Every sperm is sacred - or maybe not?

Despite the fact that sexual reproduction is the most common form of reproduction among eukaryotes, we still know surprisingly little about many related aspects. One of the key open questions is: Which sperm ultimately fertilises the egg out of the millions of sperm in an ejaculate? Is this just the result of random processes or are fertilising sperm somehow "better"? Sperm within an ejaculate vary substantially not only in their phenotypes and performance but also in their genotypes as a result of the re-shuffling of the genome during meiosis. A common belief holds that this genetic variation among sperm within an ejaculate plays no role in determining how the sperm looks and performs. However, research in our lab has challenged this long-standing idea and provided evidence that the genome of a sperm may in fact determine its phenotype, and hence benefit the offspring in the next generation. We found that selection for longer-lived sperm within the ejaculate of zebrafish males results in offspring that survive better, are more fertile and live longer than their direct siblings sired by shorter lived sperm. In addition, we showed that longerlived sperm differ genetically from their shorter-lived siblings, which suggests that the genome carried by each sperm contributes to its performance. Given these striking results, we now need to identify the underlying genes and test, whether similar processes occur in humans - this is the aim of this PhD.