Sexual behaviour and sexual selection in newts

This thesis reports an investigation of the influence of sexual selection on the sexual behaviour of the European smooth newt, Triturus vulgaris, and of the North American red-spotted newt, Notophthalmus Viridescens. Both belong to the family Salamandridae of the amphibian order Urodela. Chapter 1 introduces the concept of sexual selection, and those aspects of competition and mate choice relevant to newt sexual behaviour are discussed. In Chapter 2, observations and experiments are described which demonstrate inter male competition and mate choice in the smooth newt. Males interfere with one another's attempts to inseminate females, a form of competition known as sexual interference. Under certain conditions, males choose larger, more fecund females as mates, whereas females seem to prefer males reasonably well matched to themselves in body length. The extent to which females mate repeatedly is investigated. In Chapter 3, the sexual behaviour of the red-spotted newt in encounters between single males and females is described. Males adopt one of two types of courtship, depending on the initial responsiveness of the female partner. Using a form of sequence analysis, the male's behaviour is described, and aspects of it are interpreted in causal and functional terms. Data on the various costs and benefits associated with each type of courtship are presented. Chapter 4 investigates the influence of sexual selection on the behaviour of the red-spotted newt. The male is sensitive to the ambient sex ratio in his vicinity, and this ratio influences which type of courtship he undertakes. In competitive situations, males interfere with one another, sometimes in a manner similar to that observed in the smooth newt. In laboratory experiments, it is shown that males prefer larger, more fecund females as mates, and that females will mate with more than one male. Chapter 5 adopts a comparative approach. The results presented in this thesis are discussed in the context of other urodele amphibians and other animals with similarly complex sexual behaviour. The various types of sexual behaviour in both species of newt are considered as alternative mating strategies, and an attempt is made to classify them in terms of contemporary ideas concerning behavioural strategies. References are listed in Chapter 6