Effects of nutrition on sexual ornaments and humoral immune responsiveness in adult male pheasants

Abstract

Female pheasants may base their choice of mates on the expression of male ornaments such as the red chin wattle and the length of the spurs. Both these ornaments are predicted to be sensitive to access to carotenoids (and vitamins). Moreover, because carotenoids also enhance immune function, it has been suggested that there is a trade-off in the use of carotenoids for ornament expression and immune function. We fed adult male ring-necked pheasants (Phasianus colchicus) with food of different nutritional quality. This relieved males from restrictions of access to dietary carotenoids and allowed us to study the simultaneous effect on ornament expression (wattle size and redness, spur length) and immune responsiveness. Two treatment groups were given either a low or a high quality fodder between late February and late May, when males were 8-11 months old. As a result of the food-quality manipulation, males in the high nutrient group achieved significantly redder wattles whereas no significant effect was found for either wattle size or spur length. There was a non-significant tendency that the antibody response to one out of two novel antigens was affected by the experimental treatment, but the mean production of antibodies against the two antigens (diphtheria and tetanus toxoid) was not significantly related to the experimental treatments. Over the experimental period, the change in humoral immune responsiveness was positively related to the increase in spur length, but not related to the change in wattle colouration. We suggest that wattle colour may be an honest indicator of males' ability to find or assimilate dietary carotenoids, but we found no firm evidence that the mechanism maintaining honesty is a trade-off between the use of carotenoids for ornament colouration and general immune function. In contrast, our study lends some support to the idea that spur length, a sexually selected trait, may reflect humoral immunocompetence in male pheasants.

Carotenoid and protein supplementation have differential effects on pheasant ornamentation and immunity

“…, 2002; Navara & Hill, 2003), our study did not support this idea. Although dietary supplementation with a carotenoid affected the colour of the wattle (see also Ohlsson et al. , 2003) and tail regrowth, it did not affect immune function, and we found no relationship between immunological competence and ornament expression.…”

“…The plasma was then extracted and stored at −20 °C until later analysis. Antibody titres were analysed using an enzyme‐linked immunosorbent assay (see Ohlsson et al. , 2003).…”

“…Dietary variation in carotenoids affects grouse comb colour (Egeland et al. , 1993) and pheasant wattle colour (Ohlsson et al. , 2003).…”

Costly carotenoids: a trade‐off between predation and infection risk?

“…, 2004; Grether et al. , 2004; McGraw & Ardia, 2004, no significant positive effect Navara & Hill, 2003; Ohlsson et al. , 2003; Saino et al.…”

Development of Badges of Status in Captive Male House Sparrows (Passer domesticus) in Relation to the Relative Ornamentation of Flock‐Mates

“…To understand how specific information becomes encoded in a particular signal, it is essential to understand the factors which influence its expression. Using plumage colouration of birds as a model, Hill (2006) described four broad, non-mutually exclusive classes of environmental factors that can influence the expression of signals of quality: (1) pigment access (Witmer 1996;Hill et al 2002), (2) nutritional condition (McGraw et al 2002;Ohlsson et al 2003), (3) parasites (Zuk et al 1990;McGraw & Hill 2000) and (4) social environment (McGraw et al 2003;Gautier et al 2008;Safran et al 2008). Using plumage colouration of birds as a model, Hill (2006) described four broad, non-mutually exclusive classes of environmental factors that can influence the expression of signals of quality: (1) pigment access (Witmer 1996;Hill et al 2002), (2) nutritional condition (McGraw et al 2002;Ohlsson et al 2003), (3) parasites (Zuk et al 1990;McGraw & Hill 2000) and (4) social environment (McGraw et al 2003;Gautier et al 2008;Safran et al 2008).…”