Abstract
Seed production is likely constrained by pollen limitation and the viability of pollen grains decreases rapidly in time due to water evaporation. Any decrease in the surface-to-volume ratio, through increase in size or change in shape of a grain, reduces the rate of water loss. However, grain size trade-offs with the number of grains that can be produced by a plant. Here, we tested the hypothesis that under higher desiccation stress pollen grains become larger and more spherical. We analyzed data on the pollen morphology of eight Rosaceae species and the desiccation intensity based on temperature, potential evapotranspiration and altitude. To explain the mechanisms underlying our results, we present a model that optimizes the size and shape of pollen grains under different conditions. We report that pollen grains under more intense desiccation stress during flowering periods tend to be larger but do not change shape. This conclusion is consistent with the results of a theoretical model presented here. Our report fills a gap in our knowledge about a fundamental process in plant reproduction. We also discuss the significance of our results in light of current palynological and ecological problems (e.g., global climate change).
Highlights
The production and morphology of pollen grains are key features of pollination biology
The model To address how temperature affects the size, shape and number of viable pollen grains delivered to stigmas, we modeled the optimal allocation of resources to the production of pollen grains
Empirical results The Principal Component Analysis (PCA) for pollen grain characteristics displayed a pattern that was consistent for all studied groups
Summary
The production and morphology of pollen grains are key features of pollination biology. Pollen limitation, which is influenced by many factors, has emerged as a one of the major forces limiting the fitness of plants and may affect plant life histories (Ashman et al 2004, Knight et al 2005). Pollen production of pollen may be strongly constrained by environmental factors (for review see Delph et al 1997), the EJSMOND ET AL. Adaptive significance of the inter- and intraspecific variability in the size-number pollen tradeoff and pollen morphology has rarely been analyzed in this context. It is reasonable to hypothesize that the size and shape of a pollen grain may affect its time to desiccation and, as a consequence, the likelihood of successful pollination under specific environmental conditions
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