Social dominance, but not parasite load, affects sperm quality and sperm redox status in house sparrows

Abstract

Sperm performance is an important component of male reproductive success. However, sperm production is costly and males need to optimize their investment in sperm quality versus the somatic traits involved in mating success, e.g. their social status. As oxidative stress affects both sperm performance and somatic functions, it has been hypothesized to mediate such a trade-off. According to the oxidationbased soma/germline trade-off hypothesis, dominant males should favour the antioxidant protection of their somatic tissues, and subordinate males should favour the antioxidant protection of their sperm. We tested this hypothesis by experimentally infecting wildcaught house sparrows Passer domesticus with Coccidia Isopora sp., an internal parasite known to deplete antioxidant resources. We predicted that (i) increased parasite load affects sperm oxidative status and sperm performance and that (ii) males with experimentally high parasite load adjust the antioxidant protection of their soma versus their sperm according to their social status. Despite a 5400% increase in parasite load, sperm performance and somatic and spermatic oxidative status remained unaffected, irrespective of male social status. Nevertheless, males increased their sperm performance over time, a pattern mirrored by an increase in the antioxidant protection of their sperm. Moreover, males at the lower end of the hierarchy always produced sperm of lower velocity, suggesting that they were constrained and privileged their soma over their germline. To conclude, high parasite loads do not necessarily affect sperm performance and oxidative status. In contrast, social hierarchy and the relative investment in soma versus sperm antioxidant protection are determinants of sperm performance.

Defence against the intergenerational cost of reproduction in males: oxidative shielding of the germline

“…Such predictions can be extended to our framework, with subordinate males predicted to invest more in oxidative shielding compared to dominant males. In house sparrows, dominant males had more oxidised and inviable sperm compared to middle hierarchy males (Mora et al ., 2016) although a recent study on the same system failed to replicate this result (Losdat et al ., 2019). Similarly, in three‐spined sticklebacks, where large genetic variation in colour has been maintained despite sexual selection, duller morphs are maintained in the population despite reduced attractiveness to females.…”

Social rank influences relationships between hormones and oxidative stress in a cichlid fish

“…While socially dominant individuals use aggression to acquire and maintain priority access to key limited resources—including food, shelter, and access to mates— subordinates may experience social suppression and limited access to these same resources (Clutton-Brock and Huchard, 2013; Milinski and Parker, 1991; Stockley and Bro-Jørgensen, 2011). Consequently, individuals of different social ranks tend to experience different levels of oxidative stress—the relative balance between the production of free radicals ( e.g ., reactive oxygen species (ROS)) and the neutralization of free radicals by antioxidant defenses (Monaghan et al, 2009; Pamplona and Costantini, 2011; Sies et al, 2017)—based on their social rank (Cram et al, 2015; Fialkowski et al, 2022; Losdat et al, 2019; Mendonça et al, 2020; Silva et al, 2018). Dominants tend to experience greater oxidative stress, especially when metabolic demands associated with reproduction and/or territory defense are high (Beaulieu et al, 2014; Cram et al, 2015; Dowling and Simmons, 2009; Georgiev et al, 2015b).…”