SRA

1. Immune function is essential to survival of animals in a world dominated by ubiquitous and diverse microorganisms. Immunological phenotypes of vertebrates vary widely among and within species and individuals, and encountering diverse microbial antigens may contribute to this variation. Maternal effects can improve offspring development and survival, but it remains unclear whether females use cues about their microbial environment to inform offspring immune function.2. To provide microbial environmental context to maternal effects, we asked if the bacterial diversity of the living environment of female zebra finches Taeniopygia guttata shapes maternal effects on egg immune function. 3. By manipulating environmental bacterial diversity, we tested whether immunological investment in eggs is higher when environmental bacterial diversity is high (untreated soil) compared to low (gamma-sterilized soil). We quantified lysozyme and ovotransferrin in egg albumen and IgY levels in egg yolk and in female blood, and we used 16S rRNA gene sequencing to characterize maternal cloacal and eggshell microbiotas. 4. We found a maternal effect on egg IgY concentration that reflected environmental microbial diversity: females who experienced high diversity deposited more IgY in their eggs, but only if maternal plasma IgY levels were relatively high. We found no effects on lysozyme and ovotransferrin concentrations in albumen. Moreover, we uncovered that variation in egg immune traits could be significantly attributed to differences among females: for IgY concentration in yolk repeatability R = 0.80; for lysozyme concentration in albumen R = 0.27. Furthermore, a partial least squares path model (PLS-PM) linking immune parameters of females and eggs, which included maternal and eggshell microbiota structures and female body condition, recapitulated the treatment-dependent yolk IgY response. The PLS-PM additionally suggested that the microbiota and physical condition of females contributed to shaping maternal effects on egg immune function, and that (non-specific) innate egg immunity was prioritized in the environment with low bacterial diversity. 5. Since immunological priming of eggs benefits offspring, we highlight that non-genetic maternal effects on egg immune function based on microbial diversity cues from the parental environment may prove important for offspring to thrive in the microbial environment that they are expected to face.