Selfish genetic elements and population viability: the impact of temperature and sexual selection

Climate change is proceeding apace. Many populations are predicted to go extinct, unable to respond rapidly enough to their changing environment. We have little understanding about the extent to which populations have the ability to evolve in response to changing temperatures. Fly species have provided much needed information about potential adaptation to environmental changes in the wild. This is largely because some of their genes are contained in tightly linked groups (inversions) that are always inherited together and passed down as a unit through the generations. This allows quantification of changes in the frequencies of genes contained within these locked chromosomal regions in relation to changing environmental factors such as temperature. Any change in these genes can only be attributed to evolution. Many populations harbour selfish genetic elements (SGEs), genes that unfairly bias inheritance to increase their spread in a population. In spite of this transmission advantage, many SGEs are transient in natural population or found at lower than expected frequencies. It is not clear what factors regulate SGEs in the wild. We will examine the impact of temperature variation on the frequency of a selfish gene (present within an inversion) in a fruit fly that cause female biased population sex ratios, and hence may cause population extinction due to lack of males. The frequency of this sex ratio distorter has remained stable for >70 years in the Northwestern USA, but the underlying reason for the observed gradient among populations remains unknown. We will quantify changes in the frequency of the sex ratio distorting gene in natural populations across a temperature gradient. One possibility is that changes in female mating behaviour may directly regulate the frequency of sex ratio drive. We have found that female multiple mating can dramatically reduce the frequency of sex ratio distorting genes in lab populations. This is due to the poor sperm competitive ability of males carrying the sex ratio gene compared to non-carrying males. We will evaluate the importance of temperature in altering female mating frequencies in the wild and therefore the level of sperm competition encountered by males carrying the sex ratio gene. We predict that low temperatures are unfavourable to sex ratio males because females live longer and may mate more frequently at lower temperature and hence the level of sperm competition is greater, reducing the paternity of sex ratio males barring their spread. This research will provide valuable information about the ability of populations to adapt to changing environments. This may provide important information about which species may turn into potential agricultural pests and disease vectors, whereas other species risk going extinct. It will also be of value to captive breeding programmes and in biological control schemes by highlighting the link between female mating frequency and the spread of unfavourable/favourable genes.