How coccidian parasites affect health and appearance of greenfinches

Abstract

Summary1. 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 birds were experimentally infected, while another half continued receiving medication. 3. Over the course of the experiment the effect of our treatments upon 14 mainly haemato-serological condition indices was recorded. Additionally, changes in colour and carotenoid content of yellow tail and breast feathers, which serve as sexually dimorphic ornamental traits, were measured. 4. Eighty-nine per cent of birds hosted chronic isosporan infection before the experiment, yet experimental inoculation with mixed parasite strains resulted in drastic but transient decreases in serum carotenoid, vitamin E, triglyceride and albumin concentrations, and reduced body mass, indicating serious pathology and probable nutrient malabsorption due to damaged intestinal epithelium. 5. Laboratory-grown tail feathers of infected birds contained 52% less carotenoids and also had smaller values of chroma and hue than those of medicated birds. 6. These results suggest that coccidian infection reduced the expression of plumage coloration by creating a deficiency of carotenoids available for deposition in ornamental feathers.

Carotenoid trade-off between parasitic resistance and sexual display: an experimental study in the blackbird ( Turdus merula )

“…These findings support the idea that sexual displays may signal male infection status as already observed in some biological models (e.g. Hill & Brawner 1998;Brawner et al 2000;Horak et al 2004;Martinez-Padilla et al 2007). Previous studies, including in blackbirds, that used antigenic challenges provided direct support for the idea that immune defences and sexual signals compete for carotenoids (Blount et al 2003;Faivre et al 2003).…”

“…Coccidian infestations are known to produce a large amount of free radicals (Allen 1997a,b) and are highly immunogenic (Martin et al 1997;Yun et al 2000;Smith et al 2002;Horak et al 2004). Infected birds were therefore forced to fight off the infection.…”

“…At this time, the level of infection was very low (fewer than 80 oocysts g K1 of faecal sample for each group). Preliminary observations showed that blackbirds kept in captivity almost always become uninfected, unlike greenfinches (Horak et al 2004). This may have been due to the conditions in which birds were kept; aviaries were cleaned twice a week and water and food were renewed daily.…”

“…On day 1, each male from the infected group was inoculated orally with 10 000 isosporan oocysts suspended in water, while birds from the control group were given an equal volume of water. This dose for infection was calibrated according to the dose used by Horak et al (2004) in greenfinches (Carduelis chloris) and should be biologically meaningful in blackbirds, given our recent observations that 0.1 g of blackbirds' faeces can contain more than 10 000 oocysts ( J. Moreau 2007, unpublished results).…”

Plasma carotenoid levels in passerines are related to infection by (some) parasites

“…At intraspecific level, positive, negative, and non-significant relationships between parasitism and plumage coloration have been reported (Hill, 2006). However, experiments performed up to now largely support the idea of a negative impact of ectoparasites (Figuerola et al, 2003) and coccidian endoparasites (Brawner et al, 2000;McGraw and Hill, 2000;Hõrak et al, 2004) on plumage coloration. Many of the colorations involved in sexual selection are derived from carotenoids (Badyaev and Hill, 2000), pigments that cannot be synthesized by birds and thus have to be incorporated from their diets (Olson and Owens, 1998).…”