Immune function differs among tropical environments but is not downregulated during reproduction in three\xa0year-round breeding equatorial lark populations

Henry K Ndithia,B Irene Tieleman,Muchane Muchai,Kevin D Matson

doi:10.1007/s00442-021-05052-0

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 (Tmin), and average maximum temperature (Tmax) differed during sampling times among the three breeding statuses per location. Tmin and Tmax 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.

Highlights

Seasonal variation in immune function can be attributed to life history trade-offs and to variation in environmental conditions (Martin et al 2008; Tieleman 2018)
We found no consistent differences between non-breeding and chick-feeding individuals for haptoglobin, nitric oxide, agglutination, or lysis (Fig. 1a–d)
Further exploration of the significant interaction of breeding status × location for nitric oxide revealed that values were higher during chick-feeding than during non-breeding in the cool and dry North Kinangop (t = 3.39, P = 0.007)

Summary

Introduction

Seasonal variation in immune function can be attributed to life history trade-offs and to variation in environmental conditions (Martin et al 2008; Tieleman 2018). These latter two phenomena are known to strongly co-vary in temperate and arctic areas, where seasonal variation in immune function has been studied. Certain events associated with an organism’s life history, such as reproduction and migration, can be resource demanding (Piersma 1997; Martin et al 2008) These events may result in trade-offs with the immune system, a critical component of self-maintenance and survival Other studies provide contrary evidence showing that immune function is maintained in the face of reproduction (Tieleman et al 2019; Schultz et al 2020) and other supposedly competing physiological processes, e.g., endocrinological changes (e.g. Vindevogel et al 1985; Allander and Sundberg 1997; Christe et al 2000; Møller et al 2003; Alonso-Alvarez et al 2007)

Methods

Results

Conclusion