In western US waterways, invasive and voracious brook trout are outcompeting native species – but a modified variant could tip the scales
There's a rather interesting study going on in Leandro Creek involving trans fish and chromosomal hijinks.
The brook trout is an invasive species there (introduced by people from the East Coast a while back). As invasive species tend to do, they're outcompeting the local fish like the cutthroat trout, which is at risk of extinction. But how do you fix a problem started so many decades ago? There's fish poison, but it poisons all the fish. So not a great option.
How about tipping the balance of males vs females in the invasive species, then? Researchers have released YY chromosome "super male" brook trout into Leandro Creek. They don't have an X chromosome to pass on, so all their offspring are male (XY). Eventually, the idea goes, there won't be any more female brook trout spawning. And then they'll just stop reproducing and die out, leaving room for the local fish to recover.
Guess how you get a YY fish, though.
As most of us learned in school, you have two main chromosome variants. XY for males, XX for females. (There's more variation than that, but we're playing genetic math here so we'll keep it simple.) XY + XX can result in offspring that are either, as they get one chromosome from each parent. Females can only give X chromosomes though, so how do you get a YY offspring?
You trans the fish. Or initiate the fish version of mpreg, take your pick -- since we don't know how the fish actually identify, you can kind of call it whichever. The researchers dose XY males with estradiol, a feminizing hormone (in a closed environment where the subject fish and their water have no contact with the wild). These male fish then grow ovaries, enabling them to lay eggs. Regular XY male fish then fertilize those eggs. So the offspring come from two XY parents. Some will be your typical XX or XY, but others will be YY.
The YY males then get the estradiol treatment too. They lay eggs, and those eggs are fertilized by other (untreated) YY males. With only Y chromosomes to pass on, you get guaranteed YY offspring. Breeding target success!
And those are the fish that are released into the study area, to gradually tip the gender balance and put an end to wild invasive breeding. Theoretically, the program is still new.
It's a fascinating bit of problem solving, with genetic shenanigans that don't actually tinker with DNA, just chromosomal math. And depending on how you look at it, there's fish out there with two dads, or a trans mother who had a really effective reassignment procedure.
As a nonbinary individual, I'm just a little bit tickled at how the binary is being debunked here by basically fiddling with the water.
The article has more information on the program and how they're studying (and transing) the fish, and the precautions they have in place to make sure the estradiol and treated fish don't get loose and into the food chain.
