Breeding systems in Balsaminaceae in relation to pollen/ovule ratio, pollination syndromes, life history and climate zone

Abstract

Pollen/ovule (P/O) ratios are often used as 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, analysed 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 fruit set, we assigned three breeding systems: autogamy, self-compatibility and self-incompatibility. Self-pollination led to 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 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. Colonisation of temperate regions, however, is correlated with transitions towards annual life history. Pollen/ovule-ratios, commonly accepted as good indicators of breeding system, have a low predictive value in Balsaminaceae. In the absence of experimental data on breeding system, additional floral traits (overall pollen grain and ovule number, traits of floral morphology) may be used as proxies.

Plants are visited by more pollinator species than pollination syndromes predicted in an oceanic island community

“…Even though studies have been focused on understanding the relationships between plant-animal interaction and the evolution of floral traits 1,78,79 , little is known about the relationship between ecological and evolutionary specialization 4 . Our results showed that restrictive flowers were related to higher ecological specialization levels than unrestrictive flowers.…”

Nectar traits differ between pollination syndromes in Balsaminaceae

“…Voucher specimens are deposited in the herbarium of Bonn. For genetic analyses, we expanded the phylogenetic data set of Janssens et al (2009 a ) and Lozada-Gobilard et al (2019) (Supplementary data Table S1). Since several newly added taxa are currently in the process of being officially described, they are here indicated with informal names.…”

Pollination syndromes in the 21stcentury: where do we stand and where may we go?

“…Advertisement (Dellinger et al, 2019a) Amount Manual counting or use of a particle counter (e.g. Castellanos et al, 2004) Fresh or ethanol-preserved flower material Efficiency (Cruden, 2000, but also see Lozada-Gobilard et al, 2018) Quality (viability, protein content)…”

“…Lunau et al, 2015;Konzmann et al, 2019) Pollen kit, viscin threads e.g. Sudan dyes (Pacini & Hesse, 2005) Ethanol-preserved flower material Multifunctional (UV or water loss protection, pollen packaging; reviewed in Pacini & Hesse, 2005) Gynoecium Timing of stigma receptivity Documentation in the field Efficiency (Armbruster et al, 2009) Stigma size or shape Qualitative classification or measurements, scanning electron microscopy Fresh or ethanol-preserved flower material, herbarium specimens Efficiency (Cruden, 2000;Dellinger et al, 2019a) Number of ovules Quantification through microscope or HRX-CT (Staedler et al, 2018) Fresh or ethanol-preserved flower material Efficiency (Cruden, 2000, but also see Lozada-Gobilard et al, 2018) Herkogamy Spatial separation between anthers and stigma Measurements or morphometrics Fresh or ethanol-preserved flower material Efficiency (outcross pollen transfer, Opedal, 2018) Methods, type of floral material needed, and information on comparative or experimental evidence of the functional significance of certain traits in the pollination process are given. Where possible, objective (ideally quantitative) measurements on traits should be prioritised over qualitative categorisation.…”