Picky female frogs drive evolution of new species in less than 8,000 years

UC Berkeley News Center ^ | 27 October 2005 | Robert Sanders

[PatrickHenry]

Picky female frogs in a tiny rainforest outpost of Australia have driven the evolution of a new species in 8,000 years or less, according to scientists from the University of Queensland, the University of California, Berkeley, and the Queensland Parks and Wildlife Service.

"That's lightning-fast," said co-author Craig Moritz, professor of integrative biology at UC Berkeley and director of the Museum of Vertebrate Zoology. "To find a recently evolved species like this is exceptional, at least in my experience."

The yet-to-be-named species arose after two isolated populations of the green-eyed tree frog reestablished contact less than 8,000 years ago and found that their hybrid offspring were less viable. To avoid hybridizing with the wrong frogs and ensure healthy offspring, one group of females preferentially chose mates from their own lineage. Over several thousand years, this behavior created a reproductively isolated population - essentially a new species - that is unable to mate with either of the original frog populations.

This example suggests that rapid speciation is often driven by recontact between long-isolated populations, Moritz said. Random drift between isolated populations can produce small variations over millions of years, whereas recontact can amplify the difference over several thousands of years to generate a distinct species.

"The overarching question is: Why are there so many species in the tropics?" Moritz said. "This work has led me to think that the reason is complex topography with lots of valleys and steep slopes, where you have species meeting in lots of little pockets, so that you get all these independent evolutionary experiments going on. Perhaps that helps explain why places like the Andes are so extraordinarily diverse."

When isolated populations of the green-eyed tree frog (gray and brown) met again 8,000 years ago, they found that each had changed in subtle ways. The calls of the male frogs were different, and more importantly, hybrid offspring were less viable. One population that was cut off from its southern kin (pink) found a way to ensure healthy young. Females, who choose mates based only on their call, began selecting mates with a the southern call type. Over thousands of years, this behavior exaggerated the pre-existing differences in call, lead to smaller body size in males of the "isolated southern population" and resulted in rapid speciation between the two populations of the southern lineage (pink and brown). (Nicolle Rager Fuller/National Science Foundation)

Moritz; lead author Conrad Hoskin, a graduate student at the University of Queensland in St. Lucia, Australia; and colleagues Megan Higgie of the University of Queensland and Keith McDonald of the Queensland Parks and Wildlife Service, reported their findings in the Oct. 27 issue of Nature.

The green-eyed tree frog, Litoria genimaculata, lives in the Wet Tropics area of northeast Queensland, a rugged tropical region of Australia along the Pacific Ocean's Great Barrier Reef. The frog, which is green with reddish-brown splotches, is common around streams and grows to about 2 1/2 inches in length.

Because of geographic isolation that began between 1 and 2 million years ago with the retreat of rainforest to higher elevations, two separate frog lineages developed in the northern and southern parts of the species' coastal range - only to be reconnected less than 8,000 years ago as the climate got wetter and warmer and the rainforest expanded.

Hoskin and his colleagues found that the northern and southern calls of the male frog, which are what females pay attention to in the mating game, had become different from each other. Yet despite this difference, reflected in the call's duration, note rate and dominant frequency, the two lineages could still breed with one another.

The southern females, however, were more picky about their mates than the northern females. And in one area of contact that had become isolated from the southern range, the southern females were extremely picky, to the extent that they almost never mated with northern males.

In laboratory breeding experiments, the biologists discovered the reason for this choosiness: While northern and southern lineages could breed successfully, they apparently had diverged enough during their million-year separation that offspring of southern females and northern males failed to develop beyond the tadpole stage. Though crosses involving northern females and southern males successfully produced frogs, the offspring developed more slowly than the offspring of pairs of northern frogs.

Field studies confirmed the laboratory results. Researchers could find no hybrid frogs in the contact zones that were the offspring of southern mothers, judging by the absence of any southern mitochondrial DNA, which is contributed only by the mother.

Hoskin and colleagues argue that because southern females have the most to lose in such cross-breeding, there may have been selection pressure to evolve a mating strategy to minimize dead-end mating with northern males. This appears to have occurred in the contact region where a population of the southern lineage had become isolated from the rest of its lineage and had developed a preference for certain male calls. The male frog call in this population has diverged significantly from both the northern and southern lineage calls.

"If females have a reason not to get the mating wrong, and they have some way of telling the males apart - the call - the theory is that this should create evolutionary pressure for the female choice to evolve so that they pick the right males," Moritz said.

This so-called reinforcement has been controversial since the time of Charles Darwin, with some biologists claiming that it requires too many steps for evolution to get it right.

"Some have argued that it's just too complicated and that it is not really necessary, and there have been few convincing demonstrations. In their view, differences between populations arise because of natural selection or genetic drift or mutation or some combination of those three, and reproductive isolation is just some glorious accident that arises from that," Moritz said. "We do have very compelling evidence. We have addressed various lines of evidence and conclude that there has been reinforcement and that has given rise to a new species based on very strong female choice."

As a comparison, they looked at a second contact zone on the border between north and south, where frogs were not isolated from either lineage.

"Reinforcement does not appear to occur at the more 'classic' contact between northern and southern lineages, and we speculate that this may be due to gene flow from the extensive range of the southern lineage into the contact zone," Hoskin said. "This problem does not exist at the other contact because the southern lineage population is very small and occurs primarily within the contact zone."

Because the frogs in the isolated contact area had a distinctively different call, and because they were effectively isolated from surrounding populations by mating preference, Hoskin and colleagues concluded that female choice led to this new species.

Interestingly, evolutionary theory would predict that the southern and northern frog populations would drift apart into two distinct species. In the case of the green-eyed tree frog, Moritz said, a subpopulation of the southern species drifted away not only from the northern species, but also from the southern. That was unexpected, he said.

Moritz noted that geographic isolation in this "dinky bit of rainforest in Australia" has split many species, and that reinforcement at zones of recontact may be generating other new species.

"In this tropical system, we have had long periods of isolation between populations, and each one, when they come back together, have got a separate evolutionary experiment going on. And some of those pan out and some don't. But if they head off in different directions, the products themselves can be new species. And I think that's kinda cool. It gives us a mechanism for very rapid speciation."

The research was supported by the U.S. National Science Foundation, the University of Queensland and the Australian Cooperative Research Centre for Tropical Rainforest Ecology and Management.

[VadeRetro]

Very nice! This part made me smile.

Creationists ignore refutations of their arguments and keep repeating the same ones (cf. Arthur).

[mlc9852]

I don't care about that school board. I just want the weaknesses of evolution explained and I'll be happy. Most people already agree God is the creator so our work is pretty much done.

[mlc9852]

Ask any lawyer about "evidence". It is indeed the interpretation that matters. You surely aren't saying scientists always agree with the evidence, are you? Because you know that would be a lie.

[mlc9852]

Can't help myself. And I enjoy imaging the veins popping out of your neck every time you reply to me.

[mlc9852]

And none of what you mentioned depends on whether we evolved from apes or not. Not one iota.

[savedbygrace]

For one thing, if there are no assumptions, then all data was directly observed and recorded without interpretation. According to the article itself, that is not the case, therefore assumptions are involved.

Are you sure YOU understand science?

You seem to have a reading comprehension problem, since you still think I was referring to the research, rather than the ARTICLE, as I have plainly stated at least twice. I have not been referring to the research, since there are no links to the research in the article.

Do you have any links to the research? Oh, that's right, I asked that before, and you've already ignored the request twice.

[VadeRetro]

It's still a frog. It did not turn into a salamander or a snake.

It's still in the taxonomic order Salientia, yes. Now here are the taxonomic levels as they typically pertain to animals.

Domain (Older taxonomies may not show this one)
Kingdom
Phylum
Subphylum
Superclass
Class
Order
Family
Genus
Species
Subspecies

I highlighted order for you. Frogs are a whole order.

Taxonomy, the effort to classify the kinds of life, goes back about a century before Darwin to Linnaeus in the 1750s. It's nothing but an effort to lump similar things into bins. It can be obvious at time, but it can be rather arbitrary, a beauty-contest decision at others.

What evolution says about making a whole new order is it's a branching divergence over time. It starts with a common ancestor. Two groups diverge into subspecies (what we would call "varieties" in the plant world). Later yet you have speciation. Eventually, the two groups not only are notably different from each other but have spawned species differences within themselves and you call them "genera." (Thought I was going to say "genuses," didn't you?)

Eventually, diverging genera would be seen as different families. And so forth.

The higher up the taxonomic level a difference goes, the more diverged it is. You saw a headline that says a new species formed in 8000 years. The point of the story is that this happened faster than we normally think it does. You waved the whole thing away as not being a change at the level of taxonomic order.

Depending on why I think you said that, your argument is either a deliberate strawman or seriously uninformed.

[dread78645]

A Creationist FAQ

---

Q: What is the principle evidence for Creationism?
A: The Holy Bible, of course. After all, is it likely that the author of the Universe would be mistaken about its age?

Q: But isn't the Bible religion and not science?
A: Truth is truth. It's a poor sort of science that ignores truth.

Q: But isn't there a lot of evidence for evolution?
A: Not really, most of it is from university professors writing papers for each other. If they didn't write papers they wouldn't have jobs.

Q: How big was Noah's ark?
A: Big enough.

Q: But what about radioactive dating?
A: Hey, everybody knows that stuff is bad for you. Stick with good Christian girls.

Q: What about the fossil evidence?
A: The real fossils are university professors writing papers for each other.

Q: Is there any other evidence for creationism besides the Bible?
A: Yes.

Q: Can you give us some?
A: Yes.

Q: Could you give us a specific example?
A: Yes.

Q: What would be a specific example of evidence for Creationism?
A: I've already answered that question.

Q: What about the Antarctic ice core data?
A: Now I put it to you. Coop up a bunch of men in a Quonset hut in the worst weather in the world, with nothing to do but gather data and drink, and what do you expect?

Q: Did the dinosaurs coexist with man?
A: Look, the liberals were preaching coexistence with the Communists, and you saw what happened to them.

Q: Should Creationism be taught along with Evolution in the schools?
A: Creationism should be taught instead of Evolution in the schools.

Q: Doesn't the Geologic Column prove that the Earth is very old?
A: The geologic column proves that some things are on top of other things and some things are underneath other things. But we already knew that, didn't we.

Q: Hasn't evolution been demonstrated in the Laboratory?
A: Students are demonstrating everywhere these days. To their shame, many professors are demonstrating also.

Q: Aren't Hawiian wallabies an example of Evolution in action?
A: No.

Q: Why not?
A: Because they aren't.

Q: What is a kind?
A: A kind is cards of the same rank. Thus 4 aces and a king are four of a kind, but four spades and a heart are not.

Q: Doesn't genetic variation indicate that life has been going on a long time?
A: Let's be up front about this. That's deviation, not variation, and yes, there is a lot of deviancy out there. That just shows that there has been a lot of Sin since the garden of Eden.

Q: What about Neanderthal Man?
A: Hey, you take one of those geezers and put him in tweeds and give him a pipe and he could be a professor anywhere.

Q: Some scientists state that the earth's continents are drifting around on top of a molten interior which has shaped life as we see it now. Are they right?
A: As you well know the Bible says that beneath the surface of the earth is Hell where there is eternal fires and brimstone. If the continents appear to be moving around that is Satan's doing.

Q: Why do almost all of the scientists believe in Evolution?
A: The real scientists don't. As for the rest of them, that's a very good question, isn't it?

Q: Are you talking about a Satanic conspiracy?
A: Did I say anything about a conspiracy? You might want to think about the shape the world is in since the Evolutionists and the Liberal Humanists captured academia and how Evolution is hand in hand with Godless Communism and crime in the streets but I certainly wouldn't want to say anything about a Satanic conspiracy. I just want you to think about it with an open mind.

-- A Creationist FAQ

[b_sharp]

I'm posting for the lurkers.

[Liberal Classic]

Nonetheless, it is the application of evolutionary theory that makes the continued exploitation of mineral resources economical.

[Liberal Classic]

Ah, you are trolling then.

[b_sharp]

"We don't know that they were all originally the same before the communities were divided. We don't know what the calls of the male frog sounded like before they were divided."

If the females do not respond to some but respond to others and the two group's calls are different, then logic dictates that the females currently respond to only one call. If the communities were at one time combined then the calls must have been the same. It is easy to determine if the two groups have shared genes in the past.

You can speculate that the females responded to two different calls if you want but that would not change the speciation event.

"Speculation. Why is this kind of stuff given such high credibility by evolutionists? Can it be because it aligns with what they already believe?"

You speculate very well, however you did not ask why evolutionists believe what they believe. Is it possible your speculation is backwards and we evos believe in evolution because the evidence has such high credibility?

[b_sharp]

"And many are much smarter than you"

How did you determine this?

[js1138]

About thirty years ago there was much talk that geologists ought only to observe and not theorize; and I well remember someone saying that at this rate a man might as well go into a gravel-pit and count the pebbles and describe the colours. How odd it is that anyone should not see that allobservation must be for or against some view if it is to be of any service!

-- Charles Darwin, letter to Henry Fawcett, who had defended Darwin before the British Association for the Advancement of Science against a critic who said Darwin's book was too theoretical and that he should have just "'put his facts before us and let them rest," quoted from Michael Shermer, "Colorful Pebbles and Darwin's Dictum: Science is an exquisite blend of data and theory"

[jennyp]

You are a tailless primate, just like the other great apes (chimps, bonobos, gorillas, orangutangs and gibbons). With them you share such features as brachiating limbs and grasping hands.

This chimp, from some zoo, IIRC suffered from some kind of disease that caused him to lose his hair.

[Junior]

Data can be interpreted without making assumptions. It can be interpreted in the light of all the other tests and observations that have gone on before. You seem to think "if we haven't done all the work ourselves, then everything we haven't touched personally is an assumption." I'm afraid you'd be wrong there.

[highball]

I don't care about that school board.

So why are you posting here? You won't read the articles about the trial, you won't listen to any new information, and yet you insist on sounding off. You do your side little credit when its obvious that you don't know what's going on.

Please, read the articles. Learn about the issues raised by the trial (I'd like you to also learn about the lies your side is telling, and then see if you approve of their tactics.

Once you've done that, come back and join in.

All honest viewpoints are welcome in the discussion, but willfully ignorant ones can't be taken seriously. Deliberate, willful ignorance should never be respected.

[RunningWolf]

evidence is all in the interpretation

Yep

[RunningWolf]

Well theyes lurkers sho' aint impressed by all the 'scientists'

[mlc9852]

Just ignore my posts. You really have no reason to respond to me, do you?