The evolution of courtship rituals

Sammanfattning: The fact that many animals engage in highly ornamented and conspicuous display behaviours in connection with reproduction has received much attention in zoology ever since Darwin launched his theory of sexual selection. This thesis intends to investigate the evolution of such display behaviour. I argue that courtship displays partly evolve to manipulate a prospective mate or a partner contrary to the idea that display evolves to transmit information.An analytical model is developed in which a reproductive conflict in a monogamous species is studied. The male and female are in conflict over when to start reproduction. Females benefit from staying coy and evaluating the male for some time, while the males are eager to start as soon as possible. In the model the optimal duration of female coyness is a trade-off between the benefit of waiting and gaining information about the male and the cost of postponing reproduction.The same problem was then studied in a simulation using artificial neural networks as the female decision mechanism. Artificial neural networks are models of how neural systems work which allow us to incorporate aspects of real behavioural mechanisms that are difficult to handle with game theory. It is shown that males through their courtship display can influence the decision of the female to their own advantage by manipulating females into an earlier start of reproduction. When a manipulation becomes efficient females tend to develop a reduced sensitivity to that particular display and males respond by modifying their display. The result is an ongoing process that never settles.The conflict studied is just one example of reproductive conflicts that occur between a male and a female in a monogamous species. In fact, conflicts continue also after pair formation and concern the amount of parental investment. In a review of display in monogamous species I show that such pair display is not limited to the mate choice period and that both sexes can be active. These observations could be explained if display evolves in interactions involving conflict.Today it is popular in evolutionary biology to view animals as rational decision-makers. For instance, during courtship females are considered to make optimal choices of partners based on male display that supposedly transfers information about his quality and condition. In a final and more general study we question this view. Considerations of real mechanisms suggests that manipulation is always possible and that evolutionary stable solutions may not exist, due to the fact that adaptation takes time and that evolution cannot anticipate the future. Thus, evolution may proceed out of equilibrium and phenomena may occur to which the idea of rationality or purpose may be difficult to apply.