Pollinator or pedigree: which factors determine the evolution of pollen nutrients?
A prime example of plant–animal interactions is the interaction between plants and pollinators, which typically receive nectar and/or pollen as reward for their pollination service. While nectar provides mostly carbohydrates, pollen represents the main source of protein and lipids for many pollinators. However, the main function of pollen is to carry nutrients for pollen tube growth and thus fertilization. It is unclear whether pollinator attraction exerts a sufficiently strong selective pressure to alter the nutritional profile of pollen, e.g., through increasing its crude protein content or protein-to-lipid ratio, which both strongly affect bee foraging. Pollen nutritional quality may also be merely determined by phylogenetic relatedness, with pollen of closely related plants showing similar nutritional profiles due to shared biosynthetic pathways or floral morphologies. Here, we present a meta-analysis of studies on pollen nutrients to test whether differences in pollen nutrient contents and ratios correlated with plant insect pollinator dependence and/or phylogenetic relatedness. We hypothesized that if pollen nutritional content was affected by pollinator attraction, it should be different (e.g., higher) in highly pollinator-dependent plants, independent of phylogenetic relatedness. We found that crude protein and the protein-to-lipid ratio in pollen strongly correlated with phylogeny. Moreover, pollen protein content was higher in plants depending mostly or exclusively on insect pollination. Pollen nutritional quality thus correlated with both phylogenetic relatedness and pollinator dependency, indicating that, besides producing pollen with sufficient nutrients for reproduction, the nutrient profile of zoophilous plants may have been shaped by their pollinators’ nutritional needs.
KeywordsForaging Nutrition Meta-analysis Plant–insect interactions Pollen quality Pollination Resource use
We thank the many authors who analyzed pollen nutritional content and thus made this meta-analysis possible. We are also very grateful for the constructive comments provided by three anonymous reviewers, which significantly improved the presentation of this study.
Author contribution statement
SDL, JS, and FAR conceived the study. The data set was compiled and edited by FAR. Statistics were designed and performed by SDL and FAR. FAR, SDL, CJvdK, and JS wrote the manuscript. All authors discussed the results, commented on the paper, and agreed to the final version.
Our work was supported by the Deutsche Forschungsgemeinschaft (LE 2750/5-1 and SP 1380/1-1). CJvdK was supported by a Veni Grant (number 016.Veni.181.025) from the Dutch NWO.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
For this type of study formal consent is not required.
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