Can female livebearers become male?

[CalmedByFish]

I've been hunting through the internet, and am only finding anecdotal evidence being declared as authoritative fact, as if an anecdote is a doctorate. 🙄 I'd love some actual scientific fact, if you know of any sources. 

My anecdote: About a month ago, I meticulously sorted through endlers that were a couple months old, collecting all the females into one container. My method is to wait until the belly fin opens into an obvious fan, so I know for sure it's not a gonopodium. (I don't look for gonopodiums, since a female's fan-shaped fin can be folded into a stick shape.) All endlers put into the female container had shown me an obvious open "fan." 

Over a month later, at least 1/5 of those females have developed male colors (females stay silver), and a gonopodium. 

I assume the XX chromosomes don't change. But I'm not certain.

I know that in humans, hormones can cause physical characteristics that are atypical for the XX or XY chromosomes the human has. So I'm wondering if I have XX endlers whose hormones have changed to make reproduction possible. 

I really have no idea. Anybody have actual science on this? 

(Maybe @Biotope Biologist or @Hobbit?)

Edited November 26, 2021 by CalmedByFish

[Scapexghost]

From my experience young livebearers always look female. I know Cory has said that non-dominant male swordtails with supress their male features in order to avoid confrontation, and will later express those male traits once other males are removed.

[Flumpweesel]

I agree with @Scapexghost more likely that the males where masquerading as female this seems quite common in fish world. If livebearer develop hermaphroditic qualities we will be over run.  And there would be a lot of evidence as a lot of people keep single sex groups. 

Boys can be sneaky when it comes to getting to play with the girls. I wonder if genetics are moving towards beating the sorters net  rather than dominant fish aggression.  

[GameCzar]

On 11/25/2021 at 11:38 PM, Scapexghost said:

From my experience young livebearers always look female. I know Cory has said that non-dominant male swordtails with supress their male features in order to avoid confrontation, and will later express those male traits once other males are removed.

Interestingly enough, the Amazon Molly species IS all female, but still reproduce.     It being native to the Rio Grande, I've been fascinated by their reproductive behavior. 

[gardenman]

I've had "female" swordtails with no sword, gonopodium, and of the female body shape that then grew swordtails and a gonopodium. They kept the female body shape (males are generally thinner and more streamlined and not as bulky.) Were they always genetically male and just slow developing? Maybe. It sure seems like they change though. When I set up my ten-gallon tank I put in one male and three females. The male was actively spawning with all three females, but then one of the females became a male. She became the dominant male in the tank and harassed the other male. It's interesting. I've kept fish forever and I would have sworn all three were females, but the one "female" became a male. A slow developer or did she change?

[mountaintoppufferkeeper]

There have been quite a few studies of livebearers of one type or another. The link below is one that found there may be some link to presence of predators with a later maturing male. I wonder if that is to stay drab while they observe and adjust to those predator tactics then start coloring up or standing out from the group.

I know my tanks that have had livebearer species in with larger fish. Theh tend to loose numbers over the first two weeks before they stabilize and start to grow in numbers again.

 

Reference

https://scholar.google.com/scholar?hl=en&as_sdt=0%2C6&q=livebearer+fish+late+maturing&btnG=#d=gs_qabs&u=%23p%3DvcG9edRTfLUJ

[Biotope Biologist]

Guppies and other livebearers are very interesting fish to study! 

Their behaviour being very sexually driven makes for an interesting study design. Of the articles I've seen and books I've read referencing guppies and mollies specifically the males can change the shape and size of their gonopodium as well as their coloration in the presence of stressors. Predators as @mountaintoppufferkeeper referenced prefer brightly colored males because they are easier to pick out as opposed to drab females who blend in to their background. This is sexually beneficial for livebearers as the females have to carry live young. The other factor that changes male gonopodium and coloration is the presence of phenotypically dominant males and the percieved ranking in the pecking order. The further down the pecking order the more drab the male and the less developed the gonopodium is. 

 

While sexual changes in marine fish and possibly freshwater(?) is a newer topic it is well documented and the list is growing each day. For many marine fish sex is dynamic. It is very hard to guarantee that a male with good genetics will come along especially in colony fish. So in many species colonies all present female until the dominant female in the pecking order undergoes a massive hormonal change to become male. See clownfish and sheepshead wrasse as the most commonly referenced species.

[PineSong]

When I was reading up on platy genetics, I read that some platies are XX, some are XY, and some are XW--and the W makes them changeable, though I don't recall the specifics of whether they just 'can' change or necessarily 'must' change or what environmental factors impact that. I was looking for info on color genetics so I didn't focus on that.

I had a batch of platy fry on September 2nd that I am still observing daily for signs of being male as of today, November 26. I first saw some of them developing gonopodiums at least a month ago, and moved them to my males only tank as I identified them. I have continued to have to move one or two per week since then. It was a small batch of fry, maybe 9 or 10, born in QT. All but two have turned male.

Likewise, in September I bought a breeding trio of French blue star endlers from a club swap meet. They looked like adult fish to me, size wise. After they were in their 10g for more than a month, I was surprised to see my trio was now a reverse trio--one of the plain uncolored fish presumed to be female colored up and became male. I guess they were younger than I recognized. 

[Gator]

@CalmedByFish; Back in the '80's, I noticed that in the absence of a male over a prolonged period, at least on female Guppy of a group will develop into a male, but is sterile. What I did to prevent this is to butt a 5G tank against the tank with the females so they could see each other, but not reach each other. Problem solved.  

[Hobbit]

This is a super interesting topic! I’m glad @Biotope Biologist and @mountaintoppufferkeeper weighed in with the studies. I can only offer more anecdotes and “what I’ve read” vagueness. 😄 

Like others explained, I’ve frequently read that in some fish species, males will hide their male-ness until they think they’ll have a chance to mate. In the meantime, they’ll develop female traits to avoid aggression with the dominant male(s).

My anecdote is platy-related. I’ve been watching my juvenile platys so I can separate the males from the females before they have a chance to interbreed. I pulled what I thought were 5 males out of the juvi tank and put them with the adults. But there’s a VERY dominant male in there, and lo and behold, none of the juveniles have continued developing male traits. One was already half way to a gonodopodium and he hasn’t reversed that, but he hasn’t developed it either. The others… well, I may have just misread them. They might actually be females. 😄 But I think the only way to know for sure is to put them back with their young siblings and see what they do.

Edited November 29, 2021 by Hobbit

[Griznatch]

 I pulled all the males I could find out of my last big batch of guppies (summer babies). This last month, two of the medium sized females switched to males. Not chasing around any other females, but that could be because I introduced an active mature male to widen the gene pool. Either way, they are big robust males, not streamlined like my usual ones. I'll keep an eye out on them, see if they start acting any different.

Edited November 29, 2021 by Griznatch
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