Variation in Circulating Testosterone during Mating Predicts Reproductive Success in a Wild Songbird

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 behavioral 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 behaviors, 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.

Incorporation of fresh leaves of wormwood (Artemisia herba alba) and/or rosemary (Rosmarinus officinalis) in the diet of rams: Effect on testicular function, sexual behavior, and blood parameters

“…Blood testosterone level is an important indicator of fertility and reproductive activity (Apfelbeck et al, 2016 ; Preston et al, 2012 ). This steroid hormone promotes sexual behavior and cognitions in order to facilitate mate acquisition or mating directly (Roney et al, 2003 ).…”

“…Blood testosterone level is an important indicator of fertility and reproductive activity (Apfelbeck et al, 2016;Preston et al, 2012).…”

Testosterone, territorial response, and song in seasonally breeding tropical and temperate stonechats

“…For example, in an experimental study in dark-eyed juncos (Junco hyemalis) , testosterone treated males suffered fewer losses of paternity than control males [97]. Supporting the fitness relevance of testosterone during mating, earlier studies in European stonechats found that variation in testosterone concentrations during mating, but not during parental stages, was associated with reproductive success in temperate stonechats [72]. Similar to stonechats, testosterone concentrations also peaked during nest-building and mate guarding in temperate barn swallows (Hirundo rustica, [20]), blue tits ( Cyanistes caeruleus, [16]) and in tropical Seychelle warblers (Acrocephalus sechellensis, [98]).…”

“…In Europe, we randomly assigned two decoys from Austria and in East Africa eight decoys from each of the two populations, Kinangop (Kenya) and Arusha (Tanzania). In stonechats, stimulation with a decoy and playback does not change circulating testosterone concentrations [ 72 ], and hence to analyze testosterone profiles data from passively and actively caught birds were combined.…”

“…The behavioral endocrinology of temperate and tropical stonechats is also well studied. During the breeding season, territorial behavior in temperate stonechats has been shown to depend on testosterone [ 8 , 71 ] and individual variation in testosterone concentrations during mating, but not during parenting, relates to variation in reproductive success [ 72 ]. However, temperate male stonechats do not show short-term increases in testosterone concentrations during simulated territorial intrusions despite an aggressive response towards the intruder [ 73 ].…”