Abstract
Sperm function and quality are primary determinants of male reproductive performance and hence fitness. The presence of rival males has been shown to affect ejaculate and sperm traits in a wide range of taxa. However, male physiological conditions may not only affect sperm phenotypic traits but also their genetic and epigenetic signatures, affecting the fitness of the resulting offspring. We investigated the effects of male‐male competition on sperm quality using TUNEL assays and geometric morphometrics in the zebrafish, Danio rerio. We found that the sperm produced by males exposed to high male–male competition had smaller heads but larger midpiece and flagellum than sperm produced by males under low competition. Head and flagella also appeared less sensitive to the osmotic stress induced by activation with water. In addition, more sperm showed signals of DNA damage in ejaculates of males under high competition. These findings suggest that the presence of a rival male may have positive effects on sperm phenotypic traits but negative effects on sperm DNA integrity. Overall, males facing the presence of rival males may produce faster swimming and more competitive sperm but this may come at a cost for the next generation.
Highlights
Sperm quality and performance determine male reproductive success and are under strong selection (Birkhead, 1998; Birkhead, Hosken, & Pitnick, 2008; Fitzpatrick & Lüpold, 2014; Snook, 2005)
We found that sperm phenotypes appear to change in order for sperm to perform better during fertilization, but possibly at the cost of reduced genome integrity indicated by the higher amount of sperm exhibiting double-strand breaks in males exposed to high male–male competition
Our findings show a clear effect of male social environment on sperm phenotypes and DNA quality
Summary
Sperm quality and performance determine male reproductive success and are under strong selection (Birkhead, 1998; Birkhead, Hosken, & Pitnick, 2008; Fitzpatrick & Lüpold, 2014; Snook, 2005). These stressors may in turn negatively affect the overall quality of sperm within an ejaculate (Cornwallis & Birkhead, 2007; Pizzari, Cornwallis, & Froman, 2007) due to a possible stress-induced increase in the production of reactive oxygen species (ROS; Aschbacher et al, 2013; Schiavone, Jaquet, Trabace, & Krause, 2013) and activity of transposable elements (Capy, Gasperi, Biémont, & Bazin, 2000), which may cause mutations during gamete production These factors may result in DNA alterations and damage ranging from point mutations to unrepaired double-strand breaks. Our findings indicate a potential trade-off between sperm phenotypes and the integrity of the sperm genome
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