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Helfenstein, Fabrice

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Helfenstein, Fabrice
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https://libra.unine.ch/handle/123456789/762

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  • Publication
    Accès libre
    Oxidative stress affects sperm performance and ejaculate redox status in subordinate house sparrows
    (2017-5-15)
    Rojas Mora, Alfonso Luis 
    ;
    Firth, Alexandra
    ;
    Blareau, Sophie
    ;
    Vallat, Armelle
    ;
    Helfenstein, Fabrice 
    Oxidative stress (OS) is the result of random cellular damage caused by reactive oxygen species that leads to cell death, ageing, or illness. Most physiological processes can result in OS, which in turn has been identified as a major cause of infertility. In promiscuous species, the fertilizing ability of the ejaculate partly determines the male reproductive success. When dominance determines access to fertile females, theory predicts that lower ranking males should increase resource investment into enhancing ejaculate quality. We hypothesized that subordinate males should thus prioritize antioxidant protection of their ejaculates to protect them from OS. We put this hypothesis to the test, by chronically dosing wild House Sparrows with diquat (∼1mg/kg), an herbicide that increases pro-oxidant generation. We found that, although they increased their antioxidant levels in the ejaculate, diquat-treated males produced sperm with reduced velocity. Importantly, and contrary to our hypothesis, males at the bottom of the hierarchy suffered the largest reduction in sperm velocity. We suggest that resource access hinders individuals' ability to cope with environmental hazards. Our results point at OS as a likely physiological mechanism mediating ejaculate quality, while individual ability to access resources may play a role in constraining the extent to which such resources can be allocated into the ejaculate.
  • Publication
    Accès libre
    Antioxidant allocation modulates sperm quality across changing social environments
    (2017-5-4)
    Rojas Mora, Alfonso Luis 
    ;
    Gning, Ophélie 
    ;
    Meniri, Magali 
    ;
    Glauser, Gaëtan 
    ;
    Vallat, Armelle
    ;
    Helfenstein, Fabrice 
    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.
  • Publication
    Métadonnées seulement
    Alternative reproductive tactics, sperm mobility, and oxidative stress in Carollia perspicillata (Seba's short-tailed bat)
    (2017-1-1)
    Fasel, Nicolas Jean
    ;
    Wesseling, Charlotte
    ;
    Fernandez, Ahana Aurora
    ;
    Vallat, Armelle
    ;
    Glauser, Gaëtan 
    ;
    Helfenstein, Fabrice 
    ;
    Richner, Heinz
    In social systems with alternative reproductive tactics, sneakers face a stronger sperm competition than harem males, and hence are predicted to allocate more resources to ejaculates. Antioxidants can protect sperm against oxidative stress, and thus their allocation to the ejaculate may depend on social status. In this study on the frugivorous bat Carollia perspicillata, we assessed for harem and sneaker males, four sperm mobility traits, blood and ejaculate markers of the redox balance, and the ejaculate to blood ratios of the redox markers. Under higher sperm competition, sneaker males should allocate proportionally more antioxidant resources to the protection of sperm than harem males. In contrast, harem males should favour pre-copulatory functions, which comprise the protection of blood. We found significantly higher sperm velocity and sperm survival in sneakers. There was no correlation between sperm mobility and sperm enzymatic antioxidant activity or ejaculate levels of lipid peroxidation (oxidative damage). Ejaculate levels of lipid peroxidation and sperm survival showed a significantly positive correlation, which could be attributed to the role of reactive oxygen species for sperm capacitation. Harem and sneaker males showed similar levels of redox balance markers in ejaculate and blood. However, harem males showed a higher ratio of oxidized over reduced glutathione in blood, which may indicate higher cellular stress due to higher metabolism. Overall, our findings suggest that sneakers of C. perspicillata compensate for a stronger sperm competition by higher sperm mobility.