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Radika Michniewicz and Fabien Aubret

Abstract

In ectotherms, thermal acclimation and behavioural thermoregulation have evolved to match organismal performance with local or temporary thermal conditions. In semi-aquatic species, however, this matching encompasses a trade-off: organisms that thermoregulate close to optimal muscle function on land will inevitably depart from that optimum when entering water, a medium that may differ drastically in temperature. With regard to predator evasion and foraging success, how do semi-aquatic ectotherms deal with such a challenge? We experimentally raised young semi-aquatic Tiger snakes in either terrestrial or semi-aquatic environments over 11 months. When tested in a standardised enclosure, young snakes raised in a semi-aquatic environment selected slightly, but significantly higher mean body temperatures than their terrestrially raised siblings (respectively 30.3°C versus 29.5°C). The former allowed their body temperature to remain higher than 32°C for twice as long as the latter group (4.4 hours vs 2.1 hours). Locomotor performances (swimming speed) were, unsurprisingly, strongly linked to body temperature. Entering water with a higher body temperature (30°C versus 19°C) delayed a sharp drop in locomotor performances, and thus lengthened maximum performance time. We hypothesise that young snakes, by allowing their body temperature to reach above their usual optimum body temperature, may delay the drop in locomotor efficiency in case of foraging opportunity or in order to escape a predator.

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Fabien Aubret, Mélodie Tort, Radika J. Michniewicz, Gaëlle Blanvillain and Aurélie Coulon

Reptile sheltering behaviour, despite profound life history ramifications, remains poorly investigated. Whether or not individuals share a suitable shelter or, conversely, exclude conspecifics may depend on associated costs (resource partitioning, sexual harassment, disease or parasite contamination) and benefits (predation risk dilution, thermal resilience, information sharing). We performed two experiments on field caught wall lizards (Podarcis muralis), a highly territorial species, to investigate the relative roles of sex and body size in night sheltering. In the first experiment, random pairs of lizards were offered two identical shelters. Lizards either shared a shelter, or sheltered separately. In the second experiment, different random pairs of lizards were offered only one shelter so as to elicit a share or compete response. Body size and sex both appeared as significant drivers for sheltering patterns. Unexpectedly, wall lizards often chose to share shelters. When only one shelter (too small to accommodate two adult lizards) was available, many lizards rejected the sheltering option in preference for aggregation. Such aggregative behaviour was not sex dependant, and may reflect thermoregulatory or anti-predatory benefits. Our results nevertheless suggest that cooperative behaviour may exist in wall lizards.

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Jonas Durand, Arnaud Legrand, Mélodie Tort, Alice Thiney, Radika J. Michniewicz, Aurélie Coulon and Fabien Aubret

Alteration in anti-predatory behaviour following geographic isolation has been observed in a number of taxa. Such alteration was attributed to the effect of relaxed selection in the novel environment, reinforced by the cost of anti-predatory behaviours. We studied aspects of anti-snake behaviour in 987 adult and juvenile wall lizards Podarcis muralis from two mainland areas (heavy snake predatory pressure) and two islands (low snake predatory pressure), isolated from the mainland 5000 and 7000 years ago. We conducted a scented retreat site choice experiment using the odours of five different snake species (saurophagous, piscivorous or generalist feeder). Mainland lizards avoided shelters scented by saurophagous snakes, but not those scented by non saurophagous snake species. Long isolated lizards (7000 years ago) showed no anti-predator response to any snake, suggesting a total loss of anti-predatory behaviour towards saurophagous snakes. More recently isolated lizards (5000 years ago) however showed anti-snake behaviour towards a former sympatric adder species, and a tendency to avoid the scent of a sympatric generalist feeder snake. There was no difference in the anti-snake responses between adult and juvenile wall lizards from all four sites, suggesting a limited role for experience (behavioural plasticity) in the expression of anti-snake behaviour in wall lizards.