An immune challenge of female great tits decreases offspring survival and has sex-specific effects on offspring body size

Abstract

Investment in immunity is expected to decrease (costly immunity) or enhance (terminal investment) reproductive performance. Here, we tested the effects of activation of the immune system in female great tits (Parus major) on (1) their reproductive effort and (2) the survival and body condition of their offspring, controlling for chick sex. We injected females tending 3-day-old chicks with sheep red blood cells (SRBC) or saline (control) and recorded their provisioning rates 6 days later, during the expected peak of antibody production. We measured tarsus length and body mass in 11-day-old chicks and monitored changes in brood size. We found that female provisioning rates were unaffected by the SRBC challenge. An analysis without an outlier, however, showed a significant challenge-by-hatch date interaction. This interaction indicated that female provisioning rates decreased with hatch dates in the SRBC but not in the control nests, suggesting a stronger effect in later breeders. Chick body mass was not affected by female immunisation nor by its interaction with chick sex. However, we found a significant challenge-by-sex interaction on offspring tarsus. In SRBC nests, the difference in tarsus length between male and female chicks was lower than in controls, suggesting sex-dependent effects of the challenge on offspring structural growth. Finally, chick mortality was greater in SRBC nests compared with controls, but chick survival probability was not affected by sex. Overall, our results support the costly immunity but not the terminal investment hypothesis in the great tit.

Spring reproductive success influences autumnal malarial load in a passerine bird

“…Although commonly mentioned in the literature, but rarely reported, we predict a significant increase of parasitemia in spring, illustrating spring recurrences (or spring relapses, Applegate, 1971). In light of the studies which showed a trade-off between activation of the great tit’s immune system and their reproduction (e.g., Ots & Hõrak, 1998; Grzędzicka, 2017; Kubacka & Cichoń, 2020), we predict a negative relationship between winter and/or spring parasitemia and reproductive success. Finally, in view of the energy expenditure associated with reproduction (Visser & Lessells, 2001; Nilsson & Råberg, 2001), we also predict that infected individuals who invest substantially in reproduction will later experience higher parasitemia (Hanssen et al, 2005).…”

Hard life for sons in the nest? Sex-dependent offspring mortality in great tits in relation to breeding habitat and age

“…So, the larger size and the presumably greater energy demand during development may make males more sensitive to adverse environmental effects than females (Swenson 1986, Jones et al 2009, Rosivall et al 2010, Bouvier et al 2016). On the other hand, some studies did not find an influence of adverse conditions on sex-specific survival in great tits, for instance by increased pollution levels (in 15 days old nestlings; Eeva et al 2012), by increased competition among siblings (Nicolaus et al 2009) or by handicapping the parents (Kubacka and Cichoń 2020). These latter results suggest that male-biased offspring mortality may not be explained exclusively by higher sensitivity of male offspring to adverse environmental conditions.…”