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.

[Quark2005]

Things have really begun to slip for you evolutionists when junk science starts to look like "a welcome break".

You have the expertise to criticize the scientific research methods of these evolutionary biologists based on a press release? Impressive.

Science isn't junk just because you don't like the outcome.

[Liberal Classic]

Yeah, I believe the earth is flat and I believe you're a moron.

I forgot evos have no sense of humor.

I am a human being created to be a human being. Can't speak for you.

Honesty still isn't your strong suit, is it?

And I enjoy imaging the veins popping out of your neck every time you reply to me.

I don't call people morons, I don't accuse people of having no sense of humor, I don't call people inhuman, I don't call people liars, and I don't post just to get a rise out of folks. These examples are from this thread alone.

I can only come to the conclusion mlc9852 is trolling.

Now, if you have a point to make about my posts, make it.

[Amish with an attitude]

I do admit succumbing to the moment by using a tactic from page one of the evoulutionists play book.

I guess it's time to banish me to placemarkerdom.

[flevit]

I would dare say you have NO IDEA what a "one catastrophe" could or could not do, one castatrophy, could have many different compositions weather,deluges,respites,deluges, earthquakes,tremors,earthquakes,eruptions,steamvents,respites, repeat. not to mention how this would effect radiometric decay(unknowable pressures,temperatures,leaching,etc..).multiple strata doesn't demand long ages.

fossil fish scream out rapid burial and preservation/hardening, the are preserved with no sign of decay.

[Quark2005]

I would dare say you have NO IDEA what a "one catastrophe" could or could not do, one castatrophy, could have many different compositions weather,deluges,respites,deluges, earthquakes,tremors,earthquakes,eruptions,steamvents,respites, repeat.

So you're a saying that the "catastrophe" that you hypothesize is violent enough to cause massive geological and meteorological upheaval but that it very neatly deposited tribolites and primitive cephalopods in Paleozoic strata, dinosaurs in Mesozoic strata, modern mammals in Cenozoic strata. Interesting.

...not to mention how this would effect radiometric decay(unknowable pressures,temperatures,leaching,etc..)

We know exactly what this would do to radioactive decay. It would cause varying unrelated isotopic dating methods to give disparate results. When this type of result is observed, there is not enough statistical certainty to give an exact date. However, when "calmer" processes such as slow sedimentation cause rock formation, different dating methods given a very statistically certain date, sometimes to a certainty of 0.3% in certain K-Ar dating processes. A catastrophic upheaval cannot explain why different isotopic dating methods would collude to give an exact dating result.

multiple strata doesn't demand long ages.

No, but the age it takes to deposit multiple strata leaves signs determinable not only from radiometric dating but sequence stratigraphy - this area belongs to the research field of sedimentology.

fossil fish scream out rapid burial and preservation/hardening, the are preserved with no sign of decay.

Rapid burial, yes. Rapid hardening? Fossilization takes hundreds of thousands of years. What mechanism do you propose that suddenly turns bone into solid rock?

I certainly hope you don't think we should replace modern biology and earth science education with this sort of reasoning. We're in serious trouble as scientifically advanced nation if that ever becomes the norm.

[Quark2005]

I do admit succumbing to the moment by using a tactic from page one of the evoulutionists play book.

You mean you actually did years of real research work, formulated hypotheses, wrote research papers, submitted them peer review and had them published in an actual respected journal, invited broader peer review and eventually had your groundbreaking results published in a respected journal like Nature or New Scientist? I'm interested in seeing your work.

[RunningWolf]

After reading your links the context to what was said to mlc, I disagree with your contention that mlc is trolling. Thats the way I see it you might see it different.

I already answered your demand and said that I am sure some of your posts are very good.

I don't know if you are a scientist or not but if you are, my point is I would like to see more science.

Wolf

[Antonello]

Wrong question. Is it more likely that these frogs have taken a unusually fast track to evolve into separate species or is an external factor causing embryonic and 'early childhood' developmental problems for the populations? I believe it was a nematode or some such which was causing frogs to develop extra limbs and other malformations here in the states. Industrial pollution (pesticides?) got the rap first, but turned out to not be the case. For instance, in this article fungus is cited as a problem.

Here, extra legs and here Scientific American, page 2 mentions parasites other causes are noted.

It takes no great leap to find potential for attribution here, well outside of aberrantly rapid evolution. Isolated populations will be exposed to different environmental factors, including vegetation, chemicals (natural and manmade, the latter in precipitation or runoff) and quite possibly different pathogens. One population exposed to a chemical (natural or manmade) or a pathogen, be it viral, bacterial, fungal, or parasitic, will naturally successfully breed only those who can adapt to or are resistant to that pathogen or chemical and still produce viable young.

That change could handily occur in just a few generations, not even 8000 years.

The other population, not exposed, might not fare as well if the pathogen or traces of the chemical are transferred in the act of breeding and that population has little or no natural resistance to the pathogen.

A significant difference between the case you are citing and the frogs in the article is that your case is about a phenomenon that appeared within a single community of frogs and the article's case is about a split group that only exhibits the defect when interbred. However, your suggestion that exposure of one group to a pathogenic or parasitic environmental agent might have happened. In that case, it would have contributed to the environmental pressures that, through natural selection, favored genetic drift that was successful at overcoming this change to the environment.

However, while an infected parent might pass along a pathological infection to its offspring, it is unlikely that this would become a heritable entity. Especially if the infectious pathogen prevents viability.

In short, a pathogenic infection is more likely to have been a factor responsible for the genetic drift of one group than to have become a heritable trait itself.

[furball4paws]

Lamarck lives!

[Thatcherite]

And here, all this time we thought it was the seismic data. Hmmmm. Have to have a talk with the guys in geophysics....

The OP, mlc852, on these threads has repudiated the earth sciences, because they show no evidence whatsoever for a global flood around 5,000 years ago. So she won't be interested in anything that the geophysics boys have to say any more than she is interested in hearing from the biologists. She also said, prior to that that her only argument is with evolution, so either (a) she is one confused bunny, or (b) she is one of the many creationists who calls all science that contradicts her religious beliefs "evolution". That particular inanity is more common than you might think. She has a lot of opinions about all kinds of stuff, but remains strangely (well, not strangely at all) evasive whenever the subject of creationists lying under oath in the courtroom comes up.

[Thatcherite]

Doh! Should have said misspeaking of course. It sounds so much less sinful. Misspeakers still get to heaven, I reckon.

[mlc9852]

I thought they were IDers and not creationists, though I have a hard time keeping them straight. And why would you think the flood happened only 5,000 years ago? Could have been much longer, couldn't it? And I love science. I often post interesting science articles. I just don't buy evolution as in humans came from ape-like creatures. I have stated the same thing over and over yet you continue to state things I have never said. And you have the nerve to complain about others lying. Maybe they lied, maybe they didn't. Are you familiar with depositions before a trial and then what is stated at trial? Often different because people forget things. But we will see how the judge rules soon and then we can stop having these silly arguments.

[Antonello]

Lamarck lives!

Is that a comment regarding the sentiment Smokin' Joe is demonstrating, or have I inadvertently suggested that the physical development of the parent is gifted to the child?

(Smokin' Joe pinged as a courtesy since I mentioned his name)

[Thatcherite]

You: Sorry - I believe the flood happened and it was world-wide and that eventually Noah's ark will be found. Until then, I have faith.

Me: So your earlier statement that you just reject evolution was false. You reject geology, paleontology, hydraulics, soil mechanics, genetics, botany, zoology, amongst others. And you don't reject evolution, on the contrary you require it to have been operating at breakneck speed for the few-hundred years between the flood receding and widely-recorded history, since full biological diversity had already been restored by then.

You: You summed it up very well. Thanks.

Well, well well, lets see part of your most recent post on this issue:

And I love science. I often post interesting science articles. I just don't buy evolution as in humans came from ape-like creatures. I have stated the same thing over and over yet you continue to state things I have never said.

Everyone, living proof that a compulsive misspeaker needs a good memory.

[Thatcherite]

Misspeaking is a poor idea when all of your words are on record placemarker.

[Smokin' Joe]

I was referring to an ongoing infection of a population, or resistance thereto. Similar to the resistance europeans had to smallpox, but the Indians did not, only affecting the ability of the species to interbreed. The separate populations may be separated by viral infection as well.

Inherited disease is not one of Lamark's ideas, iirc, any more than congenital syphilis.

[mlc9852]

Where do you see a conflict?

[mlc9852]

Do you see this as a political or scientific matter? I think it is more political for you.

[furball4paws]

"However, while an infected parent might pass along a pathological infection to its offspring, it is unlikely that this would become a heritable entity. "

Didn't mean to impugn you. Obviously if the acquired trait is passed down it's Lamarckian, so you pass with flying colors, but it's not easy to figure out if SJ agrees with that.

The best I can gather is that he thinks a pathological infection could be a force for Natural Selection, as well it might.

But one has to be real careful with parasites. If the parasite is relatively specific as its host(s) and it's too successful, then it dooms both its host and itself.

[furball4paws]

But the genetic transmission of resistance to an infection would be Lamarckian, unless it was rooted in some genetically superior immune system. Then it wouldn't be specific to any particular disease.

P.S. I think you are referring to measles, not smallpox, with the American Indians. the American Indians never were exposed to measles until it was too late. Most Europeans had constant exposure to it and had developed an immune response. Bam! Not a natural resistance like partial sickle cell anemia does for Africans against malaria.