Buzzing about bee genes
Regular Naked Genetics listeners will remember that a couple of months ago Kat Arney went to the joint spring meeting of the Genetics Society, the British Society for Developmental Biology and British Society for Cell Biology, held at the University of Warwick. One strand of talks explored so-called newly tractable systems - new model organisms that geneticists are finally able study for the first time, flippantly summarised as ‘bees and trees’. To get the buzz about our insect friends, she chatted to Paul Hurd from Queen Mary University of London.
Paul - So what fascinates me I guess are honeybees. They fascinate me for a number of reasons. They're important pollinators, they're important for maintaining genetic diversity in flowering plants, and plants of course are required for all animal life because they fix carbon from the atmosphere and produce carbohydrate. So they occupy a pretty crucial place in ecosystems.
From a genetic point of view, they're interesting because a bee genome, a bee larva doesn’t just have the capacity to become a bee – they can become three different types of bee. The question is, how is it that one genome can become three different animals? What is it that enables that to happen?
Kat - So this is more complex than in humans, we have males and females. This is much more complicated than that.
Paul - I think it probably is more complicated. So obviously in humans, we all come from a zygote and that zygote has the potential to form 200 or so different cell types. For bees, that same zygote has the potential to form 200 different cell types put that up in three very different organisms. So, I think it is more complicated, yes.
Kat - So introduce me to the different characters in the honeybee hive. Who do we have in there?
Paul - So top of the pile is queen bee. Queen bee is the largest insect in a hive. She’s the reproductive female - she can lay fertilised or unfertilised eggs. If she lays an unfertilised egg, the resulting larva becomes a male which is also reproductive. If she were to lay a fertilised egg, which is what she tends to do most of, that larva will grow and develop into a non-reproductive female worker bee. So two females bees in a hive, one can reproduce – the queen - one can't reproduce – the worker.
Kat - What do we know about what's going on in terms of the control of the genes that are doing this switch and controlling these different types of bees?
Paul - So this is what we’re interested in looking at. Honeybee caste determination whether you become a queen or a worker is dependent on diet. So what the larvae eats within the first three or four days of it hatching actually determines what it will become as an adult. If the larva eats royal jelly, a specialised substance, a nutritional substance produced ironically by the workers, the larvae develops into a queen. If the larva is fed boring carbohydrate-rich nectar pollen, then she’ll become a worker.
Kat - This is a switch that’s affecting the outcome basically based on diets. That seems quite strange to determine something as important as, are you going to be able to reproduce in your life or not.
Paul - Absolutely. I mean, the bees really are what they eat. There has never been a clear example of an organism really is what it eats. The reason why we’re interested in this is because the two bees are genetically identical, but what they eat changes what they become, we think this is happening at an epigenetic level, the layer of information on top of the genes which controls genome output.
Kat - So there's increasing interest in humans about how the environment thinks we do, the things we’re exposed to, the things we eat influence how our genes turned on and off this sort of layer of tags and switches. What do we know about how that’s happening in bees that’s making the switch between queen or worker?
Paul - We don’t really know. That’s one of the things that we’re looking at, but to some extent, the components of royal jelly do at least give the impression that it’s a pretty good epigenetic diet. So there are things within that diet that we think will be directly affecting gene expression, the switching on and off of genes, and it’s that that we’re trying to tease apart.
Kat - There are some health food shops that will sell you royal jelly and stuff like that, and people will eat it and say, “It must be good for my health.” That could actually be concerning if it’s making that sort of switch?
Paul - I think royal jelly should definitely come with a health warning. I would certainly not eat it. I've seen how it can change bee development from one organism into another so I would treat it with caution.
Kat - Here at the Spring meeting, we’ve just had a series of talks about people who were looking at other unusual insect systems where there are different varieties or castes of insects. Tell me about some of those.
Paul - So there are a number of Hymenoptera that have this caste based system. One obvious one are ants. Ants work in a slightly different way in that there's no nutritional difference. It’s thought that its pheromone chemical signalling that determines choice of caste in ants. Bumblebees – it also seems to be a chemical based system rather than a nutritional based system. Finally, termites and as we saw in the talk today, nobody really knows the ecology of termite caste differentiation.
So, one thing they all have in common is that they're all eusocial. So eusocial insects have this caste determining system because of kin selection. They're all genetic. They're related and so, their hive as a whole looks after the one reproductive queen for the sake of the whole colony.
Kat - So it’s all these organisms – they're all genetically the same, but they're putting themselves into different roles and jobs to support the overall structure of that society.
Paul - Yeah, so it’s a classic case of E.O. Wilson’s kin selection theory where, because of the genetic relatedness of all the organisms within the hive, they act as one super organism for the good of the one reproductive animal within that colony.
Kat - I love JBS Haldane’s quote that he’d be prepared to lay down his life for something like two brothers or eight cousins. I guess it’s on a grand scale.
Paul - Absolutely, on a kind of 50,000 scale!
Kat - What do we still really need to know? What are the really burning questions?
Paul - I think the really burning question is still a fundamental one which is, if the genome is the book of instructions, how is it that that book of instructions can be read and interpreted in multiple different ways in response to various environmental cues? I think that’s the fundamental question in honeybees.
The other question in honeybees that’s kind of related is, what happens to honeybees when their food is contaminated with pesticides and how pesticides that have ingested by honeybees change their physiology and behaviour? I think that’s also a good question in the field.
Kat - This is such a big issue in the environmental world with the neonicotinoid pesticides and the concern that if we run out of bees, we’ll run out of food.
Paul - Absolutely. With the current decline in honeybee colonies then there will be at some stage, the inability to supply humans with food. And so, it’s a crucial question. A lot of great neonicotinoid workers has been done out of the UK from Jeri Wright in Newcastle that showed, ironically, bees are actually addicted to neonicotinoid-treated plants because nobody ever thought that a neonicotinoid which is an agonist of nicotine, may cause bees to become addicted to the pesticide.
And so, she showed in a great piece of work that bees will always feed on neonicotinoid-treated pollen versus non-neonicotinoid treated pollen because the poor bees were addicted to nicotine.
Kat - One final question, your lab keeps honeybees, you work on honeybees. Do you get honey out of them?
Paul - We do get honey out of them! East London honey is the best honey - I can recommend any East London honey you see is definitely worth buying. Everybody has flowers in their window boxes, in their nicely manicured gardens. So in actual fact, city bees are probably the happiest bees in the UK.
Kat - Paul Hurd, from Queen Mary University of London.