Reptile & Amphibian Forums

I am currently interested in gathering data on snakes known to swim or raft between land masses...any help would be much appreciated.

Richard Wells

...Python reticulatus or Morelia nauta?

Hi Steno,

well, actually all island populations somehow came there once. Most of them "traveled" on a log, or were blind passengers on boats, ship or other vehicles (e.g. the brown tree snake at Guam, which was imported by ship). Others became "vicims of geographic changes". There are indeed many more snakes and other reptiles than P. reticulatus or M. nauta.

@Dear Richard, perhaps something that you already have read, but maybe not:

CHRISTOPHER C. AUSTIN, 2000, Molecular Phylogeny and Historical Biogeography of Pacific Island Boas (Candoia), Copeia 2000 No. 2
http://www.museum.lsu.edu/Austin/WeCopeia, 2003(1), pp. 81–94
Body Size Evolution in Snakes: Evidence from Island Populations
SCOTT M. BOBACKb Site Images&pdfs/AustinCandoia2000.pdf
-----
JAVIER A. RODRÍGUEZ-ROBLES, DALE F. DENARDO and RICHARD E. STAUB, 1999, Phylogeography of the California mountain kingsnake,
Lampropeltis zonata (Colubridae), Molecular Ecology (1999) 8, 1923–1934 Blackwell Science, Ltd.
-----
Zolta´n Tama´ s Nagy, Ulrich Joger, Michael Wink, Frank Glaw
and Miguel Vences, 2003, Multiple colonization of Madagascar and Socotra by colubrid snakes: evidence from nuclear and mitochondrial gene phylogenies, The Royal Society
http://www.mvences.de/p/p1/Vences_A58.pdf
-----
SCOTT M. BOBACK, 2003, Body Size Evolution in Snakes: Evidence from Island Populations, Copeia, 2003(1), pp. 81–94
http://web6.duc.auburn.edu/~bobacsm/islmain.pdf

Hope there something interesting for you to read.

Cheers,
Wulf
-----
http://www.leiopython.de - the white-lipped python site -
http://www.herpers-digest.com - herp related eBooks search -

Hi Steno and Wulf,

The notion that snakes are capable of expanding their ranges over large bodies of water - particularly salt water - is taken for granted, but there is a paucity of direct observational data to support the idea. As one who has personally witnessed the massive displacement of rafts of vegetation during the flooding of tropical rivers, it would be easy for snakes to be thrust well out to sea on such material, but who has actually searched such detritus for its faunal passengers? Similarly, occasional observations of terrestrial snakes that are usually found in association with water - such as Pseudechis porphyriacus - have been observed at times in the open sea, kilometres from land. And I have no doubt that large snakes such as the pythons you mentioned, are not only capable of swimming out to sea, but probably readily do so between islands as population, environmental or ecological conditions dictate. I suspect that some snake distributional patterns may be based more on the founder effect of such a dispersal pattern, than as a direct consequence of sea level perturbations. Anyway, I feel it would be very enlightening to get hard data on such behaviour. Given the obvious difficulties with such investigations, I suppose the best we can hope for is the fragments of (opportunistic) sightings that are occasionally made - usually by non-herpetologists. Thanks for the references as well, Wulf.

Regards

Richard Wells

I believe there are published records of island populations of Vipera berus in the Baltic Sea (brackish) in Sweden that regularly "commute" between islands (documented by mark-recapture) - separated by only a few 100 metres, but sea-going nonetheless. I don't have the references at hand, but let me know if youy are intrested, and I will try to dig them out.

Cheers,

Wolfgang
-----
WW Home

Yes, if you don't mind Wolfgang, that paper would be useful if you can dig it up. I know of a very interesting example here in Australia where Pseudonaja textilis have managed to recently colonize an island through such behaviour - and it has resulted in a population density on the island apparently higher than the adjacent "mainland". And this gets to one of the reasons why I am interested in this aspect of snake behaviour. The initially larger population of an invading species in itself is really quite interesting. This might be indicative of an obvious survival strategy of snakes exploiting new territory - an initial unstable swamping effect of the invading species as it in effect rapidly occupies an available niche (enhanced by alteration of the usual population regulating mechanisms on the species like say the absence of the usual predators, or an abundance or variation in food supply), before a stable lower population is achieved once the ecosystem has adjusted to the altered energy flow so created. This could also partly explain why population densities of snakes may vary so much across their ranges over large land masses (and by analogy over large water masses in the case of sea snakes). I have always considered the huge populations of Notechis scutatus that once inhabited parts of Australia, as only temporary phenomena that followed environmental changes impacting on habitat. Periodic flooding of much of inland Australia may also explain some of the peculiar distributional patterns of Cannia australis and some of the Pseudonaja nuchalis complex, and ipso facto their variable abundances at sites over time. Major population crashes are believed by some observors to have occured as numbers of snakes in Australia appear to be greatly reduced. So there is a belief that snakes are dying out in Australia, and indeed this may be the case for habitat has been lost here on a massive scale, feral predators are in huge numbers, and motor vehicles have likely never had a greater presence, etc etc. But where habitat is still relatively undisturbed, snakes (Elapids) are usually in numbers more in keeping with their trophic position as high order predators - they are actually rather rare in stable systems I think. It is how snakes disperse and respond to new areas of range that may provide clues as to their adaptability and ultimately perhaps their survivability under human-induced environmental perturbations. From what I have seen, the impact of human population expansion means a pretty bleak future for snakes in the medium to long term. I think it's going to be initially a mixed bag though - with most glowing brightly before the candle goes out say like Boiga on Guam, or Pseudonaja textilis in urbanised western Sydney. Some may indeed appear to even "adapt" to human settlements say like your Cobra mates in Asia or Pseudonaja in altered agricultural landscapes of inland Australia at least for a while...higher numbers in perturbed environments...but ultimately I think even these will crash to lower more vulnerable population levels...and then its probably all-over red-rover if your a snake wanting a place in the near future I'm afraid. But here's hoping humanity will start to like snakes being around...

Regards

Richard Wells

Richard Wells wrote:
The notion that snakes are capable of expanding their ranges over large bodies of water - particularly salt water - is taken for granted, but there is a paucity of direct observational data to support the idea.

Me:
I think you have neglected the sea snakes. Harry Greene wrote in his book Snakes: "...the Yellow-bellied Seasnake (Pelamis platurus) survives waif dispersal with sufficient frequency to colonize the eastern Pacific. The latter species occasionally washes up on the coast of Siberia and as far south as New Zealand and Cape Horn but can neither survive long nor reproduce in such cold areas.

I think you were probably thinking about only terrestrial species when you made that statement. You are probably correct that most snakes cannot cross long stretches of ocean (unlike the Yellow bellied sea snake). Most island snakes have close relatives on a nearby continent, as Wulf pointed out by citing such examples as Lampropeltis zonata. Other species of snakes, including other species of Lampropeltis (e.g. L. getulus) have also colonized islands, probably when these islands were connected to the mainland. The colonization of North America by colubrid snakes was probably made via land bridges between Europe and North America and between Asia and North America. South American species of colubrid snakes may have entered this land mass via a southern land bridge, perhaps across Anarctica.

The Madagascan boas, however, probably could not have gotten there without swimming long distances. Ditto the colubrid snakes found on that continent.

Snakes are good swimmers. The two oldest known fossil snakes both have hind limbs, and are found in shallow marine deposits. A marine, mossasauroid origin can probably explain the nearly world wide distribution of snakes. Once evolved, snakes could have swam or be carried by ocean currents to far corners of the world. There are two recently published papers which support a marine, mossauroid origin for snakes. The first one is

Rest, J.S., J.C. Ast, C.C. Austin, P.J. Waddell, E.A. Tibbets, J.M. Hay, D.P. Mindell. (2003). Molecular systematics of Reptilia and the tuatara mitochondrial genome. Molecular Phylogenetics and Evolution, 29:289-297

Fig. 4 of this paper shows that snakes are nested within the lizards; snakes are not the sister group of lizards. Monitor lizards, in fact, are more closely related to snakes than they are to the green iguana or skinks. Thus the mossasauroid origin of snakes have support from molecular systematics.

A second paper which also supports a marine mossasauroid origin for snakes is:

NATHAN J. KLEY 2001. Prey Transport Mechanisms in Blindsnakes and the Evolution of Unilateral Feeding Systems in Snakes. AMER. ZOOL. 41:1321–1337

In this paper, it is shown that the blindsnakes have evolved a proprietary feeding mechanism that is almost certainly derived, i.e. not the primitive condition found in the ancestor of the snakes. Thus the macrostomatan condition is probably the primitive condition in snakes, as the 95 million year old marine fossil snakes with legs suggest.

These recently published papers strongly support a marine, mossauroid origin for snakes. As one can see, the yellow bellied sea snake ended up as far north as Siberia and as far south as New Zealand. Even though the oldest known fossil snakes are found in the vicinity of Israel, there is no reason why they or their descendants could not have dispersed widely, even globally, rather quickly early in the evolutionary history of snakes the same way that the Yellow bellied sea snake has dispersed.

I think many snakes are fully capable of taking a swim and ending up alive on islands, just as most birds are capable of flying across open water and ending up on an island. The reason why birds do not make those flights is probably similar to the reason why snakes do not regularly take a swim across the sea. It is not the fear of flying or swimming. It is probably because animals have instincts that prevent them from migrating aimlessly across long stretches of unknown terrain, because such migrations would most likely be unsuccessful, since unsuitable habitat and/or fierce competition would likely await the migrant at the other end of the expedition. Homing instincts have evolved in many animals to ensure that they do not stray far from optimal habitat. It is perhaps homing instinct that has prevented the colonization of islands by many snakes, not the fear of swimming. For those who have taken a swim, perhaps few have been successful because of competition from natives. The exceptions of course are the Madagascan boas and colubrids.

Richard Owen, a famous nineteenthcentury British anatomist, claimed snakes can "outswim the fish and outclimb the monkey." --Harry Greene

Hi Richard

Is sea-swimming also of interest (close linked to the island hoping)

If so this article might also be of interested

Bringsøe, H. 2001. Hav og hugorme. NHF, 44(2): 65-69.
(translated it would be: Sea and vipers) - it has a short english summary, which i might be able to scan to you if you like.
-----
Regards

Jan Grathwohl

HERPBREEDER.com - The Herpetological database
HERPBREEDER.dk - My private collection

Hi Jan,

Yes, I'd like it if possible.

Thanks

Richard Wells

Hi Richard

I will try to make a scan as soon as possible (spending all my spare time painting my new house at the moment, so will hopefully be next week).
-----
Regards

Jan Grathwohl

HERPBREEDER.com - The Herpetological database
HERPBREEDER.dk - My private collection