At lower elevations, perhaps neoteny amongst sirens and
amphiumas can be explained by their wetland habitat
coupled with a morphology that is specialised to an
aquatic habit, and assisted by their ability to aestivate in
mud if required. Neoteny is also likely to be associated
with the absence of fish that predate upon the salamanders
and their eggs, and perhaps compete for resources.
There is one other form of uninviting environment that is
dominated by neotenic salamanders - subterranean cave
systems and rivers. Cave salamanders from a number of
genera are native to both Europe and North America, and
the Chinese Giant Salamander is also known to inhabit
subterranean rivers. Most North American species are
fully aquatic; many are blind, with reduced pigmentation,
and full neoteny or incomplete metamorphosis is the
norm. Presumably, this confers advantages in that prey
items may be drawn into the caves by the current, and are
then located in low-light conditions by vibrations in the
limestone. Measuring around 30 centimetres in length, the
Olm has an elongated body, devoid of pigmentation, and
is completely blind, although it is also photophobic. It
must therefore depend upon acute senses of smell and
hearing; the latter of which is adapted to an underwater
existence, and is supplemented by receptors in the lateral
line. The Olm also has a couple of other interesting tricks
up its sleeve, so to speak, as it is apparently able to orient
itself using the Earth’s magnetic field, and has a battery of
electroreceptors on its head, similar to those found in
cartilaginous fish. It was once thought to be the spawn of
underground dragons. Olms are gregarious and may live
for more than 100 years.
Given the eclectic nature of this diverse group of amphibi-
ans, one could observe that although there may certainly
be dividends associated with remaining forever young, it
is no guarantee of enduring beauty!
Reference.
‘The Olm was
thought to be the
spawn of dragons.’
Graham SP, Kline R, Steen DA, Kelehear C (2018)
Description of an extant salamander from the Gulf Coastal Plain of
North America: The Reticulated Siren, Siren
reticulata. PLoS ONE 13(12): e0207460. https://doi.org/10.1371/
journal.pone.0207460
Further reading.
https://www.nationalgeographic.com/animals/2018/12/new-species-of-
giant-salamander-siren-discovered-florida/
http://www.federicocrovetto.it/index.php/it/articles/29-neoteny.html
water. The Texas Blind Salamander (Eurycea rathbuni)
was first discovered in 1895 when specimens were drawn
up from a newly-constructed well that penetrated more
than 50 metres below ground level.
The Olm (Proteus anguinus) is the only European
salamander to dwell exclusively in caves, and is the only
extant member of family Proteidae besides the North
American genus Necturus. It is endemic to the distinctive
karst formations of central and southeast Europe, where
underground rivers and caverns are common in the soft
http://www.hellbenders.org/
https://www.smithsonianmag.com/science-nature/the-salamanders-that-
refuse-to-grow-up-64827289/
Above left: Eastern Tiger Salamander (Ambystoma
tigrinum) in Badger Reservoir, Wisconsin. This consti-
tutes a rare example of neoteny induced by humans in the
wild. Image courtesy Tamara Thomsen, Wisconsin
Historical Society.
Above: Olms (Proteus anguinus), in Postojna Cave,
Slovenia. Image by Lander.