When one tail isn't enough: abnormal caudal regeneration in lepidosaurs and its potential ecological impacts

Abstract

Abnormal caudal regeneration, the production of additional tails through regeneration events, occurs in lepidosaurs as a result of incomplete autotomy or sufficient caudal wound. Despite being widely known to occur, documented events generally are limited to opportunistic single observations – hindering the understanding of the ecological importance of caudal regeneration. Here we compiled and reviewed a robust global database of both peer‐reviewed and non‐peer reviewed records of abnormal regeneration events in lepidosaurs published over the last 400 years. Using this database, we qualitatively and quantitatively assessed the occurrence and characteristics of abnormal tail regeneration among individuals, among species, and among populations. We identified 425 observations from 366 records pertaining to 175 species of lepidosaurs across 22 families from 63 different countries. At an individual level, regenerations ranged from bifurcations to hexafurcations; from normal regeneration from the original tail to multiple regenerations arising from a single point; and from growth from the distal third to the proximal third of the tail. Species showing abnormal regenerations included those with intra‐vertebral, inter‐vertebral or no autotomy planes, indicating that abnormal regenerations evidently occur across lepidosaurs regardless of whether the species demonstrates caudal autotomy or not. Within populations, abnormal regenerations were estimated at a mean ± SD of 2.75 ± 3.41% (range 0.1–16.7%). There is a significant lack of experimental studies to understand the potential ecological impacts of regeneration on the fitness and life history of individuals and populations. We hypothesised that abnormal regeneration may affect lepidosaurs via influencing kinematics of locomotion, restrictions in escape mechanisms, anti‐predation tactics, and intra‐ and inter‐specific signalling. Behaviourally testing these hypotheses would be an important future research direction.

Tail bifurcation in Tropidurus hispidus (Squamata, Tropiduridae), in a semiarid area of Northeastern Brazil

“…Here we observed another case for a Tropidurus species, likely due to the widespread distribution and high abundance of this species in Northeastern Brazil, as well as its frequent occurrence in anthropized environments. Although this phenomenon is common in nature, it likely does not affect the survival and reproductive success of individuals, as has been reported in the literature (Martins et al 2013, Passos et al 2014, Barr et al 2020) and our observation, as in one of our reports, the individual was in the process of mating.…”

“…In addition, it may be related to adverse environmental conditions caused by pollutants or pathogens that cause these malformations (Martinelli & Bogan 2013). Some records of bifurcated tails have been highlighted in the available literature on the lizard species Tropidurus torquatus (Martins et al 2013 28 (Andrade et al 2015) Ameiva ameiva (Gogliath et al 2012), Salvator merianae (Pelegrin & Leão 2016), Ameivula ocellifera (Sales & Freire 2019), and Iguana iguana (Lozano & Siro 2020), lepidosaurs (Barr et al 2020). Here we observed another case for a Tropidurus species, likely due to the widespread distribution and high abundance of this species in Northeastern Brazil, as well as its frequent occurrence in anthropized environments.…”

The Review of the Autotomy of Agamid Lizards with Considerations about the Types of Autotomy and Regeneration

“…A tail bifurcation on the regenerate often indicates that the tail can be broken in this part. However, recent research has shown that bifurcation can occur in non-autotomic species [36] too. They demonstrate that an abnormal regeneration can occur in lizards with intra-vertebral autotomy, inter-vertebral autotomy and in some species that have lost the ability to autotomy.…”

Tail Bifurcation in a Tokay Gecko, Gekko gecko (Linnaeus 1758), with notes on the natural history of the species in Ilam, Nepal

“…Caudal autotomy is a major defense mechanism in 13 lizard families (Downes and Shine 2001). Abnormal tail regenera-tion (from bifurcations to hexafurcations) is the result of previous injury rather than developmental tail deformity (Lynn 1950) and also has been reported in several lizard families (Barr et al 2020). Tail bifurcation in a Tokay Gecko was recorded by Gogoi et al (2018) in Kaziranga, Assam, India; however, this observation is the first record from Nepal.…”