Re-regeneration to reduce negative effects associated with tail loss in lizards

James I Barr,Philip W Bateman,Kate Trinajstic,Ruchira Somaweera,Catherine A Boisvert

doi:10.1038/s41598-019-55231-6

James I Barr, Philip W Bateman + Show 3 more

Open Access

https://doi.org/10.1038/s41598-019-55231-6

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Abstract

Many species of lizard use caudal autotomy, the ability to self-amputate a portion of their tail, regenerated over time, as an effective anti-predation mechanism. The importance of this tactic for survival depends on the degree of predation risk. There are, however, negative trade-offs to losing a tail, such as loss of further autotomy opportunities with the regenerated tail vertebrae being replaced by a continuous cartilaginous rod. The common consensus has been that once a tail has been autotomised and regenerated it can only be autotomised proximal to the last vertebral autotomy point, as the cartilage rod lacks autotomy planes. However, anecdotal evidence suggests that although the regenerated portion of the tail is unable to autotomise, it can re-regenerate following a physical shearing event. We assessed re-regeneration in three populations of the King’s skink (Egernia kingii), a large lizard endemic to south-west Western Australia and surrounding islands. We show that re-regeneration is present at an average of 17.2% across the three populations, and re-regenerated tissue can comprise up to 23.3% of an individual’s total tail length. The ability to re-regenerate may minimise the costs to an individual’s fitness associated with tail loss, efficiently restoring ecological functions of the tail.

Highlights

Many species of lizard use caudal autotomy, the ability to self-amputate a portion of their tail, regenerated over time, as an effective anti-predation mechanism
The tails of species with intra-vertebral autotomy are constructed as autotomisable segments; the cartilage rod that regenerates after autotomy lacks breakage planes and cannot be autotomised, with future autotomy events having occur at the most proximal vertebrae of the original tail[5,6,9,10,17,18]
From field data we show that re-regeneration occurs, and is not an isolated occurrence, in E. kingii

Summary

Introduction

Many species of lizard use caudal autotomy, the ability to self-amputate a portion of their tail, regenerated over time, as an effective anti-predation mechanism. Subsequent autotomies must www.nature.com/scientificreports take place more proximally”10; “[L]izards that experience repeated tail autotomy must lose their tails progressively closer to the tail base ...”17; “When a tail regenerates, the new portion of is made of a rod of cartilage and lacks the intravertebral breakage planes that enable an unregenerated tail to autotomize”[18] (P 154). Lizards possess the ability to regenerate a cartilage rod and associated tail from an already regenerated portion of their tail, after a shearing event through the cartilage rod, such as a bite from a predator This regrowth phenomenon, termed re-regeneration, has, as far as we are aware, only been recorded anecdotally[9,23,24] and may further enhance the capacity of regeneration to reduce negative effects associated with caudal autotomy, such as time and energy trade-offs to growth and reproduction[14,25,26,27]. In this study we investigate (1) the occurrence and use of re-regeneration across three isolated populations of E. kingii that vary in predation risk, (2) assess the internal morphology of re-regeneration using micro CT technology, and (3) discuss the potential mitigating effects of re-regeneration as well as its use in restoring tail function for lizard ecology

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