Michael Garratt, Roslyn Bathgate, Simon P de Graaf, Robert C Brooks

Oxidative stress, overproduction of reactive oxygen species (ROS) in relation to defence mechanisms, is considered to be a major cause of male infertility. For protection against the deleterious effects of ROS, animals have a variety of enzymatic antioxidants that reduce these molecules to less reactive forms. The physiological role of these antioxidants in vivo has been explored extensively through genetic inhibition of gene expression; surprisingly, many of these animals remain fertile in spite of increased oxidative stress. Copper-zinc superoxide dismutase-deficient (Sod1(-/-)) male mice are one such example for which in vivo fertility has been repeatedly reported as normal, although examination of fertility has consisted of simply pairing animals of the same strain and checking for litters. This is a fairly low criterion by which to assess fertility. Herein, we show that Sod1-deficient males have zero fertilisation success in sperm competition trials that pit them against wild-type males of an otherwise identical genetic background and are almost completely infertile when mated singly with females of a different genotype. We also show that various aspects of sperm motility and function are impaired in Sod1-deficient mice. Testing the breeding capabilities of mice under more ecologically relevant conditions and with females of different genotypes may help reveal additional physiological causes of infertility.