The relations of insects of the order Hymenoptera (bees, ants and wasps) are both unique and peculiar. Not only do their group dynamics lead to the establishment of queens which lead their colonies, but they also us to view selection and evolution first hand from the perspective of genes rather than whole organisms.
Haplodiploidy is a sex-determination system used by these insects, where the sex of an individual is determined by the number of sets of chromosomes he or she receives. In a bee colony, haploid individuals (one set) are male (drones) and diploid individuals (two sets) are either the queen or her female offspring (workers).
How? When a queen mates with a drone it stores the male sperm, which contains the entire drone genome, for years. When the queen lays eggs a decision is made and the egg is either fertilized or unfertilized. Unfertilized eggs result in drones that share 100% of their genome with the queen and fertilized eggs result in workers that share 50% of their genome with the queen as all the sperm are identical (excluding mutations) and so contain all of the father’s chromosomes and half of the queens. Thus, on average, any two workers picked at random will share 75% of their genome with each other. This is more than with their mother.
Interestingly, this means that the family tree of a single male bee (see left) if followed back several generations results in a Fibonacci sequence of the number of individuals in each generation (1, 1, 2, 3, 5…) which is commonly seen throughout nature, albeit more frequently shown in its spiral form in shells and plants using having structures with sides of length equal to the aforementioned numbers.
You might now be thinking “Gosh that’s interesting!”, and “that’s great, but why is this information useful? What can it tell us about evolution?” To answer this, the way of thinking put forward by Richard Dawkins in his popular book “The Selfish Gene”, where organisms are considered “Survival Machines” for the genes contained within them can be cited. This thought experiment suggests that if genes ‘want’ to ensure their survival, then they will express traits or phenotypes to preserve their copies in other individuals as well as their own survival machine.
Once this view is adopted, it makes sense why reproductive altruism and cooperative hive care, also known jointly as eusociality is seen in bee colonies. With all this in mind, sisters who share 75% of their genome on average will propagate their genes by assisting in the raising of more sisters birthed by one queen rather than their own daughters. Through this method of altruistic behaviour, the “selfish” gene for worker care and cooperation is preserved. This excellent example has allowed the formulation of “Hamilton’s Rule”. The rule states that genes will increase in frequency when rB > C where r = the genetic relatedness of the recipient to the actor, B = the additional benefit gained by the recipient and C = the reproductive cost to the individual performing the act. This has been used to study social behaviours in primates.
Sadly, while the maths works well on paper, genes alone cannot entirely maintain eusociality. Pheromones emitted by the queen suppress workers egg laying, notably the queen mandibular pheromone which prevents the rearing of a new queen and limits ovary development in workers via hormone alterations. Any eggs that are still laid by females aside from the queen are devoured.
As the queen ages, the output of these pheromones diminishes and supersedure begins where workers rear a new queen in a special cell, feeding it large amounts of royal jelly. Containing proteins, sugars, fatty acids and other vital components which aid the development of the next generation, Royal Jelly is fed to all developing eggs for 3 days. Queens to-be differ in that they are fed royal jelly throughout their development rather than just 3 days which triggers the formation of queen morphology.
When this new queen develops, the old queen is brutally murdered in an act known as balling where many workers surround the queen, raising her body temperature to the point of death by hyperthermia. Bees provide an excellent model organism for population genetics and what we learn from them can be applied to a wider range of research within biology. As is usually the case in nature, there is more to them than initially meets the eye.