Constitutive immune defences correlate with life‐history variables in tropical birds

Abstract

Summary 1.It has been suggested that immune defences are shaped by life history and ecology, but few general patterns have been described across species. We hypothesized that 'fast' life-history traits (e.g. short development times, large clutch sizes) would be associated with developmentally inexpensive immune defences, minimizing the resource demands of young animals' immune systems during periods of rapid growth. Conversely, 'slow' life histories should be associated with well developed antibody-mediated defences, which are developmentally costly. 2. We therefore predicted that 'fast-living' species would exhibit higher levels of complement proteins, a component of non-specific innate defence, but lower levels of constitutive ('natural') antibodies. Additionally, we predicted that constitutive immune defences in general would be higher in species with ecological characteristics that might increase exposure to pathogens, such as open nests, omnivorous diets, gregariousness, and closed forested habitat. 3. Across 70 Neotropical bird species, we found a strongly positive relationship between incubation period and natural antibody levels in adult birds, suggesting that longer developmental times might allow the production of a more diverse and/or more reactive adaptive immune system. Complement activity was positively, although weakly, correlated with clutch size, providing some support for the hypothesis that faster-living species rely more on innate defences, such as complement. Unexpectedly, solitary species had higher natural antibody titres than species that frequently join flocks. 4. Our results suggest that, despite probably widespread differences in the intensity and diversity of pathogen exposure, species-level variation in constitutive immune defences is understandable within the context of life-history theory.

Effects of early developmental conditions on innate immunity are only evident under favourable adult conditions in zebra finches

“…Likewise, NAb concentrations did not vary with clutch size or food limitation in several bird species (e.g. Buehler et al 2009a;Lee et al 2008), but significant relationships have been found with growth rate, mass differences among nestlings, prolonged fasting, body mass and environmental conditions in other species (e.g. Bourgeon et al 2010;Buehler et al 2009b;Mauck et al 2005;Parejo et al 2007).…”

“…Despite the theoretical expectations outlined above, empirical evidence of effects of early developmental conditions on innate immune function remains scarce and heterogeneous. For example, while complement activation was positively related to clutch size in a suite of tropical bird species, no such effect was found for NAbs (Lee et al 2008). In a study on European rollers (Coracias garrulus), both components varied with brood hierarchy in nestling body mass, though in opposite ways.…”

A trade-off between embryonic development rate and immune function of avian offspring is revealed by considering embryonic temperature

“…Slower embryonic development, reflected by longer embryonic periods, is thought to allow enhanced development of physiological systems, like the immune system, that increase survival and longevity [1][2][3]. Such trade-offs are thought to underlie the wellknown difference between tropical and north temperate birds in length of embryonic periods and adult survival [2][3][4].…”

Sex-Specific Effects of High Yolk Androgen Levels on Constitutive and Cell-Mediated Immune Responses in Nestlings of an Altricial Passerine

“…Therefore, it is not possible to measure the overall strength and efficiency of the immune system with a single immune assay (Adamo 2004 (Lee et al 2008;Palacios et al 2009). Thus, any variation in maternally derived components, such as androgens, may mediate increased investment in one branch of immunity at the expense of another.…”