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Reactive oxygen and nitrogen species produced by metabolism and immune defenses can cause extensive damage to biomolecules. To counteract this damage, organisms rely on exogenous and endogenous antioxidants, although their relative importance in maintaining redox balance is unclear. We supplemented captive greenfinches with dietary antioxidants--carotenoids(More)
1. The aim of this study was to examine the mechanisms by which parasites can affect the expression of ornamental traits. 2. Levels of an intestinal coccidian parasite, Isospora lacazei, were manipulated in captive male greenfinches (Carduelis chloris) by suppressing the natural infections with a coccidiostatic sulphonamide drug. Subsequently, half the(More)
Costs accompanying immune challenges are believed to play an important role in life-history trade-offs and warranting the honesty of signal traits. We performed an experiment in captive greenfinches (Carduelis chloris L.) in order to test whether and how humoral immune challenge with non-pathogenic antigen [sheep red blood cells (SRBC)] affects parameters(More)
The question why different host individuals within a population differ with respect to infection resistance is of fundamental importance for understanding the mechanisms of parasite-mediated selection. We addressed this question by infecting wild-caught captive male greenfinches with intestinal coccidian parasites originating either from single or multiple(More)
Carotenoid-based plumage coloration of birds has been hypothesized to honestly reflect individual quality, either because carotenoids are difficult to acquire via food or because of a trade-off in allocation of carotenoids between maintenance and signaling functions. We tested whether differential foraging ability is a necessary precondition for maintaining(More)
Animals' capability to absorb energy and nutrients from food poses a major internal constraint that affects the amount of resources available for allocation to maintenance, growth, signaling, and reproduction. Intestinal surface is the largest area of contact between immune system and microbial antigens; gut thus appears the main arena where trade-offs(More)
Oxidative stress results from a mismatch between production of reactive oxygen species (ROS) and the organism's capacity to mitigate their damaging effects by building up sufficient antioxidant protection and/or repair mechanisms. Because ROS production is a universal consequence of cellular metabolism and immune responses, evolutionary animal ecologists(More)
The main tenet of immunoecology is that individual variation in immune responsiveness is caused by the costs of immune responses to the hosts. Oxidative damage resulting from the excessive production of reactive oxygen species during immune response is hypothesized to form one of such costs. We tested this hypothesis in experimental coccidian infection(More)
Carotenoid-based colours have become an important model of honest signalling as carotenoids are suggested to play vital roles in several physiological functions including antioxidants and immunostimulators, while they are also required for sexual displays. However, it has been recently suggested that carotenoid-based signals may be used mainly as reflectors(More)
Differential exposure or sensitivity to stressors can have substantial effects on the variation in immune responsiveness of animals. However, the questions about the causes and consequences of these processes have remained largely unclear, particularly as regards wild animals and their natural pathogens. Here we ask how a potential marker of stress(More)