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Helfenstein, Fabrice

Nom
Helfenstein, Fabrice
Affiliation principale
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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
    Reproductive effort and oxidative stress: effects of offspring sex and number on the physiological state of a long-lived bird
    (2017-2-13)
    Merkling, Thomas
    ;
    Blanchard, Pierrick
    ;
    Chastel, Olivier
    ;
    Glauser, Gaëtan 
    ;
    Vallat, Armelle
    ;
    Hatch, Scott A.
    ;
    Danchin, Etienne
    ;
    Helfenstein, Fabrice 
    1. Individuals must trade-off between energetically costly activities to maximize their fitness. However, the underlying physiological mechanism remains elusive. Oxidative stress, the imbalance between reactive oxygen species production and antioxidant and/or repair activities, has been suggested to underlie life-history trade-offs: greater investment in reproduction supposedly generating higher oxidative damage, thus reducing life span. 2. While most studies used natural or experimental variation in offspring number to examine how reproduction affects oxidative stress, none studied the impact of offspring sex, although it could influence physiological costs and fitness, if the sexes differ in terms of energetic cost. 3. Here, we aim at further understanding how reproduction (in terms of offspring sex, experimentally manipulated and number, not manipulated) influences oxidative stress in a wild seabird, where sons are energetically costlier than daughters. We did so by conducting a chick fostering experiment (to disentangle foster and produced sex ratio) and using four oxidative stress markers plus baseline corticosterone. 4. First, the results suggest that individual physiological state before laying modulates upcoming reproductive effort. Individuals with higher pre-laying baseline corticosterone and lower antioxidant activity, estimated by their superoxide dismutase activity, subsequently invested more in reproduction, estimated by the cumulative number of days spent rearing chicks. Hence, it seems that only individuals that could afford to invest heavily in reproduction did so. 5. Then, we examined the effects of reproductive effort on individual physiological state at the end of the breeding season. Higher reproductive effort seemed to imply higher physiological costs. Oxidative stress, estimated by the ratio of oxidized over reduced glutathione, increased with more male-biased foster sex ratio among mothers but not among fathers, whereas baseline corticosterone did so in both sexes. Similarly, lipid oxidative damage to red blood cells increased with increasing cumulative number of days spent rearing chicks. 6. Our study provides the first evidence that brood sex ratio variation can affect oxidative balance, potentially in a sex-specific way, although more studies are needed to understand whether the observed physiological costs could lead to fitness costs. It also highlights the need to consider sex ratio in future studies investigating the role of oxidative stress in life-history trade-offs.