In Issues 2020
Exceptional occurrences of double, triple and quintuple tails in an Australian lizard community, with a review of supernumerary tails in natural populations of reptiles. pp. 373-391 plus Supplementary documents.
Abstract. For centuries, tail duplications in reptiles have attracted human curiosity, and publications on anecdotal observations of supernumerary tails have grown considerably over recent years. However, there is no recent review on the occurrence of supernumerary tails in reptiles and the consequent effects on individuals. We provide new data on the frequency of supernumerary tails, including unprecedented frequencies and observations of tail triplication and quintuplication, from our own studies in arid Australia and from literature reviews. Our observations include data for a gecko species (Gehyra variegata) and three species of skinks (Eremiascincus richardsonii, Lerista punctatovittata, Morethia boulengeri) for which supernumerary tails have not been reported so far. We assume that hyperregeneration (following injuries inflicted by predators, sharp-edged window glass, and unknown factors) was the cause for the cases observed by us. Our review spans two millennia of published works describing supernumerary tails in 146 identified species of reptiles and up to 16 unidentified species. We assess the taxonomic and geographic distributions and the microhabitats of these 146 species, while also commenting on the potential causes and effects of supernumerary tails. The identified species belong to 16 families of lizards, one of amphisbaenians, three of snakes, the tuatara (Sphenodon punctatus), three turtle families, and one family of crocodiles. The geographic patterns of supernumerary tails are difficult to interpret due to an imbalance in published works from the major geographic areas. The vast majority of the species affected have a terrestrial lifestyle, followed by arboreal species. The frequency of supernumerary tails is low, with multiple tails having been reported only for 59 individuals, including our new data. Little is known about the effects of supernumerary tails on their carriers. In our study, there was no indication of them affecting mobility or increasing mortality. Some authors reported handicapped movement, whereas others did not find such effects, and both males and females with tail bifurcation/duplication were able to mate successfully. Most cases of supernumerary tails are likely to be due to hyperregeneration as a reaction to injuries or incomplete breaks of vertebral fracture planes. However, only one study statistically identified the culprits as predatory mammals. In captivity, such injuries were also inflicted through attacks by conspecifics and during copulation. The few cases in natural populations that were not due to hyperregeneration were presumably caused by unknown teratogenic factors to which the individuals were exposed during ontogeny; in one case this was most likely to be radioactive contamination.
Key words. Australia, Eremiascincus richardsonii, Gehyra variegata, Lerista punctatovittata, Morethia boulengeri, Squamata, geographic distribution, herpetological history, individual effects, microhabitat, tail duplication, tail multiplication.