Question: Why do newts leave the water in the first place?

[Rupert]

I had this question lingering in my mind since I was a kid, but recently it's been haunting me:

Question:

Why do seemingly aquatic newts leave the water?

Discussion :

This is mainly a question regarding the Triturus species which tends to have a near-definite "life-cycle" of entering and leaving the water on a seasonal basis. However, it seems that most terrestrial species like Taricha Granulosa may be fully aquatic depending on the locality. I've also read anecdotes that species with a definitive land stage such as the Notophthalmus can "skip" the eft stage with no apparent ill effects.

On the other hand, I saw the terrestrial forms of Pachytritons and Pleurodeles, which I thought were aquatic to the axolotl-level!

So what's the deal? Why do newts go on land even though the aquatic life seems to be the best fit?

Some points that needs to be cleared :

a) Is the terrestrial "stage" or "period" really necessary? Do Red Efts eat something that is vital for their development that somehow only exists on land? Do the Triturus leave the pond during the summer to prepare certain nutrients/hormones that is needed for the next successful breeding season?


b) Or is the "terrestrial period" just a means to escape dangers of the water, including high water temperature and/or predators, or lack of food/space? If this is true, than in an ideal aquatic setting(whether in nature or captivity) the newts should never have to leave the water at all, right?


c) I did think about possible biodiversity/lineage issues, but considering that most newts have amazing homing abilities to return to where they were born, I think this is a moot point.


d) Conclusively, is there really any benefit to aid in "land-water transition" of newts in captivity? If the terrestrial stage is just a means to survive inhospitable water conditions, than in an ideal water condition the newt should NOT have to leave the water at all, right?

I know many experienced breeders and hobbyists believe that replicating their natural "cycle" in the wild is beneficial for the newt's well-being(especially with Triturus), but if the aquatic stage is the "preferred living condition" and the terrestrial stage is the "second best" option for them.... bluntly put, why bother - especially in terms of husbandry?

I mean, just because the newt "can" develop terrestrial form, does it really necessitate the terrestrial stage in captivity?

I did find this article online :

http://www.researchgate.net/profile...chronology/links/02bfe50fa704dc1593000000.pdf

I major is pretty far away from natural science, but I think this paper does indicate that the terrestrial period seemingly slows the growth in T. Marmoratus, and I believe this is also relevant to the Notophthalmus growing faster/bigger when skipping the eft stage.


Sorry for the wall of text, and I apologize in advance in case if i offended any hobbyists/breeders who swear by the philosophy of replicating the animal's natural life-cycle - I'm not saying anyone is wrong(yet), but just asking from a efficient husbandry point of view. Any scholarly articles/studies that I could read would be great as well.


p.s. I did think about posting this in the herpetological science section, but since I'm asking a newbie question than a true scientific discussion I thought I'd put it here.

 

[Autumncrossing]

I've always thought some left and migrated for genetic diversity and variation, other reasons might be unfavorable drought conditions, another could be less prevalent parasites, fungus, or bacteria during the colder months when they might return to the water. These are just my guesses though. I'm curious to see what others input!


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[Cliygh and Mia]

It could also be from a lack of food, and they have to go on land to find more food to eat

 

[Lertsch]

I regards to red efts, I never researched it but always assumed that the terrestrial stage protected a population from getting wiped out by disease. If the adult aquatic population fell victim to some type of waterborne pathogen the terrestrial portion of the population has a better chance of not being infected and could repopulate once they matured and become aquatic.

 

[Rupert]

But even if the animals are given ample food/perfect water conditions, they will still leave the water for land right (as efts will seemingly drown)? Except for a few cases on Notos that will skip the eft stage....

What's the evolutionary basis behind all this?

 

[Lertsch]

A healthy population could face a widespread disease at any time, or never. Having a terrestrial stage separates a portion of the population for a period of time. IF there is a disease spreading in either the terrestrial or aquatic population, they would be less likely to infect the other population because they are in separate habitats for a period of time.

 

[Mark]

Newts enter the water to breed. Some species spend longer in the water than others, especially if conditions are favourable or if the terrestrial environment is unsuitable. We exploit this in captivity by reducing the land area and by providing food in the water, thus some species can remain 100% aquatic indefinitely. In the wild those newts would simply crawl out and enter the familiar biphasic cycle.

So the answer really is that newts are terrestrial animals that have to enter water to breed. When they have finished breeding or the larvae have metamorphosed they will leave the water.

 

[dannyyyallenn]

But that can't really explain newts that are almost fully aquatic like Pachytriton and Pleurodeles. Eft or terrestrial stages for Pachytriton Labiatus especially is very rare. I know newts enter the water to breed but why would a newt species stay in the water from a young age, regardless of breeding season?

 

[Rupert]

But that can't really explain newts that are almost fully aquatic like Pachytriton and Pleurodeles. Eft or terrestrial stages for Pachytriton Labiatus especially is very rare. I know newts enter the water to breed but why would a newt species stay in the water from a young age, regardless of breeding season?

I was wondering the same thing too.

And it seems its generally true that newts grow faster in water :

http://www.caudata.org/forum/f1173-...8-difference-between-aquatic-terrestrial.html

I cant recall the thread but I remember reading that this applies to Triturus Carnifex as well.

Common sense lead me to think that bigger, faster growth = better for the animal - if so, maybe newts are aquatic animals that ESCAPE water in case of undesirable conditions in water? Or maybe not?

 

[chapmantl]

N. viridescens is my study animal. Juveniles usually leave the water during eft stage in order to avoid competition in high density populations. If competition is low and resources are plentiful, juveniles will remain in the water until they are reproductive adults.
As to the adults of this species sometimes leaving the water again, I am not sure. Back home (Indiana) they are almost fully aquatic and I had never seen a population that migrates away from breeding ponds. However, here in Tennessee it has been a frustration finding a permanent aquatic population. From what I can gather, these populations are mostly common in ephemeral habitats where ponds are likely to dry out during the summer season. I know of a few colleagues that are working on this question, however. I don't think any of it is published yet, but there is a long term mark recapture study being conducted out Mountain Lake Biological Station, Virginia. Apparently there are efts there that are known to leave the water for up to five years.