# Harnessing evolution -selecting for smaller fruit flies



## npaull (May 8, 2005)

Tonight I had an interesting idea. I want a smaller strain of wingless fruit flies to better feed thumbnail metamorphs.

It occurred to me that there's no reason why I can't harness melanogaster's well-known genetic plasticity and short generation time to force a little evolution for my benefit.

From now on, as I make my new cultures, I am straining the flies through a small-diameter mesh kitchen sieve. I made my first new culture tonight. Some of the flies pass through fairly easily, but to get a good number requires a fair amount of tapping. I figure if I'm diligent, I can carry this on for many generations until the flies start to fall through easily. After that, I can find a smaller mesh and keep going. I can think of no theoretical reason why this wouldn't work to decrease average fly size. By how much I can reduce them, I have no idea.

One potential hitch would be if there is significant sexual dimorphism in size. Another would be if a change in some other characteristic makes them fall through the mesh better (ie they elongate, get more slippery, etc). We'll see how it goes.

Anyone tried this before or heard of similar efforts?


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## Pumilo (Sep 4, 2010)

Interesting effort. Could be a market for a smaller fly amongst thumb and pumilio keepers if you can pull off a noticeably smaller fly.


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## edwing206 (Apr 9, 2008)

I've never tried anything like that but Ray(stemcellular) was able to culture stunted melanogaster by using cold water to make his cultures instead of hot water.


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## varanoid (Jan 21, 2011)

You have far more patience then me my friend. Good luck. I hope you succeed.


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## Ed (Sep 19, 2004)

It'll take a bit to isolate out the genetics for the smaller flies. Older maggots keep the younger maggots from feeding in the optimimal areas as so you are probably going to need to watch your flies a bit as selecting from first emergences carries with it the genes for intolerance to older cultures while later emergences could be due to competition. 

Aren't there genetic strains designated minature?


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## Rain_Frog (Apr 27, 2004)

Ed, I was told that "mini white" didn't live up to the hype as being much smaller and that they were slow producers.

"chico" strain carries a gene that can be lethal, thus causing production issues.

One thing I noticed is that some of my wingless cultures dried out prematurely and they produced flies about half the size of normal wingless.


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## earthfrog (May 18, 2008)

At the very least the experiment would tell you whether the flies were small merely due to their sex (male) or if it were also due to other factors such as limited food supply, for instance. 
Maybe one of your controls could be to greatly limit culture size---you could start out with 20 flies instead of 50, for instance. That would take awhile though, but I think it would help rule out flies that were stunted due to an imbalance in the fly/food ratio. Also, keeping the cultures at a 'controlled temp' will stabilize the yeast growth rate, which may again influence hatching size due to stunted/mature flies. 

It seems to me that the smaller flies are merely maggots morphing sooner in response to less food, but maybe the adaptation will stick if you mess with it. Interesting.


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## frogfreak (Mar 4, 2009)

It is an interesting idea.

The female flies are larger than the males, no? You could potentially end up male heavy, I'm guessing.


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## ChrisK (Oct 28, 2008)

If you can find a way to breed flies that I can feed to my Escudo metamorphs, I will be one happy camper


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## sports_doc (Nov 15, 2004)

I think this is interesting, but may only work if you are sifting the early hatches and not the later maggots, as in general all [old] cx's eventually produce 'stunted' small FF's but they reproduce poorly.

Perhaps over 10+ generations of sifting smaller and smaller [not sure how you are going to vary the mesh appropriately] FF, you will isolate 'tiny' genetics.

And then 'maybe' they will stay that way and not revert over time. 

If you are successful and they produce well, I'd buy them 

I wish you the best of luck with it.


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## tim13 (Feb 1, 2011)

evolution happens when an individual is born with a trait that allows it an increased survivability in its habitat and this trait is passed on to offspring that also have this distinct advantage over their competitors of the same species. based on that, i would go about this by making a custom fly culture filled with melanos and maybe gliders from as many different sources as possible to maximize the available gene pool. i would set this culture up so that only the smallest flies can get to the optimal breeding/feeding area through the use of a screen as you mentioned. then, if you get lucky and it dosen't crash, over many generations of decreasing the screen size, you may get the smaller breed everyone wants. I would put two culture cups together separated by the screen. in one cup make a culture with all the flies as normal, in the other i would put a banana or some other very attractive feeding/breeding foodstuff and the ones that get through the screen and breed can be added to another culture. i would wait several generations of flies before reducing screen size to allow for mutations to occur etc.


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## Ed (Sep 19, 2004)

Here is a paper on "minute" mutations. 

A Drosophila Minute gene encodes a ribosomal protein 

and you may be interested in this one 

Cambridge Journals Online - Abstract

Ed


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## What'sAGoonToAGoblin? (Sep 4, 2010)

Theoretically your idea sounds fantastic, but practically it is probably a waste of time. If you are sifting and straining melanogaster flies, then you are going to end up with a container full of male flies and your cultures will crash. 

Also, breeding "small" or "stunted" flies that were stunted because of a lack of nutritional requirements will not alter the genetics of the flies. The offspring from stunted flies will grow to the regular size if given the proper nutrition.


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## tim13 (Feb 1, 2011)

you wouldn't end up with all one sex if you did like i suggested and waited to change culture until you saw larva on the banana, then you know males and females made it through the screen. or, at the very least a female made it through to lay eggs. it can be done.


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## tim13 (Feb 1, 2011)

sorry to double post but i forgot to add an example...

when i was in high school i read a paper on how someone did a similiar experiment with mosquitos. they stuck a bunch of mosquitos in a tank of the same species. this species had a well documented temperature range and would die below a certain temp (as will anything). the person doing the experiment gradually lowered the temp of the tank over generations of mosquitos. at the end of the experiment, he had a strain of mosquito that could survive and thrive in temps that would kill mosquitos of the same species. it can be done. it takes months and a lifeform with a short generational time. bacteria for example can mutate populations very quickly to adapt.


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## packer43064 (Nov 30, 2010)

Hmmmm, I may have to try this.


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## Capybara (Oct 30, 2010)

I've done an experiment with my high school students using selective breeding to breed smaller bean beetles. I have a strain that is roughly 25% smaller than the group we started with.


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## npaull (May 8, 2005)

Thanks for the input guys. I will keep you posted on how it goes.

A few comments:

tim13, the method you describe may work fine but it's way, way more complex than necessary. Also, the idea of mixing strains of flightless flies wouldn't work, as it would restore the dominant gene for flying to the flies and you'd end up all with flying fruit flies. All you need to produce an evolutionary change in a population is a selection pressure and generational time. Given a strong enough pressure (even astonishingly weak pressures effect change if you have enough time), enough individuals and enough generations, change will happen. Theoretically, my method actually *has* to work, provided I can get enough of both sexes, I can do it for long enough, and I can get at least a couple of grades of mesh to work with. That will be the hardest part. Even if I only make it such that the flies pass through my current mesh with ease, though, it would be an improvement.

Ed, thanks for the papers.

Several people mentioned the well-known phenomenon of cultures 2nd or 3rd generation coming out small. I am going to avoid this by using only flies from the first good bloom from each culture.

I'll update as appropriate.


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## Pumilo (Sep 4, 2010)

I've wrked windows and screens for 20+ years. This place has the biggest selection of screen mesh materials I've ever seen! Factory Direct Replacement Window Screens - Window Custom Screen
Maybe they can help with a variety of screen mesh sizes.


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## npaull (May 8, 2005)

Ed, your second citation certainly seems to imply some genetic plasticity in size among melanogaster that is inducible over a reasonable span of time. It's going to be interesting to see if I can get anywhere with this.


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## earthfrog (May 18, 2008)

npaull said:


> Ed, your second citation certainly seems to imply some genetic plasticity in size among melanogaster that is inducible over a reasonable span of time. It's going to be interesting to see if I can get anywhere with this.


I'd be happy to go in with you on this if you get a system set up, and several folks can pool and compare their results using the same criteria which you designate. Let me know.


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## tim13 (Feb 1, 2011)

yea im willing to try my method and compare it with how others fare.


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## Ed (Sep 19, 2004)

npaull said:


> Ed, your second citation certainly seems to imply some genetic plasticity in size among melanogaster that is inducible over a reasonable span of time. It's going to be interesting to see if I can get anywhere with this.


It does look that way.. my only concern is that the selection won't be stable unless screened every couple of generations.... I suspect that there is going to be pressure towards the "standard" size in populations that aren't being selected for size..


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## npaull (May 8, 2005)

Interesting thought. THat may be true. But to be honest, after making one culture this way, the "selection" event added about 1 minute to the making of my culture, so it's not that onerous at all to keep doing.


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## mordoria (Jan 28, 2011)

I love the idea.


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## Ed (Sep 19, 2004)

npaull said:


> Interesting thought. THat may be true. But to be honest, after making one culture this way, the "selection" event added about 1 minute to the making of my culture, so it's not that onerous at all to keep doing.


it is something for people to consider if you stabilize them at a smaller size and people get some from you.. you'll need to supply them with some mesh to sort thier flies so they can keep the cultures from reverting.. 

Ed


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## Vagabond324 (Jan 13, 2011)

Mesh for Clothing, Bags, Screening and more!
You might want to check out this supplier of mesh, they even have a sampler pack so that you can see what to buy before hand or the sampler may just be enough for what you want.


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## izzywalker (May 4, 2007)

Good luck with that project. If you could get those down to giant springtail size almost stabilized that would be quite useful to smaller frog growers. In a semi-related note I have a culture of wingless flies I got from a guy I bought one of my frogs off of that seem severely inbred, move slower than standard flightless or wingless and are really easier to handle than any other wingless or flightless that I have used in the past. I guess you could say that they are a little slower than most cultures in movement and don't spread out immediately when thrown in a tank while every other ff strain I have worked with runs for the tank exit immediately. They seem to breed as fast as your typical wingless though which is good. I don't think that the previous owner of these selectively bred them for this, probably just kept doing new cultures with small amounts of starter flies until the family tree of them just went straight up, no branching leading to really dumb flies. 

You might try crossing your flies with another known dwarf strain even if that strain has known issues just to get the smaller genetics mixed with yours to begin with in a larger amount and then select from there. Most likely your selected lines, while occasionally experiencing issues related to the previous crossed-in small line will most likely experience considerably less of it. Just my 2 cents.


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## earthfrog (May 18, 2008)

izzywalker said:


> Good luck with that project. If you could get those down to giant springtail size almost stabilized that would be quite useful to smaller frog growers. In a semi-related note I have a culture of wingless flies I got from a guy I bought one of my frogs off of that seem severely inbred, move slower than standard flightless or wingless and are really easier to handle than any other wingless or flightless that I have used in the past. I guess you could say that they are a little slower than most cultures in movement and don't spread out immediately when thrown in a tank while every other ff strain I have worked with runs for the tank exit immediately. They seem to breed as fast as your typical wingless though which is good. I don't think that the previous owner of these selectively bred them for this, probably just kept doing new cultures with small amounts of starter flies until the family tree of them just went straight up, no branching leading to really dumb flies.
> 
> * You might try crossing your flies with another known dwarf strain even if that strain has known issues just to get the smaller genetics mixed with yours to begin with in a larger amount and then select from there. * Most likely your selected lines, while occasionally experiencing issues related to the previous crossed-in small line will most likely experience considerably less of it. Just my 2 cents.


I believe crossing species ends up bringing out the flying flies from the gene pool.


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## Ed (Sep 19, 2004)

earthfrog said:


> I believe crossing species ends up bringing out the flying flies from the gene pool.


Strain does not equal species. The cross would be between "morphs" of the same species. 

Not all strains are compatiable. 

Ed


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## DannyMeister (Sep 30, 2010)

tim13 said:


> when i was in high school i read a paper on how someone did a similiar experiment with mosquitos. they stuck a bunch of mosquitos in a tank of the same species. this species had a well documented temperature range and would die below a certain temp (as will anything). the person doing the experiment gradually lowered the temp of the tank over generations of mosquitos. at the end of the experiment, he had a strain of mosquito that could survive and thrive in temps that would kill mosquitos of the same species. it can be done. it takes months and a lifeform with a short generational time. bacteria for example can mutate populations very quickly to adapt.


I hope none of the cold resistant mosquitoes escaped and that if they did, the people in charge of this experiment are now behind bars!


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## hypostatic (Apr 25, 2011)

I feel this will be difficult. Here are some potential pitfalls/variables that you might encounter in your efforts that you should take into account when designing your experimental protocol:

Temperature
Temperature affects the timing of development, which affects the size of adults. Higher temps = smaller body size. But this does not help in creating a "breed" of smaller flies because they would revert to the WT size at lower temps. You can control for this variable by keeping a constant temperature.
Temperature and Time of Development of the Two Sexes in Drosophila

Crowding
Body size in larvae varies with crowding because of a variation in nutrition, and these flies might revert to a WT size in non-crowded conditions. So to control for this you would need to make sure you have a relatively uncrowded/small population size. This makes things difficult because small pop size = low genetic diversity, which slows down evolution. I guess you could control for this by having a really large culture?
http://www.ou.edu/journals/dis/DIS83/Technique83/2tecLefranc/Lefranc.pdf

Larval Stages
The first larval stage is much smaller than the adult flies, and they might easily across the screen mesh, thereby potentially contaminating your stock. Example: a larva that becomes a big fly crosses into where your small adults are, and mates with them. I suppose you could control for this by separating the life stages so that all the flies in a particular container are the same stage (but not necessarily the same size). Synchronizing populations is commonly done with C. elegans by bleaching adults, but I do not know of a protocol for synchronizing Drosophila.









Experimental Error
The human variable. Also the unknown variable. Something happens and your colony crashes (mold? earthquake/act of god). Months of hard work -- DESTROYED. Rightly so, you'd be an unhappy camper if this happened. So to control for this I suggest repeating your protocol on several colonies to be safe.

Genetics
This is the hardest thing to deal with because you don't really know the genotype of your flies (other than they have the mutation that causes flightlessness. You also don't know of any genes that cause small adults, so you can't just order a strain with that mutation. However, there is a well studied fly gene called "giant" where mutant adults can be almost twice as massive (but not all the adults always end up "giant"). Adults can be almost twice as massive because the mutation causes a developmental delay where larval development takes 4 days longer than normal.
http://www.cgslab.com/cgs1/phenotypes.cgi?n=76

IMO, given all that information, I think that a better alternative (or additional) way of getting a smaller fly breed could be to select for faster developing larvae, instead of screening the adults directly, because we know that faster developing larvae make smaller adults. Of course, as others have posted, if you stop your selection process the flies might revert to the WT phenotype. Also, I think an additional benefit of this method is the selection of a shorter generation time.

Sorry for such a long post . Hope no one fell asleep haha. Hope I helped and best of luck!


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