Abstract
Sexually selected signals reliably reflect individual phenotypic or genetic quality and, thus, survival prospects of holders. Telomere length is considered a good predictor of life expectancy and, consequently, exploring the links between telomere length and sexually selected traits is much needed to better understand the mechanisms that maintain the honesty of sexual signals. We manipulated the length of throat feathers in spotless starling (Sturnus unicolor) males (a sexually selected signal) before reproduction and explored its effects on telomere shortening and breeding performance in subsequent reproductive events. We did not detect an effect of the feathers clipping manipulation, but males with longer throat feathers before the experiment had shorter telomeres that also shortened more slowly than those of males with shorter throat feathers did. Moreover, length of throat feathers of males before manipulation was positively related to hatching success of second clutches. Thus, correlative but not experimental results support the expected associations between sexually selected signals, telomeres and reproduction. We discuss such results in scenarios of sexual selection where feather length reflects, but does not directly cause, telomere attrition and enhanced reproductive success. Males with longer throat feathers might be older, more experienced males (i.e., with shorter telomeres), able to buffer telomere shortening between reproductive events. Because of the absence of experimental effects, differential incubation effort of females cannot explain the detected association with hatching success, but other sexually selected traits that covary with throat-feather length could be responsible. Exploring those physiological and/or morphological characteristics related to throat-feather length should therefore be the matter of future research.
Highlights
The evolution of signals, defined as behavioral, morphological or physiological characteristics that function transferring information among organisms (Otte, 1974), have attracted the attention of evolutionary biologists for decades (Maynard-Smith and Harper, 2003)
It was suggested that male traits that are selected by females do not need to be related to phenotypic or genetic quality of holders, it is accepted that, mainly because of costs associated to intra sexual competition, these traits would rapidly evolve reflecting the quality of males (Macías-García and Ramírez, 2005)
The association between telomere length and throat feather length differs for males and females (GLM, interaction between sex and telomere length, F1, 56 = 15.60, p < 0.001)
Summary
The evolution of signals, defined as behavioral, morphological or physiological characteristics that function transferring information among organisms (Otte, 1974), have attracted the attention of evolutionary biologists for decades (Maynard-Smith and Harper, 2003). Telomere length has even predicted reproductive success in wild birds (Boonekamp et al, 2014; Parolini et al, 2017; Bauer et al, 2018) and detecting relationships between a sexually selected character and telomere length and/or attrition would suggest that the trait reflects (i.e., signals) phenotypic and/or genetic quality of the holder. If throat feathers function in social, non-sexual, communication of males, the experimental reduction could increase stress levels due to social interactions and an effect on telomere deterioration should be detected These interactions in starlings occur even at non-breeding period as seen in the European starling (Sturnus vulgaris) (Feare, 1984). If throat feather length negatively affects mating success and, reduces reproductive effort, telomere deterioration would be lower in males with experimentally shortened throat feathers
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