Abstract
Sexually dimorphic ornamental traits are widely regarded as indicators of nutritional condition. However, variation of nutritional condition outside the reproductive and the ornament production seasons has rarely been considered, although it affects the generality of information content, especially for ornaments that may be used across the year. We measured several indicators of migratory and molt condition in male and female blackcaps (Sylvia atricapilla) during their autumn migration, and quantified their crown reflectance. We detected robust correlations between migratory and molt condition indices, and the correlation structure was similar in the two sexes. Furthermore, the across‐season measure of body condition was positively related to the darkness of the black crown in males, while being unrelated to reflectance traits of the reddish crown in females. Our results reinforce the possibility that some melanin‐based ornaments may be year‐round indicators of individual quality via their dependence on nutritional condition.
Highlights
Condition-dependence is a fundamental concept in sexual selection research
Condition-dependence may link signal expression to the additive genetic background of condition (Rowe & Houle, 1996), thereby building a connection between mate choice and adaptation to the prevailing environment (Lorch et al, 2003), at the same time lessening the chance that directional selection by mate choice depletes the additive genetic variance of the signal (Tomkins et al, 2004)
The robust correlations between summer molt condition and autumn migratory condition should be interpreted in light of what we know about nutritional reserve management and year-round environmental preferences in this migratory songbird
Summary
Condition-dependence is a fundamental concept in sexual selection research. Costs of mate choice (in terms of time, energy, and opportunity) necessitate benefits that outweigh these costs. Recent research of condition-dependent signals has brought new suggestions for general mechanisms connecting organismal performance and signal expression (Emlen et al, 2012; Koch et al, 2017; Lailvaux & Irschick, 2006) Another promising direction might be the use of overarching, multidimensional approaches to condition (Milot et al, 2014). Production leaves ample time for signal deterioration (Delhey et al, 2010) and for signal functioning outside the breeding season (Lemel & Wallin, 1993; Queller & Murphy, 2017) This in turn leads us back to our previous question on the general quality indicator value of plumage signals. We estimate the main axes of body condition variation and relate these axes to crown color expression in males and females
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