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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 as a life history constraint: pespectives from a bat species with alternative reproductive tactics/
    (2018)
    Meniri, Magali
    ;
    Helfenstein, Fabrice 
    ;
    Fasel, Nicolas
    Au cours de cette thèse, j’ai étudié le rôle du stress oxydant en tant que contrainte pour les traits d’histoire de vie, en utilisant les chauves-souris Fer de lance à lunettes (Carollia perspicillata) comme modèle d’étude. Chez cette espèce, les mâles présentent trois tactiques de reproduction alternatives qui ont des succès reproducteurs différents, et dont l’acquisition pourrait être influencée par les conditions de vie précoce. Tout d’abord, j’ai étudié l’effet du stress oxydant comme contrainte pendant le début de vie. J’ai induit un mauvais départ en utilisant une restriction alimentaire suivit par un rétablissement de la nourriture ad libitum. Bien que j’aie trouvé que la croissance générait du stress oxydant, je n’ai pas trouvé de coût physiologique à court-terme (stress oxydant et glucocorticoïdes) associé à la croissance compensatoire effectuée. De plus, la survie pendant la première année n’était pas clairement impactée par notre traitement. Ces résultats suggèrent que les jeunes ont été capable de mitiger efficacement les conséquences à court-terme d’un mauvais départ. Ensuite, j’ai étudié le rôle du stress oxydant comme contrainte pour la reproduction, afin de tester si la protection anti-oxydante peut représenter un médiateur du compromis d’allocation entre les traits pré- et post-copulatoires, permettant ainsi d’expliquer la qualité spermatique supérieure trouvée précédemment chez les mâles opportunistes. Au cours d’une expérience où j’ai manipulé expérimentalement les tactiques de reproduction des mâles, j’ai trouvé que tous les mâles, quelle que soit leur tactique, présentaient une qualité spermatique similaire (morphologie et capacité natatoire). Bien que les dommages oxydatifs impactassent négativement la capacité natatoire, le profil redox à la fois dans le sang et les éjaculats était le même pour tous les mâles. Globalement, nos résultats suggèrent qu’un compromis d’allocation entre l’investissement dans le soma et les éjaculats pourrait ne pas avoir lieu chez cette espèce. Comme d’autres études avant nous, nous n’avons pas trouvé de corrélation entre les capacités natatoires et la morphologie des spermatozoïdes, ce qui remet en question l’existence d’un lien fonctionnel entre ces deux traits. Enfin, nous proposons que les mâles puissent appliquer une stratégie de « bet-hedging gamétique » où la production de spermatozoïdes à la morphologie hautement variable pourrait permettre d’optimiser les capacités de fertilisation de l’éjaculat pour des risques de compétition spermatique variable.
    En conclusion, nous avons trouvé que le début de vie était associé à des niveaux élevés de stress oxydant, bien que la croissance compensatoire n’ait pas entrainé de coûts physiologique sur le court-terme. De plus, le stress oxydant ne semble pas contraindre l’expression des tactiques de reproduction alternatives. Je suggère donc que le stress oxydant ne représente pas une contrainte forte chez les chauves-souris Fer de lances à lunettes. Je propose également que les mâles harems puissent investir à la fois dans les traits pré- et post- copulatoires, afin de conjointement attirer les femelles et d’assurer la fertilisation. Enfin, je prône que les études expérimentales devraient, le plus possible, être conduites dans l’environnement naturel plutôt qu’en cages, et ai donc créé un piège sélectif à cet effet.
    , In this thesis, I investigated the role of oxidative stress (OS) as a constraint for life history traits, using Seba’s short-tailed bats (Carollia perspicillata) as a model species. In this species, males exhibit three alternative reproductive tactics having unequal pay-offs, and whose acquisition could be impacted by early life conditions. First, I studied the effect of OS as a constraint during early life. I induced early adverse conditions using food restriction followed by ad libitum feeding. Although we found that growth generated oxidative damage, we did not find physiological short-term costs (OS and glucocorticoids) to compensatory growth. Moreover, survival during the first year was not significantly impacted by our treatment. These results suggest that pups were able to efficiently mitigate the short-term consequences of early-life adverse conditions. Then, I tested the role of OS as a constraint for reproduction and investigated whether antioxidant protection could mediate the trade-off between pre- and post-copulatory traits, and thus explain the higher sperm quality found previously in sneaker males. In an experiment where we manipulated males’ reproductive tactic, we found that all males, regardless of their tactic, exhibited similar sperm quality (sperm swimming performance and sperm morphology). Although oxidative damage negatively impacted sperm swimming performance, the redox profile of blood and ejaculates were similar for all males. Overall, our results suggest that a trade-off between investing in the soma or in the ejaculate might not occur. As other studies before, we did not find a correlation between sperm swimming performance and sperm morphology, which questions the existence of a functional link between those two traits. Finally, we propose that males may apply a “gametic bet-hedging” strategy, whereby they would produce highly morphologically variable sperm to optimize their sperm fertilizing abilities across varying sperm competition risks.
    In conclusion, we found that early life was associated with elevated levels of OS, although compensatory growth did not entail physiological costs on the short-term. Moreover, oxidative stress did not seem to constraint the expression of alternative reproductive tactics. Overall, I suggest that OS might not represent a strong constraint in Seba’s short-tailed bats. I suggest that harem males might invest in both pre- and post-copulatory traits to both attract females and secure fertilizations. Finally, I advocate for experimental studies to be conducted in the natural environment rather than in cages, and I designed a selective trap for that purpose.
  • 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
    Accès libre
    Badge Size Reflects Sperm Oxidative Status within Social Groups in the House Sparrow Passer domesticus
    Rojas Mora, Alfonso Luis 
    ;
    Meniri, Magali 
    ;
    Glauser, Gaëtan 
    ;
    Vallat, Armelle
    ;
    Helfenstein, Fabrice 
    The phenotype-linked fertility hypothesis proposes that male ornaments reflect male fertility. Male ornaments could honestly signal sperm quality due to the high susceptibility of sperm to free radicals on the one hand and the negative impact of oxidative stress on ornament elaboration on the other hand. Thus, only males with superior antioxidant defences could bear the cost of more elaborated sexual ornaments without suffering adverse fitness costs. Yet, in species where males experience differential access to fertile females, a trade-off emerges between investing into traits favouring mating opportunities (e.g. secondary sexual ornaments, social dominance, mate-guarding behaviours, etc.) or into traits favouring sperm competitive ability (e.g. sperm numbers and quality). When male sexual ornaments promote greater access to fertile females, a negative relationship can then be predicted between ornamentation and sperm quality. We tested the latter hypothesis and the phenotype-linked fertility hypothesis in wild House Sparrows Passer domesticus by exploring the relationships between sperm quality, melanin-based ornamentation, and redox status in blood and sperm. We found no correlation between badge size and sperm swimming performance. However, we found that within a social group, large-badged males better protect their ejaculates from oxidative stress, and thus produce less oxidized ejaculates. Additionally, we found that badge size did not reflect social dominance, and thus the protection of the ejaculate is independent of males’ ability to monopolize resources. Our results suggest that badge size might reflect male investment into the antioxidant protection of their sperm relative to a given social environment, and thus females may accrue both direct and indirect benefits by mating with large-badged males producing less oxidized ejaculates.