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

Abstract

A currently popular hypothesis states that the expression of carotenoid‐dependent sexual ornaments and immune function may be correlated because both traits are positively affected by carotenoids. However, such a correlation may arise for another reason: it is well known that immune function is dependent on nutritional condition. A recent study has suggested that the expression of ornaments may too depend on nutritional condition, as males in good nutritional condition are better at assimilating and/or modulating carotenoids. Thus, carotenoid‐dependent ornaments and immune function may be correlated because both are dependent on nutritional condition. To elucidate if, and how, ornamentation and immune function are linked, pheasant diets were supplemented with carotenoid and/or protein in a fully factorial experiment. Carotenoid treatment affected wattle coloration and tail growth, but not cellular or humoral immunity. Immunity was unrelated to males’ initial ornamentation including wattle colour. Males in better body condition, measured as residual mass, increased their wattle coloration more when carotenoid supplemented. Protein positively affected humoral but not cellular immunity, but had no effect on ornaments. Cellular, but not humoral, immunity increased with male body condition. Thus, there was no evidence that an immune‐stimulatory effect of carotenoids resulted in wattle coloration honestly signalling immune function, but wattle coloration may still signal male body condition.

Carotenoids modulate the effect of coccidian infection on the condition and immune response in moulting house sparrows

“…Interestingly, the effect of carotenoid supplementation on immune responses vary between studies conducted on various avian species where different immunological tests were used. For example, carotenoids may have positive effect on cellular immunity (Blount et al, 2003;McGraw and Ardia, 2003;Saino et al, 2003;Cucco et al, 2006), on humoral immune response (McGraw and Ardia, 2003;Aguilera and Amat, 2007), on innate immune function (McGraw et al, 2006) or on none of the variables measured (Navara and Hill, 2003;Smith et al, 2007). Our results, in line with previous studies, suggest the inherent variability of birds in their carotenoid-dependent immune function.…”

“…The mechanisms behind the neutralising action of carotenoids can be explained by the immunostimulating and immunoregulating effects of these pigments (reviewed by Møller et al, 2000;Catoni et al, 2008), which may play an important role in the defence against parasites. Most of the previous studies, where the availability of carotenoids was experimentally manipulated, indicate that increased availability affects the plasma carotenoids concentration and stimulates the immune response of birds and fish (Blount et al, 2003;McGraw and Ardia, 2003;Saino et al, 2003;Grether et al, 2004;Peters et al, 2004;Cucco et al, 2006;Hõrak et al, 2006;Kolluru et al, 2006;McGraw et al, 2006;Aguilera and Amat, 2007) [but see Navara and Hill (Navara and Hill, 2003) and Smith et al (Smith et al, 2007)]. This is exactly what we also found, i.e.…”

“…Our results, in line with previous studies, suggest the inherent variability of birds in their carotenoid-dependent immune function. Note, however, that there are only some species with elaborate carotenoid-based plumage colouration, where carotenoids seem to have no effect on at least some components of the immune system (Navara and Hill, 2003;Smith et al, 2007).…”

Is testosterone immunosuppressive in a condition-dependent manner? An experimental test in blue tits

“…Some studies have found a positive effect of both supplemental proteins (Smith et al, 2007) [but see Gonzalez et al (Gonzalez et al, 1999)] and carotenoids (McGraw and Ardia, 2005) on humoral immunocompetence and these may have been the factors that increased antibody titres in the E diet males relative to the control diet males. Contrary to other studies (Lochmiller et al, 1993;Gonzalez et al, 1999;Blount et al, 2003;McGraw and Ardia, 2005) [but see McGraw et al (McGraw et al, 2006)], we found no effect of extra protein or carotenoids on the PHA response.…”

Birds receiving extra carotenoids keep singing during the sickness phase induced by inflammation

“…For example, the environmental conditions determining the availability of dietary micronutrients with immunomodulatory effects can alleviate the cost of mounting an immunoresponse. Carotenoids are a clear example in this respect (Blount et al 2003;McGraw and Ardia 2003;Smith et al 2007;Pap et al 2009;Sepp et al 2011;McGraw and Toomey 2013). These pigments have attracted the attention of ecologists because of their dual role.…”