Toads point to new mechanism for evolution

[Geriatrix]

Cane toads are shining light on a new process by which genetic traits evolve, say Australian researchers.

They say it has "revolutionary" implications for our understanding of evolution.

Professor Rick Shine of University of Sydney and colleagues report on what appears to be a parallel process to natural selection, called "spatial sorting," in this week's Proceedings of the National Academy of Sciences.

"It's a pretty radical concept. It's the first really new mechanism for evolutionary change for 150 years," says Shine.

"It's a very different process to anything that Darwin talked about because you're having traits evolve not because they help you survive or reproduce, but because they help you disperse faster."

According to Darwin, traits accumulate within a population if they help individuals survive better or have more offspring.

But cane toads are showing that in a dispersing population, traits can evolve without offering any benefit to survival or reproduction.

Cane toads were introduced into Australian state of Queensland in the 1930s and have now spread as far east as Kununurra and as far south as Sydney, says Shine.

He says the invasion front has accelerated dramatically with each generation evolving longer legs and being able to run faster and further than the one before.

"We know it's evolutionary because the kids of toads from different areas run just as fast as their parents," says Shine.

"So the question is what process has caused that evolutionary change?"
Spatial sorting

Natural selection predicts that the toads at the invasion front survive better or have better reproductive success, but studies have shown otherwise.

"None of the evidence says that's the case," says Shine.

Indeed, research shows cane toads at the front are more vulnerable to predators because they have not had a chance to poison them.

Also toads at the front suffer spinal arthritis and don't reproduce as much as other toads.

"So is there any other process that could have assembled this incredibly fast running toad?"

Drawing on previous mathematical models, Shine and colleagues developed a new model that supports a process called "spatial sorting".

This process results in the accumulation of genes that are good for dispersal, without there having to be an advantage to reproduction or survival.

"Individuals at the front line are going to be a very non-random set. They're going to be very bold and adventurous souls. They're going to be fast-moving, fast dispersing," says Shine.

As fast-moving mums mate with fast-moving dads, the genes for such things as long legs and high activity levels traits that help dispersal will accumulate.

"The process can work even if there is not survival or reproductive advantage," says Shine.
Natural selection?

Spatial sorting doesn't replace natural selection, says Shine, rather it runs in parallel with it, and within its bounds.

"Spatial sorting can only occur if natural selection doesn't oppose it," he says.

"If there was too strong a survival disadvantage to be at the invasion front, it simply wouldn't happen. Natural selection would be knocking off the toads at the front."

While Shine expects "squeals of outrage" from people trained in evolutionary biology in response to the idea, some don't think it's so radical.

"I think it's a really significant advance in evolutionary biology," says Professor John Endler, author of Natural Selection in the Wild, who reviewed Shine's article for publication.

Hmm, surely someone thought of this before

 

[TJ99]

Ok, but isn't dispersing just another way of ensuring the survival of the species?

 

[Geriatrix]

Ok, but isn't dispersing just another way of ensuring the survival of the species?

"Ensuring" suggests premeditation and planning. You will attract some teleological arguments if you're not careful with your discourse.
I'd say "results" instead.

 

[TJ99]

"Ensuring" suggests premeditation and planning. You will attract some teleological arguments if you're not careful with your discourse.
I'd say "results" instead.

Fair enough, "ensuring" isn't the right word. Dispersing results in improved chances of survival for the species.

 

[Ancalagon]

Yeah I'm not quite sure how this is that different to natural selection as we currently understand it. I mean, frogs with long legs will benefit from reduced competition from within their own species.

 

[SoulTax]

Fair enough, "ensuring" isn't the right word. Dispersing results in improved chances of survival for the species.

Ye, I dont see what is so revolutionary about this idea either. The ability to survive and reproduce will encompass a huge variety of things. The ability to survive will encompass things like spreading to new areas, following a food resource, finding new food resources, being fast, being strong, being poisonous, being sneaky, etc.... This spacial sorting simply falls into the propagation of survival attributes. Nothing radical about this idea at all.

 

[Vox Ego]

Dispersing results in improved chances of survival for the species.

Quite right.
Especially if you look at it will require less energy to fight for food or mates due to the lower numbers.
It can also be extrapolated that there might also be a stronger genepool now due to the distance that has to be travelled through this "dispersal" and it weeding out the weakest first.

I'm not sure how this does not fit in with Darwin's theory.
/shrug

 

[Vox Ego]

Cane Toads are actually an interesting subject for study considering that they are not native to Oz.

 

[SoulTax]

Cane Toads are actually an interesting subject for study considering that they are not native to Oz.

Ye perhaps they have evolved slightly longer limbs for travel because its a quicker evolutionary step to take to find a habitat that works for them, over adapting their temperature control, diet, whatever....
Maybe they are still in evolutionary emergency mode, and they are moving accross OZ, trying to find a place to settle down. As they dont find it, they are continuing to advance. Perhaps once they find their Niche, they will calm down and their leg length will reduce slightly.
Perhaps they have simply found a new niche on a foreign continent, that of the migrating species. Either way, its plainly survival orientated. I think that this OZ scientist has just spent so long studying them, that he is pissed off he hasn't gotten anything useful out of it. So he tries to coin a phrase, by grasping at straws in the hopes that he will leave his mark on the scientific community.

Quite sad actually.