Figure Legends
Figure 1. Experimental design and timelines for the diet manipulation and diet selection studies. In the first experiment, zebra finches were given one of three diet treatments that varied in protein and lipid content and blood and fecal samples were collected to assess how diet influenced complement activity, baseline and stress-induced corticosterone concentrations, and the gut microbiome. In the second experiment, we simulated an infection in established zebra finch pairs using the bacterial endotoxin lipopolysaccharide (LPS), and quantified feeding behavior in immune challenged and control individuals, as well as birds housed near either a control pair (no immune threat), or birds housed near a pair given an immune challenge with LPS (social cue of heightened infection risk). To investigate how a direct and perceived immune threat shape macronutrient feeding preferences, we created two isocaloric diets with varied lipid and protein ratios and quantified how much of each diet birds consumed. Fecal samples were collected from all individuals to assess changes in gut microbiota and blood samples were collected from focal individuals (LPS-focal, Saline-focal) to quantify changes in complement activity, corticosterone, and testosterone (males only).
Figure 2. Effect of diet treatment (high fat, equal ratio, high protein), time (day 0, day 8), and hemolytic complement activity (CH50) on (a) observed richness and (b) Shannon diversity index of zebra finch microbiotas in zebra finches fed diets differing in macronutrient content (experiment 1).
Figure 3. Effect of diet treatment (high fat, equal ratio, high protein), time (day 0, day 8), and stress-induced corticosterone concentrations (ng/ml) on (a) observed richness and (b) Shannon diversity index of zebra finch microbiotas in zebra finches fed diets differing in macronutrient content (experiment 1).
Figure 4. (a) Proportional abundance of bacterial phyla across diet treatment groups (high fat, equal ratio, high protein) and time (day 0, day 8) in zebra finches fed diets differing in macronutrient content (experiment 1). Each bar represents a sample from an individual bird. Phyla with less than 1% relative abundance are collapsed into the category < 1%. (b) Relative abundance of the four most common phyla where individual points represent the relative abundance of each phylum from an individual bird. Black circles denote the mean (±SE) relative abundances across treatments.
Figure 5. Grams of high lipid and high protein diet consumed per day in zebra finches challenged with lipopolysaccharide (LPS) or saline (a, b) and in focal birds that were either housed next to sick-conspecifics (LPS-focal) or healthy conspecifics (saline-focal) (c, d). Data are reported as means ± standard error.
Figure 6. Physiological responses of focal birds housed in view of conspecifics injected with saline or LPS (experiment 2). (a) Hemolytic complement activity (CH50), (b) plasma corticosterone concentrations, and (c) plasma testosterone concentrations in zebra finches that were housed next to healthy (no cue of infection, saline-focal) or sick-conspecifics (cue of infection, LPS-focal) in experiment 2. All data are reported as means ± standard error.
Figure 7. Alpha diversity metrics are negatively associated with consumption of the high fat diet in focal birds (LPS-focal, saline-focal). Panels depict (a) the number of observed ASVs (observed richness) and (b) Shannon diversity. Points represent individual birds. Pre-treatment (day 0) samples are indicated by circles and post-treatment samples (day 5) are represented by triangles.