Gut microbiota of homing pigeons shows summer-winter variation under constant diet indicating a substantial effect of temperature

Abstract

AbstractBackgroundGut microbiotas play a pivotal role in host physiology and behaviour, and may affect host life-history traits such as seasonal variation in host phenotypic state. Generally, seasonal gut microbiota variation is attributed to seasonal diet variation. However, seasonal temperature and day length variation may also drive gut microbiota variation. We investigated summer-winter differences in gut microbiota in 14 homing pigeons living outdoors under a constant diet by collecting cloacal swabs in both seasons during two years. Because temperature effects may be mediated by host metabolism, we determined basal metabolic rate (BMR) and body mass. Immune competence is influenced by day length and has a close relationship with gut microbiota, and it may thus be a link between day length and gut microbiota. Therefore, we measured seven innate immune indices. We expected gut microbiota to show summer-winter differences and gut microbiota to correlate with metabolism and immune indices.ResultsBMR, body mass, and two immune indices varied seasonally, other host factors did not. Gut microbiota showed differences between seasons and sexes, and correlated with metabolism and immune indices. The most abundant genus (Lachnoclostridium 12, 12%) and associated higher taxa, were more abundant in winter, though not significantly at the phylum level, Firmicutes. Bacteroidetes were more abundant in summer. The Firmicutes:Bacteroidetes ratio tended to be higher in winter. The KEGG ortholog functions for fatty acid biosynthesis and linoleic acid metabolism (PICRUSt2) had increased abundances in winter.ConclusionsThe gut microbiota of homing pigeons varied seasonally, even under a constant diet. The correlations between immune indices and gut microbiota did not involve consistently specific immune indices and included only one of the two immune indices that showed seasonal differences, suggesting that immune competence may be an unlikely link between day length and gut microbiota. The correlations between gut microbiota and metabolism indices, the higher Firmicutes:Bacteroidetes ratio in winter, and the resemblance of the summer-winter differences in gut microbiota with the general temperature effects on gut microbiota in the literature, suggest that temperature partly drove the summer-winter differences in gut microbiota in homing pigeons.