Morphological, functional and evolutionary aspects of tail autotomy and regeneration in the ‘living fossil’Sphenodon (Reptilia: Rhynchocephalia)

Abstract

Tail autotomy and regeneration are less known in Sphenodon ('Reptilia': Rhynchocephalia) than in Squamata. We examined museum specimens, Sphenodon guntheri (N = 8) and Sphenodon punctatus (N = 172), wild Sphenodon punctatus (N = 19) and Sphenodon sp. skeletons (N = 8). In S. punctatus, unlike in typical Squamata, sexes had similar relative (intact) tail lengths, and regeneration frequencies; tail and body growth was isometric. Tail breakage was usually intravertebral, usually followed by ablation of a variably sized terminal vertebral piece, partly deviating from lizards. Hypothetically, imperfect autotomy results from sphenodon's primitiveness. As in squamates, tail-losers were morphologically more left-side dominant than tail-retainers. Individual directional asymmetries in digit morphology and in digit injury were correlated (in lizards observed only at population level); tail-losers had more fluctuating asymmetry but their exclusion did not facilitate morphological taxonomic distinctions (no 'Seligmann effect'). In S. punctatus, extents and directions of sexual dimorphism paralleled differences between tail-retainers and tail-losers, females resembling tail-losers, also accounting for character interdependence (developmental constraints; employing a method similar to phylogenetic contrasts). The variation in the location of tail injury was correlated with the continuum of variation between injured and intact (pholidotic) morphotypes. These last two phenomena remain to be explored in Squamates.

Bite‐force performance of the last rhynchocephalian (Lepidosauria:Sphenodon)

“…Corresponding to the relationship between bite force and territoriality in lizards, bite force has been shown to predict reproductive success; the hardest biters enjoy reproductive success nearly four times greater than similarly sized males with the weakest bites (Lappin & Husak 2005;Husak et al 2009). As with lizards (e.g., Lappin & Husak 2005), confrontations between male Sphenodon can be intense and lead to injuries (Buller 1877;Gans et al 1984;Gillingham et al 1995;Seligmann et al 2008). Pathologies occasionally found on Sphenodon dentaries may be the result of healed wounds or infections from wounds incurred during aggressive territorial encounters (Fig.…”

Microscopical observations on the regenerating tail in the tuataraSphenodon punctatusindicate a tendency to scarring, but also influence from somatic growth

“…Studies on specific tissues that are regenerated in the tail have shown that the new cartilaginous tube and the spinal cord are similar to those of lizards (Alibardi & Meyer‐Rochow, , , ; Alibardi, ). Also, the regenerating scales, although smaller than the original ones and with irregular outlines (Seligmann et al, ), follow a morphogenetic process that resembles that seen in lacertilians (Alibardi & Maderson, ).…”

Tail breakage frequency as an indicator of predation risk for the aquatic snake Natrix maura

“…This could be a consequence of extended exposure to potential predators and thus an increased cumulative likelihood of injury and non-zero probability of survival following injury (Schall and Pianka, 1980;White et al, 1982;Willis et al, 1982;Seligmann et al, 2008;see Gregory and Isaac, 2005 for an alternative explanation). In Rhinechis scalaris, a terrestrial colubrid, an ontogenetic shift has been reported in the frequency of tail breakage, with the incidence of tail loss increasing as a logistic function of snake size (Pleguezuelos et al, 2010) resulting from predatory selection for medium-sized R. scalaris by their main predators (see also Gil and Pleguezuelos, 2001).…”

“…Tail breakage in snakes has been described as an effective antipredator strategy (Kaufman and Gibbons, 1975;Greene, 1988;Savage and Slowinsky, 1996;Aubret et al, 2005). Given that in snakes tail breakage is without regeneration and the conspicuous nature of this injury, comparisons between individuals, populations, and species are easy (Akani et al, 2002;Seligmann et al, 2008;Pleguezuelos et al, 2010). However, the interpretation of this injury is controversial (Willis Seligmann et al, 1996;Placyk and Burghardt, 2005), and it has been proposed that tail breakage may simply be evidence of inefficient predation (Schoener, 1979;Willis et al, 1982;Medel et al, 1988;Mushinsky and Miller, 1993) instead of predation risk (Jacksić and Busack, 1984).…”