posted
That's pretty cool. Wonder if there was some sorta mutagen in the environment that sped that up... or if there were just really strong environmental forces to encourage them to go vegetarian.
Posts: 3295 | Registered: Jun 2004
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posted
I know this is a significant morphological change, but does it really count as speciation? From what I've read about this, researches have not yet determined if these are reproductively incompatible with the parent population and they haven't even determined if this is the result of genetic changes rather than developmental plasticity. Even PZ acknowledges this in the comments.
I mean, yeah, it's damn cool, but I think it may be premature to call it speciation.
Posts: 3275 | Registered: May 2007
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quote:Many species are perfectly reproductively compatible with other species.
I realize that. I was merely indicating that this "shortcut" to species classification may not be available here and that it's going to take a much harder look at their genetic makeup and other factors to determine if what we are seeing really should be considered a new species.
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posted
I think that a lot of separate species have been so classified without any such look at their genetic makeup.
Posts: 16551 | Registered: Feb 2003
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*shrug* I realize that "species" is largely an artificial construct, but I'm still inclined to wait for the scientists involved to actually classify this as a new species before I do.
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posted
I'm not familiar with this type of lizard, or the type that died out on the island. They're the same genus, though; any chance that they interbred, and the new type of lizard is a hybrid?
Posts: 16059 | Registered: Aug 2000
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posted
There seems to be next to no chance of interbreeding. Every lizard they tested had mitochondria inherited from the original females dumped there, so unless there was really bizarre sex-biased interbreeding the likes of which are hardly ever seen, there was no interbreeding.
Also, the attributes we see in the lizards on the island were not present in the native population.
pooka: the changes definitely took time to spread amongst the population, but some of the changes (jaw shape and strength, diet) were probably pretty gradual, while the digestive system changes might have happened relatively rapidly if one individual had a mutation that activated the right promoter region.
Posts: 15770 | Registered: Dec 2001
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posted
I suspect the cecal valve was probably already present as a variation in the population, it's just survival negative/neutral in the original environment and survival positive in the new. Though I have to admit I'm not really sure why that would be.
Posts: 11017 | Registered: Apr 2003
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quote:Originally posted by pooka: So it took 30 generations, or it occured within one generation at some point during that 30?
Sort of both. The stomach adaptation most likely started as a minor mutation in one or a few individual lizards. This allowed those lizards to digest plant matter a bit easier and thus have a more stable food source. Only slight to begin with, but that slight advantage was passed on as they reproduced. The mutation also varied, as all do, and those that were closer to what we see in the lizards now were even more likely to survive and to pass on their genes.
So it started with at least one individual in one generation. Possibly more than one. But the mutation wasn't the complete stomach as we see now. It's the result of evolving over those 30 generations. (Or however many generations since the first mutation happened.)
Posts: 3852 | Registered: Feb 2002
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In response to the smug condescension, I'd just like to point out that one conclusion some could draw from the speed of the transformation in these lizards is that God is very active in the world and willing to help even small reptiles. Posts: 2432 | Registered: Feb 2001
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In the comments to the article, someone mentioned that the cecal valve is not present anywhere in that genus, and only in one species in the entire family, I think.
Here's the quote (just search for genus) on the page:
quote:No cecal valves have ever been observed before in this species or genus, and are in fact very rare in the entire family Lacertidae (only known in the specialized herbivore Galliota*).
We likely won't know for certain without a lot more work, but I suspect the cecal valve complex is not expressed in the species unless a mutation causes the activator to be expressed. In other words, it would not merely be a case of an infrequent trait becoming frequent, but of a new gene appearing (albeit in the simplest fashion; what do you expect in 30 generations?).
Posts: 15770 | Registered: Dec 2001
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posted
I wonder if they have well preserved genetic samples from the original population.
If so it would make a number of really fascinating genetic studies. First you determine how many of the original lizards have descendants in the surviving population. Then you could indentify the key genes involved in the adaptation and whether is their sequence or their expression that's changed. Then you could try to identify the mutations that occurred and even reverse engineer some of the steps in the process.
This could be great fun.
Posts: 12591 | Registered: Jan 2000
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posted
It sounds like they do- the source article specifically mentions that all lizards from the derived population they tested were confirmed to be descended from the original invasive group. The genetic follow-up studies to this will be really exciting, I think. The emergence of the cecal valve trait, in particular, will be fascinating to examine from an evolutionary development perspective.
I wonder if I can get my thesis advisor to sponsor a collection trip to Pod Mrcaru...
quote:Originally posted by Noemon: I'm not familiar with this type of lizard, or the type that died out on the island. They're the same genus, though; any chance that they interbred, and the new type of lizard is a hybrid?
That was my first thought.
But if not, then wow, that's pretty amazing.
Posts: 21898 | Registered: Nov 2004
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posted
This is really an amazing research opportunity. There are so many people tracking evolution by comparing genetic mutations in divergent history and trying to ascertain using estimates of mutation rates exactly when the to species diverged. There is a lot of interesting stuff in trying to identify what certain genes may have done in an early ancestor compared to what they do in different descendent populations today. But there are so many assumptions that go into to it that even loads of genetic data the results are still speculative.
Now this is a chance to do this in more or less real time. It would be even better if we had genetic samples from all 30 generations, but what they have is just so amazing.
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posted
Always, but the original population is probably all they have, and that's sufficient for many of the biggest questions.
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posted
Are you sure they don't have samples from the parent population or are you just speculating.
If the study had been started in the last 20 years, it would have been standard procedure to save samples from the parent population for future genetic analysis. They might not have been saved optimally for the current best techniques but they would have been saved.
Of course this study was started in the early 70s and I can't even begin to speculate about what would have been done back then. Still I think there is a decent chance that they would have saved some samples for future analysis (assuming they weren't lost or destroyed during the 36 intervening years).
Posts: 12591 | Registered: Jan 2000
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posted
I've been careful to use words like probably. I don't know for sure, but having read the whole thread below the article, those who have commented with knowledge have only referenced genetic markers as being recorded. If there are genetic samples out there, they're under the radar right now.
Posts: 15770 | Registered: Dec 2001
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