Any individual that has both a mother and father will have 50% of their genes coming from each parent. For most traits, these maternal and paternal genes work in harmony. There are, however, some traits in which particular offspring behaviors benefit one parent, but harm the other. This can result in a genetic conflict within an individual's own development and behavior. One potential example of such a conflict concerns whether honey bee workers ought to lay eggs in the presence of their mother, the queen. The father benefits genetically when workers lay eggs; but worker egg laying must come at the expense of the queen's reproductive output. Therefore, the genes in workers that come from their mother ought to oppose worker reproduction and "police" any worker-laid eggs by destroying them. The goal of this project is to mathematically model within-genome conflicts to predict the conditions under which "imprinted" genes might evolve (i.e., genes that produce different effects in offspring depending on whether they come from the mother or father). This project will also selectively breed honey bees to determine if the expression of worker laying and worker policing behavior depends on the parent-of-origin for their genes. Tissue samples then can be preserved for later genomic analyses to find which genes are imprinted. Investigators now recognize that imprinted genes and within-genome conflict are common in nature. Within-genome conflict has been implicated in human health problems, such as some complications that may arise during pregnancy. Thus, understanding the evolution and expression of within-genome conflict in an easily manipulated system, like honey bee colonies, is likely to have broad impacts for understanding general questions of how genotypes are transformed into phenotypes.
Honey bee workers are functionally sterile in the presence of the queen. However, they do have the ability to activate their ovaries and lay male eggs. Workers are unable to lay female eggs as they never mate and sex determination in honey bees is dependent on the number of chromosomes an individual has. Males have one set and are haploid whilst females have two sets and are diploid. As such, unfertilized eggs become males and fertilized eggs females. This method of sex determination also means that the only way for a fathers genes to pass into the next generation of males is if his daughters lay male eggs. However, queens are able to produce sons and any loss in assistance from workers could result in a reduction in the number of her offspring that make it through to the mating pool. As such, selection should act such that genes inherited from the father encourage worker laying whilst those inherited from the mother deter it. To explore this we used Africanized and European honey bees. Africanized honey bees are known to activate their ovaries & commence laying faster after the colony becomes queenless than European honey bees. By crossing European and Africanized honey bees and placing them into queenless colonies for up to 28 days, we explored whether or not workers exhibited behaviors consistent with those predicted from theory. Our behavioral observations included: worker laying, brood rearing, and foraging. Ovary dissections are still to be completed. Preliminary results are consistent with parent-of-origin specific effects. Workers with a European mother and African father (EA) were observed laying more than any other cross (AA, AE, or EE). Other interesting results seem to suggest that individuals with an Africanized mother (AA and AE) foraged more than individuals with a European mother (EE and EA) who tended to perform more brood rearing tasks.
