Sexual selection and costs of sexual signalling in a wolf spider

Abstract

There are two major theories of sexual selection that both assume female choice of a costly male trait. They differ in respect to how they consider the costs of a trait; Fisherian self-reinforcing theory of sexual selection assumes no condition dependence of the costs, while viability indicator or handicap theory is based on the condition dependent costs of male trait. This thesis concentrates on sexual selection and especially on costs of male sexual signalling. As a study object I have used the wolf spider Hygrolycosa rubrofasciata, in which males court females with an audible drumming signal. The studies were mainly conducted in laboratory but there is also some field data presented. Females of the species actively prefer to mate with the most actively drumming males. Male drumming activity is dependent on male phenotypic condition and it is positively related to male viability. Drumming may serve as a honest indicator of viability since it provokes costs on the drumming males. More actively drumming males suffer increased mortality. This mortality may be due to energetically highly expensive drumming. There is also a possibility for direct predation costs on more actively drumming males. Especially large males suffered high energetic expenditure per mass unit. Under harsh conditions larger males seem to be better surviving suggesting that larger males may have more resources to use than smaller males. This study provides convincing empirical evidence that an viability indicator process based on costly male traits reflecting heritable viability and thus genetic benefits for offspring is involved in the evolution of sexual selection through female choice.