A case of limb regeneration in a wild adult Podarcis lilfordi lizard

* Correspondence: cortada.salas@gmail.com Regeneration refers to the ability of an adult organism to restore injured or completely lost tissues and organs (Alibardi, 2010). In reptiles, successful regeneration is usually restricted to the replacement of the tail, mainly in lizards that perform tail autotomy (self-amputation) as a defensive strategy (Clause and Capaldi, 2006; Alibardi, 2010). When chased or seized by a predator, small-sized lizards, such as Lacertidae species, have the ability to deliberately release their tail, which keeps moving after being detached from the body. The intense movement of the shed tail distracts the attention of the predator, facilitating the lizard’s escape (Higham et al., 2013). In evolutionary terms, this defensive mechanism, together with the role that the tail can play in locomotion (Cromie and Chapple, 2012), energy storage (Chapple and Swain, 2002), or intraspecific interactions as a status-signaling badge (Fox et al., 1990), likely favored tail regeneration throughout evolutionary time (Meyer et al., 2002; Clause and Capaldi, 2006). Indeed, tail regeneration is rare in large-sized species, such as in Varanidae lizards, where the ability to fight back allows them to not rely on tail autotomy as a defensive mechanism (Maginnis, 2006). In contrast with urodel amphibians, which are known to regenerate both functional tails and limbs (Bryant et al., 2002), even those lizards that successfully regrow the tail after it is damaged fail to achieve a functional restoration of lost limbs (Alibardi, 2010, 2017). Lilford’s wall lizard (Podarcis lilfordi) is a lacertid species endemic to the Balearic Islands. It is currently restricted to the Cabrera archipelago and the offshore islets of Mallorca and Menorca, as it has become extinct in the main islands (Salvador, 2014), likely due to the Neolithic introduction of allochthonous predators (Pinya and Carretero, 2011). Remaining populations of P. lilfordi inhabit environments with low terrestrial predation pressure, frequently attaining high densities (up to 7815 individuals/ ha, Pérez-Mellado et al., 2008). In such conditions, insular Podarcis individuals tend to be aggressive towards conspecifics, particularly adult males towards juveniles, with tail and toe amputation and even cannibalism tending to be common (Castilla and Van Damme, 1996; Cooper et al., 2015). Here we report a case of limb regeneration in one of these microinsular populations. On 23 June 2014, during a lizard collecting campaign on Sa Dragonera islet, Mallorca (39°35′16′′N, 2°19′42′′E), we found an adult male (snout–vent length (SVL) >60 mm) of P. lilfordi with the left hind limb amputated up to the knee. Below the knee, the limb presented a regenerated appendage of approximately 10 mm in length, with scale rings, externally resembling a tail (Figure). Compared with the other conspecifics observed on the islet, this specimen seemed to have normal morphological features regarding apparent body mass, number of digits per limb, and general body structure, without any other anomaly Abstract: We report here a case of spontaneous limb regeneration in a wild Podarcis lilfordi lizard from the Balearic Islands. The animal had lost a hind limb, which regenerated posteriorly into a tail-like appendage. Despite not representing a functional regeneration, the growth of this structure after limb amputation suggests that survival of the individual may have been favored by the less restrictive conditions prevailing in insular environments. Nevertheless, such cases are extremely rare in lizards, with no reported cases over the last 60 years.