Metabolic rate diversity assigns unique resource acquisition roles to foragers within a honeybee colony

Metabolic rate (MR) is the biological rate at which organisms process energy and is often considered to be a fundamental driver of structure and function through all levels of biological organization. One of the basic mechanisms by which MR directly impacts life history is through its influence on foraging behavior and energy acquisition. This suggests that individuals with different MR likely vary in their foraging strategies. In groups such as social insects in which energy acquisition is a collective and emergent outcome of such individual differences, this phenotypic diversity is likely to have a strong impact on their life history and performance. Previous studies have shown that honeybee (Apis mellifera) foragers maximize their energetic efficiency rather than rate of energetic gain while foraging, but how the MR of individuals have an impact on these foraging currencies is not known. Using artificially selected genetic lines of honeybees with different MR (Slow and Fast bees), we investigated if individuals of Slow or Fast MR phenotypes differ in their foraging strategies. We found that across both high and low resource condition treatments, Slow MR foragers showed higher energetic efficiency than Fast foragers and were hence visited more flowers during a singer foraging trip. This study provides empirical evidence for an adaptive role of phenotypic diversity of MR in a colony of social insects and provides a framework to test this role on a broader biological scale.