pollinator-dependent versus autogamous Clarkia sister taxa: testing evolutionary predictions
Article first published online: 4 JUN 2009
© The Authors (2009). Journal compilation © New Phytologist (2009)
Special Issue: Plant adaptation - following in Darwin's footsteps
Volume 183, Issue 3, pages 630–648, August 2009
How to Cite
Mazer, S. J., Dudley, L. S., Delesalle, V. A., Paz, H. and Galusky, P. (2009), Stability of pollen–ovule ratios in pollinator-dependent versus autogamous Clarkia sister taxa: testing evolutionary predictions. New Phytologist, 183: 630–648. doi: 10.1111/j.1469-8137.2009.02886.x
- Issue published online: 17 JUL 2009
- Article first published online: 4 JUN 2009
- Received: 28 January 2009Accepted: 8 April 2009
- developmental instability;
- mating system;
- ontogenetic variation;
- sex allocation;
- P : O ratio
- • It has been proposed that natural selection should favor distinct temporal patterns of sex allocation in selfing vs pollinator-dependent taxa. In autogamous selfers in which pollen receipt is highly reliable, selection should favor genotypes that maintain low and stable pollen to ovule (P : O) ratios throughout flowering. By contrast, in outcrossers the optimum P : O ratio of an individual's flowers will depend on pollinator abundances and mating opportunities, both of which may vary over time. In this case, selection may favor temporal variation among flowers in the P : O ratio. An opposing prediction is that selfing taxa will be developmentally more unstable than outcrossers because of lower homeostasis caused by high homozygosity.
- • We compared temporal changes in the P : O ratio in two pairs of sister taxa in the genus Clarkia. We examined hundreds of glasshouse-raised maternal families representing three wild populations each of the outcrossing, insect-pollinated Clarkia unguiculata, the facultatively autogamous Clarkia exilis and the outcrossing and selfing subspecies of Clarkia xantiana: ssp. xantiana and parviflora, respectively.
- • Temporal change in the P : O ratio was significantly greater in both outcrossers than in their selfing sister taxa, although the proportional changes in the P : O ratio (relative to the first bud produced) did not differ significantly between sister taxa (0.07 < P < 0.10).
- • Our results provide partial support for the hypothesis that the P : O ratio is more stable in selfing than in outcrossing taxa and reject the hypothesis that selfers are less stable.