Island Biodiversity.. Darwin, Wallace.... Finches, leachianus

[Allen Repashy]

I will probably put this thread somewhere else, but thought i would start it here since I see some relevance to the topic at hand.

When we look at island bio diversity, and the evolution of species, there are some interesting questions that do not have easy answers.. for example.

If a species "Island Hops" from one island to a nearby island... and finds different living conditions that require it to adapt....... (Galapagos Finches would be the classic example, but leachianus could work here also) .... the species must adapt or become extinct.... Perhaps the conditions allow a small number of specimens to find enough similarities to survive, but if they are successful and reproduce, Pressure of different conditions could then become a limiting factor and the species would need to adapt..... And adapt they do... In the case of leachianus, we can see different head structures for example based on the fact that on some islands, there is little fruit compared to others which require more carnivorous strategies for survival. In Darwin's Finches, we have different beak shapes based on different seed availability....

We also now know that things can happen MUCH faster than previously thought from studies of volcanic Islands such as Krakatoa that in recent times where life was completely exterminated by eruptions. What we previously thought took a thousand years, took less than a hundred........ Just look at what selective breeding of things like leopard geckos and crested geckos has done in captivity....... The pressure we put on breeding programs to "conform" to a desired trait can in my opinion never be as much pressure as nature puts on a species to evolve or die......

Ok, back to geckos......

Say we have a stable population of leachianus on an island that have evolved enough to be arguably separate species... .. then, a leachianus from a different island that has also evolved differently...... manages to raft itself to this island with the established population.... what happens? does this animal change the population because it breeds with the established population.... or are the different genetics "absorbed" for lack of a better word, by the population and within a few generations, these animals all "evolve" back to the same as the current population.......

To make this more clear.... lets take a hypothetical situation..... Take this established population on the island that has completed its evolution based on its environment..... remove EVERY animal from the island..... but keep EVERYTHING else constant (I said hypothetical ....... Now, that same gecko rafts to this island... possibly a gravid female, possibly a couple geckos make it.....

With all the conditions being the same, do these "new" leachianus evolve into the same "species" as the previous occupants of the island because all the environmental factors are the same? How long does it take? Consider for argument, that these "new" geckos rafted from the same island as the original population that established its self there, which now has been exterminated.

The big factor here is that the environmental conditions remain the same, which would be an oxymoron, because if nothing changes, then there should be no extinction.....

So now, along comes MAN .... screws everything up... introduces non native species that cause this "extermination" to occur....
and then MAN decides to try and fix his errors, and successfully goes back and exterminates the introduced species..... now we have an island that is hypothetically like the one I mentioned above..... "Exactly the same, but Completely different..... "

So now man tries an experiment.... he can not re introduce the exterminated geckos, because there are not any remaining... so he decides to repopulate the island with either a neighboring similar species or sub species..... or even a captive bred population that was actually decedents of this original population, but it had been inbred and out bred because of lack of genetic diversity in the captive population.

Do these new geckos stay as the same introduced "species" or "variety" once on this island, or do they evolve to the conditions of the island..... if the conditions on the island are the same as they once were, does this new population evolve to be indistinguishable from the once extinct population? Does it take 10 years, 50, 100, 500 .... ....... I wonder.

Have I lost everyone here? LOL .....

Anyone.... Anyone..... Bueller?

[genevieve]

Allen,

I would think that this would fall under the realm of convergent evolution (one of my all time favorite types of evolution). As I am sure you know (but I will expound on for those without a science background), convergent evolution occurs when species in geographically distinct areas occupy the same ecological niche and therefore end up looking similar morphologically. Such as seen here (a nice example of the convergent evolution of marsupials in Australia that live in the same niches as placentals in the rest of the world):



I think that if a sufficient group of aniamls (leachies in this case) were reintroduced back into the niche that they formerly occupied, or similar animals (leachies) were placed into a new niche, they would eventually appear morphological close to the animals (leachies) that formerly occupied that niche. However, since things are not static, and the genetic base for evolution would not be the same, there is a good chance that they would not be identical to the ones that were formerly there. Also, since some beneficial features are the product of selective pressure for random mutations, which are variably rare in their occurance (like lightening striking twice), it is possible that an animal (leachie) like the ones that previously inhabited the niche would never again come about by chance. I think that the time frame on morphological changes is directly dependent on the amount of selective pressure and the rate of mutational change in the species.

Genevieve

[umop_apisdn]

oh man, allen...i started to try to reply to your hypothetical situation there...but i got so into it that i completely stopped making any sense.

but here were my major points to make:

inbreeding = homogenizing the gene pool
outbreeding = a mix of everything is possible, from homogenizing some genes to diversifying genes, from no change at all to adding genes previously absent in said population.

then, when you put offspring from inbreeding and outbreeding back on the island, the same selective pressures can come into play. essentially, you have changed the evolutionary "direction" that the original population was headed, but it could still be headed in the same general direction. man, im still not making sense.

god i hate hypothetical genetics. ANYTHING can happen. but when you have time to sit down and think it all out its really cool.

[Brian]

Originally Posted by Allen Repashy

Say we have a stable population of leachianus on an island that have evolved enough to be arguably separate species... .. then, a leachianus from a different island that has also evolved differently...... manages to raft itself to this island with the established population.... what happens? does this animal change the population because it breeds with the established population.... or are the different genetics "absorbed" for lack of a better word, by the population and within a few generations, these animals all "evolve" back to the same as the current population.......

Sorry I missed this great post.

Wouldn't this depend on the rate of colonization to the island? Which can be predicted by that theory on the size of islands versus proximity, etc. I forget the actual theory though.

I mean a high rate would act to keep the population similiar to the one the rafters are comming from. A low rate would mean absorption or even a seperate population or no absorption.

I guess a lot would also depend on the pressures on the new island. If pressures were harsh enough to stop colonization at some point weird stuff could happen as well.

Anyone think I'm totally off base?

[Philippe deVosjoli]

Allen wrote a long post under the 'Anyone keeping GT thread" inquiring about what would happen when leachies are introduced in habitat. This is a complex subject that would not produce a definite answer because selective pressure and environmental conditions which in the past led to current morphs would not be the same as current ones.
A more valuable approach would be to identify and correlate trait trends with ecological conditions. This would give us an idea of adaptive trends in leachies in response to environmental conditions.
Let me give you an example. We have wondered about the purpose of the bright white blotches in various leachie morphs and we suspect that the more open a forest, the more likely a morph may show bright white blotches. This has to be further investigated. As to the purpose of these blotches, we can also speculate (crypsis, interspecies recognition, other) but the right course would be to carry out experiments.
More questions: Why do Nuu Ana and Nuu Ami, which are found in short sclerophyll forest develop bright yellow spots? Nuu Ana has the lightest color irises of any leachie. Is this an adaptation?
Identifying the repertoire of adaptive traits would seem a worthwhile subject.

Last but not least, we know that in leopard geckos, incubation temperature can have a significant effect on phenotype (external appearance) as can rearing temperatures. Could incubation and rearing temperatures have an effect on the phenotype of leachies? This is area definitely worth investigating.

So in conclusion, there's a great deal of valuable work that can be done by hobbyists.

[JayS]

I agree.The hope is that persons will be honest with their labeling of locality.The only problem being that people are misinformed about the true locality(morph)they keep (crosses?).I for one own some I got easily 12 years ago or better and have no clue this pairs origin.Has any DNA work proven helpful at all with respect to differentiating localities?

[genevieve]

Jay,

I believe that is being covered (kinda) under the thread with Morphs in the name, also in this forum. Pretty much the answer seems to be "depends on who you ask".

Genevieve

[Brian]

What's the predation like for these guys? Could sexual selection being doing anything with regard to morphology.

[danscantle]

Hot damn! What a thread!

The Galapagos Finches were such a great example because you could see evolutionary change in action across a temporal and ecological habitat. On islands where two species of finch live in sympantry their beak depths show a bimodal distribution (small beak, large beak), which each species occupying one peak and no significant overlap between species. On islands where the same species occur in isolation from the other bird, the beak size is much different, being more of an intergrade (medium beak). Considering that beak depth is a proxy for nut cracking this isn't surprising. In sympatry the small beaks occupy a different niche than the large beaks - the eat smaller seeds, and thus interspecific competition is minimalized. Large beaked birds are very inefficient at eating small seeds, and vice versa.

So what would happen to leachies? I bet in a few generations there would be a noticable change in the phenotype of their heads if they lived in an abundance versus and absence of fruit. There must be a trade off between being able to eat fruit well and being able to eat live prey well. Morphological change doesn't necessarily correlate with the mutation rate. Small changes to the genes triggering developement can have enormous results.

[genevieve]

Originally Posted by danscantle

Morphological change doesn't necessarily correlate with the mutation rate. Small changes to the genes triggering developement can have enormous results.

I agree, Dan. What I was trying to go for was mutations that create the basis for traits that were not previously present in the genetic code of the species. In general selective pressure to accentuate/ downplay features that are already present is going to have a far larger impact on the evolutionary direction of the species than random mutation.

Anyways, just wanted to clarify that point.

Genevieve