A comparative study of courtship behaviour of Triturus alpestris alpestris (Laurenti, 1768) and Triturus alpestris cyreni (Wolterstorff, 1932) (Amphibia, Caudata): an evolutionary perspective

In this study we are interested by the courtship of two allopatric subspecies of the Alpine newt, Triturus alpestris alpestris and Triturus alpestris cyreni. We investigate the behaviour of two closely related taxa, in experimental conditions, to display the basis of behaviour evolution and isolating mechanisms prominently. We have identified 24 behaviours in the male display and principally three in the female (negative, static, positive). Sexual encounter will be divided in four stages: orientation during which animals are meeting, fan and lean-in exhibition phases during which the male displays and the spermatophore transfer sequence where the male deposits a spermatophore and displays also. The qualitative differences between subspecies are weak and concern principally amplitude of movements. From a qualitative level some differences were underlined. So T. a. alpestris touches the female with his snout frequently, whereas T. a. cyreni whips more often. The two subspecies do not use the same strategy with a non-responsive female. Indeed the T. a. alpestris male can easily enter in spermatophore transfer phase without the positive response of female. In order to attract the latter, he executes worm-like movements: in this way he lures a negative female. On the contrary, T. a. cyreni rarely deposits a spermatophore when the female is not receptive. He therefore makes very little use of the lure system. The analysis of male behaviours in relation with female response has allowed us to establish a model which assumes that some behaviours are exhibited by the male only when his internal energy and that of the female go beyond a particular level. Some stereotyped behaviours (e.g. distal fan) concern movements whose amplitude is variable. This movement modulation could be the foundation of a behaviour evolution and isolating mechanism. The female is indeed sensitive to these variations : in this way communication is possible between transmitter and receiver. The new variants problem is thus resolved. The fanning frequencies vary with temperature. They are weak at low temperatures. We consider this modulation as an adaptation to extreme and unpredictable habitats, e.g. in high altitude lakes and temporary ponds. The observed behavioural differences are in a lower level than between separate species, like Triturus helveticus and Triturus vulgaris. Moreover sperm transfer is likely between the two taxa. The present data confirm the existence of two distinct subspecies as detected by previous authors using allozyme and osteological analysis.