Sex-specific development of cell-mediated immunity under experimentally altered rearing conditions in blue tit nestlings

Abstract

In birds, poor rearing conditions usually have negative effects on T-cell-mediated immune response.However, earlier studies demonstrate that fitness-related traits such as body mass may show sex-specific patterns when subject to alteration of rearing conditions. Therefore, to investigate whether deterioration of rearing conditions influences the development of immune function differently in male and female nestlings, we performed brood size manipulation experiments on blue tit (Parus caeruleus) nestlings. To alter rearing conditions, some broods were increased by three nestlings soon after hatching, while other broods were left non-manipulated. Immune response was assessed as a hypersensitivity reaction to phytohaemagglutinin in 11-day-old nestlings. Additionally, we studied the consequences of brood size manipulation for fledgling body mass and tarsus length. The enlargement of brood size had different effects on the cellular immune responses of male and female nestlings, with males being more negatively affected than their female nest-mates. Sex-specific effects of poor rearing conditions were also recorded for tarsus length, such that tarsus growth was more retarded in female than in male nestlings. We discuss the effects of deterioration of rearing conditions on sex-specific development of cell-mediated immunity with respect to sexual dimorphism of size and developmental strategies in male and female nestlings.

Seasonal change in sexual differences in nestling size and survival: a framework to evaluate sex-dependent environmental sensitivity in the wild

“…This agrees with most experimental studies on species with large brood sizes (Oddie 2000;Potti et al 2002;Råberg et al 2005;Dubiec et al 2006;Nicolaus et al 2009, but see Tschirren et al 2003;Chin et al 2005) and a few observational studies (Dhondt 1970;Eeva et al 2012, but see Dietrich-Bischoff et al 2008). Our approach was observational and, therefore, a clear demonstration of the causal link was not possible.…”

“…For example, the tarsus grows faster than body weight or wing length and reaches a maximum around 10 days old (Royama 1966). In terms of wing length, sex differences in growth strategies have been reported in many studies (Oddie 2000;Råberg et al 2005;Dubiec et al 2006;Nicolaus et al 2009). Since the female is the more dispersing sex, they may invest more in wing length than in body weight under poor conditions (Greenwood 1980).…”

“…Poor external environmental conditions and poor parental conditions should similarly affect the nestlings. In addition, past experimental studies have not controlled the external environment either; these studies examined the sexual differences of environmental stochasticity by changing the food intake per nestling by adding or removing clutches (Råberg et al 2005;Dubiec et al 2006;Nicolaus et al 2009). In this sense, we need not change the main conclusion that female nestlings are more valuable under poor environmental condition.…”

“…However, some recent studies of birds with large brood sizes and small SSD suggested that the smaller sex is more sensitive to poor conditions (Oddie 2000;Potti et al 2002;Råberg et al 2005;Dubiec et al 2006;Nicolaus et al 2009), although other studies have shown the opposite pattern (Tschirren et al 2003;Chin et al 2005;Dietrich-Bischoff et al 2008). In the case of strong sibling competition for food delivered by parents, a larger body size may be advantageous (competitive advantage hypothesis, Nilsson and Gårdmark 2001;Nicolaus et al 2009).…”

Sex-biased terminal investment in offspring induced by maternal immune challenge in the house wren ( Troglodytes aedon )

“…Thus, we suggest that a sex-specific trade-off between growth and immunity may explain, at least in part, why sons and daughters may not noticeably differ in average measures of immunity. This sexually dimorphic variability in immune function may help to explain greater developmental sensitivity of sons than daughters [26,[57][58][59], and is also consistent with the hypothesis that the quality of sons, particularly in polygynous mating systems, is mediated through size and daughters through immune function. Further studies of sex-biased allocation to offspring and sex-specific variability in the immune system across taxa and contexts may provide insight into the evolution of sexual dimorphism in this trait.…”