Data from: A sex-linked supergene controls sperm morphology and swimming speed in a songbird

Sperm are perhaps the most diverse cells in the animal kingdom, with enormous morphological variation between taxa, between species, between males and within an ejaculate. Considerable interest in sperm diversity has arisen following the realisation that sperm competition (post-copulatory sexual selection) is a powerful selective force in many organisms, and that sperm morphology has co-evolved with female reproductive tract morphology. However, the relationship between sperm morphology, sperm motility and fertilisation success is only partially understood. The extent to which between-male variation is heritable is largely unknown, and remarkably few studies have investigated the genetic architecture of sperm traits, especially sperm morphology. Here we use high-density genotyping and gene expression profiling to explore the considerable sperm trait variation that exists in the zebra finch Taeniopygia guttata. We show that nearly all of the genetic variation in sperm morphology is caused by an inversion polymorphism on the Z chromosome acting as a ‘supergene’. These results provide a striking example of two evolutionary genetic predictions. First, that in species where females are the heterogametic sex, genetic variation affecting sexually dimorphic traits will accumulate on the Z chromosome. Second, recombination suppression at the inversion allows beneficial dominant alleles to become fixed on whichever haplotype they first arise, without being exchanged onto other haplotypes. Finally, we show that the inversion polymorphism will be stably maintained by heterozygote advantage, because heterozygous males have the fastest and most successful sperm with no apparent fitness cost