Intracolonial genetic diversity in honey bee (Apis mellifera) colonies increases pollen foraging efficiency

Authors: ECKHOLM, BRUCE - University Of Arizona; Anderson, Kirk; WEISS, MILAGRA - University Of Arizona; DeGrandi-Hoffman, Gloria

Submitted to: Behavioral Ecology-Sociobiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2010
Publication Date: 6/20/2011
Citation: Eckholm, B.J., Anderson, K.E., Weiss, M., Hoffman, G.D. 2011. Intracolonial genetic diversity in honey bee (Apis mellifera) colonies increases pollen foraging efficiency. Behavioral Ecology-Sociobiology. 65:1037-1044.

Interpretive Summary: When queens mate with many drones, her offspring create a colony with multiple patrilines and high levels of genetic diversity. Recent studies have shown that increased genetic diversity within a colony increases the variation in how frequently certain tasks such as removal of dead bees or nest protection occur. In our study, we showed that colonies that were genotypically diverse (i.e., queen mated with 20 drones) reared more brood, had greater foraging rates and collected more pollen than colonies headed by queens that mated with a single drone (i.e. genotypically similar colonies). However, the genotypically similar colonies collected a greater variety of pollen than the genotypically diverse colonies. Further, the composition of collected pollen types was very different among the genotypically similar colonies compared with the genotypically diverse colonies. The response threshold model predicts that the likelihood of a worker performing a particular task depends on genotype and that in genetically diverse colonies certain genotypes are more likely than others to perform certain tasks. Our findings are what would be expected based on the response threshold model. Based on the lower variety of pollen types collected by the genotically diverse colonies, we can assume that they sent out fewer scouts to search for pollen. Those scouts then guided the majority of foragers to the food sources. In contrast, the genotypically similar colonies sent out more scouts that recruited fewer foragers resulting in a greater diversity of pollen. However, less pollen was collected by the genotypically similar colonies than the genotypically diverse. Our study shows that the genetic composition of the colony plays an important role in the efficiency of pollen collection, and that colonies headed by a well mated queen are better able to optimize the effectiveness of their foraging efforts.

Technical Abstract: Multiple mating by honey bee queens results in colonies of genotypically diverse workers. Recent studies have demonstrated that increased genetic diversity within a honey bee colony increases the variation in the frequency of tasks performed by workers. We show that genotypically diverse colonies, each composed of twenty subfamilies, rear more brood and collect more pollen at higher foraging rates than do genotypically similar colonies, each composed of a single subfamily. However, genotypically similar colonies collect greater varieties of pollen than do genotypically diverse colonies. Further, the composition of collected pollen types is less similar among genotypically similar colonies than among genotypically diverse colonies. The response threshold model predicts that genotypic subsets of workers vary in their response to task stimuli. Consistent with this model, our findings suggest that genotypically diverse colonies send out fewer numbers of foragers that independently search for pollen sources (scouts) in response to protein demand by the colony, resulting in a lower variety of collected pollen types. The coopertive foraging strategy of honey bees involves a limited number of scouts monitoring the environment that then guide the majority of foragers to high quality foood sources. The genetic coomposition of the colony appears to play an important role in the efficiency of this behavior.