Trade-off between immunocompetence and growth in magpies: an experimental study

Abstract

A trade-off between immunity and growth has repeatedly been suggested, mainly based on laboratory and poultry science, but also from experiments where parasitism intensity was manipulated in field bird populations. However, as resource allocation to different activities (or organs) during growth is difficult to manipulate, this trade-off has only been experimentally tested by studying the effects of non-pathogenic antigens. By providing some nestling magpies (Pica pica) with methionine, a sulphur amino acid that specifically enhances T-cell immune response in chickens, we investigated this trade-off by directly affecting allocation of limited resources during growth. Results were in accordance with the hypothetical trade-off because nestlings fed with methionine showed a lower growth rate during the four days of methionine administration, but a larger response when fledglings were challenged with phytohaemagglutinin (a measure of the intensity of T-lymphocyte-mediated immune responsiveness) than control nestlings. Surprisingly, we found that control and experimental nestlings fledged with similar body mass, size and condition, but experimental nestlings suffered less from blood parasites (Haemoproteus) and had fewer lymphocytes (a widely used measure of health status) than control nestlings, suggesting a negative effect of blood parasites or other pathogens on nestling growth.

Immunocompetence and its costs during development: an experimental study in blue tit nestlings

“…An exaggerated allocation to T-cell-mediated immunocompetence therefore trades-off with growth and has clear (survival) costs in blue tits nestlings. In the only other study to date that has directly manipulated allocation to immunocompetence in the wild, Soler et al (2003) found that growth in magpies was initially reduced while T-cell-mediated immunocompetence was increased. However, neither fledging condition nor survival to fledging was affected (Soler et al 2003).…”

“…Nestlings were ordered by their weight and the treatment of the heaviest chick was decided at random. The treatment of all other chicks then alternated down the size hierarchy (see also Soler et al 2003). The individual markings on the feet of the nestlings were remade at every consecutive visit until chicks could be ringed (at around days 8-10).…”

“…In addition, sulphur amino acids themselves may directly affect T-cell production (Kinscherf et al 1994). Methionine supplementation hence changes the priority rules (sensu Zera & Harshman 2001) of resource allocation (Soler et al 2003). Here, I study costs (in terms of a reduction in growth and survival) of an experimentally induced exaggerated allocation into T-cell-mediated immunocompetence in blue tit (Parus caeruleus) nestlings.…”

“…Recently, Soler et al (2003) showed that supplementing methionine to passerine (magpie, Pica pica) nestlings induces a higher T-cell-mediated immunocompetence and reduces growth. Methionine, a sulphur amino acid, appears to be required in higher amounts than endogenous sources supply (Grimble & Grimble 1998).…”

“…Both immunocompetence and survival are condition-dependent traits (Sheldon & Verhulst 1996). Therefore, the investment in immunocompetence needs to be manipulated directly to study whether such investments indeed show a trade-off with other fitness components and what are the costs of such a trade-off (Lochmiller & Deerenberg 2000;Norris & Evans 2000;Soler et al 2003).…”