Socially responsive yolk steroids correlate with gene expression in early extra-embryonic membranes

Females communicate non-genetic information about the environment to their developing offspring to generate potentially adaptive phenotypic variation. For example, birds allocate steroid hormones to their egg yolks in response to social stimuli and these hormones can induce long-lasting changes to offspring physiology and behavior. However, little work has explored how multiple yolk steroids respond to social challenges, despite their shared biosynthetic pathway, or how they impact early development. Here, we conducted simulated territorial intrusions to identify socially responsive yolk steroids using liquid chromatography with tandem mass spectroscopy (LC-MS-MS) and explored their relationship with gene expression patterns in extra-embryonic membranes during the earliest stages of embryonic development in house sparrows (Passer domeseticus). We also characterized how yolk hormones changed across development, from embryonic day 0 (ED0) to ED5. We found that yolk hormone concentrations largely declined with embryonic development, but at ED0 multiple hormones along the androgenic pathway were elevated in response to the number of territorial intrusions a female experienced, with yolk testosterone and progesterone showing the strongest responses. At ED3, these socially responsive yolk hormones were related to gene expression in extra-embryonic membranes linked to key developmental processes, like growth and immune function. These data highlight a critical early window during which yolk hormones may impact offspring traits through changes in extra-embryonic gene expression.