Sexual reproduction & competition, mating systems, and courtship among bee species.
Mating Systems
The mating systems of bee colonies are based on females, where females can mate with one or many males and the males will compete with one another for access to females. These systems bees use to mate can be characterized as monandrous, polyandrous, or hyperpolyandrous. [2]
Monandrous is when a female (queen) bee only mates with one male (drone) bee in its lifetime and the resulting offspring will be fertilized with the sperm of one male. This phenomenon is typically observed in eusocial bees, such as bumblebees. One genetic advantage of this system is that the offspring produced from the same sperm have better unit cohesion, better cooperativity, and increased reproductive fitness. When the colonies work together more effectively, the overall reproductive potential and health of each bee increases.
Polyandrous systems can be described as a female queen mating with multiple males in one lifetime. Once a polyandrous queen bee mates, it may store the sperm of multiple drones to fertilize eggs in the hive. One benefit to this system is increased genetic variation because more males can contribute to the gene pool in the colony.
The third system of mating is hyperpolyandry, where one female will mate with many, many males. In this scenario, one queen can mate with up to twelve drones in its lifetime, generating the highest genetic diversity out of all mating systems. One specific benefit of hyperpolyandry is resistance against bacterial and viral infections (Delaplane et al, 2015) [3], however, it leads to increased intrasexual competition and sexually transmitted diseases among colony members. [2]
Female Courtship
Social and solitary bee species have different courtship patterns, since social bee species engage in polyandrous and hyperpolyandrous mating, while solitary bee species engage in monandrous mating. Drone males in solitary bee colonies have intense competition from other males to mate with a female. Drones typically hatch before the females and may wait at the female's food source for mating. Other males may search for possible mates in swarms. One way a male can deter other drones from mating with a female is by marking a female with a pheromone that signals to other males not to mate with her. [1]
Epigenetic Inheritance: Workers and the Queen
In social insects such as honeybees, epigenetics plays a very important role in caste systems. Individuals that are very close or identical can hold vastly different phenotypes depending on the treatment of these individuals in the brood phases. All workers and queen bees are genetically identical and their differences arise from environmental differences. Research has shown that the additional servings of royal jelly have a role in DNA methylation rates among females (Foret et al, 2012) [5]. All bee larvae will be fed a certain amount of royal jelly produced by the worker bees, however, the ones that are destined to become queen bees will be fed extra royal jelly rations. This extra portion of royal jelly will cause changes in phenotype seen in the queen bees, such as the maturation of reproductive organs, a larger overall size, and a longer life span. A queen bee can lay several hundred thousand eggs in its lifetime but worker bees are incapable of reproduction and cannot lay eggs. [1]
Haplodiploidy
Haplodiploidy is a sex-determining system of all hymenopterans, where unfertilized eggs will develop into haploid drones (males) and fertilized eggs will develop into diploid workers (females). Because males only have one set of chromosomes and females have two sets of chromosomes, female workers are always more genetically similar to each other than to their parents or brothers. [1] Workers are unique in genetics, in that they are 75% genetically similar to each other whereas in typical mendelian genetics, siblings are usually 50% genetically similar [1]. The figure to the left is a map of the genetic inheritance pattern observed in bees (as well as other hymenopterans). Worker bees tend to favor their sisters over other members of their family [1]. Hughes et al have shown that this increased genetic relatedness is a large part of the development of eusociality (Hughes et al, 2008) [5].
Further Reading
Wilson-Rich, N., Allin, K., Carreck, N., & Quigley, A. (2014). The Bee A Natural History. Princeton University Press.
Hill, R. W., Wyse, G. A., & Anderson, M. (2016). Animal Physiology (4th ed.). Sinauer Associates, Inc. Publishers.
Delaplane, K., Pietravalle, S., Brown, M. A., & Budge, G. (2015). Honey Bee Colonies Headed by Hyperpolyandrous Queens Have Improved Brood Rearing Efficiency and Lower Infestation Rates of Parasitic Varroa Mites. PLoS ONE, 10(12). https://datadryad.org/stash/dataset/doi:10.5061/dryad.kr076
Foret, S., Kucharski, R., Pellegrini, M., Feng, S., Jacobsen, S., Robinson, G., & Maleszka, R. (2012). DNA methylation dynamics, metabolic fluxes, gene splicing, and alternative phenotypes in honey bees. PNAS, (109), 13. https://www.pnas.org/content/109/13/4968
Hughes, W., Oldroyd, B., Beekman, M., & Ratnieks, F. (2008). Ancestral Monogamy Shows Kin Selection Is Key to the Evolution of Eusociality. Science, 320(5880), 1213-1216. https://science.sciencemag.org/content/320/5880/1213