Do Life History Traits Influence Patterns of Maternal Immune Elements in New World Blackbirds (Icteridae)?

Abstract

Avian immunology developed originally by investigating domesticated poultry species (Galliformes), but in recent decades eco-immunological studies of wild bird species have revealed that avian immune systems are more diverse than initially assumed. This study compares six immunological elements in eggs of six species within the same family, the New World blackbirds (Icteridae),whose members differ most notably in two life history parameters, brood parasitism and body size. We measured the maternal immune investment of passive immune components in both yolk and albumen: lysozyme, ovotransferrin, and immunoglobulins (Igs), and LPS-specific Igs. We predicted that brood parasites would have higher levels of immune activity for both innate and adaptive immunity compared with non-brood parasites, and that increased body size could increase microbial exposure of larger animals, resulting in an increase in some adaptive immune responses, such as LPS-specific Igs. We found that brood parasites had significantly higher levels of Igs and lysozyme levels in albumen, but significantly lower levels of Igs in yolk compared with non-brood parasites. Igs in yolk scaled according to body size, with the smallest organisms (the brood parasites) having the lowest levels, and the largest organism (common grackle) having the highest. Our results confirm the findings of other studies of comparative immunity among species in a single taxon that (1) similarities in immune investment cannot be assumed among closely related species and (2) single measures of immune defense cannot be assumed to be indicators of a species’ overall immune strategy, as life history traits can differentially affect immune responses.

Large Mammals Have More Powerful Antibacterial Defenses Than Expected from Their Metabolic Rates

“…Moreover, as selection tends to act on integrated traits (Bennett and Huey 1990), scaling inference based on processes that affect host fitness (i.e., control of bacterial infections) will inherently be more insightful than studies solely based on cell concentrations. Few scaling studies of immunity to date have relied on integrated immune functions, and others either involved few species, narrow taxonomic groups, or found body mass effects but did not estimate allometries (e.g., Nunn 2002;Blount et al 2003;Nunn et al 2003;Lee et al 2008;Schneeberger et al 2013;Tian et al 2015;Fassbinder-Orth et al 2019;reviewed in Downs et al 2020).…”

Large Mammals Have More Powerful Antibacterial Defenses Than Expected from Their Metabolic Rates

“…Moreover, as selection tends to act on integrated traits (Bennett and Huey 1990), scaling inference based on processes that affect host fitness (i.e., control of bacterial infections) will inherently be more insightful than studies solely based on cell concentrations. Few scaling studies of immunity to date have relied on integrated immune functions, and others either involved few species, narrow taxonomic groups, or found body mass effects but did not estimate allometries (e.g., Nunn 2002;Blount et al 2003;Nunn et al 2003;Lee et al 2008;Schneeberger et al 2013;Tian et al 2015;Fassbinder-Orth et al 2019;reviewed in Downs et al 2020).…”