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A Skink's Tail 

Thread - Skinks

On 28/11/2002 Ray wrote:

Does anyone know the biochemistry / genetics behind skink losing and replacing their tails?

David Allen responded:

The following is reprinted from Webster Publishing's 'Frogs & Reptiles of
Australia' without permission but with, I hope, indulgence.
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 Most skinks readily drop (autotomise) their tails when attacked or molested: the regenerated tail is usually a little shorter than the original, and slightly different in colour and patterning.

Several only distant related genera contain members that have an unusual (and presumably defensive) mechanism whereby their body scales (especially from the back and sides) can be easily lost. The scales detach in response
to relatively slight but sharply applied local pressure as can happen by accident from a fingernail during capture. The flat smooth scales are lubricated to some extent by plasma-like fluid from the detach area, and they slip away easily (a).

Presumably, this can also happen when a predator's claws or teeth make initial contact, and if the grip is not strong enough the lizard may be able to escape. These "slip" scales occur in most Carlia skinks, some Ctenotus, and also Bassiana platynota (a). They have also been described as "tearaway" scales in some members of the Lerista nichollsi species group and in some Ctenotus.
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Peter Macinnis added:

Ray, I seem to recall something about blood vessels that "clamp off" at the break, but that is all -- is your interest in the loss or in
the regeneration?  If it is regeneration, it goes further than just skinks.

There is an excellent book by an author called Twitty (don't snicker) called "Of Scientists and Salamanders".  I think Harry Recher may have studied with Twitty -- he knew a lot about the work, and recommended the book to us in the late 60s.  Twitty marked his salamanders by clipping various of their toes to label them in binary (dare I say digital?) but the toes grew back, destroying their ID -- I think Harry said Twitty ended up suiciding, but I don't know whether it was out of frustration or not.

I join you in your curiosity, but it is the occasional forked tail I would see as a youth that I want most to know about -- and why they aren't around any more . . .

PS -- unlike David, I wouldn't have thought of looking at that CD-ROM, as it is not one on which I work.  But as far as copyright is concerned, it would be a foolish publisher who objected to a quote that short and attributed -- and that publisher's lawyer would be enriched without any benefit to the publisher.  In short, David's quote falls squarely within the common-sense definition of "fair dealing", especially as it is (a) in context and (b) even though archived, not visible to normal search engines as far as I know.
Chris Forbes-Ewan  replied:

Branching off at a tangent (again), below my signature block are two messages from last year about possible adverse consequences to the love life of a skink that has lost its tail.

----- Original Message -----
From: Forbzy
Sent: Thursday, September 06, 2001 8:49 PM
Subject: Losing your tail means an end to any hope of romance for at least four months

... at least, it does for skinks, according to an article in Australasian Science (Sep 99).

As everyone knows, a skink (and most other lizards) will shed its tail if captured from the rear by a predator. This gives the skink a sporting chance of escaping with its life. But this comes at a huge cost to the lizard's chances of reproducing.

It takes about four months (thought to be about 10% or more of the lifetime of a skink) for the tail to regrow. During this time, the skink is very unlikely to mate, because tail waving is part of the courtship process.

Even when the tail grows back, it usually does so imperfectly, leaving the poor skink with a greatly reduced chance of having a successful love life than those who have their original tails.

I just thought you might like to know :-)
From: Podargus
Sent: Sunday, September 09, 2001 12:33 AM
Subject: Re: Losing your tail means an end to any hope of romance for at least four months

Forbzy wrote
> ... at least, it does for skinks, according to an article in Australasian
> Science (Sep 99).

I haven't read the article yet but will chase it up.  I assume it refers to one species.
> As everyone knows, a skink (and most other lizards) will shed its
> tail if captured from the rear by a predator. This gives the skink a
> sporting chance of escaping with its life. But this comes at a huge
> cost to the lizard's chances of reproducing.
Actually all skinks do not lose their tail in this way, and certainly not most other lizards.  Common in geckoes, but as far as I know does not occur in say agamids (dragons) and varanids (goannas), even the small ones. Some species can part from their tail without mechanical interference, just the threat as it were, there is a term for it which escapes me now.  This is generally regarded as diversionary, as the severed tail moves about in a most remarkable manner.
> It takes about four months (thought to be about 10% or more of the
> lifetime of a skink) for the tail to regrow. During this time, the skink
> is very unlikely to mate, because tail waving is part of the courtship
> process.
It should not matter to a male, after all as discussed here recently, it is advantageous for a male to mate as often and with as many partners as possible.

Again I take it that the article refers to one species, not all mating behaviour in skinks with the ability to auto detach their tails, wave their tail as part of mating behaviour.
> Even when the tail grows back, it usually does so imperfectly, leaving
> the poor skink with a greatly reduced chance of having a successful
> love life than those who have their original tails.
I've never seen one that was 'perfect'.  Occasionally one sees two or even three regrowing from the severance point.

> I just thought you might like to know :-)

Thanks Chris, nothing like a bit of sex ;-)

Podargus
Ken Simpson added:

I think that the tails of skinks and others have a pre-programmed fracture site in one of the bones.  This breaks when the tail is grabbed and then as stated above to prevent blood loss the bit that is left behind wriggles around to distract the predator and hopefully give to beastie a chance to get away.

Ray replied:

Chris F-E, whilst the breeding propensity for tail dancing skinks may well be handicapped by tail loss, the fact that skinks have developed the tail-shedding capacity would indicate that natural selction at one time favoured those who could over those who could not.

I guess that now all skinks have the capacity, female skinks can afford to favour those male skinks which were fast enough or discrete enough to escape and keep their tails.

Or perhaps, the tail-sheding genes are associated with the X-chromosome and it matters less to male skink whether she has a tail or not?