Lack of salamanders in the south

[VoodooJackal]

I hope this is the correct place for this. But is there any reason the the southern hemisphere has a lack of salamanders and newts? Australia I can see. But it seems like there should have been some migration into Africa and South America. Just a question of idle interest.

 

[Kaysie]

A vast majority of salamanders do not do well in tropical temperatures. Bolitoglossid salamanders live at high elevations in the tropical regions, but as far as I know, there are no 'tropical' salamanders. They like it cold!

 

[tylototriton]

Like Kaysie said, most salamanders do not do well at do well at warm temperatures. I suspect that this has something to do with the fact that a majority breath through their skin, and so their skin must remain moist and cool to allow the greatest amount of O2 to be absorbed. Likewise is true with the species that have lungs, their lungs still must remain moist in order to absorb O2. The warmer it is, the harder to absorb O2. Like Kaysie said, Bolitoglossids can be found in the tropics, but they are often found at the higher, cooler climes, and only in the moister areas.

Alex

 

[oregon newt]

A vast majority of salamanders do not do well in tropical temperatures. Bolitoglossid salamanders live at high elevations in the tropical regions, but as far as I know, there are no 'tropical' salamanders. They like it cold!

That's what I was thinking, but I was wondering why they evoloved into cold-liking animals, I fyou can understand that. Couldn't they just have adapted to the heat many years ago?
Edit: Just read Alex's post. That answered my question.

 

[fishkeeper]

Also, whatever niches caudates might want to get into by adapting to warmer temps are likely already taken by lizards, frogs, or fish.

 

[mikebenard]

This is an interesting problem - biologists have been interested in finding explanations for the worldwide distribution of many groups of organisms for over a century and a half.

I agree in part with what Kaysie and Alex said. Physiological limits probably do provide part of the reason for why salamanders do not occur in some parts of the world.

However, temperature alone cannot explain the worldwide distribution of salamanders. For instance, not all plethodontids in the tropics have a high-elevation distribution.

The other thing to consider is the biogeographic history of salamanders: where and when did salamanders originate, and what did the world look like then?

The best fossil evidence indicates that most modern salamanders arose about 160-170 million years ago, in what is now Asia (sirenids are an exception). At that time, Asia, Europe and North America formed one big continent "Laurasia" that was separating from the other big continent "Gondwanaland".

Thus, salamanders have been evolving in Asia, Europe and N. America for the last 160 million years, at least.

Gondwanaland included what is now Africa, South America, Australia, India, and Antarctica. Salamanders never had the opportunity to live in Australia, and only recently (geologically speaking) have had the opportunity to move into and evolve in Africa and South America.

However, the potential for salamanders to evolve into and survive in tropical environments is clearly shown by the plethodontids that exist in tropical central and South America, including the Amazon Basin, Yucatan pennisula and other low-elevation sites.

Mike

 

[fishkeeper]

Hey Mike,

Is their any explanation for the superficial similarity of Taricha to Asian newts and Notopthalmus to the European ones?

 

[tylototriton]

If I had to hazard a guess I would say convergent evolution. Granted, all the species came from a common ancestor, and at some point populations got separated. These populations evolved separately, but because they evolved in similar habitats they came to be quite similar to each other. This concept is based on natural selection and maximum "fitness" in the habitat. This is just me conjecturing. I'm sure Mike can explain better.

Alex

 

[mikebenard]

Alex is probably right - the similarities are the result of convergence. Weisrock et al's (2006 Molecular Phylogenetics and Evolution) recent phylogeny of Salamandridae indicates that Taricha and Notophthalmus are more closely related to each other, than they are to any other salamander. Cynops, Pachytriton and Paramesotriton may be nested within the genus Triturus. Tylotriton is the sister taxa to ((Taricha+Notophthalmus) and (Cynops, Pachytriton and Paramesotriton)).

This indicates that the similarities you see between Notophthalmus and Triturus, and Asian salamandrids and Taricha, have evolved multiple times. Whether that is due to natural selection or genetic drift is another question.

Mike