Methods of Making Increase Colonies

October 2014

Conflict Between Worker Bees

by John Connor


Earlier we discussed the role of conflict within the hive as it applies to queens and drones. While the hive is usually considered to be a model of harmony between individual bees, there is a growing body of research that explains how workers engage in conflict with each other from time to time, and play favorites to those bees that share a genetic closeness to them. In The Origin of the Species, 1859, Charles Darwin was perplexed by one key aspect of life within a social insect society—what is the advantage for a bee (or similar creature) that does not reproduce, but works in a social unit with many other non-reproducing individuals.

In 1964 William Hamilton suggested that a trait could be inherited without direct reproduction. He argued that someone could have reproductive fitness, the ability to pass on personal genetic information, even if he or she has no offspring. While traditional fitness counts the number of children one has, ‘inclusive fitness’ considers all others who share genes with a person or organism. So if you never mate but help a full sibling raise children, it is as if half of those children are your own, at least from a genetic perspective. This is measured by a term called the coefficient of relatedness. With worker bees, those workers that help their mother, the queen, raise future queens, also insure that their genes are transmitted to the next generation.

The basis of worker to worker conflict is a feature of the haploid-diploid mechanism of sexual determination, as the degree of relatedness differs from one worker bee to another. In honey bees and most other hymenoptera, the relatedness between sisters is higher than with other animals. Since drones are haploid they carry one copy of chromosomes from their mother, but none from a father. Diploid females are fertilized and carry two copies of genes, called alleles.

This also means that all the sperm of a single drone are identical, or clones (overlooking the chance of new mutations). If a queen mates with only one drone (which is unlikely in nature), all of her daughters will share 50% of their genes from the father, but only 25% of their genes are from their mother.  The coefficient of relatedness, among the offspring daughters is 1/2+1/4=3/4 or 75%. When compared to the relatedness of diploid organisms, such as humans, the result is only ¼+¼ or 50%. Genetically, then, as a worker bee you have a better chance of passing on your genetic information if you help your sister queen build a successful colony, than humans do with a sister.

The worker bees that share the same mother and the same father are called ‘super-sisters’ because they are so highly related. Passing genes through relatives and the fitness gained is called ‘kin selection’. It is here that the mathematics supports the advantage of being a worker bee rather than a queen. It is a better deal to be a worker that will share 75% of the genes in a new queen, than to be a queen that will only share 50% of the genes of the new queen. Hamilton argues that the advantages of sterile worker bees that are highly related plays an important role in the development of sociality within the Hymenoptera, which has occurred 11 times, more than all other organisms combined.

Hamilton’s argument becomes more complex when you realize that the average honey bee queen mates with 14.6 drones (18 in commercial queen producers in California), according to reviews of the topic by Dr. David Tarpy. This results in the average relatedness to fall between 0.75 and 0.25, or about 0.5, the same as most diploid organisms. It can be argued that multiple mating developed after the formation of social units had evolved.

Role of super-sisters in the bee colony
A number of detailed research studies have been conducted to determine the advantage, if any, of being a super-sister worker bee within a colony. Katherine Noonan in Behavioral Ecology and Sociobiology (2010) looked as these studies and reported that worker bees are able to recognize each other if they are members of the same group of super-sisters, and distinguish them from half-sisters. In 2010 she reported that worker bees are able to recognize queen larvae from their own supersisterhood (Ethology, 2010). This leads to the question, do super-sisters demonstrate favoritism or nepotism toward related sisters? In the second Noonan study, she indicted that kin recognition may be an artifact of task specialization related to feeding behavior.

Researchers Moritz and Heisler (1992, Insects Sociaux) fed dyed sugar syrup to one ...