Parallel erosion of a testis-specific Na+/K+ ATPase in three mammalian lineages sheds light into the evolution of spermatozoa energetics
Understanding how extant physiological landscapes arise from novel genetic interactions is key to elucidating phenotypic evolution. Sperm cells exemplify a striking case of functional compartmentalization shaped by molecular adjustments, notably regarding energy metabolism. Here, we examine the impact of gene duplication and loss on the evolution of sperm energetics in mammals. Our findings reveal that the acquisition of an exclusive mechanism controlling the sperm plasma membrane Na+ gradient, critical for glucose uptake, emerged in the ancestor of mammals through gene duplication, which originated the Na+/K+ ATPase transporting subunit alpha 4 transporter (Atp1a4). Furthermore, we demonstrate that testis-specific expression of Atp1a4 was acquired after the divergence from monotremes. Notably, we identify three independent pseudogenization events of Atp1a4, including in pangolins, the naked mole-rat (Heterocephalus glaber) and toothed whales. The recurrent loss of function in Atp1a4 coincides with the erosion of the testis-specific glycolytic pathway in these lineages. Furthermore, enrichment analysis of striped dolphin (Stenella coeruleoalba) and naked mole-rat testis transcriptomes also suggests significant alterations in sperm capacitation processes. Overall, we show that the elaboration of a sodium-dependent glucose uptake wiring was a key innovation in the energetic landscape governing mammalian spermatozoa, with secondary gene loss in three separate lineages pointing to drastic alterations in motility and capacitation processes. Our findings illustrate how metabolic pathways co-shaped by gene duplication and erosion define extant physiological phenotypes. SignificanceThe sperm cell exhibits a distinct morphology, characterized by exceptional functional and energetic compartmentalization between the midpiece and the flagellum. Here, we demonstrate that the evolution of a sodium-dependent glucose uptake mechanism, driven by gene duplication and giving rise to Atp1a4, was a key innovation promoting efficient glucose usage in mammalian sperm. Additionally, we identify independent losses of Atp1a4 in three lineages--pangolins, naked mole-rats, and toothed whales--coinciding with the reduction of glucose-dependent pathways, such as glycolysis. Our findings highlight how gene expansion and erosion shape metabolic pathways, offering insights into the genetic innovations underlying physiological diversity in reproductive biology.