Posted on 06/08/2004 3:30:58 AM PDT by PatrickHenry
The first eyewitness to the birth of a new species may be a University of Arizona graduate student. Her new findings could help biologists identify and understand the precise genetic changes that lead one species to evolve into two separate species.
Laura K. Reed and her advisor Therese Markow, a UA Regents' Professor, made the discovery by observing breeding patterns of fruit flies that live on rotting cacti in western deserts. Whether the closely related fruit fly populations, designated Drosophila mojavensis and Drosophila arizonae, represent one species or two is still debated by biologists, testament to the UA researchers’ assertion that the insects are in the early stages of diverging into separate species.
The team's findings will be published the week of June 7 in the online early edition of the Proceedings of the National Academy of Sciences.
The seeds of speciation are sown when distinct factions of a species stop reproducing with one another. When the two groups can no longer interbreed, or just prefer not to, they stop exchanging genes and eventually go their own evolutionary ways, thus forming separate species.
While the evolutionary record is brimming with examples of speciation events, biologists haven’t been able to put their fingers on just what initiates the reproductive isolation, Reed said. Several researchers have identified mutant forms of certain genes associated with the inability of fruit flies to hybridize with closely related species. However, in all cases those genes were discovered long after the two species diverged. Therefore, those genetic changes could either have caused the speciation, resulted from it or even be incidental changes that happened long after the two species diverged.
Reed said the difficulty is researchers need to catch the genetic schism while it’s still brewing. Now she and her advisor have managed to do just that.
In the wild, the two fruit flies Drosophila mojavensis and Drosophila arizonae rarely, if ever, interbreed, even though their ranges overlap in a broad swath along the northern Mexican coastline. In the lab, researchers can coax successful conjugal visits between members of the two groups. But even under laboratory conditions such matings aren’t always fruitful. Drosophila mojavensis mothers typically produce healthy offspring after mating with Drosophila arizonae males, but when Drosophila arizonae females mate with Drosphila mojavensis males, the resulting sons are sterile. Reed said such limited capacity for interbreeding suggests the two groups of flies are on the verge of becoming completely separate species.
Another finding adds support to that notion. Previous research had shown that for a strain of Drosophila mojavensis from southern California's Catalina Island, mothers always produce sterile sons when mated with Drosophila arizonae males.
Because the hybrid male's sterility depends on the mother’s genetic heritage, Reed and Markow conclude the genetic change, or polymorphism, responsible for creating sterile sons must not be firmly established in Drosophila mojavensis populations -- a telltale sign that the change is recent.
Reed wanted to know just how deeply the polymorphism causing male sterility had suffused the Catalina Island Drosophila mojavensis populations. In other words, do just some of the Catalina Island mothers produce sterile sons when mated to Drosophila arizonae males? When Reed did the experiment, she found that only about half the crosses resulted in sterile sons. That result implies that only half the females in the Catalina Island population had the gene (or genes) that confer sterility in the hybrid male offspring.
Surprisingly, when she tested Drosophila mojavensis females from other geographic regions, Reed found that a small fraction of those populations also exhibited the hybrid male sterility polymorphism. “That polymorphism exists in every population I looked at,” Reed said. “It just happens to be that whatever factors are causing sterility are at higher frequencies in the Catalina Island population.”
Further experiments demonstrated that the sterility trait is caused by more than one genetic change. “I think there are many genes -- 4 or 5 probably, maybe many more,” Reed said.
Now that the researchers are hot on the trail of a set of “speciation genes,” the next task will be to identify them. For help in the hunt, the team will take advantage of the newly begun Drosophila mojavensis genome sequencing project, which will provide a complete roadmap of every gene in the species.
“Evolutionary biologists are excited to figure out what causes what we see out there—the relative forces of selection and drift -- whether things are adapting to their environment or variation is random," Reed said.
"Another important component to that is how that variation is partitioned into separate species. Once you’re a separate species, you have an independent evolutionary trajectory to some other species -- an independent set of tools, or genetic potential, relative to other species. So this partitioning of genomes is an important cause of the variation we see in nature.”
There exists no paper trail for you between the ages of four months and seven months. Begone, phantom!
"Whether the two closely related fruitfly populations, designated Drosophila mojavensis and Drosophila arizonae, represent one species or two is still debatable among biologists"
And...
"biologists haven't been able to put their finger on just what initiates the reproductive isolation."
And...
"Further experiments demonstrated that the sterility trait is caused by more than one genetic change. "I think there are many genes--4 or 5 probably, maybe many more," Reed predicted."
And...
"There's a huge amount of biodiversity out there, and we don't know where it comes from."
Looks like there is still plenty of research to do.
I can't even imagine what they'll think when some future biologist unearths your fossilized remains.
I'm basically hoping they'll say, "Damn if he didn't get all the mileage out of THAT body."
Excellent parody of the creationist position, but it is a bit on the vicious side. Lets play nicely, now.
"...a bit on the vicious side. Lets play nicely, now."
That was being nicey-nice, even after 2 cups of good Columbian joe.
Yep, a decent set of hemispheres...
I'm not totally clear on the theory here. Is it the changes in the female fly's genes that causes the sterile hybrid or is it the male's??? You'd have to use one male and several females then several males and one female to distinguish the difference. The text isn't clear on this.
Well, the Department of Homeland Security evinces one Creationist claim. There was a communications gap between the FBI and the CIA. Now there are two gaps between the DHS and FBI and between the DHS and CIA. In this case, the two gaps are at least as wide as the first gap. Not to mention the Kenndey's Missle Gap, General Turgidson's Mineshaft Gap, and Candidate Kerry's General Giap. (Last sentence no verb, in the rain.)
Explanation for literal-minded creos: As in ... "Win one for the Gapper."
Indeed; there was an attempt several years ago to compile a master list of Creationist arguments, and assign an unique numerical designation to each one, such that we could all reduce the amount of typing expended on these threads. Basically, when a Creationist showed up and invoked one of the standard arguments, the Evo's would look it up, and reply: "Ah; that's #47, to which the standard rebuttal is Evo argument #14.... thank you for participating in the discussion."
Unfortuneately, it did go over very well.....
According to this Negros and Caucasians in the early 1700's were different species. But then we became one species again in the 1960's.
Either they neeed to do a lot more work on this or they have to phrase things much better
I meant: "did NOT go over well"
I thought we decided it had already been done: An Index to Creationist Claims.
Thank you for your thoughtful contribution.
That is kind of an unclear statement. I don't think it really refers to preferences (i.e., I prefer to exchange genes with redheads but that doesn't mean that my descendants will form a separate species from brunettes) but rather talks about different species that CAN interbreed but do not do so under natural conditions (such as tigers and lions, who can create liger and tigon hybrids)
Thanks, that'll spark my day.
Actually, it's a rarely discussed phenomenon that Australian aborigines who conceive children with non-aborigines tend to have extremely high rates of miscarriage and stillbirth. This is likely attributable to the 70,000-50,000 year genetic separation of aborigines from the rest of mankind.
Got any hybrid info on other distinct groups like pygmies?
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