Immune function differs among tropical environments but is not downregulated during reproduction in three year-round breeding equatorial lark populations

• Published in: Oecologia
• Main Authors: Ndithia, Henry K., Matson, Kevin D., Muchai, Muchane, Tieleman, B. Irene
• Other Authors: Netherlands Fellowship Programme, Netherlands Organization for Scientific Research, Young Academy project grant, University of Groningen, the Schure-Beijerinck-Popping Fonds, J.L. Dobberke foundation
• Format: Article in Journal/Newspaper
• Language: English
• Published: Springer Science and Business Media LLC 2021
• Subjects: Ecology, Evolution, Behavior and Systematics; Arctic
• Online Access: http://dx.doi.org/10.1007/s00442-021-05052-0; https://link.springer.com/content/pdf/10.1007/s00442-021-05052-0.pdf; https://link.springer.com/article/10.1007/s00442-021-05052-0/fulltext.html

Abstract Seasonal variation in immune function can be attributed to life history trade-offs, and to variation in environmental conditions. However, because phenological stages and environmental conditions co-vary in temperate and arctic zones, their separate contributions have not been determined. We compared immune function and body mass of incubating (female only), chick-feeding (female and male), and non-breeding (female and male) red-capped larks Calandrella cinerea breeding year-round in three tropical equatorial (Kenya) environments with distinct climates. We measured four immune indices: haptoglobin, nitric oxide, agglutination, and lysis. To confirm that variation in immune function between breeding (i.e., incubating or chick-feeding) and non-breeding was not confounded by environmental conditions, we tested if rainfall, average minimum temperature ( T min ), and average maximum temperature ( T max ) differed during sampling times among the three breeding statuses per location. T min and T max differed between chick-feeding and non-breeding, suggesting that birds utilized environmental conditions differently in different locations for reproduction. Immune indices did not differ between incubating, chick-feeding and non-breeding birds in all three locations. There were two exceptions: nitric oxide was higher during incubation in cool and wet South Kinangop, and it was higher during chick-feeding in the cool and dry North Kinangop compared to non-breeding birds in these locations. For nitric oxide, agglutination, and lysis, we found among-location differences within breeding stage. In equatorial tropical birds, variation in immune function seems to be better explained by among-location climate-induced environmental conditions than by breeding status. Our findings raise questions about how within-location environmental variation relates to and affects immune function.