The Ecology of Genome Evolution - Connecting Population Genetics and Reproductive Biology

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Genetic variation is the fuel of evolution, and understanding its distribution and maintenance in wild populations is a core aim of evolutionary biology. This aim has gained renewed prominence as we try to understand how populations will adapt to changing environmental conditions. Genetic diversity is influenced by population size, and this is a key concern for conservation biologists. However, other factors will influence genetic diversity in wild populations, and understanding these is vital if we are to understand how species have evolved in the past, and how they will do so in future. Two factors implicated in this respect are the breeding structure of the species and the rate of genetic recombination, a mechanism occurring in all sexually reproducing species by which genetic material is exchanged between pairs of chromosomes, resulting in parents and offspring having different combinations of genes. Recombination is a very important process and has been shown to be correlated with higher levels of genetic diversity. I will examine the role that recombination and the mating system play in determining how genetic diversity is distributed and maintained in the fruit fly Drosophila melanogaster. D. melanogaster is a model species that is successfully used in many areas of research. Its natural populations are of great interest because it has become a cosmopolitan species, adapting to many new environments over the last few thousand years. Like humans, it is thought to have originated in Africa, colonising the rest of the world relatively recently, and populations outside Africa have low genetic diversity compared to those in Africa due to small numbers of individuals founding new populations. I will collect flies around the species' range, including Europe and North America as well as Africa, because the species is thought to have reached America more recently than Europe - several hundred rather than several thousand years ago. I will use our extensive knowledge of the fruit fly genome to carry out one of the largest studies of genetic variability in the wild to date, by examining levels of genetic diversity in each population. This will allow me to look at the effects on genetic diversity of range expansion and adaptation to new habitats, as well as the influence of genetic recombination. By examining regions of the genome that differ in the rate at which this process occurs, I will explore the relationship between recombination and genetic diversity, and assess whether populations vary in terms of how these parameters are related. I will also look at how the mating system influences genetic diversity, from both the male and female perspectives. Firstly, we know males of many species are brightly coloured or exhibit elaborate displays to attract females. Male fruit flies experience similar pressures, with choosy females only mating with males they deem suitable. Chosen males may therefore father many offspring, whilst others have none. This reduces the number of males fathering the next generation, and thus the number of genetic variants passed on by males. By measuring how strong this sexual selection on males is and how it varies between populations, I will examine how this affects genetic variability in the wild. Secondly, in populations where the species is well adapted to its habitat and nutritional resources are abundant, females will have enough energy to produce large numbers of eggs. When nutritional sources are low, for example in environments where the species is newly established or competition for resources is high, some females may not be able to produce any eggs. This reduces the number of females contributing to the next generation, and thus the genetic variability passed on by females. I will examine whether females in different populations are prepared for breeding by looking at patterns of egg development, to see how female reproductive status influences genetic diversity in the wild.