The locomotion of Podarcis lizard species, and the effects of tail autotomy

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Date
2023-06-20
Authors
Κουτρουδίτσου, Λυδία Κ.
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Abstract
Lizards are a diverse group of reptiles that have successfully adapted to various habitats worldwide. Their locomotion abilities have evolved to accommodate different environments, including running and climbing. Locomotion is crucial for their survival, prey capture, and social interactions. This study investigates the impact of caudal autotomy (tail shedding) on lizard locomotion, along with the associated benefits and costs of this behaviour. Specifically, it focuses on four species from the genus Podarcis found on Mount Chelmos (P. peloponnesiacus, P. erhardii, P. ionicus, and P. muralis) and their preferred microhabitats. The primary objective of this study is to gain insights into the trade-offs and adaptations related to locomotion and tail autotomy in these species. Male lizards with three different tail types (original tails, autotomized, and regenerated tails) were collected from Chelmos mountain, and two experiments were conducted. The first experiment examined locomotion differences based on tail type (original, autotomized, and regenerated) on both level and inclined surface. The second experiment involved inducing artificial autotomy on lizards with original tails to observe locomotion differences before the animals adapted to running without a tail. The collected lizards were housed individually in controlled laboratory terraria with regulated temperature and lighting conditions. They were provided with food and water and later released at their original collection sites. Morphological measurements were taken, and the Body Condition Index (BCI) was calculated based on weight and length. Sprint performance was assessed using a custom trackway with video recording, conducting trials on a level and am inclined surface. To analyze the data, spatio-temporal gait characteristics, absolute and relative speed (Froude number) were measured using specialized software. Statistical analyses, including generalized linear models and ANOVA, were performed to assess the effects of species, incline, body condition, temperature, and tail type on speed and gait characteristics. Additionally, a correlation analysis was conducted to examine the relationship between speed performance and morphological traits. The results revealed variations in absolute speed, Froude number, spatio-temporal gait characteristics, and between the two experiments. The four species exhibited different locomotor modulation strategies, with P. peloponnesiacus and P. ionicus following a stride length modulation strategy, while P. erhardii and P. muralis followed a stride frequency modulation strategy. It was concluded that locomotor modulation strategy is more dependent on size than microhabitat, although ecological niche still plays a role in performance. The study demonstrated that tail autotomy initially reduces speed performance similarly across all species. However, once the species adapt to the change in center of mass and the loss of the appendage, those following a stride frequency modulation strategy benefit from the absence of the tail. The importance of the tail as a counterbalance was highlighted by the reduction in speed performance observed in species employing a stride length modulation strategy, as well as the reduction in speed performance after tail regeneration. Furthermore, while Froude number proved useful in understanding intra and interspecific locomotor differences regardless of size, it was less effective in cases where species exhibited changes in posture during running.
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Keywords
Locomotion, Tail autotomy, Autotomy, Lizard, Reptile, Podarcis
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