Autotomy in Psammophis?

Vyas and Patel, 2013:
"During handling the live snakes the first author experienced tail autotomy (Fig. 5) in three specimens. All three specimens lost the tails immediately and tried to escape, as reported in Gecko species and the Checkered Keel-back water snake (Xenochrophis piscator Schneider, 1899) (personal observation of Raju Vyas). When the specimen was handled at the most posterior part of the tail, it displayed a forceful turning movement, rotating swiftly, which resulted in the de-tailing of the snake.
The posterior part of tail portion was left in the hand and the de-tailed animal escaped. Few members of Psammophis are known for such caudal autotomy (Broadley, 1987). Tail autotomy was reported in P. crucifer (Daudin, 1803), P. schokari, P. punctulatus (Duméril, Bibron et Duméril, 1854), P. biseriatus Peters, 1881, P. condanarus and P. rombeatus."

This interpretation of the tail loss corresponds with that of Broadley (1987):

Examples of this truncated tail are abundant. See for example http://www.ispot.org.za/node/175184, probably a P. subtaeniatus.

I think the interpretation of autotomy by Broadley (and others) is at least disputable. I tend to consider the breakage of tail ends in Psammophis as a case of 'normal fracture'.  In the case Vyas and Patel describe (and those that Broadley refers to) there was 'a forceful turning movement, rotating swiftly'. It seems rather normal that a thin tail would break off in this case, as a result of the forceful movement, NOT as a result of a sort of deliberate self-defense mechanism to distract the predator. If this would be considered autotomy, any loss of limbs or body parts as a result of being caught by something would be called autotomy, for instance when a truck wheel rips off the arm of a traffic victim. We don't say then that this is a deliberate strategy, as we have two arms and can still continue living.

I tend to agree with Todd and Wassersug (2010), who use the term 'pseudoautotomy' for cases of intervertebral breakage, without tail generation. Pseudoautotomy is further divided in specialized (having morphology that facilitates breakage) and non-specialized (with long and fragile tails without morphological breaking points). They consider the cases in Broadley 1887 as pseudoautotomy. They studied Thamnophis sauritus, which shows apparently the same escaping behaviour as Psammophis: quickly rotating along the longitudinal axis.
There was little bleeding, which could result from physical adaptation (reduced blood flow to the tail) to cold climate, and would increase the risk of tail damage.

Sheehy (2006) investigated the relative tail-length of snakes in relation with habitat use, for instance total or partial arboreality. His findings are over all not very impressive. Snakes that are arboreal or mainly terrestrial and sometimes arboreal (e.g. when escaping predators or when hunting) tend to have longer tails than snakes that have burrowing habits, but that is not very surprising. One aspect of tje study concerns the tail length in relation to movement. No conclusive evidence exists that longer tails are in general advantageous for fast movement (but it is not taken in consideration that Psammophis has a rather stiff body and tail that are very accommodated for whip-like locomotion, unlike for instance Thamnophis). Sheehy suggests other factors favor long tails: high incidence of tail loss as is found in the genera Nerodia and Thamnophis, as a result of predation attempts, could favor long tails as an anticipation to possible predation. Snakes do not have a morphological specialisation for tail loss, like some lizards have. Only breakage between vertebrae occurs, and never as a result of neural control, but always a result of 'physical resistance, which is often facilitated by twisting or rotating the body in one direction until the tail snaps off'. There is also no real regeneration.
I quote: "Many long-tailed terrestrial species are also active, diurnal predators that rely on speed to procure prey (Greene 1997). However, if fast moving terrestrial snakes possess adaptations for speed, and long RTL is not required for speed, then alternative selective pressures are likely responsible for maintaining long tails in these species. Furthermore, because many of these species are known to possess stub tails (Greene 1997), it is reasonable to infer that the long tails of these terrestrial species might be a mechanism for defense. Many of these species rely on speed for escaping predators, and quickly fleeing increases the likelihood of a predatory attempt being directed to the tail instead of the body (Greene 1973). A long tail can subsequently break
allowing the snake to escape."
As I said, Sheehy does not take in account that the specific body and tail characteristics of Psammophis (relatively rigid) in combination with the very long tails are possibly favorable as a powerful means for fast acceleration. Furthermore, it seems a rather unlikely hypothesis that long tails would have developed as something that the snake can use to leave behind for the predator.

In 2006, Carlo Comazzi experienced a case of tail breakage in a specimen of Psammophis orientalis. He published some pictures of the broken tail part in the Psammophiid-group on Facebook. Here they are:


There was no rotating movement involved, just a brisk movement when the snake was caught by the tail.

Francis Cosquieri: "I had similar happen to me with a P. schokari once, and in the wild a number of animals I have seen seem to have damaged tails." Het adds, that in his case, there was a "very quick rotating movement, not really anything more than the jerk a lizard might give. I notice though that many scared Psammophis will spin rapidly in the hand when grabbed, I believe this aids autotomy."
In both cases, the observers noticed that the broken tail section kept moving for at least a minute.
Francis published the following picture of a sibilans with damaged tail
that arrived (click for larger format):

Hoogmoed and Avila-Peres 2011 describe a case in which a specimen of Dendrophidion dendrophis threw off its tail: "All of a sudden, without being touched, the larger part of the tail broke off somewhere in part of the twisted area and the snake continued
crawling away." But these cases seem to be very rare.

N. B. Ananjeva and N. L. Orlov (1994) define caudal autotomy as: "fracture of caudal vertebrae in definite regions", whereby the loss of the tail is so to say 'predefined' and occurs in places 'meant to break in case of emergency' (my words). tHEY STATE: "Unlike most lizard species, snakes do not demonstrate functional autotomy with intravertebral fracturing (Etheridge, 1967; Arnold, 1984) usually although an intravertebral plane of weakness in the caudal vertebrae of Pliocercus was noted (Bellairs and Bryant, 1985). The tail breaks in snakes as in agamid lizards between adjacent vertebrae, i.e., intervertebrally.
And: "Recent research shows that some colubrid snakes demonstrate relatively high incidence of tail autotomy in museum collections (Mendelson, 1993). These data and some field observations (including our examination of a specimen of
Xenochrophis piscator) show assuredly that snakes also use caudal autotomy as an antipredator mechanism."