Selection on behaviour and life histories across generations in a natural population

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Insects make up the vast majority of animal biodiversity and have been studied intensively in the lab, providing numerous insights into how evolution works. However, there is now a serious imbalance between what we know about evolutionary biology in the lab and what we know about how things actually work in nature. This discrepancy is a source of concern for two reasons: Firstly, laboratory situations may be misleading as they remove sources of selection that may be very important in wild populations; for instance, it may be that male crickets that sing louder get more mates in the lab but in the field this is balanced by being more likely to be eaten by birds. Secondly, we urgently need to improve our understanding of how natural populations can respond to environmental change, and for this, we need studies of insects as well as vertebrates. Four years ago we began monitoring a population of field crickets in a Spanish meadow. Over the last 2 years we have studied the population intensively, tagging every individual and recording their lives using a network of 96 video cameras. The reproductive success of every individual and the pattern of relationships across generations have been estimated using DNA fingerprinting techniques. This has already provided important insights, such as showing that males vary more than females in how many offspring they have and that the traits displayed by males that have lots of mates are different from the traits typical of males that have lots of offspring. In this project we will dramatically improve our video monitoring and our ability to determine the relationships between individuals (by using new digital camera technology and new SNP genotyping techniques). We will combine information across years about the population as a whole, how individuals are related, their life histories, behaviour and reproductive success. This comprehensive information about every individual will allow us to address our major aims of determining how much genetic variation is present and whether natural and sexual selection, which drive evolution in populations, are consistent across years or whether they vary a lot. This is important because if in some years certain types of individual do well, whereas in others, different traits are more advantageous, this will help maintain genetic variation. Such variation allows populations to adapt to environmental change, so we need to understand how much there is and how it is maintained. A related aim will be to investigate how population density affects selection, something that we can only investigate with data from a number of years. A second set of objectives relate to examining aspects of sexual selection that have been well studied in laboratories, but neglected in the wild. These include finding out whether particular males and females or particular pairs of mates tend to be more successful either because they have genes that produce offspring that are intrinsically superior to the offspring of some other pairs or because certain combinations of individuals are more genetically compatible with one another, for instance because they are not close relatives. We will address these questions by comparing the reproductive success of pairs of wild crickets and examining how they differ genetically from one another. This will also allow us to look for evidence of genes that can persist in populations even though they reduce the fitness of one sex, because they increase the fitness of the other sex, something that has been demonstrated in the lab, but little studied in the wild. We will use the comprehensive data we have on the life histories of all the crickets in our population to investigate the question of whether short lived animals such as crickets actually die of old age, or whether they just keep going until something kills them. There are very few studies of the lives of wild invertebrates so even major questions like this remain to be answered.