Immune profiles vary seasonally, but are not significantly related to migration distance or natal dispersal, in a migratory songbird

Abstract

A central tenet of ecoimmunology is that an organism's environment shapes its optimal investment in immunity. For example, the benefits of acquired (relatively pathogen specific) versus innate (nonspecific) immune defenses are thought to vary with the risk of encountering familiar versus unfamiliar pathogens. Because pathogen communities vary geographically, individuals that travel farther during seasonal migration or natal dispersal are predicted to have higher exposure to novel pathogens, and lower exposure to familiar pathogens, potentially favoring investment in innate immunity. During the breeding season, migratory animals’ exposure to familiar pathogens should increase, potentially favoring investment in acquired immunity. We hypothesized that song sparrows Melospiza melodia adjust their constitutive immune profiles in response to risk of encountering novel versus familiar pathogens. We predicted that individuals migrating longer distances (inferred from stable hydrogen isotope analysis of claws) and less philopatric individuals (inferred from microsatellite assignment testing) would rely more heavily on acquired than innate defenses. We also predicted that reliance on acquired defenses would increase throughout the early breeding season. Consistent with trade‐offs between acquired and innate defenses, levels of immunoglobulin Y (acquired) varied negatively with macrophage phagocytosis activity (innate). Levels of acquired relative to innate immunity did not vary significantly with migration distance or philopatry, but increased throughout the early breeding season. Macrophage phagocytosis was not significantly repeatable between years. Song sparrows appear to shift from innate defenses immediately after migration to acquired defenses with increasing time at the breeding grounds. These patterns highlight the plasticity of constitutive immune defenses in migratory animals.

Introduction to ecoimmunology: An integrative approach

“…Researchers can also focus more specifically on certain aspects of an immune response, using for example macrophage phagocytosis activity tests the functionality of macrophages (Kelly, MacGillivray, Hobson, MacDougall‐Shackleton, & MacDougall‐Shackleton, ). Specialized approaches are also available in a number of species, including assessing acquired immunoglobulin Y titers in birds (Kelly et al., ). Specific antibody responses to lipopolysaccharide (LPS), a mitogen used to mimic bacterial infection, were assessed in zebra finches (Grindstaff & Merrill, ).…”

“…Researchers can also focus more specifically on certain aspects of an immune response, using for example macrophage phagocytosis activity tests the functionality of macrophages (Kelly, MacGillivray, Hobson, MacDougall-Shackleton, & MacDougall-Shackleton, 2017).…”

“…Specialized approaches are also available in a number of species, including assessing acquired immunoglobulin Y titers in birds (Kelly et al, 2017). Specific antibody responses to lipopolysaccharide (LPS), a mitogen used to mimic bacterial infection, were assessed in zebra finches (Grindstaff & Merrill, 2017).…”

“…Invertebrate species investigated in this current issue are the bumblebee ( Bombus impatiens ), the weevil ( Curculio sp., Coleoptera), the gallfly ( Eurosta solidaginis , Diptera), and larvae of the lepidopteran Pyrrharctia isabella (Czerwinski & Sadd, ; Ferguson & Sinclair, ). Avian species include the house wren ( Troglodytes aedon ), the golden eagle ( Aquila chrysaetos ), the song sparrow ( Melospiza melodia ), the European starling ( Sturnus vulgaris ), and the zebra finch ( Taeniopygia guttata ) (Bowers, Sakaluk, & Thompson, ; Grindstaff & Merrill, ; Kelly et al., ; MacColl et al., ; Pryor & Casto, ). Reptilian species represented in the current issue are the green anole ( Anolis carolinensis ), the gopher tortoise ( Gopherus polyphemus ), and the snapping turtle ( Chelydra serpentina ) (Beck, Thompson, & Hopkins, ; Goessling et al., ; Tylan & Langkilde, ).…”

“…Understanding how environmental context and life history shapes immunological profiles is another common question. Kelly et al (2017) demonstrated that song sparrows shift from innate to more acquired immune defenses when transitioning between life history stages of migration to breeding. Comparing seasonal responses in hemocyte numbers, phenoloxidase activity, humoral antimicrobial activity, melanization response, and the ability to survive fungal infections in three species of insects that have different overwintering strategies reveals that there are no generalizable patterns of immunity with changes in season (Ferguson & Sinclair, 2017).…”