Thermorégulation comparée des vipères d’Europe. Etude biotélémétrique

Abstract

A biotelemetric study of thermoregulation under semi-natural conditions in six species of temperate and cool temperate eura-siatic vipers (112 days of continuous recordings of stomach temperature) has given the following results : 1) When a thermal gradient is available during digestion, vipers keep their internal temperature within rather narrow limits (± 1.5 to 2.0° C of a certain temperature, the “preferred temperature”). 2) Between 8 May and 26 August, this preferred temperature remained the same for the six species studied, independent of sex or stage of annual cycle. 3) The preferred temperature of a large viper gradually changes during digestion, from 32.42 ± 0.09° C at the beginning of digestion to 30.51 ± 0,20° C at the end of it. 4) The maximum stomach temperatures observed in field conditions range between 35.0 and 35.5° C. The daily maximum temperature averages 34.46 ± 0.09° C at the beginning of digestion, and 32.32 ± 0.20° C at the end of it. 5) The different species use different micro-environments for thermoregulation but achieve similar results. Vipera berus stays longer in the open than other species. Its preferred temperature is the same as that of other vipers, but it takes a longer time for an animal to reach it. Almost certainly, the preferred temperature does not correspond to the physiological optimum for a given function ; it likely results from a compromise between different and even contradictory constraints. Northern and southern European vipers have similar preferred temperatures ; the adaptation of northern species to cool environments must therefore be explained in another way. This adaptation is most likely mainly achieved through different circadian rhythms of activity and differences in the use of cover. However, the interspecific differences are always small and the present-day species distribution is most likely the result of historic factors and subsequent interspecific competition.