Honey Bee Polyandry: The Secret to Their Success. Yep, a nice catchy headline, but for most beekeepers the polyandrous nature of honey bees is not much of a secret at all. When a virgin honey bee queen takes her risky mating flight to a drone congregation area she will have sex with many drones (male bees) before returning home. It’s quite possible that she carries the sperm of over 30 drones back to her hive. Over the next few days it migrates to her spermatheca and gets mixed up, but not all sperm will be equally represented.
Getting my head around genetics
I recently saw a video on Bob Binnie’s channel in which he interviewed Keith Delaplane, of the University of Georgia, about polyandry.
Anything to do with genetics tends to make parts of my brain leak out of my ears, but after watching that interview I whipped out my copy of Queen Breeding and Genetics by Eigil Holm, followed by some frantic searching on the interweb. Who knows, maybe this time it will make sense, thought I. I’m gradually getting my little mind around this subject.
The main problem with writing a blog about beekeeping is that nothing I think of to write about is new; somebody has already been there, done that (probably more competently). The main thrust of what I try to do is to get down to actual practical beekeeping, although I do wander about sometimes. This latest bout of researching honey bee genetics does have some implications for my beekeeping, which I will come to, but for now I going to blast through some basics.
Chromosomes and all that
The queen is made from a fertilised egg, just like worker bees, but her diet and the way she was cared for during her development ensured that she was special. Not many fertilised eggs get to become a monarch. At a genetic level her cells contain 32 chromosomes, made up of 16 from her mum and 16 from her dad. When she lays an egg, it only has 16 chromosomes. A process called meiosis randomly mixes up bits of genetic material from her chromosomes (some from mum, some from dad) to make the 16 chromosomes in the egg. This happens in humans too; in females while she is a developing foetus, and in males at puberty.
So, each egg laid by a queen will be unique, with a different combination of DNA from her parents. As she lays her egg she fertilises it with a tiny amount of sperm from her spermatheca, which has been kept safe since her mating flight. The sperm has 16 chromosomes, so that when the two combine we get back to the 32 chromosomes that make a female bee (worker or queen). Because there is sperm from so many different drones inside the spermatheca (I think the record from natural mating is over 70) the resulting workers tend to be half-sisters. Half sisters have the same mum but different dads. There will also be so called super-sisters, made from the same mum and the same dad.
Why super-sisters? That’s because every sperm produced by a single drone is identical. In humans, meiosis happens in boys, meaning that each sperm carries a mixture of DNA from his mum and dad, so each sperm is different. This does not happen in honey bees. The drone comes from an unfertilised egg; he only carries DNA from his mother. The 16 chromosomes in his sperm are not mixed up with a bit from each parent, because there is only one parent.
Advantages of hyper polyandry
It so happens that this process of creating multiple subfamilies (patrilines) within a colony is extremely beneficial. Some of these groups will have a combination of genes which cause certain behaviours to be expressed more strongly than others, such as gathering honey, feeding larvae, or defending the hive. Research shows that hyper-polyandrous queens head colonies that tend to out perform those headed by queens who have only mated with a few different drones. Everything about the way honey bees mate is geared towards massive mixing up of genes to produce huge diversity, even inside a single colony. This must have been an evolved process that succeeded because it enabled the bees to adapt to environmental changes over time.
Having great genetic diversity may offer survival advantages to bees through adaptation, and certain genes being ‘activated’ by different conditions, but there are limits. For example, the European honey bees have not evolved with parasitic mites, whereas bees in Asia have a long history of such co-evolution. Our bees that do manage to survive varroa infestation without collapsing are having to call on genes that were advantageous for something else, and just happen to help with managing mites.
Anyhow, what does that mean for little ole me trying to raise queens that make loads of honey, don’t sting me very often, and don’t swarm away at the slightest opportunity? I don’t live in an isolated area, and I don’t practise instrumental insemination (yet), so I have to accept that I have no control over the drones that my virgin queens mate with. Nature has no problem with this, but nature doesn’t always produce great bees for beekeepers.
Some bee breeders create a closed population of bees which are cut off from other bees. The closed population needs to be large enough to retain diversity, and new blood can be brought in periodically to keep things fresh. All of that is controlled with isolated mating and instrumental insemination, which is way beyond what I can do. Most queen producers are not breeders; they take breeding material from ‘proper’ breeders and open-mate virgin daughters with local drones. It works well, but it is subject to nature’s desire for randomness and diversity.
Rethinking queen selection
The main thing that strikes me from all of this, apart from how incredible honey bees are, is that I need to rethink my expectations a little. I fall into the trap of thinking that my greatest colonies must be headed by a great queen. I then try to reproduce those excellent qualities by grafting from that queen. But hang on. The majority of the behaviours within a colony are the result of the multiple subfamilies at work in the hive. Sure, they have the same mother, but it is the particular mix of drone sperm that was matched to that queen’s eggs that has caused the perfect blend of qualities that I’m looking for. How likely is it that the daughter queens of that breeder, open mated, will result in the same traits? I’m guessing it’s all a bit of a lottery.
I still think it’s worth selecting my best queens for making new queens, and I definitely believe that colonies with good qualities should be given plenty of drone comb. The more good drones that we have in our area, the more likely we are to get well mated queens with, hopefully, the traits that we desire. Equally important, and often overlooked, is the removal of drone comb from horrible colonies, and changing their queens. When selecting queens, I need to look at traits that are specific to that queen, not just the subfamilies, when choosing a breeder. These are some I can think of:
- lays lots of eggs in a beautiful brood pattern
- strong pheromones, nice retinue of workers around her
- well mated, longevity?
Even these few traits are partly dependant on factors outside of the queen’s genetics. The ability to lay lots of eggs can be held back by the number of workers and the amount of nutrition available. However, under good conditions some queens will be able to lay more eggs than others, and that is down to the queen. The brood pattern is a great thing to look out for in my opinion. I presume that brood breaks in winter or during dearths are not so much about the queen, but her workers. Whether or not a queen gets well mated (lots of sperm from lots of drones) could simply be a matter of luck. However, at least if we select breeder queens that were well mated and live for many years there is a chance that some of that is because of her genes. Maybe she has a bigger spermatheca, or stayed out on mating flights longer until she mated with a lot of drones…I’m speculating.
All of those good beekeeping traits like gentleness, honey gathering, hygiene and so forth seem to be due to the combination of queen plus drones; a combination unlikely to be consistently repeated using open-mating. It therefore remains my job to be ruthless with badly behaved colonies and weak ones that need endless nursing; they should be removed and a new queen + drone combo given the chance.