Sperm Evolution in Birds

The main function of sperm is to fertilize ova. Despite this uniform function, sperm cells show an immense variation in shape and size across the animal kingdom. This project aims to answer why and how sperm cells evolve and diversify in the most species-rich order of birds, the Passeriformes or "perching birds". We already know that sperm size and shape is highly variable in this group, but surprisingly little is known about sperm biology in most species compared to what we know about their general breeding systems, ecology and life history traits. Our project is organised in three work packages. First, we will reveal much of the unknown diversity of sperm in selected species from around the world. We will then reconstruct the evolutionary history of sperm diversification across the Passeriformes tree of life and identify major shifts in sperm traits. Second, we will identify the genes underlying sperm traits, how they are expressed in the testicles when the sperm are formed, and how they are organised in the genome in different species. This should enable us to understand the link between genes and the sperm phenotype. Third, we will examine the different types of selection that can shape the variation in sperm sizes among males in well-studied populations of a few selected species. Together, the three work packages will advance our understanding of some key factors responsible for the evolution of the diversified sperm in birds.

An unanswered question in evolutionary biology is why sperm cells have become so diversified across the animal kingdom. Over the last 10 years our research group has made significant contributions to the study of sperm form and function in passerine birds. The current proposal seeks to increase our knowledge of the mechanisms of how sperm cells evolve and diversify in these species. We will reconstruct the evolutionary history of sperm diversification across all 140 families of perching birds (Order Passeriformes) and identify major innovations/shifts in sperm morphology. We will explore the genetic architecture of various sperm components, how these genes are regulated during spermatogenesis, and how the major shifts in sperm evolution can be explained at the genetic and genomic level. We will also explore the types of Darwinian selection acting on sperm phenotypes. We combine our own expertise on sperm phenotypes with external expertise on functional and comparative genomics, and with ongoing, long-term population studies of selected species where the fitness of sperm phenotypes (i.e. fertilization success) can be measured in a competitive context. The project has the potential to advance our understanding of some fundamental questions in biology, such as the "evolution of sperm diversification" and "the genetics of a phenotype", which have relevance to all species with sexual reproduction.