Specialization and adaptation in pollen sterol use by wild bees

Area of Science:

• Biochemistry
• Ecology
• Evolutionary Biology

Background:

• Sterols are vital membrane components and hormone precursors in eukaryotes.
• Honeybees uniquely use pollen sterols, differing from most insects that convert plant sterols to cholesterol.
• Understanding bee sterol acquisition is crucial for insect herbivore research.

Purpose of the Study:

• To determine if direct pollen sterol utilization is common across all bee species.
• To identify and quantify the specific pollen sterols consumed by diverse bee species.
• To explore the ecological and phylogenetic drivers of sterol composition in bees.

Main Methods:

• Sterol content (sterolome) analysis was performed on 56 bee species from major families.
• Quantification of specific sterols, including Δ5 sterols, 24-methylenecholesterol, isofucosterol, and β-sitosterol.
• Comparative analysis of sterol profiles between generalist and specialist bee species.

Main Results:

• Common pollen sterols like 24-methylenecholesterol, isofucosterol, and β-sitosterol were prevalent in most bee species.
• A minority of bee species exhibited distinct sterol profiles, indicating specialized requirements.
• Generalist bees consumed more 24-methylenecholesterol, suggesting adaptation to widely available plant sterols.
• Asteraceae specialists utilized unique pollen sterols, potentially resolving the Asteraceae paradox.

Conclusions:

• Bee sterol composition is primarily influenced by ecological factors, such as diet and foraging habits.
• Phylogenetic relatedness appears to play a lesser role in shaping bee sterol profiles.
• The findings highlight adaptive strategies in bees for acquiring essential sterols from diverse pollen sources.