When salamanders
invaded the Dinaric Karst: convergence, history, and reinvention of
the troglobitic olm
It is a very good time to
be interested in salamanders. Partly because of my reading-up on
other areas of direct interest (like cryptic diversity [...],
the discovery of new species, declines in global biodiversity,
Cretaceous biogeography, radical homoplasy, polymorphism, and
evolutionary reversals), I am returning again and again to the
salamander literature. Mostly, these studies are about
plethodontids, where a lot of really neat research is being done. I
will post to the blog about most of this at some stage (if you can’t
wait that long see Hanken 1999, Parra-Olea et al. 2001,
Chippindale et al. 2004, Mueller et al. 2004 and
Min et al. 2005 to see where I’m coming from).
It’s not a plethodontid
(it’s a proteid), but one of the most unusual and interesting of
amphibians has to be the Olm (Proteus anguinus), an unusual
long-bodied cave-dwelling salamander from SE Europe. Olms were the
first specialised cave-dwelling animals (so-called stygobionts or
troglobites) to be discovered, they were traditionally identified as
dragon larvae by local people, and they remain mysterious and the
source of controversy, debate and discovery. I’ve had a special
affinity for olms since seeing them (live) in the former Yugoslavia
in 1987, and after a colleague published a brief article on them in
2004 I ended up compiling and publishing my olm-related thoughts. In
the interests of re-cycling that text I reproduce it here, in
updated form.
What might be the most
fascinating fact concerning olms is the most poorly-known and least
mentioned one: the 1986 discovery of a surface-dwelling olm,
described in 1994 by Boris Sket and Jan Willem Arntzen. So olms
aren’t just ‘unusual long-bodied
cave-dwelling salamanders’ – they now exist in two
forms, the cave-dwelling White olm Proteus anguinus anguinus
and the surface-dwelling Black olm or Brown olm
P. a. parkelj. Unlike the unpigmented nominal form
with its skin-covered eyes, P. a. parkelj (presently known
only from Bela Krajina in SE Slovenia) is dark brown or black and
has externally visible (albeit small) eyes. Because White olms
produce melanin when kept in sunlight (and are thus not albinistic
as sometimes implied), the difference in colour between the two
forms is not unexpected. However, there are also other, more
important differences separating the two.
P. a. parkelj differs from the nominal form in also
having a proportionally shorter, broader and more muscular head,
fewer teeth, a proportionally longer body and a proportionally
shorter tail and limbs (Sket & Arntzen 1994).
|
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Cave
explorer Maxime Landini watching the proteus -also called human
fish - in 'Postojna cave'. |
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Proteus
anguinus and the cave diver. |
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Proteus
anguinus, also called "human fish". |
Most of the features which
distinguish P. a. parkelj
from P. a. anguinus are plesiomorphies [= features
not unique to olms, but present also in related salamanders] and
hence P. a. parkelj may be the ancestor of the White olm.
Having said that, one of the most interesting contentions made
recently about olms (Sket 1997) is that the different cave-dwelling
olm populations may have evolved independently from different
ancestral populations. If this is correct it may be that the
different White olm populations represent different species which
resemble one another by convergent evolution, and which have partly
or mostly fused as they have met up within the Dinaric karst system.
Sket (1997) thought that morphological and genetic differences
observed among olms might provide support for this view and,
ironically, if correct it would mean that several old species names
proposed for different cave-dwelling olms might need to be
resurrected. Fitzinger (1850) named seven new olm species within his
genus Hypochthon (H. zoissii,
H. schreibersii, H. freyeri, H. haidingeri,
H. laurentii, H. xanthostictus and H.
carrarae), though given that the type localities for some of
them were just a few km apart, it’s unlikely that they really were
distinct taxa.
It’s worth saying that
olms almost certainly aren’t ancient relicts, or living fossils. In
fact, they must be young and recently evolved. Why? During the
Pleistocene, the Dinaric area was so close to areas that were fully
glaciated that temperature there must have been at or below
freezing. This is far too cold for olms, which require temperatures
of 6-18ºC for their eggs and larvae to develop (and toward the upper
end of that range is best). Furthermore, karstification and the
development of underground streams only began in the Dinaric region
during the late Pliocene at the earliest, apparently. In view of
these problems, olms either (1) survived in surface waters in the
region, where summer temperatures were just about tolerable (but
where winter temperatures would have made life difficult), or (2)
moved into the area from a warmer, southerly refuge (Griffiths 1996,
Sket 1997). It isn’t yet known which was the case: more research is
needed. Whatever, troglobitic olm populations must have evolved
within the last 10,000 years or so, and presumably the specialised
troglobitic morphology of living olms evolved during this time.
Similarly recent invasions of cave systems appear to have occurred
among various troglobitic fishes.
As mentioned earlier, olms
were the earliest troglobites to be discovered. While it’s been
stated on occasion that the species was discovered as recently as
1875 (Laňka & Vít’s 1985, Keeling 2004), olms first became widely
known in 1689 when Baron
Johann
Weichard Valvasor wrote about the animals in his book on the
Yugoslavian province of Carniola (on which see below). However, it
wasn’t until the mid-1700s that the animals become the subject of
proper scientific debate. At this time Slovenian scientist Giovanni
Scopoli ‘discovered’ olms and realized just how extraordinary they
were (Scopoli 1772). He planned to describe the animal
scientifically and enhance his reputation by doing so. We know that
Scopoli sent pictures of olms to Carl von Linne and that Linne and
Scopoli disagreed as to whether the animals were a distinct new
genus (Scopoli’s view), or the juveniles of something else (Linne’s
view). However, the Austrian anatomist J. N. Laurenti became very
interested in olms at the same time as Scopoli (apparently because
of a specimen Scopoli had sent to one of the Laurenti’s friends)
and, in 1768, published the first scientific description of the
species (Laurenti 1768). This is the ‘official’ date of the White
olm’s scientific discovery. Laurenti’s choice of generic name for
the olm (Proteus) is based on the Greek god Proteus but it
is not Proteus’ shape-shifting ability that Laurenti had in mind,
but rather his status as shepherd of sea creatures. Laurenti’s work
on the olm did not actually become that well known and it was Karl
von Schreibers’ work of the 1790s and early 1800s which made olms
well known among scientists.
Olm distribution has been
the subject of much confusion and speculation. Presently, olms are
restricted to the Dinaric Karst, a region that extends from the Soca
(formerly the Isonzo) River (near Trieste) in SE Friuli-Venezia
Giulia, Italy to the Trebišnica River in eastern Herzogovina. In
between Italy and Herzogovina, olms also occur in southern Slovenia,
southern Croatia and parts of Bosnia. Little known is that the
species has been recorded from localities in France (Moulis) and
Germany (Harz). These extralimital records are all apparently due to
human introduction however. They are also found in the Parolini
Grotto, Vicenza, northern Italy, but their presence here is due to
human introduction also. Of further interest, the locality mentioned
by Valvasor (1689) – the spring of Lintvern, near Vrhnika – is
actually outside of the Dinaric Karst, and is unlike the other areas
inhabited by olms in geology and geomorphology. It seems that
Valvasor made the logical (but incorrect) assumption that Lintvern
(which is a garbled form of the German word Lindwurm, meaning
dragon) was so named because it was the source of olms (which were
fancifully regarded as dragon larvae at the time).
Keeling (2004) implied
that Carniola (note: not Carinola) might be the Italian part of the
olm’s range and also wondered if Carniola might still be part of
Austria. Carniola is today called Kranjska and was controlled by
Austrian royalty until 1918 (consequently, the ruling classes there
spoke German until the 20th century). It is today part of central
Slovenia and is thus not either the Italian part of the olm’s range,
nor an Austrian extension of the species’ range.
Bizarrely, olms were
traded during Victorian times as exotic pets and were apparently
available in Britain as such (which raises the remote possibility
that they might have been introduced to British cave systems in the
same way that they were in French, German and Italian ones). During
the 1950s it was reported that olms were present in the Carpathian
karst of eastern Serbia, and in 1960 a team of speleologists from
Ljubljana led an expedition to the region to investigate this
possibility. They didn't find any olms there, and nor has anyone
else since.
Olms have been
horrendously over-collected for scientific use and were also
apparently collected by farmers for use as pig food. One of the
greatest problems facing olms today is metal poisoning caused by
industrial pollution and a number of populations have declined as a
result of such. P. a. parkelj is under strict legal
protection. Olms have been protected in Slovenia at least since 1949
and elsewhere in their range they are widely recognized as deserving
protection.
Finally, regarding diet
and breeding, olms apparently mostly detect their prey using
chemical clues and the detection of water currents but they also
possess electroreceptive organs in the head and thus presumably
employ electroreception. Despite their vestigial nature, the eyes of
White olms are not completely useless and are able to detect light.
Olms appear to mostly prey on aquatic crustaceans but also eat
snails and insect larvae. Captive specimens have eaten worms and
adults may be cannibalistic on occasion. When I visited Postojina we
were told that the olms on display were not fed both because their
food proved hard to procure, and because they were quite able to
survive for years without feeding. Indeed there was apparently a
specimen kept at the Faculty of Biotechnology in Ljubljana which
survived for an astonishing 12 years without food. Olms are
long-lived, reaching sexual maturity between 7 and 14 years, and
almost certainly ordinarily live for more than 50 years, though ages
twice this have been suggested by some writers.
References
-
Chippindale, P. T.,
Bonett, R. M., Baldwin, A. S. & Wiens, J. J. 2004. Phylogenetic
evidence for a major reversal of life-history evolution in
plethodontid salamanders. Evolution 58, 2809-2822.
-
Fitzinger, L. 1850.
Ueber den
Proteus anguinus der Autoren. Sitz.-Ber. Akad. Wiss.,
Math.-naturw. Cl. 5, 291-303.
-
Griffiths, R. A. 1996.
Newts and Salamanders of Europe. T & A D Poyser (London).
-
Hanken, J. 1999. Why are
there so many new amphibian species when amphibians are declining?
Trends in Ecology & Evolution 14, 7-8.
-
Keeling, C. 2004. Olm.
Mainly About Animals July 2004, 20-21.
-
Laňka, V. & Vít, Z.
1985.
Amphibians and Reptiles. Hamlyn (London).
-
Laurenti, J. L. 1768.
Specimen Medicum Exhibens Synopsis Reptilium Emendatum.
Joan. Thomae (Vienna).
-
Min, M. S., Yang, S. Y.,
Bonett, R. M., Vieites, D. R., Brandon, R. A. & Wake, D. B. 2005.
Discovery of the first Asian plethodontid salamander. Nature
435, 87-90.
-
Mueller, R. L., Macey,
J. R., Jaekel, M., Wake, D. B. & Boore, J. L. 2004. Morphological
homoplasy, life history evolution, and historical biogeography of
plethodontid salamanders inferred from complete mitochondrial
genomes. Proceedings of the National Academy of Sciences
101, 13820-13825.
-
Parra-Olea, G. & Wake,
D. B. 2001. Extreme morphological and ecological homoplasy in
tropical salamanders. Proceedings of the National Academy of
Sciences 98, 7888-7891.
-
Scopoli, J. A. 1772.
Annus Quintus Historico-Naturalis. C. G. Hilscher (Lipsiae).
-
Sket, B. 1997.
Distribution of
Proteus (Amphibia: Urodela: Proteidae) and its possible
explanation. Journal of Biogeography 24, 263-280.
-
- . & Arntzen, J. W.
1994. A black, non-troglomorphic amphibian from the karst of
Slovenia: Proteus anguinus parkelj n. ssp. (Urodela:
Proteidae). Bijdr. Dierk.
64, 33-53.
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Valvasor, J. W. 1689.
Die Ehre des Herzogthums Crain. W. M. Endtner (Nuernberg).
Name: Darren Naish
Location: United Kingdom
With six
years of tedious PhD work on theropod dinosaurs behind him,
Darren Naish stares longingly from his office window at the
birds outside and wonders… why did I bother? Like a one-legged
dog in pursuit of a stick thrown far far away, he takes long
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Sources:
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http://darrennaish.blogspot.com/2006/03/when-salamanders-invaded-dinaric-karst.html
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images -
http://www.ipak.org/slovenia/photo/source/34.html,
http://www.ipak.org/slovenia/photo/source/32.html
&
http://www.ipak.org/slovenia/photo/source/35.html
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