Applying a Reaction Norm Framework to Examining Variability in Egg Size Produced by Honey Bee (Apis mellifera) Queens

    Phenotypic plasticity arises through three primary mechanisms: genetic, environmental and the interaction between the two (Martin et al 2021). Although the Martin et al paper focused on applying the reaction norm framework to exploring immunology, I believe the premise can be extrapolated to other fields of ecological importance. For example, a November 2020 study from Amiri et al examined factors influencing variation in the size of eggs produced by honeybee (Apis mellifera) queens.

    Amiri et al found that certain genetic lineages produced larger eggs on average. However, there was significant variability of egg size produced by queens within the same lineage. This suggests that external factors, outside of genetics, influence egg size plasticity. Amiri et al looked into two environmental conditions that could influence egg size:  colony size and nutritional status. Colony size is a factor of the social environment within the hive. Queens within larger colonies produce smaller eggs size on average than conspecifics in small colonies. Nutritional status of the nest also significantly impacted egg size. Queens in overfed colonies produced significantly smaller eggs on average than queens in pollen-restricted colonies. Overall, genotype and colony size had a greater impact on eggs size than the experimentally manipulated food availability.

      The larger egg size is associated with greater survival of offspring. When presented with unfavorable conditions the queens produced larger eggs to ensure survival of offspring.  The ability of a queen to modulate egg size depending on environmental conditions might demonstrate a conserved life history strategy from a presocial ancestral line. Modern honeybees form complex hives where nurse worker bees provide brood care for offspring. Larger colonies have more workers available for brood care, therefore the queen does not need to invest in producing larger eggs. Survival in a larger colony will already surpass that of a small colony because of the surplus of nurse bees caring for brood.

    The reaction norm framework could further be applied to premise of the honeybee study to elucidate the degree at which a queen’s genotype produces certain egg sizes across a gradient of environmental factors. Amiri et al covered genetic and environmental factors that affect egg size as distinct mechanisms. However, they did not explicitly explore the interface of genetic and environmental factors. Despite not recognizing the interface of how genotype and environment give rise to plasticity, the researchers applied a reaction norm framework. They compared queens from the same genetic lineage in their environmental studies. In their examination of the effect of colony size, they found that sister queens similarly produced smaller eggs when in larger colonies. In smaller colonies, the sister queens also both produced larger eggs. Unfortunately, their interface studies only explored a binary of environmental factors (overfed vs. pollen restricted and large vs small colony size). Nonetheless, this research leaves room for future studies to examine the gradient of environmental factors that can affect egg size and consequently survivability. These metrics may be important tools for conservation and management of honeybee and other social bee populations.

Sources:

Amiri, E., Le, K., Melendez, C. V., Strand, M. K., Tarpy, D. R., & Rueppell, O. (2020). Egg‐size plasticity in Apis mellifera: honey bee queens alter egg size in response to both genetic and environmental factors. Journal of evolutionary biology, 33(4), 534-543.

Martin, L. B., Hanson, H. E., Hauber, M. E., & Ghalambor, C. K. (2021). Genes, Environments, and Phenotypic Plasticity in Immunology. Trends in immunology.