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

Justyna Kubacka,Mariusz Cichoń

doi:10.1007/s10211-020-00351-w

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.

Highlights

Mechanisms underlying life history decisions can be better understood by studying their relationship with immune function, which, being part of self-maintenance, is expected to be traded-off with reproduction (Stearns 1992; Zuk and Stoehr 2002)
In sheep red blood cells (SRBC) broods, the difference in tarsus length between female and male chicks was smaller compared with control broods (Fig. 2)
When we explored this interaction by testing whether the female provisioning rate varies with the hatch date in each of the two treatment groups separately, we found that it was unrelated to hatch dates in control broods (F(1,9) = 0.43, p = 0.529) but decreased with hatch dates in SRBC treatment x hatch date 0.51 (1, 19) 0.483 0.048 (0.067)

Summary

Introduction

Mechanisms underlying life history decisions can be better understood by studying their relationship with immune function, which, being part of self-maintenance, is expected to be traded-off with reproduction (Stearns 1992; Zuk and Stoehr 2002) This generates two complementary predictions, assuming that resources are limited (Norris and Evans 2000). In birds, the former prediction has been widely tested experimentally, showing that increased breeding effort negatively affects immune function and parasite load (Knowles et al 2009; González-Medina et al 2015; Colominas-Ciuró et al 2017). A non-pathogenic antigen allows studying the costs of the immune response independently of the negative effects caused by multiplication of a pathogenic microorganism

Methods

Results

Discussion

Conclusion