Abstract
Testosterone is an important sex hormone and mediates reproduction in male vertebrates. There is ample evidence that testosterone coordinates the expression of physiological, morphological and behavioural traits during reproduction and many of these traits are under sexual selection. However, only few studies so far have examined if individual variation in testosterone is correlated with reproductive success. Because socially monogamous bird species pass through different phases within a breeding cycle and each of these phases requires the expression of different behaviours, the relation between testosterone and reproductive success could vary with breeding stage. Here we investigate the link between reproductive success and testosterone in European stonechats – a socially monogamous songbird with biparental care. Previous studies found that territorial aggression in breeding stonechats depends on testosterone and that testosterone levels peak during the mating phase. Thus, high testosterone levels during mating may influence reproductive success by promoting territorial aggression and mate guarding. We found that males with two breeding attempts produced a similar number of fledglings as males with three breeding attempts. However, males with two breeding attempts expressed higher levels of testosterone than males with just one or those with three breeding attempts, regardless of whether testosterone was measured during the mating or the parental phase of the first brood. Furthermore, testosterone levels during mating, but not during parenting correlated with the total annual number of fledglings. Thus, individual variation in levels of plasma testosterone predicted reproductive success in stonechats.
Highlights
Reproduction in male vertebrates is mediated by androgens which activate spermatogenesis and facilitate the expression of secondary sex characteristics and reproductive behaviors (AdkinsRegan, 2005; Nelson, 2005)
The total annual number of fledglings was positively related to circulating post-capture testosterone concentrations during the mating phase (Figure 2A)
There is ample evidence that testosterone coordinates the expression of physiological, morphological, and behavioral traits during reproduction and many of these traits are under sexual selection
Summary
Reproduction in male vertebrates is mediated by androgens which activate spermatogenesis and facilitate the expression of secondary sex characteristics and reproductive behaviors (AdkinsRegan, 2005; Nelson, 2005). The androgen testosterone enhances mating effort by mediating reproductive behaviors, such as courtship (e.g., Fusani, 2008), copulation (e.g., Balthazart et al, 1995), song (e.g., Ball et al, 2002), and territorial aggression (e.g., Wingfield, 2005), as well as sexually selected morphological traits in many bird species (Adkins-Regan, 2005; Nelson, 2005). Prolonged periods with elevated levels of testosterone can incur costs and may decrease survival (Wingfield et al, 2001) because males with high levels of testosterone tend to invest less into. In polygynous species without paternal care, males invest mostly into mating and as a consequence testosterone levels tend to be elevated throughout the breeding season (e.g., Beletsky et al, 1992). Depending on the social mating system, the species-specific life history, and the balance between mating effort, survival and parental care, the role of testosterone can differ between species
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