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.”
No, I don't. It's actually something I've been wanting to look into again when I have the chance - probably whenever I make it to a library again after I'm done with my current research. I'm curious about Pygmies and also about the Khoi-Khoi and Hottentots (Bushmen) of Namibia. I'm also curious about some of the most isolated Native Americans (particularly the Patagonians) and the Maori.
The information on the Australian aborigines was some research I stumbled across about 7-8 years ago that I found of interest, but didn't follow up on. At the time I was rather distracted with what I was actually researching (sexual customs amongst Oceanic peoples) so I just kind of read over it and noted it in the back of my mind. Then I was reminded of it on another FR thread and just now on this one, and so I've wanted to look into it again sometime when the opportunity arises.
Hmm.. Just to clarify, when I say "read over it" I don't mean I scanned over it and skipped on. I actually found it quite interesting at the time, and read the entire journal article and examined the statistical figures and everything. In fact, I strongly suspect I made a copy of it and will find it again when I organize all my research debris in a couple months or so. I'd meant to follow up on the citations but just never got around to it what with everything else going on.
It intrigued me at the time for the very implicit reason I brought it up here: the concept that Australian aborigines may be virtually a subspecies from a purely biological standpoint, although that's a highly volatile and obviously controversial postulation.
Boy, do you need to read some history.
Ever wonder why African Americans are, on average, much lighter than West Africans?
Bad history, never mind the bad model.
"To die. In the quagmire."
Huh? The first time this has been witnessed? Well, MAYBE witnessed?
Gee, I've been repeatedly told by those adhering to evolutionary theory that this has been observed countless times.
Guess they lied.
From a purely biological point of view, it's just a question of whether a group has been separated long enough from the original stock for the inevitable accumulation of mutations to make speciation a fact. Humans are a relatively recent species, so I suspect that interbreeding is possible, most of the time, even among the most different-looking groups, who probably haven't been isolated from the rest all that long. But I've never seen any actual research.
There were later waves of migrations to Australia. The one that brought in the dingoes with it was much later, IIRC.
That said, sometime last year I confronted one of the "Ape! Just an Ape!" lawyers on these threads (i.e, a creo who was making apes out of most of the hominid series) with links and pictures of the prominent brow ridges and non-prominent chins to be seen on some of the aborigine tribesmen. Not saying how or by whom it happened, but somebody or other had the AdminModerator remove the post, no doubt on anti-racism grounds. It is hard to talk about this stuff, especially to people who will use any excuse at all to run from the data.
I feel a psychic bond forming. Or just some kind of groupie thing.
"The clearest evidence for evolution are the creationists, for they have not evolved"
No, but we get to evolve in the afterlife.
Probably some confusion with the horsefly.
I can't tell if you're really that ignorant or just lampooning the creationist position. Scary, that.
"I can't tell if you're really that ignorant or just lampooning the creationist position."
I'm sometimes rude, but rarely ignorant. I prefer harpoons but will settle for the lampoon today.
"Yesterdie. In Fleet Street."
Bond. Psychic Bond. (One hopes it's not some kind of gropey thing.)
Perhaps you meant "grope"?
I've seen a horse fly and a peanut stand....
Better be careful. She's an evolutionist. That means the devil's got the first claim on her.
I never found that era of history to be of interest. I was using it to demonstrate the sloppiness of the article. Maybe I should have used the south in the early 1900's. I know that several states had laws against interracial marriage etc? The point is: Preference does not make a species.
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