Does sexual selection accelerate adaptation in the wild?

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Our aim is to understand how sexual selection (variation among males in their ability to gain fertilisations) affects how populations evolve in response to change. This is a very broad question with implications for understanding how all sexually reproducing populations will respond to the challenges of environmental change. Although sexual selection was originally conceived to explain traits that appeared to reduce survival, it also has the potential to accelerate adaptation. If males that are well adapted to the environment have increased mating success, then genes that contribute to this adaptation will proliferate, both through their naturally selected contributions to survival (because well adapted males live longer and can perform better) and through their sexually selected contributions to reproduction (for instance because the males that are better adapted to the environment also mate at a higher rate). There have been laboratory based studies that address the question of whether sexual selection will tend to accelerate or retard adaption, but they give conflicting results. What is lacking is an experimental study that retains the natural context: it is this context that imposes the true costs and benefits of sexual selection. Understanding the interactions between natural and sexual selection in the process of ecological adaptation is not only a fundamentally important issue in evolutionary biology, but also has implications for understanding how populations will adapt to changing environments. For example, if sexual selection accelerates adaptation this suggests that populations should be managed to allow sexual selection to occur.We will conduct experiments on a natural population of crickets, utilising our 'WildCrickets' project - a long term study of a meadow in Spain. This project has the unique capacity to provide detailed information about the lives of every individual in the population through a network of 160 digital video cameras and annual DNA fingerprinting. We will replace all the males in the population with males bred from other populations so that half come from populations that are similar to our meadow and half come from high altitude where conditions are very different. For sexual selection on males to reinforce natural selection, it is a requirement that less well adapted males have reduced expression of male sexually selected traits and mating rate. This is a very simple assumption and many biologists probably regard it as uncontroversial, but in reality, it has only been tested in a very limited way in either the field or the lab. Fundamentally, we lack a clear test of this assumption and the arising major prediction that sexual selection increases adaptation. A strong test requires an experiment that directly compares well adapted and less well adapted males over the entire adult lifespan. We will make the comparison, measuring the expression of sexually selected traits, the realised reproductive success of males and the naturally selected success of their offspring. We will do this by using our video cameras to monitor the entire adult lives of the introduced crickets and the females left in the meadow and then coming back the next season and doing the same with their offspring. By using DNA fingerprinting we will know which offspring come from which males. Only males with some success in gaining fertilisations will leave any offspring, but there will still be variation in success amongst fathers, allowing us to compare the longevity and activity of individuals whose fathers were successful in sexual selection with offspring of males that were less successful.