To understand how honeybees have evolved it is essential to consider the way their sex is determined, and how members of a colony are related.
Bee Sex Determination and Genetics of Worker Bees
A female bee has two complete sets of chromosomes (diploid), while a male has only one (haploid). In a colony there are many sterile female workers, a fertile queen (who has already mated), and males who can fly off to mate with unfertilised queens.
- The female makes gametes (unfertilised 'eggs') by separating out her chromosomes so that each female gamete has only one complete set of bee genes – there are many possible genetic types of unfertilised egg possible (the queen produces many eggs with accurate copies of the chromosomes she inherited, plus others where genes have been sorted into novel combinations).
- The male drone only has one complete set of bee genes, so he can only make one type of sperm.
- When a male (drone) mates with a female (young Queen) his sperm are stored inside the queen to fertilise her eggs.
- The queen has control over whether her gametes are fertilised by drone sperm (to produce a diploid female worker or queen), or whether they are left unfertilised to produce a haploid male drone.
How Primitive Social Bee Workers and Queens are Related
Because all the worker bees have a single father they are all closely related to one another and their queen. In terms of 'selfish gene theory' (Richard Dawkins) it makes good sense for all the workers to co-operate and help their queen survive and reproduce – they will be more closely related to the 'sisters' she will produce than they would be to their own 'children'. In terms of passing on the genes inside a worker bee it is better to forego the ability to reproduce and concentrate on helping the queen.
Honeybee Worker/Queen Relationships and the Evolution of the Superorganism
It makes good sense for worker bees of the more 'primitive' species to co-operate because they all have the same mother and father (primitive colonial female queen bees mate with only a single drone). At first glance all this changed when honeybee queens (European Honey Bee Apis mellifera) developed the habit of mating with several different male drones on their 'mating flight'. The worker bees in a hive no longer all share the same father.
In the early stages of social bee evolution the worker/queen/drone system made good genetic sense, and as colonies proliferated it became the colonies (not individual bees) that became subject to 'evolution by natural selection' – the better adapted colonies survived to reproduce (new colonies are produced by swarming), while the less well adapted colonies died out.
This competition between colonies gave advantages to colonies better able to control the internal environment of their hives. A quick look at the control of hive temperature makes the point.
Hive Temperature Control and Honeybees
Worker bees respond to cooling in their hive by behaviours (innate, and therefore genetically determined) that will warm it up. All the workers in a primitive species colony are genetically similar, so they will all have the same temperature sensitivity. Contrast this with the modern honeybee colony, where the workers are not so closely related to one another (different groups of 'sisters', each with a different 'father'). Here there will be several different genetic types of worker bee, each with a slightly different temperature sensitivity. When the hive cools slightly the most sensitive group will begin to warm the hive up, and if this is insufficient the temperature will continue to fall alerting the next most sensitive group, and so on. This leads to a finely graduated response to a change in temperature, and therefore to very efficient temperature regulation.
The Honeybee Superorganism
The sophisticated way a colony (hive) of honeybees can respond to changes of temperature has been hinted at (there are many different types of possible behaviour as temperatures in the hive fluctuate, and there is a graded response as more groups of 'sisters' are co-opted to respond). The same type of thing happens to control foraging effort, rates of comb building, rate of egg-laying by the queen, and so on. The internal working of the hive begins to look like the internal working of a single individual.
Each honeybee is a complex individual animal, and the whole hive behaves as if it were a single creature – the honeybee colony is a superorganism!
Sources:
- The Buzz about Bees: Biology of a Superorganism, Jürgen Tautz - Verlag Berlin Heidelberg 2008, SPRINGER, ISBN 87978-3-540-78727-3
- The Selfish Gene, Richard Dawkins, Oxford University Press 1976, ISBN 0-19-286092-5
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