Testing the developmental stress hypothesis in canaries: Consequences of nutritional stress on adult song phenotype and mate attractiveness
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
Available from: Liam R Dougherty
- "The majority of the remainder of effect sizes categorized as " vocalizations " were for effects of stress on dimensions of birdsong. There is reason to predict that birdsong is linked to dimensions of the stress response as the brain centers responsible for song develop early in life, during which time conditions also determine adult stress resistance (Buchanan et al. 2004; Pfaff et al. 2007; Muller et al. 2010). Both may stem from a common phenotype (Spencer and MacDougall-Shackleton 2011), rather than song responding to fluctuations in adult stress. "
Behavioral Ecology 01/2015; DOI:10.1093/beheco/arv195 · 3.18 Impact Factor
Available from: Marcel Eens
- "Males were weighed at the beginning of the recording and individually allocated to a cage (50×61×40 cm attenuated room along with a single female in the adjacent cage (50×61×40 cm 3 ) with visual and acoustic contact (see also Müller et al. 2010). Females were selected from the same population and were unrelated to the male they were allocated to. "
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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; 67(11):1-8. DOI:10.1007/s00265-013-1586-6 · 2.35 Impact Factor
Available from: Marcel Eens
- "As such we control for potentially confounding effects of brood sex ratio, brood size and hatching order. Male chicks were used in a different experiment
. Body mass gain (to the nearest 0.01 g) of all chicks was measured early in the morning until day 20, when the growth curve has levelled off. "
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Maternal effects occur when the phenotype of the offspring is influenced by the phenotype of the mother, which in turn depends on her heritable state as well as on influences from the current and past environmental conditions. All of these pathways may, therefore, form significant sources of variation in maternal effects. Here, we focused on the maternal transfer of carotenoids and vitamin E to the egg yolk, using canaries as a model species. Maternal yolk carotenoids and vitamin E are known to generate significant phenotypic variation in offspring, representing examples of maternal effects. We studied the intra-individual consistency in deposition patterns across two years and the mother-daughter resemblance across two generations in order to estimate the level of heritable variation. The effects of the current environmental conditions were studied via a food supplementation experiment, while the consequences of past environmental conditions were estimated on the basis of the early growth trajectories.
There was a significant effect of the current environmental conditions on the yolk carotenoid and vitamin E deposition, but this effect varied between antioxidant components. The deposition of yolk carotenoids and vitamin E were linked to the process of yolk formation. Past environmental conditions did not contribute to the variation in yolk carotenoid and vitamin E levels nor did we find significant heritable variation.
The transfer of carotenoids or vitamin E may be an example where current environmental variation is largely passed from the mother to the offspring, despite the numerous intermediate physiological steps that are involved. Differences in the effect of the environmental conditions as experienced by the mother during laying may be due to differences in availability as well as physiological processes such as competitive exclusion or selective absorption.
Frontiers in Zoology 08/2012; 9(1):17. DOI:10.1186/1742-9994-9-17 · 3.05 Impact Factor
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