Flies, Merlot and Evolution?

We’ve had a fruit fly problem at our house for many months. Various extermination methods have failed to significantly reduce their population. When they first arrived, they were quite uncouth and annoying house guests, but over time, I must say, they have become, at least in one respect, better mannered. Specifically, they sobered up and no longer swim in our wine.

The first few generations of flies loved merlot. They couldn’t get enough of the stuff. They loved it so much, I’d find a number of them swimming in it every time I lifted my glass to my mouth. I’d either fish them out and pinch them out of existence, or, I’d just close my eyes and drink—either way, same result for the swimmers, they went to fly hell.

After a while, my daughters tired of the flies swimming in their glasses of juice and declared war on the rascals. They learned to make fruit fly traps consisting of small glassfuls of the flies beverage of choice (sure, they could have used cheap vinegar, but noooo, they insisted on using the expensive stuff…in the name of science). They covered the glasses with saran wrap then punctured the wrap with pinholes (flies check in, but they don’t check out).

They set these traps in the kitchen at night, night after night, and always awoke to glassfuls of drowned flies. Over time, the girls noticed less and less flies in their traps and I noticed I was eating less of them in my merlot (I was starting to acquire a taste for their earthy bouquet). Finally, last week we all noticed and commented that the drownings stopped completely.

Successful extermination? No! Our kitchen fruit fly population is about the same as it was months earlier. So, why do they no longer kamikaze dive into red wine? AA? Cirrhosis? They realized fruit goes better with white?

Apparently, fruit flies possess some degree of mini-cognitive ability. But, I don’t believe that accounts for our fly population going on the wagon. They would have had to pass that information from generation to generation, and I can’t see that happening (hey, Buzz, see that idiot McFly drowning over there? Don’t do that! And tell your kids not to do it either).

My guess is that it was accelerated evolution in action. I think my daughters selected something in or out of the genome of our population of fruit flies with their wine traps. Do you agree? If so, what was the affected trait?

And lastly, if fruit flies can evolve the ability to count, ours had better learn to do something useful soon, like preparing my taxes, or the war will continue.

That would be my guess. The fruit fly life cycle from egg to reproduction is only a week or two long, so a number of fly generations have likely passed, during which you have introduced a very strong selection pressure for “not being attracted to Merlot”.

Maybe it’s a quibble, but what you’re seeing is not so much evolution in action, but selection in action (and not even natural selection if we really want to quibble). Evolution implies new genes, new species, etc. Your flies are almost certainly the same species and probably even have the same genes. What you’re selecting for are certain expressions of those genes. It’s possible you’ve completely eliminated certain genes from the population, but a Merlot-seeking behavior is probably the result of more than a single gene at work and there are probably some non-expressing carriers of those genes. If you stop killing all the Merlot-seekers, a few generations should see that trait restored to the population. (And you’re certainly only removing that gene from the local population. It’ll be restored as soon as a few flies wander in from next door.)

But quibbles aside, it’s certainly a perfect illustration of how selection works.

I doubt it’s evolution. A few generations of selection pressure in a small population will, at best, fix an already-present genetic variant. There are many other factors to consider, many of which are more parsimonious than invoking evolution. For instance: there might be different species of flies, or a better odor in your trash can, or the flies don’t like wine after it’s been opened a few days, or they don’t like the current variety, or they spend their larval development on a different food source, or there’s some difference in temperature or airflow in your house, etc. (I spend a big chunk of my life thinking of factors that might screw up my fruit fly experiments.)

ETA: in response to dracoi, the simplest definition of “evolution” that I’ve seen is simply “change in gene frequencies over time”, which absolutely includes fixing an allele in a small population.

Not really. At its simplest, evolution is defined as any change in gene frequencies in a population. It doesn’t require any new alleles, much less speciation.

Agree with this. It may be possible you have eliminated a preference of the flies through strong selection if the population is truly closed. However, it will be very difficult to prevent the trait from re-emerging.

However, it has recently been demonstrated that environmental effects on adults can be passed on to offspring through epigenetics. It’s possible that epigenetic effects, rather than selection, has changed the preference of the flies.

Well, ‘possible’, sure, but do you have a plausible mechanism for some kind of epigenetic change?

There’s at least a clear, plausible mechanism for genetic change (preferential mortality of those attracted to wine, over some tens of generations, reducing the frequency of a hypothetical wine-smells-good gene). I’m not saying definitely this is what happened, but it’s at least plausible.

I predict that your children’s children will have developed a taste for bugs in their wine.

Now that’s evolution.

SHHHH! Don’t let a creationist hear you say that!

I doubt that epigenetics would have a big impact on the offspring of the soddened bugs or the ones who avoided the wine, frankly.

I mean, what acquired trait would be inherited here?


Sure, epigenetic inheritance of olfactory preference is not impossible. There is some precedent for a treatment given to parents affecting behavior of offspring, though those results are controversial.

However, reaching straight for a hypothetical epigenetic mechanism to explain a simple phenomenon like this is quite an overreach.

In the end there just aren’t that many conceivable ways to transmit information from the brain (or any other organ) to the germ cells. It’s pretty much limited to endocrine signalling, which is great for telling the germ cell about overall stress levels or nutritional status and other big things like that. But I can’t buy that there is any way that a olfaction -> memory -> endocrine -> germ cell -> epigenetic modifier pathway can ever transmit information with sufficient detail to specify a behavioral response to a specific odorant.

I’m thinking of the story recounted by Darwin about the Galapagos. When they first arrived there, the birds were so tame and unafraid they would land on a sailor’s arm while he was pouring a glass of water, and attempt to drink water from the glass. Later visitors remarked that the birds stayed about 3 feet away, and a generation later one visitor recounted a child with an 8-foot stick whacking birds at a watering hole.

The suggestion is that maybe there is a “skittish” gene that’s very easily mutated that turned up and down. (Too skittish, don’t eat as well; too nervy, you die). As the birds without fear got killed by humans, the ones more skittish survived. As long as “be afraid” is an easily-tuned gene (mutations as to its value are easy to happen) then the behaviour responds very quickly to environment.

Perhaps this is what’s happened to your fruit flies. they don’t so much need to lose a gene, as the “I like X” for various components that make up Merlot has been adjusted via mutation and selection to choose each generation the ones that aren’t as crazy about Merlot. The various wine tatses, IIRC, are various interesting organics prodced by the grape and by the fermentation. I suppose the flies have genes that very easily “tune” to the various components.

Your ideal strategy would be to make traps featuring a variety of distinctive fruits and wines and vinegars, to try to trap all the different flies with different strong attractors.

It’s just a theory.

OK, but seriously, it could be evolution, or it could be that you had more than one candidate gene pool/subspecies there already - and you wiped out one allowing the other to thrive - which is also evolution (but only part of it).