Testing the Evolutionary Consequences of Haploid Selection in Animals

Selection occurring during the haploid gametic phase of any sexually reproducing eukaryote may have far-reaching consequences for major biological processes. Selection acting on a haploid genome results in efficient removal of deleterious alleles and rapid fixation of beneficial alleles, which in turn affect adaptation, genetic load and the evolution of recombination rates. Despite their potential importance, we know surprisingly little about the genetic processes occurring during the time window after meiosis until the fusion of male and female pronuclei. This is particularly true for haploid selection in the gametes of predominantly diploid animals. Male gametes (sperm) are produced in vast numbers but only few fertilise eggs and therefore offer a strong opportunity for selection. A prevailing view that such haploid selection is of minimal consequence in animals has been recently overturned by evidence from our lab, which revealed strong links between sperm phenotype and offspring fitness, as well as sperm phenotype and its haploid genotype. The genetic mechanisms underlying these observations are currently poorly understood. In this project, I will tackle three key questions arising from these recent findings: i) How strong are purifying and positive selection during the haploid phase? ii) What are the mechanisms maintaining genetic variation in genes expressed during the haploid phase? iii) How does haploid selection affect the interaction between male and female gametes? By combining carefully designed innovative experimental approaches with cutting-edge single-cell genome and transcriptome sequencing technologies, this project will provide entirely novel insights into the process that is shared by all eukaryotic life. Findings from this project will illuminate not only the fields of evolutionary biology and genetics but far beyond into the areas of animal breeding and human reproduction.