Breeding systems in Balsaminaceae in relation to pollen/ovuleratio, pollination syndromes, life history and climate zone
Pollen/ovule (P/O) ratios are often used as a proxy for breeding systems. Here, we investigate the relations between breeding systems and P/O ratios, pollination syndromes, life history, and climate zone in Balsaminaceae.
We conducted controlled breeding system experiments (autonomous and active self-pollination and outcrossing tests) for 65 Balsaminaceae species, analyzed pollen grain and ovule numbers, and evaluated the results in combination with data on pollination syndrome, life history, and climate zone on a phylogenetic basis.
Based on the fruit set, we assigned three breeding systems: autogamy, self-compatibility, and self-incompatibility. Self-pollination led to a lower fruit set than outcrossing. We neither found significant P/O differences between breeding systems nor between pollination syndromes. However, the numbers of pollen grains and ovules per flower were significantly lower in autogamous species, but pollen grain and ovule numbers did not differ between most pollination syndromes. Finally, we found no relation between the breeding system and climate zone, but a relation between climate zone and life history.
In Balsaminaceae reproductive traits can change under resource or pollinator limitation, leading to the evolution of autogamy, but are evolutionary rather constant and not under strong selection pressure by pollinator guild and geographic range changes. Colonization of temperate regions, however, is correlated with transitions towards annual life history. Pollen/ovule-ratios, commonly accepted as good indicators of breeding system, has a low predictive value in Balsaminaceae. In the absence of experimental data on the breeding system, additional floral traits (overall pollen grain and ovule number, traits of floral morphology) may be used as proxies.
