Constitutive immune function is not associated with fuel stores in spring migrating passerine birds

• Published in: Ecology and evolution 2024-06, Vol.14 (6), p.e11516-n/a
• Main Authors: Ronanki, Shivani, Hegemann, Arne, Eikenaar, Cas
• Format: Article
• Language: English
• Subjects: Autumn; Behavioural Ecology; Biologi; Biological Sciences; Bird migration; Correlation; Ecology; Ecophysiology; Ekologi; Energy; Evolutionary Ecology; fuel stores; Fuels; immune function; Immune response; Immune system; Immunoglobulins; Microorganisms; Migratory birds; Migratory species; Movement Ecology; Natural Sciences; Naturvetenskap; optimal migration theory; Pathogens; Physiology; Song; Species; Spring; Spring (season); spring migration; stopover ecology; Tradeoffs; Zoologi; Zoology
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.11516

Migratory birds may either upregulate their immune system during migration as they might encounter novel pathogens or downregulate their immune system as a consequence of trade‐offs with the resource costs of migration. Support for the latter comes not least from a study that reports a positive correlation in autumn migrating birds between fuel stores and parameters of innate and acquired immune function, that is, energy‐exhausted migrants appear to have lowered immune function. However, to our knowledge, no study has tested whether this pattern exists in spring migrating birds, which may face other trade‐offs than autumn migrants. Here, we investigate if in spring there is a relationship between fuel stores and microbial‐killing ability, a measure of innate immune function, and total immunoglobulin (IgY), a measure of acquired immune function, in four migrating bird species: chaffinches (Fringilla coelebs), dunnocks (Prunella modularis), song thrushes (Turdus philomelos) and northern wheatears (Oenanthe oenanthe). Our findings indicate no significant correlation between fuel stores and either microbial killing ability or IgY levels when considering all species collectively. When analysing species separately, we found a significant negative correlation between fuel stores and microbial‐killing ability in chaffinches and a positive correlation between fuel stores and IgY levels in wheatears. In song thrushes, but not in any of the other species, there was a significant negative correlation between relative arrival date and microbial‐killing ability and between arrival date and IgY levels. Sex did not affect immune function in any of the species. Our study suggests that the relationship between immune function and fuel stores may be different during spring migration compared to autumn migration. Differences in the speed of migration or pathogen pressure may result in different outcomes of the resource trade‐off between investment in immune function and migration among the seasons. Constitutive immune function is not linked to fuel stores in spring migrating birds. However, there is a negative relationship between immune function (% Escherichia coli killed) and arrival date. This suggests that there are seasonal variations in pathogen pressures and migratory speed which could impact the resource trade‐off between investment in immune function and demands of migration.