Large pollen at high temperature: an adaptation to increased competition on the stigma?

Abstract

Pollen availability is a major constraint of plant reproductive success. Because pollen size tradesoff with the quantity of produced grains, the link between climate characteristics and the determination of pollen size is of fundamental importance. To minimize the rate of water loss due to desiccation, a plant should produce larger grains that also have a lower surface-to-volume ratio. We used a comparative analysis to examine the hypothesis predicting increase in pollen size as a response to desiccation intensity. To test the hypothesis, we correlated the data on pollen size with the climate characteristics, temperature and desiccation intensity of the flowering period, for 232 plant species of 11 taxonomic groups. The analysis showed a positive relationship between the pollen size and temperature, but not with the desiccation intensity. We discuss the potential mechanisms by which increased temperature is an indicator of high competition among pollen grains on the stigma, which in turn is expected to promote large pollen. Our work provides insight into the temperature dependence of pollen production in plants and reveals a link between environmental temperature and the intensity of limitation of plant reproductive success by pollen availability. The result is relevant in the context of global 123Plant Ecol (2015) 216:1407-1417 DOI 10.1007/s11258-015-0519-z climate change. We also discuss why environmental temperature has to be controlled in studies dealing with pollen production, particularly in investigations of size-number trade-off.

Cedrus atlantica pollen morphology and investigation of grain size variability using laser diffraction granulometry

“…Consequently, we propose that due to the size variability in Cedrus atlantica pollen, and lack of evidence for climatic influence, it would not be possible to use this as a proxy for climate or environmental reconstruction, as differences in the size of fossil pollen may simply result from the observed natural variation in size between pollen grains. Our findings contrast the suggested climatic influence on grain size observed in other species (Ejsmond et al 2011(Ejsmond et al 2015Griener & Warny 2015), and underscore the need for further investigation of the complex controls on pollen grain size .…”

“…Ejsmond et al (2011) analysed eight Rosaceae species and found grain size increased under desiccation stress (determined by temperature, potential evapotranspiration and altitude). A positive relationship was also found between temperature and pollen size in 232 plant species from 11 taxonomic groups, suggesting possible climatic influence on size during the flowering period (Ejsmond et al 2015) and offering potential for pollen grain size to aid in reconstructions of past environments.…”

“…The influence of temperature on grain size as demonstrated by Ejsmond et al (2015) was suggested to relate to pollen performance, whereby a trade-off exists between the size of the grain and the quantity of grains produced (Vonhof & Harder 1995). The competitive ability of pollen increases with temperature during the flowering period, and this increased competition promotes larger pollen grains (Ejsmond et al 2015).…”

“…The competitive ability of pollen increases with temperature during the flowering period, and this increased competition promotes larger pollen grains (Ejsmond et al 2015). The lack of any temperature influence on Cedrus atlantica pollen size may be due to it being a wind-pollinating species.…”

Pollen diversity of the tidal swamp rice (Oryza sativa L.) cultivars collected from South Kalimantan, Indonesia

“…A few studies have demonstrated that some environmental factors, such as temperature and drying conditions, does not affect this structure, but only change the size and chemical composition (Delph et al, 1997;Ejsmond et al, 2015). Schneider et al, (2009) reported another factor which can influence the pollen morphology (size), such as cytology (ploidy level), ecology, floral morphology or physiological constraints.…”