Is this Evidence of Evolution in a SIngle Generation?

Researchers comparing genes in hatchery steelhead -- such as the front fish pictured here, missing an adipose fin -- found they developed significant genetic differences from wild steelhead in the course of a single generation.
John McMillan / Oregon State University

In a study just recently published in the journal Nature, researchers compared the differences in genetic expression between offspring of 1st generation Steelhead (Trout) raised in a hatchery(HxH) vs. offspring of Steelhead from the wild (WxW). For the study, both sets of offspring were reared in identical environmental conditions (in the hatchery).

What the researchers found was quite unexpected.

Results clearly revealed that the two sets of offspring differed genetically across 736 genes, in just a single generation. A large proportion of these genes are associated with three traits: wound healing, immune response and metabolism

The researchers were previously aware that such changes (due to domestication) could occur in shorter lead times, but did not expect it to happen over so many genes in just one generation. When trying to understand the causal mechanism, researchers were able to rule out maternal effects, genetic drift, sampling noise, or false discovery. What they believe might play a role is strong selection due to overcrowding in a small environment.

Some take aways from the study:

Such rapid adaptation could occur via three complementary mechanisms: (i) selection could result in small allele frequency changes at many loci, as in traditional quantitative genetics models17, (ii) selection could act directly on a few regulatory loci18 or (iii) there could be physical changes to the genome that are functionally relevant but that do not involve a change in the nucleotide sequence (that is, heritable epigenetic modifications)19. These three mechanisms leave different signatures at the genomic level, but all create changes that can be directly detected by measuring the global patterns of gene expression.

*emphasis mine.

And:

[These results] clearly illustrate that there are differences in gene expression between the offspring of hatchery and the offspring of wild fish that are substantially beyond the level expected between two groups of unrelated families having equivalent amounts of hatchery ancestry (that is, the results cannot be explained by sampling noise or false discovery).

The study seems to show that in just one generation, an adaptive event (involving multiple traits influenced by over 700 genes) has occurred that can be traced to differences in genetic expression. Now, the evolutionary implications of this study are not at all discussed in the articles or by the researchers themselves, which is why I'd like to gauge the resident experts here.

Could this be evidence of a "saltatory" event? Possibly due at least in part to heritable epigenetic effects?

Link to study is here:
www.nature.com...
Article:
mainenewsonline.com...

a reply to: PhotonEffect

Have they tried to repeat the experiment to other species of fish ? It may just be that this kind of thing is inherent to this specific species of fish ?

How many times have they observed this happening ? There's always the possibility it could be a fluke unless they can observe repeat the process many times no ?

It's pretty cool though, but I wouldn't be jumping ahead of myself claiming it's evidence for evolution, it certainly looks like it could be used as evidence to support the theory though

a reply to: Discotech

Right, but this thread already assumes that evolution does in fact happen. That part is not up for debate here.

What is up for debate is if this study is showing that it happened in just one generation. The prevailing view is that evolution can/does not happen that quickly, but over the course of many generations and thousands or millions of years.

To answer your question about it being species specific: The researchers think not

a reply to: PhotonEffect

I don't know much about genetics beyond high school biology and things I've read here and there since, but I believed in Epigenetics before I ever heard mention of it. So just speculation based on my limited understanding, but I would guess epigentic influences present in the parents' DNA is at play in influencing the gene expression of their offspring. I would further guess that these epigenetic changes and influences don't always work out for the best, but are based on the best attempts DNA makes based on the knowns of the environment.

a reply to: PhotonEffect

Hmm, interesting.

It would, of course throw traditional definitions of the processes of evolution totally in the garbage and shows that epigenetic changes can be heritable.

The thing was, the evolutionary models for genetic population change seemed to make sense, to have a rationale; i.e: evolutionary theory has explanatory power.

What could be the forces that shaped, and allowed such epigenetic switches to exist?

It looks a bit odd that the salmon were, essentially, pre-programmed to adapt to domestication.

a reply to: PhotonEffect

I've read what I can of the paper, most of it is beyond me to be honest, it's a shame they don't offer a conclusion with some of the researchers thoughts about it as it would be interesting to see their take on it, rather just the actual results.

I hope though they get funding to do more research it's certainly a step in the correct direction to proving the theory of evolution.

It would be interesting as well to see it done in controlled conditions in a laboratory in order for them to observe what happens when outside conditions like temperature rises, quality of water have on them and see if they evolve differently depending on conditions, then we could see if it truly is an evolutionary trait.

If there were a fish to rapidly change steelhead would be it.
Considering Steelhead and Rainbow trout are the same species of fish.
Rainbow trout are in freshwater rivers.
Steelhead can go in both freshwater rivers, the great lakes, and Oceans.

They look similar at first but as they mature adults rainbows and steelheads look a bit different.
This means some rainbows at one point learned how to change their gills from freshwater to saltwater. or they learned at one point to turn off that urge to go to the ocean.

Salmon are also weird in that salmon and trout occasionally mate and produce hybrids. Now get this, A GM atlantic salmon which grows at double rate mated with a brown trout. This frankentrout grew even faster than the GM salmon and outcompeted it.

originally posted by: PhotonEffect
a reply to: Discotech

...The prevailing view is that evolution can/does not happen that quickly, but over the course of many generations and thousands or millions of years.

...

It would seem to me that any genetic change must occur in the course of a single generation (though epigentic markers possibly build influence across generations?) We consider evolution to be something which takes place over many generations, but that is more of a retroactive perspective. When we look back at the evolution of a modern species from it's most ancient antecedent, we can identify the points in time at which various evolutionary milestones which we've found evidence of happened, but we don't typically have a long string of generations with which to compare.

I'll make up a fictional example since I have no well of actual knowledge to go to on this topic. Let's say Zebras didn't originally have tails, but then the Tsetse fly started spreading trypanosomiasis (sleeping sickness) among the Zebras, who were then easy prey for all manner of predators. The Zebras population dwindled as more and more of them fell prey to the deadly combination of Tsetse fly and hungry Sabretooth Tiger bites. The downward population trend threatening the Zebras very existence was finally rectified when Zebras evolved tails to swat the Tsetse fly away, reducing the incidence of sleeping sickness, thus reducing the suceptibility to hungry Sabretooth Tigers. (I just realized I'm capitalizing all of the animal names.)

Anyhow - so did the tail begin as a small nub, growing a few millimeters with each subsequent generation, or did one generation suddenly have a full-length tail? If it was just a few millimeters with each generation, when do we consider it evolution? Is it a matter of degree? Is it evolution once the genetic expression turns into something useful which affects the species in a profound way (in this example, a long-enough tail to swat away the Tsetse fly?) Or is every step, every genetic differentiation building toward what ultimately becomes a profound change for the species considered "evolution?"

Maybe in some cases (as in the fish), a profound and obvious change takes place in a single generation (owing to a profound change in environment stressing change/evolution of the species.) Other times, maybe it does happen bit by bit, a few millimeters of tail at a time. While we would see those minute changes only in comparing many generations of separation, each step would be "evolution" if we looked close enough.

I'm rambling long to get to this, but I'm working it out in my head as I type. It seems to me, evolution only ever happens in a single generation; it just happens that most profound and obviously differentiated changes only occur over many generations of evolution/genetic changes. I also believe that most evolution takes place as a result of epigentic changes in parent generations (expressing more fully in each subsequent offspring generation.)

originally posted by: dogstar23
Anyhow - so did the tail begin as a small nub, growing a few millimeters with each subsequent generation, or did one generation suddenly have a full-length tail? If it was just a few millimeters with each generation, when do we consider it evolution? Is it a matter of degree? Is it evolution once the genetic expression turns into something useful which affects the species in a profound way (in this example, a long-enough tail to swat away the Tsetse fly?) Or is every step, every genetic differentiation building toward what ultimately becomes a profound change for the species considered "evolution?"

I always considered each stage as the process of evolution, so each time the tails grows each generation is it evolving but not evolved, once we reach the generation where the tail is fully formed then the zebra is "evolved" while the process from no tail to nub to bigger nub to tail is the evolution

Any changes that occour genetically as noted above can only be deemed to be hybridization.
Nor can this be believed to be naturally occouring,neither can the claim be made that nothing was introduced into the enviroment which influenced the changes to occour...
The changes listed also appear to be a regression rather then a progression as old information seems to have been once again adopted during selection.

I think evolution in a lot of situations happens very fast.

Why would zebra's slowly get a tail. There is no evolutionary advantage to have a 2 cm long tail. It would not have increased its breeding success.
Seems like DNA somehow interacts with the environment in a way where it gains knowledge and makes an adjustment in the next generation. zebra's likely had the tail DNA all along, it only needed to be activated.

I've been throwing around a idea in my head for a while, ever since I started reading about the crazy things the human body does autonomously (even without the brain), watching a T-cell actively pursue a bacteria, seeing the way DNA is expressed in cell division, and a few things i've read about epigenetics. I've been wondering if maybe there is a second consciousness in multi-celled organisms that have some semblance of a colony organism, a consciousness that is independent of the brain but more an amalgamation of cell reactions to outside stimuli. Furthermore, I wonder if these reactions of the "colony" side of our physiology can be expressed in epigenetic changes.

I have nothing to back this up with, but I think its a fun bit of fantasy.

Great post!

a reply to: jellyrev

Considering Steelhead and Rainbow trout are the same species of fish.
Rainbow trout are in freshwater rivers.
Steelhead can go in both freshwater rivers, the great lakes, and Oceans.

It's interesting that with completely different migratory lifestyles, and presumably some physiological differences, that these trout can still remain the same species.

originally posted by: chr0naut
a reply to: PhotonEffect

Hmm, interesting.

It would, of course throw traditional definitions of the processes of evolution totally in the garbage and shows that epigenetic changes can be heritable.

Do you think that's what's happening here?

originally posted by: 5StarOracle
Any changes that occour genetically as noted above can only be deemed to be hybridization.

But it's the same species of fish.

a reply to: Slanter

Cool post.

I also think we will soon learn that most, if not all, instinctual behavior is actually the result of epigenetic factors, and not [just] random genetic mutation.

Because it's the only explanation that makes sense.

originally posted by: PhotonEffect

originally posted by: chr0naut
a reply to: PhotonEffect

Hmm, interesting.

It would, of course throw traditional definitions of the processes of evolution totally in the garbage and shows that epigenetic changes can be heritable.

Do you think that's what's happening here?

It would be pre-emptive to make the assumption. I'd like to see far more studies with similar result to feel confident. Also, it is possible that the interpretation of the results is skewed somehow.

It is easy for a researcher to succumb to pressures to produce 'novel' results, so as to stand out from the competition. That is why there is a process of peer review, hopefully to weed out bias.

With topics that impinge on evolution, however, many peers are themselves committed to a particular viewpoint and therefore can apply a 'group bias' to interpretation of results.

a reply to: PhotonEffect

I hadn't thought of that, but epigenetics would be a handy way to explain the complexities of instinctual behaviour wouldn't it?

originally posted by: PhotonEffect

In a study just recently published in the journal Nature, researchers compared the differences in genetic expression between offspring of 1st generation Steelhead (Trout) raised in a hatchery(HxH) vs. offspring of Steelhead from the wild (WxW). For the study, both sets of offspring were reared in identical environmental conditions (in the hatchery).

So the hatchery has predators?

a reply to: chr0naut

I tend to agree with you on all points.

But let's shelve the cynicism for a minute and assume that the researchers were not compromised and their results are true. Can it be considered, by the current definition, to be evolution (in one generation)?

Also, to be published in Nature, it would have to be peer reviewed, yes?