Pollen sterols are highly diverse but phylogenetically conserved

Area of Science:

• Plant biochemistry
• Insect nutrition
• Evolutionary biology

Background:

• Phytosterols are vital for plant cell membranes and hormone synthesis.
• Insects, including bees, require sterols but cannot synthesize them, relying on dietary intake, primarily from pollen.
• Unlike many insects, bees cannot dealkylate dietary phytosterols to cholesterol, necessitating the use of unmodified pollen sterols.

Purpose of the Study:

• To analyze the diversity of sterols in UK wildflower pollen.
• To investigate the evolutionary reasons behind pollen sterol variation compared to vegetative tissues.
• To understand the sterol requirements of honeybees and their foraging strategies.

Main Methods:

• High-resolution chemical analysis was employed to identify and quantify sterols.
• The sterol profiles of 78 different pollen sterols from 295 UK wildflower taxa were cataloged.
• Phylogenetic analysis was used to correlate sterol distribution with plant lineage.

Main Results:

• A wide diversity of 78 sterols was identified across 295 UK wildflower taxa.
• Pollen sterol composition showed strong correlations with plant lineage, conserved at the subfamily level.
• Key sterols for bees, such as Δ5 sterols (β-sitosterol, 24-methylenecholesterol, isofucosterol), were abundant in most pollens.
• Honeybee sterol profiles were not matched by any single pollen type, indicating a need for mixed pollen foraging.

Conclusions:

• Pollen sterol composition is influenced by plant evolutionary history and lineage.
• The sterol profiles in pollen suggest adaptation to meet the specific nutritional demands of pollinators like bees.
• Honeybees likely forage from multiple plant species to obtain a balanced sterol profile essential for their survival.