Abstract
Outbreaks of emerging infectious disease offer a unique chance to study viability selection in action in short time windows. Finch trichomonosis, caused by a protozoan Trichomonas gallinae emerged in Great Britain in 2005 and led to epidemic mortality and a significant population decline of greenfinches, Carduelis chloris in UK and Northern European countries in subsequent years. We recorded covariation between plumage characteristics and trichomonosis-induced mortality among wild-caught greenfinches brought into captivity in Tartu, Estonia. Occurrence of fault bars (markers of stressful conditions experienced during feather growth) on tail feathers was five times higher among the dead birds than among survivors. Black (eumelanotic) compartments of tail feathers of survivors were on average 22 % darker than feathers of dead birds. Such pattern is best explained by proposed pleiotropic effects of genes involved in eumelanin production on immune function. These findings suggest that melanin-based coloration can evolve via mechanisms that are independent of visual information provided by the pigment.
Highlights
Parasites, including infectious diseases can be arguably considered as a major source of mortality in wild animal populations (Lochmiller and Deerenberg, 2000)
Clear symptoms of trichomonosis were detected on necropsies of three birds of five
We suspect that only the birds with weakest immune systems died of trichomonosis while others managed to control their infections in the aviary
Summary
Parasites, including infectious diseases can be arguably considered as a major source of mortality in wild animal populations (Lochmiller and Deerenberg, 2000). Mounting anti-parasite defenses can deplete hosts’ energy reserves and other maintenance resources, making them vulnerable to predation (Møller and Erritzøe, 2000) or effects of harsh environmental conditions (Moret and Schmid-Hempel, 2000) Hosts differ in their vulnerability to infections and these differences may be mirrored in their appearance. Additional information about the individuals’ state during feather growth is provided by the physical properties of the feathers such as different parameters of size and structure (e.g., Desrochers et al, 2009) All these parameters have a potential to impinge on fitness either by viability selection, affecting thermoregulatory and aerial performance and crypsis (reviewed by Bortolotti, 2006) or by signal selection conveying information about individual quality in inter- and intrasexual selection and other social contexts (reviewed in Hill and McGraw, 2006; McGraw, 2008; Svensson and Wong, 2011)
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