Testing the developmental stress hypothesis in canaries: consequences of nutritional stress on adult song phenotype and mate attractiveness
ABSTRACT The complex songs of songbirds are thought to have evolved through sexual selection. Sexually selected signals must be associated
with costs in order to ensure their honesty as indicator of male quality. Costs may relate to the development of the neural
substrate underlying song learning, which develops already very early in life. Song may, therefore, serve as an indicator
of the early developmental history. This nutritional stress hypothesis has initially been confirmed for a variety of species,
but recent studies using zebra finches as a model species reported somewhat inconsistent effects, and the functional consequences
of changes in adult song phenotype remain unclear. We tested the nutritional stress hypothesis in canaries by manipulating
either the brood size or the food quality postfledging. The brood size manipulation had a significant effect on early development,
and low food quality postfledging led to a transient reduction in body mass. However, we did not find evidence that any of
the song traits measured reflected the early developmental conditions, which is in conflict with the nutritional stress hypothesis.
Canaries may be less vulnerable to nutritional stress or are able to compensate stressful conditions during early development.
However, if males compensated, this compensation may have come at a survival cost. Female mate choice decisions were independent
of the developmental history of a male. Instead, females preferred males singing longer song bouts, a trait that may contain
a heritable component.
KeywordsDevelopmental stress-Sexual selection-Growth-Bird song
- SourceAvailable from: Johannes RojahnInternational Review of Research in Mental Retardation - INT REV RES MENT RETARD. 01/2009; 38:239-287.
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ABSTRACT: Bird song is considered to have evolved via sexual selection and should as such honestly signal aspects of the quality of its bearer. To ensure honesty, the immunocompetence handicap hypothesis proposed a dual role of testosterone, having positive effects on sexual signalling but suppressive effects on immune function. However, recent studies showed that it is rather an immune activation that suppresses the androgen production. This reversed chain of causation may significantly alter the pathways, which translate the effects of parasites and pathogens into changes in the expression of male sexual traits. We infested male canaries with Ixodes ricinus tick nymphs to investigate the causal relationships between (ecto-)parasites, testosterone and sexual signalling, here singing behaviour. We focused on flexible song traits, which may quickly reflect changes in the infestation status, and tested whether these effects relate to changes in the plasma testosterone levels or health state. The experimental tick infestation altered the males’ song performance by reducing song consistency, a trait that had previously been identified to reflect male quality. The tick infestation lowered the plasma testosterone levels and had a negative effect on the health status in terms of a reduced hematocrit. Our pathway analysis then revealed that it is the parasite-induced reduction of the plasma testosterone levels but not of the health state that caused the changes in song consistency. Thus, our study supports the view that it is the effect of parasites and immune activation on plasma testosterone levels that generates the trade-off between immunocompetence and sexual signalling.Behavioral Ecology and Sociobiology 11/2013; · 3.05 Impact Factor
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ABSTRACT: The concept of a macroevolutionary trade-off among sexual signals has a storied history in evolutionary biology. Theory predicts that if multiple sexual signals are costly for males to produce or maintain and females prefer a single, sexually selected trait, then an inverse correlation between sexual signal elaborations is expected among species. However, empirical evidence for what has been termed the 'transfer hypothesis' is mixed, which may reflect different selective pressures among lineages, evolutionary covariates or methodological differences among studies. Here, we examine interspecific correlations between song and plumage elaboration in a phenotypically diverse, widespread radiation of songbirds, the tanagers. The tanagers (Thraupidae) are the largest family of songbirds, representing nearly 10% of all songbirds. We assess variation in song and plumage elaboration across 301 species, representing the largest scale comparative study of multimodal sexual signalling to date. We consider whether evolutionary covariates, including habitat, structural and carotenoid-based coloration, and subfamily groupings influence the relationship between song and plumage elaboration. We find that song and plumage elaboration are uncorrelated when considering all tanagers, although the relationship between song and plumage complexity varies among subfamilies. Taken together, we find that elaborate visual and vocal sexual signals evolve independently among tanagers.Proceedings of the Royal Society B: Biological Sciences 08/2014; 281(1788). · 5.29 Impact Factor