Moved by religion: Mexican cavefish develop resistance to toxin

[w1z4rd]

COLLEGE STATION, Nov. 4, 2010 — A centuries-old religious ceremony of an indigenous people in southern Mexico has led to small evolutionary changes in a local species of fish, according to researchers from Texas A&M University.

Since before the arrival of Christopher Columbus to the New World, the Zoque people of southern Mexico would venture each year during the Easter season deep into the sulfuric cave Cueva del Azufre to implore their deities for a bountiful rain season. As part of the annual ritual, they release into the cave’s waters a distinctive, leaf-bound paste made of lime and the ground-up root of the barbasco plant, a natural fish toxin. Believing the cave’s fish to be gifts from their gods, they scoop up their poisoned prey to feed upon until their crops are ready to harvest.

However, a team of researchers led by Dr. Michael Tobler, an evolutionary ecologist at Oklahoma State University, and Dr. Gil Rosenthal, a biology professor at Texas A&M, has discovered that some of these fish have managed not only to develop a resistance to the plant’s powerful toxin, but also to pass on their tolerant genes to their offspring, enabling them to survive in the face of otherwise certain death for their non-evolved brethren.

Their findings recently were published in the online journal “Biology Letters.”

http://scienceblog.com/39940/moved-by-religion-mexican-cavefish-develop-resistance-to-toxin/
Wow, interesting info.

 

[murraybiscuit]

interesting.
although you can't discount the possibility that the tribe did something to pi55 the rain god off, or that the fish cried out to the god of dryness and he rescued them...

 

[rwenzori]

although you can't discount the possibility that the tribe did something to pi55 the rain god off, or that the fish cried out to the god of dryness and he rescued them...

Yes, there's that. Good thinking.

 

[Techne]

"kick-started the evolutionary process of natural selection"? Lol.

Sounds to me like this is just the necessary outcome of discernible and often quantifiable causes. Now where is the genetic data so that we can see what happened in greater detail.
In those fish that did survive after exposure to the toxin:
1) Which genes (or set of genes) did this toxin cause to up-regulate or down-regulate?
2) How did this change in gene expression affect the adaptability of the organisms?
3) What effect does this toxin have on epigenetics?
4) Did these new "toxin-tolerant" variants develop independently from any relation to the environment via chance or not?

Nice find though, it will allow future studies to focus more on the effect that the toxin has on those that do survive its exposure.

 

[burden]

"kick-started the evolutionary process of natural selection"? Lol.

Sounds to me like this is just the necessary outcome of discernible and often quantifiable causes. Now where is the genetic data so that we can see what happened in greater detail.
In those fish that did survive after exposure to the toxin:
1) Which genes (or set of genes) did this toxin cause to up-regulate or down-regulate?
2) How did this change in gene expression affect the adaptability of the organisms?
3) What effect does this toxin have on epigenetics?
4) Did these new "toxin-tolerant" variants develop independently from any relation to the environment via chance or not?

Nice find though, it will allow future studies to focus more on the effect that the toxin has on those that do survive its exposure.

Yeah Techne, you see, it's called selection pressure whereby the original allele is suppressed and other mutant or recessive alleles increases in frequency allowing the survivors to breed with each other and give their offspring their genetic code: evolution.

What data do you need to see in greater deal??
-fish find barbasco plant toxic: fact
-fish die from barbasco plant: fact
-some fish survived barbasco plant: fact

Give me another reason other than evolution.

1) No genes. The ones that were immune survived
2) Gene expression doesn't change. Only via populations over a period of time, not individuals
3) the allele that causes the immunity towards the toxin allows for that phenotype to show. this phenotype increases in frequency as it is the only phenotype (allele) available. the rest are killed by toxins
4) all organisms carry a wide variety of alleles, most of them are recessive. the environment doesn't change characteristics in individual organisms Techne, only the increase in such alleles and phenotypes. Snow doesn't make rabbits white, white rabbits are just better adapted to survive and natural selection just leads to an increase in white rabbits.

I think you have a bad understanding of evolution, I think you are confusing it with Lamarckism

 

[Techne]

burden, the data for this study is limited and not enough to fully understand the emergence of the resistant allele.

All we know is that:
1) "these fish have managed not only to develop a resistance to the plant’s powerful toxin, but also to pass on their tolerant genes to their offspring, enabling them to survive in the face of otherwise certain death for their non-evolved brethren.".
2) "They found that the mollies annually exposed to the barbasco indeed were more resistant than the fish further upstream — to the extent that they were able to swim in the noxious water nearly 50 percent longer."
3) "Mollies able to tolerate the poisonous conditions survived and passed those traits to their offspring, resigning those that perished to their fate of serving as a ceremonial feast for the Zoque."

If you read the paper, you will realize:
1) There is no analysis of the genomic differences found between the resistant and the non-resistant fish.
2) There is no data on the effect that the toxin has on:
A) Gene expression
B) Epigenetic changes

So here are a few possible ways that a population with such a resistant allele can emerge.
1) Some fish in the original population express a gene (or a set of genes) that are able to detoxify/metabolize the toxin naturally. Those that do not, were killed and gave rise to a population of resistant fish.
2) None of the fish in the original population are able to detoxify/metabolize the toxin naturally. The toxin induced a set of genes that interfered with various control mechanisms, which in turn causes an increase in mutations to happen. Some of these mutations resulted in the formation of new proteins (or group of proteins) that are able to detoxify/metabolize the toxin. Those fish without the mutation were killed and gave rise to a population of resistant fish.
3) All of the fish in the original has a gene (or a set of genes) that are able to detoxify/metabolize the toxin, however, they are not expressed under normal conditions. When some of the fish are exposed to the toxin, epigenetic (or perhaps just genomic/proteomic/metabolomic) changes cause a change in gene expression that in turn results in the activation of the gene (or a set of genes) that is/are able to detoxify/metabolize the toxin (the cytochrome P450 family of proteins is a nice candidate). Those fish without the this adaptability were killed and gave rise to a population of that are more adaptable to the toxin.

Any of these ways or even a combination of these ways could be why there is now a resistant population. We just don't know what effect that this selection pressure (the toxin) has on the epigenetics as well as genomics/proteomics/metabolomics of the fish.

To reply to your "answers":
1) Of course the toxin has an effect on the activity of genes and gene expression. (I think you might have misread it, my bad, I meant which set of genes are caused to be up-regulated, meaning which genes' expression are changed)
2) Of course gene expression changes in response to selection pressure. That is a basic biological fact . Gene expression does not stay constant and the toxin will DEFINITELY have an effect on gene expression. Again the data for mRNA levels, epigenetic changes, the effect it has on the proteome etc. is not known.
3) We know very little about how this allele emerged (see above).
4) Of course environment change characteristics in individual organisms. This is a biological fact. Read up on epigenetics.

Next time when you want to tell someone else they have "a bad understanding of evolution" or are confused, please try and understand their point of view first.

 

[burden]

Sigh. I don't have time to reply to that wall of text, I'll do that sometime this week.

As for: "Of course gene expression changes in response to selection pressure"

It doesn't. Genes don't change in response to selection pressures, selection pressures only lead to desired genes that already exist to increase in frequency. Individual bacteria, ergo genes didn't become immune to penicillin. Surviving bacteria simply passed their traits.

Did you look at my link? You seem to confuse evolution with Lamarckism, which is a very common mistake people make.
Individual's don't change, populations do, its textbook biology. BTW epigenetics is the *inheritance* of phenotypes

 

[Techne]

Please read again and try to understand what I mean by "gene expression changes in response to selection pressure". When a gene is expressed, it expresses mRNA which in turn is turned into protein (not always of course because other factors do play a role).
Some genes are not expressed while others are, and yes gene expression of many genes (not all) DOES IN FACT change in response to selection pressure. It is a simple fact.

To view epigenetics as simply the "*inheritance* of phenotypes " is simplistic. Read up on the ability of epigenetically related enzymes and their ability to methylate and demethylate cytosine (one of the DNA bases). The methylation status of cytosine acts as a switch for genes. Hypermethylated regions act as suppressors of gene activity. And yes selection pressures can and do have an effect on the epigenetic/methylation status of the genome and it can be passed on to the next generation.