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Antioxidant allocation modulates sperm quality across changing social environments

Alfonso Luis Rojas Mora, Magali Meniri, Ophélie Gning, Gaëtan Glauser, Armelle Vallat & Fabrice Helfenstein

Résumé In promiscuous species, male reproductive success depends on their ability to mate with fertile females and on the fertilizing ability of their sperm. In such species, theory predicts that, owing to a trade-off between pre- and post-copulatory reproductive traits, males with lesser access to females should increase resource investment into those sperm traits that enhance fertilization success–usually referred to as ejaculate quality. This prediction has been validated in several taxa, yet studies on the physiological mechanisms modulating ejaculate quality are lacking. Sperm cells are highly vulnerable to oxidative stress, which impairs male fertility. Therefore, males that better protect their sperm from oxidative stress are expected to achieve higher ejaculate quality. Based on theoretical expectations, and since social dominance is a major determinant of mating opportunity, we predicted that subordinate males should invest more into the antioxidant protection of their sperm in order to achieve higher ejaculate quality. We maintained 60 male and 60 female wild-caught house sparrows Passer domesticus in outdoor aviaries, where we experimentally manipulated male social status to test our predictions. We measured cellular oxidative stress and enzymatic antioxidant activity in blood and sperm both before and after manipulating social ranks. Before manipulating the social status, we found that ejaculate viability correlated with oxidative stress level in sperm, with dominant males producing more oxidized and less viable ejaculates. Further, males at the lower end of the hierarchy produced ejaculates of similar quality to those of dominant males, suggesting that restricted access to resources might limit male reproductive strategies. After experimentally manipulating the social status, males matched their ejaculate quality to their new rank, while increases in antioxidant investment into ejaculates paralleled increases in ejaculate viability. Oxidative stress has been proposed as a general constraint to the evolution of life histories. Our results highlight oxidative stress and strategic antioxidant allocation as important proximate physiological mechanisms underlying male reproductive strategies.
   
Mots-clés sperm competition, Social dominance, antioxidants, Oxidative stress, Glutathione, superoxide dismutase, reproductive physiology, reproductive strategy, soma/germline allocation trade-off, sperm quality, sperm velocity, sperm motility
   
Citation Luis Rojas Mora, A., Meniri, M., Gning, O., Glauser, G., Vallat, A., & Helfenstein, F. (2017). Antioxidant allocation modulates sperm quality across changing social environments. PLoS ONE, 12, 0176385-0176385.
   
Type Article de périodique (Anglais)
Date de publication 4-5-2017
Nom du périodique PLoS ONE
Volume 12
Pages 0176385-0176385
Liée au projet Oxidative stress in avian semen: causes and consequences ...