As a scientist who studies fruit flies, I get this a lot: “You study effects of stress in what?” Yes, we delve into research on how stress affects Drosophila melanogaster. This helps us understand how stress works in general, which can also help us understand how stress affects us.
But what are Drosophila? You might recognize them as a swarm of tiny flies in your kitchen swirling around your plate of bananas. Annoying, true, but they are also one of the most studied animals in science.
But why? Why do scientists put this much effort into researching a fly? It is not a pest, does not spread diseases, nor do we eat or admire them. And you’d be surprised at how extensively we study them. Especially compared to other animals, seemingly of higher importance to us.
Well, we study them not because we are particularly interested in how fruit flies deal with stress. We study them but because it is a living being, not so much unlike us. Beyond that, we can study it quickly, cheaply, and with not much paperwork, unlike with human study participants.
In this blog post, I will explain why scientists are so interested in fruit flies. The same reasons would apply to other weird research areas: nematodes, mice, rats, sea urchins, and even monkeys.
Conclusions beyond the animal studied
We study fruit flies to understand how animals work. Not only fruit flies, but animals in general. They’re overall easy to study, and you might not have thought about it, but if you do, it makes perfect sense. Flies are a lot like other animals because they all share a common ancestor from a long time ago.
In a similar thought, scientists study yeast cells with the main goal of understanding not how yeast cells work specifically, but how cells work in general. You’d be surprised how much a yeast cell and a human cell have in common, and if you look around, science is full of such examples.
Scientists turn to rats quite often, and it raises fewer eyebrows since many people have heard that rats, as mammals, are actually quite similar to us. Scientists can and do induce cancer in rats (yes, animals also can have cancer) to study how it develops and how to cure it. That would be highly unethical to do in humans, but the good thing is we don’t have to. We have other animals to work with. And not only animals.
Genetics as a science started with Gregor Mendel studying peas. You learnm this in school biology not because inheritance of wrinkled seeds is important to know about, but because it reveals a bigger pattern in how all traits in similar organisms carry over to the next generations. Mendel chose peas because they grow fast, and some characteristics, like color or wrinkledness, are easy to notice.
Fruit flies also contributed their fair share to our understanding of genetics. Thomas Hunt Morgan first described how fruit flies inherit mutant traits, but his student, Alfred Sturtevant, proceeded to develop the first gene map ever. Mind you, at a time when scientists did not even know where genes are located or even what a gene is.
But are fruit flies even like us at all?
So you might shrug in disbelief. “Hey, yes, scientists study rats, because they are mammals, but fruit flies? What do we have in common with those little creatures?” Well, quite a lot.
First of all, our DNA and that of fruit flies share around 60% of genes that are similar in function. Even more so, around 75% of human genes that are attributed to specific diseases have a similar gene in fruit flies. So, what does that mean? Well, genes are a blueprint to build life, so it means that the instructions to build a human and a fruit fly are quite overlapping. And, as a consequence, many inner and outer workings of us and flies are similar.
For example, all life is formed from cells. And these cells work extremely similarly across species and types of living things. You might have learned in biology that plants have different cells compared to animals. But not entirely. Textbooks will draw your attention to differences between plant and animal cells, like cell walls, chlorophyll, and that’s about it. This misses the point that everything else—nucleus, mitochondria, ribosomes, and a long list of organelles—are the same, and they work extremely similarly across plants, insects, frogs, and monkeys.
Thus, similarly, just as it makes sense to study cells in a dish in a lab, it also makes sense to study flies. Not because we learn how flies work, but because we learn how a fully functional living organism works.
Fast, simple, and cheap to grow
So, if we wanted to learn how a full-fledged animal works, why not study humans, rats, or worms? Well, we actually do study all of them, but more on that later. Growing rats in a lab is expensive, and keeping humans in a lab is unethical. So, enter a cheaper alternative: a fly, or a worm.
On one hand, it might seem that specifically Drosophila was chosen as an accident. Thomas Hunt Morgan had them at home (like many of us do), so he decided to use them. That might appear coincidental, but the reason why flies stuck in science is far from a coincidence.
- First off, fruit flies grow extremely rapidly. A fruit fly develops from egg to adult in a mere 9 days. Do you want to study how maternal stress affects children’s adult life? Sure, find a pregnant woman who is in stress (should not be a problem these days), wait for her child to be born, grow up, and then you have your results in 25 or so years. Or, alternatively, you can design a study with flies, and have your results in about two weeks. Great! Even rats would take months to do so.
- Flies also age rapidly. In two months, you can find out how a specific toxin that the animal was exposed to in early development affects its aging, or how a specific mutation in a specific gene can slow down aging. Amazing, if you ask me.
- In addition, flies are also cheap to grow; they eat cornmeal with sugar and agar in most labs, which is super cheap compared to what other animals eat. They take up very little space; hundreds of flies can fit in a 250 ml bottle. Compare that to the space needed to keep hundreds of chickens or mice.
- On top of that, flies are simple to grow. They are not very finicky about their conditions, they do not need large enclosures, or access to a veterinarian. If you have to abandon a lab in a hurry when a pandemic starts, they will be alright. They don’t need daily feeding, walks, or specific nutrients. If power goes out at your lab, not a big problem.
Even more so, you can literally send a bottle of fruit flies to another lab via post. And even if the receiving party forgets to pick up the parcel for weeks, the flies may still survive—true story, don’t ask how I know it, or why I wrote it in the third person.
Fewer ethical concerns
We, humans, are actually concerned about the animals that we raise in our labs. We really do: chickens in labs are kept waaay better than the chicken you get your eggs from. Rats have veterinary and animal wellbeing supervision throughout their lifetime in the lab, but their conspecifics face snap-traps and rat poison in human basements. It is important to ensure the well-being of animals participating in studies, but it is often not possible to exclude suffering.
But are we equally caring for all animals? We would love to say, yes, but that is not true, because we actually do care about animal more if it more like us. We can relate that they suffer because they do similarly to us.
Rats are like us and people might be sad about them trying to find an exit through a maze or getting skincare cream tested on them. But what if that animal is a fly? Well, you can cut open a living fly’s skull and live record the fly’s brain activity, and there is no law to stop you.
Simply put, you can do more harsh things to flies compared to other animals, and you don’t even need permission to do them. Just do it. If you want, you can create mutant flies, zombie flies, and flies that glow in the dark. And speaking of that!
Availability of different mutant flies
So, no one cares about scientists creating mutant flies, and boy, scientists are creative. Let’s say you want to test whether scent is important for a fly to find food. A valid question, becasue it may also be able to find it using other senses. How to test it? Quite easily, you can order a specific mutant line of flies whose genes for developing a normal olfactory system are turned off. And that is just one example; there’s more.
Do you want to know if flies can mate without seeing their partner — order blind flies. Interested in how sleep deprivation affects aggression — order flies that can’t sleep. The list goes on. Do you need a fly that does not feel pain, has PTSD, or is paranoid about being watched? Not a problem, order relevant mutant flies with same-day delivery.
Self-reinforcing system
The ability to develop mutant flies, has translated into a large market, and also opportunities to study all kinds of things. It’s a self-reinforcing system.
We know a lot about flies, becasue we have researched them. We have subsequently developed tools to study fruit flies, and it allows us to study them even more. There exists video recording hardware and software, for example, to specifically study the development of fruit fly larvae. We can use gene editing to modify fruit flies to suit our needs, and we can also push boundaries to test new gene editing techniques with fruit flies.
Simply, we have a vast amount of knowledge about fruit flies, becasue we have studied them for over a hundred years. And this knowledge in turn, lets us ask and test scientific questions that go far beyond our imagination.
However, the most important reason why scientists study fruit flies is that, when combining all of the above, you realize that it allows us to easily and quickly test new ideas.
And the ability to do that is well illustrated in a book by Stephanie E. Mohr: “First in Fly: Drosophila Research and Biological Discovery.” At one point, the author draws your attention to a hereditary study done on chickens. The study lasted for more than ten years, and ended without results, becasue it’s so hard and expensive to raise chickens. Later, a similar study was attempted in flies, and completed in a mere year, giving our understanding of how new mutations are passed onto progeny. The study included 6,000 flies, which would be unattainable in a study with chickens, even given 10 years of studying.