Differences in Nectar Traits between Ornithophilous and Entomophilous Plants on Mount Cameroon.

Štěpán Janeček,Raissa Dywou Kouede,Francis Luma Ewome,Karolína Hrubá,Jan E J Mertens,Robert Tropek,Yannick Klomberg,Ishmeal N Kobe,Marcus Mokake Njie,Kryštof Chmel

doi:10.3390/plants10061161

Abstract

Despite a growing number of studies, the role of pollinators as a selection agent for nectar traits remains unclear. Moreover, the lack of data from some biogeographic regions prohibits us from determining their general importance and global patterns. We analyzed nectar carbohydrate traits and determined the main pollinators of 66 plant species in the tropical forests of Mount Cameroon (tropical West Africa). The measured nectar traits included total sugar amounts and proportions of sucrose and hexoses (i.e., glucose and fructose). We report the nectar properties for plants visited by five pollinator groups (bees, butterflies, moths, hoverflies, and specialized birds). Our results indicate that, rather than specific evolution in each of the five plant groups, there was a unique nectar-trait evolution in plants pollinated by specialized birds. The ornithophilous plants had a higher proportion of sucrose and produced larger sugar amounts than the plants pollinated by insects. We also demonstrated a significant phylogenetic signal in the nectar properties in some lineages of the studied plants.

Highlights

Nectar represents one of the most important flower rewards for pollinators of zoophilous plants
The high concentration of hexoses is caused by the hydrolysis of sucrose before its excretion by cell wall invertases [9], whereas the glucose:fructose ratio is modified in various metabolic pathways [10]
WeWe found thatthat whereas the nectars are aregenerally generallymore moreoften oftendominated dominated sucrose found whereas studied insect-pollinated plants hadhad similar compositions the studied insect-pollinated plants similar compositionsofofnectar, nectar,they theydiffered differed from ornithophilous plants

Summary

Introduction

Nectar represents one of the most important flower rewards for pollinators of zoophilous plants. Nectar became much more common than other plant exudates that have different primary functions than pollinator rewards [1,2,3]. Nectar is a liquid with a complex composition [4], its main compounds are carbohydrates, assuring its high energetic value [5]. Nectar metabolites are similar to those in phloem sap, their amounts can largely differ [8]. There are two interesting features of nectar carbohydrate composition: (1) nectar contains much higher amounts of hexoses (glucose and fructose) than phloem sap and (2) the ratio between sucrose and hexose in nectar does not reflect simple sucrose hydrolysis and differs from the 1:1 ratio. The carbohydrate composition can be modified by the activity of enzymes secreted as nectar compounds [11] or by organisms living in nectar [12]

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Discussion

Conclusion