Immune challenge of female great tits at nests affects provisioning and body conditions of their offspring

Abstract

The trade-off between animal's parental reproductive effort and survival is still poorly understood. Parental allocation between the workload during breeding attempts and the parents' own body conditions can be assessed through the offspring quality. Here, I questioned whether the immune responsiveness of female great tits may be considered as a mediator of this trade-off. Specifically, I tested whether (1) the parental reproductive effort decreases, (2) the food composition provided to chicks changes, and (3) whether the nestling immunocompetence and body mass decrease after experimental immunisation. Two populations of great tit Parus major occupying nest boxes were studied in Niepołomice Forest and Krzyszkowice Forest (Southern Poland) in 2011 and 2012, respectively. Three days after hatching, half of the females were challenged with sheep red blood cells (SRBC), while other females were injected with phosphate-buffered saline PBS (control). Six days later, food provided by the parents was collected from nestlings. After another 2 days, the offspring's body mass was measured and wing web swelling in response to an additional phytohaemagglutinin (PHA) injection. In both years, immunocompetence and in 2012 also body mass in the offspring of SRBC-immunised mothers were lower than in control nestlings, indicating a cost of mounting the immune response in the female. Six days after the start of the female treatment, the number of caterpillars and the volume of food items provided by parents to chicks were higher, whereas the number of spiders was lower in nests with SRBC treatment than in control ones. This might be explained by compensational parental feeding after recovery from the inflammation of a female. Thus, the trade-off between parental effort and survival of parents is mediated by the costs incurred for their immunity and can be assessed by the amount and quality of food provided to the nestlings and the offspring condition.

Keywords: Breeding attempt; Caterpillars; Nestlings; Parental investment; Phytohaemagglutinin (PHA) injection; Sheep red blood cells; Spiders.

Fig. 1

Timeline of experiment in both experimental (SRBC) and control (PBS) nests. Horizontal line is the time-axis; ticks are given for each day of the experiment, while labels (= treatments) are below the appropriate ticks

Fig. 2

Nestling wing web swelling and body mass in the control (PBS) and experimental (SRBC) group, in 2011 (a, c) and 2012 (b, d). Each box plot shows the group 75th percentile, 25th percentile and median, while whiskers are maximum and minimum values

Fig. 3

Number of caterpillars, spiders and all food items and volume of food provided by the parents to their offspring in the control (PBS) and the experimental (SRBC) groups. Above graphs are given results of Mann-Whitney U tests; in all cases df = 1. Each box plot shows the group 75th percentile, 25th percentile and median, while whiskers are maximum and minimum values

Fig. 4

Relationships between chick diet composition in the case of rich food (caterpillars: a–d) and poor food (spiders: e–h) and their wing web swelling response to PHA injection and body mass in control (PBS) and experimental (SRBC) nests