Reproduction Abstracts

Introduction: Mass-specific metabolic rate, the rate at which an organism consumes energy per gram of body weight, is negatively associated with body size in metazoans. Since the basal metabolic rate of a whole organism represents the sum of its cellular metabolic rates, small species have higher cellular metabolic rates and are capable of processing resources at a faster rate than large species. Recent studies have shown that mass-specific metabolic rate positively influences the size of sperm among mammals. Most of the cellular metabolic rate is represented by ATP production, which is essential for sperm flagellar beating, hence motility. We hypothesized that mass-specific metabolic rate could influence sperm energetic metabolism at the cellular level if sperm cells ‘inherit’ the metabolic rate of organisms that produce them and, in turn, influence sperm function.

Materials and methods: Data on body mass, testes mass, total sperm length, sperm swimming velocity, mteabolic rate, and sperm ATP content were obtained from the literature for 41 mammalian species and analyzed using phylogenetic generalized least-squares method.

Results and discussion: We found that the mass-specific metabolic rate positively influences sperm swimming velocity independently of its effect on sperm size. Moreover, our analyses show that species with a higher mass-specific metabolic rate have a higher ATP content per sperm and a higher length-adjusted ATP concentration, which are possitively associated with sperm velocity. In conclusion, independently of its effect on the production of larger sperm, the mass-specific metabolic rate is able to influence sperm velocity by increasing sperm ATP content in mammals.