Brood size manipulation showed little effect on baseline innate immune function in great tit (Parus major) nestlings and parents

Abstract

The trade-off between current and future reproduction is universal and forms the basis of life-history theory. Brood size manipulations is one of the most common way to test this trade-off. Although the effect of brood size manipulation on immune response have been tested in many studies, little is known about baseline innate immune function. To fill this gap, I created three groups (enlarged, reduced and control) by brood size manipulation. I used three types of immune assays, including bacteria killing assays (BKA), haemagglutination and haemolysis assays (HLHA) and haptoglobin assays, to get a diverse and extensive measurement on baseline innate immune function. My study aims to be an integrated exploration on the trade-offs between parental effort and immune function in parents and between growth rate and immune function in nestlings. My study has showed no clear evidence for a trade-off on baseline innate immunity caused by brood size manipulation. However, I found that both nestlings and adult males had higher lysis capability than females and a negative correlation between lysis and body mass. These results suggest a trade-off between the complement system and growth rate, as well as different life-history strategies by males and females in relation to immune system development.

Popular Abstract

Species struggle to survive and produce offspring. Only those individuals that succeed to pass on their genes contribute to the next generation. We know that in nature, resources are limited and decisions have to be made for everyone. Individuals have to decide how much resource should be used for survival and reproduction. Parents need to take care of the nestlings and feed them. The investment in this process is the cost of reproduction.

My research focused on the immune system of a bird called great tit (Parus major). We know that immune function is important, because it protects the body from harmful pathogens (for example, germs and viruses). Because of that, the immune system can be seen as one index of survival probabilities. The immune system is complicated and delicate. A good immune system requires teamwork from several parts. Immune function can be divided along several dimensions: baseline (when there is no pathogen in the body) or response (when pathogens are already in the body); innate (conserved and not specific to one kind of pathogen) or acquired (developed and often specific to a special kind of pathogen). I searched the literature and found that although there are many studies on immune function, little has been done about baseline innate immune function. Therefore, I decided to work on this specific part.

For my work, I used nest boxes in the forest area near Vombsjön, Sweden. In spring, great tits build their nests inside the boxes. I experimentally adjusted the cost of reproduction by brood size manipulations. This manipulation is performed by adding nestlings from one nest to another, so that parents with more nestlings need to do more work and those with fewer nestlings need to work less. I called those nests with more nestlings “enlarged”, and those with less nestlings “reduced”. Some nest boxes retained the same number of nestlings and become “control” nests. Later, I measured the weight and took blood samples from the parents and nestlings to see if the innate baseline immune system differed between these three groups. I used the up-to-date methods to analysis the strength of immune function of the blood samples and quantified four parameters of immune function. Then, I also used the blood samples to determine the sex of the nestlings.

Unexpectedly, my results showed that the immune indices were nearly the same for all three groups. This result could be caused by the warm and nice weather in this spring resulting in no manipulation of parental effort. Besides this main result, I found that male nestlings are heavier and grow faster than females. I also found that females had better lysis ability than males. Only for male nestlings, heavier nestlings had higher haptoglobin concentrations. This suggests different immune system development strategy between males and females. I have also found that those nestlings that hatched later had higher haptoglobin concentrations.

Another important result of my work is that I found heavier nestlings to have worse lysis ability. Interestingly, in previous studies by other researchers, nestlings with higher weight were found to have better immune response. This implies that the development of baseline immunity and immune response restrains each other and individual need to choose between them.

• author: Liu, Tiancheng
• supervisor: Arne Hegemann; Jan-Åke Nilsson
• organization: Degree Projects in Biology
• course: BION02 20221
• year: 2023
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 9113471
• date added to LUP: 2023-04-14 12:12:42
• date last changed: 2023-04-14 12:12:42