Abstract
BackgroundSexual signals produced by males play a central role in sexual selection, but the relationship between these traits and the quality of the bearer are often ambiguous. Secondary sexual traits may represent genetic quality of the bearer, resulting in positive relationships with physiological state, or may be costly to produce, showing trade-off with physiological state. A number of studies have explored the relationships between secondary sexual traits and other functional traits, but few have studied their fitness consequences. We studied the link between diverse physiological traits and both morphological and behavioural sexual traits and examined how their interplay influences offspring viability in the three-spined stickleback.ResultsMale sticklebacks showing nest building and courtship behaviour were smaller than those not investing in reproductive activities. There was no evidence that the expression of red nuptial colouration and the quality of courtship behaviour of males are positively related to their metabolic rates, swim ability, oxidative damage and mtDNA copy number. However, individuals showing larger red nuptial colour areas had higher levels of oxidative DNA damage in their sperm. Male courtship behaviour and aggressiveness, but not red colour area, were good predictors of offspring hatching and survival.ConclusionsOur results suggest that, in our study population at the southern edge of the species’ distribution, sexual colouration of male sticklebacks was not a good indicator of their body state, but both courtship quality and aggressiveness during the courtship are reliable cues of their gamete quality, influencing the viability of their offspring. Thus, females that choose mates based on their courtship behaviour will have high fitness. In the study population, which represents a fast pace-of-life with high reproductive rate and short lifespan, sexual ornaments of males may not honestly signal their physiological and physical state because they invest at maximum in a single reproductive season despite high costs.
Highlights
Sexual signals produced by males play a central role in sexual selection, but the relationship between these traits and the quality of the bearer are often ambiguous
Fish with and without a nest did not differ in residual standard metabolic rate, residual maximum metabolic rate, critical swimming speed (Ucrit), the level of oxidative Deoxyribonucleic acid (DNA) damage in sperm and mitochondrial DNA (mtDNA) copy number in muscle (P ≥ 0.323; Additional file 1: Table S1)
Aggression and relative size of red colour area were not related to residual standard metabolic rate (rSMR), residual maximum metabolic rate (rMMR), Critical swimming speed (Ucrit), mtDNA copy number and body weight (P ≥ 0.078; Additional file 1: Table S2)
Summary
Sexual signals produced by males play a central role in sexual selection, but the relationship between these traits and the quality of the bearer are often ambiguous. Fast-living individuals invest more in sexual ornaments or weapons and benefit from increased mating success or higher dominance status [18] but have shorter life span than slow-living individuals that invest less in these sexual traits [19,20,21]. This is because the expression and maintenance of sexual traits are costly and divert resources away from other functional traits of the bearers, including somatic maintenance [16, 19]. In fishes, reduced mtDNA copy number is associated with a dysfunction of mitochondrial activity in aged [25, 26] and larva fish [27], but it is unknown whether mitochondrial function can influence the expression of sexual traits
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