Some amphibians stay in an eternal state of childhood much like the fictional character Peter Pan, this is known as paedomorphosis (‘child form’) and is only exhibited in newts and salamanders. I’m sure that most of you will be familiar with the axolotl (Ambystoma mexicanum), which is known for its ability to breed despite being in a permanent juvenile form. This state however can be artificially changed with the introduction of iodine which stimulates the production of thyroxine (Coots & Seifert, 2015), essentially forcing the axolotl to grow up and become a tiger salamander.
Paedomorphism, also known as neoteny, is occasionally observed in newts here in the UK. It is quite widespread and is a morphological trait that extends into Scotland (Paterson, 2017). It is uncommon to find newts that exhibit neoteny despite the fact that it can be driven by both genetic and environmental factors. In the spring of 2015, whilst surveying the Orton Brick Pits SSSI/SAC for great crested newts (Triturus cristatus), my colleague and I came across a small number of paedomorphic smooth newts (Lissotriton vulgaris). We found two individuals in bottle traps (which were being used to monitor great crested newts), whilst another was found whilst surveying a nearby pond by torchlight (Allain & Goodman, 2017).
Paedomorphism can occur by a number of means of which it is a usual consequence of damage to the pituitary gland. This also helps to explain why most paedomorphic newts are often albinos, as this too can be caused by damage to the same region. The newts we found however were not albino, they were the typical colouration for smooth newts (see photos). To explain the cases we observed, it is important to look at other causes of paedomorphism in newts. The environment can play a big part as well in determining whether or not an individual becomes a paedomorph.
Some newts will overwinter in the pond if the conditions are favourable, including an abundant source of food. This may happen if the larva fails to metamorphose before the autumn/winter – becoming trapped in its aquatic state. This can be risky as the pond may freeze solid or run out of food in the time running up to the spring, thankfully for any newts that do hedge their bets, the low temperatures means their metabolisms are much lower than usual. They grow slower but over a longer period of time, meaning come the spring months they have attained their adult size but still possess their juvenile characteristics. Some of these newts will metamorphose whilst others won’t.
Is the aim of these newts attempt at eternal youth in response to climate change? What are the triggers? These are questions that must be addressed with future research.
Whilst stuck in this stage, they can’t unfortunately breed or venture onto land. Lissotriton spp. newts are far more susceptible to paedomorphosis than their larger cousins, the great crested newt. No one is sure why and more research is certainly needed in the area. Whilst exploring my university campus in Berkshire, I stumbled across a couple of paedomorphic smooth newts whilst surveying a pond with a group of like-minded friends. We intend to document this phenomenon and track the individuals through time to see if they do eventually complete their metamorphosis. For now, recording where paedomorphosis occurs and in which species will help us to understand this peculiar quirk of evolution more thoroughly.
If you want to know more about our observation then please follow this link to our paper (also referenced below).
References
Allain, S. J. R. & Goodman, M. J. (2017). New records of paedomorphic smooth newts (Lissotriton vulgaris) at a site in Cambridgeshire, U.K. The Herpetological Bulletin, 141, 40.
Coots, P. S. & Seifert, A. W. (2015). Thyroxine-Induced Metamorphosis in the Axolotl (Ambystoma mexicanum). Salamanders in Regeneration Research: Methods and Protocols, 141-145.
Paterson, E. (2017). Observation of a paedomorphic palmate newt (Lissotriton helveticus) in Scotland. The Herpetological Bulletin, 139, 34-35.
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