Siren-like: The Amazon molly uses its powers of seduction to lure the males of related fish species into largely fruitless matings. For the most part its offspring are asexual clones, say researchers.
Credit: Dunja K. Lamatsch
SYDNEY: New research has shown that an all-female species of fish has survived without sexual reproduction for up to 100,000 years.
"Basically… the Amazon molly should have gone extinct already," said evolutionary biologist Laurence Loewe, from the University of Edinburgh in Scotland, as asexual vertebrate species are thought to rapidly suffer from damaging mutations to their DNA.
Though researchers have previously suspected the fish's surprising longevity as a species, this is the first formal evidence to confirm it, said Loewe. Along with biologist Dunja Lamatsch, of the University of Würzburg in Germany, Loewe is coauthor of a study reporting the find in the journal BMC Evolutionary Biology.
Independent women
Contrary to its name, the Amazon molly (Poecilia formosa) is found not in Brazil, but in the river systems of Mexico and the U.S. state of Texas. Small and silver-coloured, the uniqueness of the species derives from its unusual mode of asexual reproduction.
The mollies produce eggs complete with all the necessary genetic material for the development of their offspring. This means that the 50 per cent genetic contribution provided by sperm in most other animal species, is not required.
Its presence is still needed, however, with the sperm acting solely as a "mechanical trigger" to kick-start the embryo's development, said Loewe. For this reason the female fish get friendly with males from other species, including the cave molly (Poecilia mexicana) and the sailfin molly (Poecilia latipinna). The mollies use behavioural and chemical cues to "seduce" these males and "enforce copulation," he said.
But reproducing asexually, without the recombination of two sets of parental genes, should ultimately be harmful for a species, said Loewe. "There are many asexual species that are known to be quite short lived." This is because without the input of paternal DNA, harmful genetic changes tend to build up over many generations.
With this in mind, Loewe and Lamatsch used mathematical computer models to simulate the evolution of the Amazon molly. What they discovered was that the species may be up to 100,000 years old, and by their reasoning should have died out from DNA damage around halfway through this lifetime.
Doubt about mutation Danger
Why does asexual reproduction mean dangerously fast genetic degradation? I'm assuming that the Amazon Molly was sexed, and lost it due to a mutation (hence still needing the 'manual trigger'). Surely with enough reproduction mutations should tend to average out? i.e as many "mutation fixes" as mutations.
Re: Doubt about mutation danger
The reason asexual reproduction tends to make species short-lived is its tendency to produce a build up of harmful mutations in the genes of each successive generation. The problem with mutations is that they DO tend to be harmful (a mutation is generally the result of genetic damage), the "natural fix" for this is sexual reproduction, which introduces another set of DNA which doesn't contain the bad mutation and counters its effects. (Sort of like the article is suggesting they might be doing by sneaking in DNA from individuals of related species) Hope that makes sense!
re: Re: Doubt about mutation danger
You didn't answer his/her question, you just summarized the article. The question is: shouldn't positive mutations counteract negative mutations, and therefore allow organisms to survive via only asexual reproduction?
I don't know the answer to that question, it seems that in our world the exchange of DNA via sex gives sexually reproducing organisms a great advantage over asexually reproducing organisms. However, there are plenty of examples in the unicellular world of organisms surviving and prospering via only asexual methods (certain species of Tetrahymena and others). But even in the bacterial world the exchange of some DNA (via a sex-pillus or conjugation) is very useful for their prosperity.
This article is great, because it's very exciting to find a multicellular organism that reproduces asexually. It would be nice to find a few more.
re: Re: Doubt about mutation danger
I think he did answer the guys question, and I think you're again asking a question he's already answered. The fact is that given a completely random mutation, what are the odds it'll do something beneficial to the species? Without sexual reproduction, the chances of the good genes passing on and the bad genes not passing on are thrown out of whack when compared to with sexual reproduction.
The chance of a negative
The chance of a negative mutation is far higher than the chance of a positive mutation due to the level of complexity of the organism. Too put it another way, there are so many things that can go wrong that the equation won't balance. Also the likelihood of a second mutation directly repairing a previous mutation is extremely finite.
Doubt about mutation Danger
If asexual reproduction were to happen perfectly, you would end up with an exact clone. However, in the process of developing a single cell into a multicellular organism (a fish) or creating the sex cell in the first place, there's bound to be errors in transcribing the DNA. There are a finite number of ways in which an error can be beneficial or neutral, and an infinite number of ways in which it can be harmful. With sexual reproduction the alternate set of DNA either eliminates or masks this (if it’s recessive) in the resulting offspring, or if it’s dominate then that offspring stands less of a chance of surviving to reproduce culling the error from the gene pool. In an asexual organism the errors have no check and these errors will start to collect, and as was said previously the chances that one mutation will undo another is very improbable. Eventually the species as a whole will be so full of errors so inefficient at survival they will (or so was thought) go extinct.
To use a metaphor, make a photocopy of an image, then copy the copy and so on. The random errors will collect (what are the chances one error will correct another) until the image is unrecognizable.
Do the MATH!
What is not being stated is that those eggs with genetic variations or "mutations" that are harmful will tend to not create viable offspring. They will die off!
Those eggs that tend to have a more stable genetic structure will create viable offspring. They will pass on that "stability" to the next generation.
Over time, those that survive will become more and more stable and hence bring about what is perceived to be impossible.
Ain't nature neat!
Nature rocks
Heck yea it is neat! But who knows what will happen in the end, it is very complicated, no one can be sure that they have the right answer, probably....
I found this article to be facinatingly informative. KUTOS to the author and scientists involved in this.
there is danger
DNA codes for proteins for the most part. proteins have very specific structures so much so that one change will throw the entire good working protein on the rubbish heap. So the likely hood of a mutation occurring thats a disadvantage far outweighs the chance of a mutation occurring thats advantageous to the species.
It's Molley and Polley, not Molley and Steve
<sarcasm>We need a Constitutional amendment to define marriage between a male fish and and female fish. These asexually reproducing all-female fish are destroying the basis of marriage and thus our whole society.</sarcasm>