![]() ![]() Thus, the ability of animals to preserve signals against degrading micro-organisms may reflect their defence competence, not only because of the relationship between the exaggeration of signals and associated increase in immune-suppressive hormones in blood (Folstad & Karter 1992), but also because well-maintained, non-degraded structures will inform about the ability to fight degrading microbes (Shawkey, Pillai & Hill 2009 Ruiz de Castañeda et al. Behavioural defences or non-specific innate immune responses, which represent the most important antibacterial barriers (Playfair & Bancroft 2004), are active against a wide range of micro-organisms, likely including those able to degrade signalling traits (Horrocks et al. By evaluating traits that reliably signal immune capacity, receivers are able to choose less infected mates with genes conferring pathogen resistance that would be inherited by their offspring (Hamilton & Zuk 1982 Folstad & Karter 1992). 2007), as well as traits signalling the immune capacity of holders (Hamilton & Zuk 1982 Clayton 19 Møller, Christe & Lux 1999 Zuk & Johnsen 2000). Micro-organisms include important degrading agents such as bacteria and fungi that digest the keratin (Burtt & Ichida 1999) modifying colour-based signals (Shawkey et al. Thus, these signals may require additional maintenance costs related to defending them from exposure to the physical and biological environment. Any signal based on morphological structures is prone to deterioration due to abrasion (Burtt 1986) or damage induced by degrading organisms. Reliability of signals is mainly thought to depend on costs associated with their production, showiness and/or maintenance (Maynard-Smith & Harper 2003), and an important part of maintenance costs is related to resources allocated to prevent signal degradation. Those results will help to understand the evolution of ornamental signals.Ī variety of morphological, behavioural and physiological signals of animals that evolve in social contexts (Westneat 2012) allows individual senders to inform about certain characteristics that will influence decisions of receivers (Endler 1993 Ruxton & Schaefer 2011). Our results suggest that selection pressures exerted by feather-degrading bacteria on hosts may promote evolution of particular morphologies of secondary sexual traits with different susceptibility to bacterial degradation that reliably inform of their bacterial load.This is further supported by the relationship detected between antimicrobial properties of uropygial secretion and the level of feather degradation. ![]()
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