Host-microbiota association in a migratory species: Constitutive humoral immunity in the partially migratory bat Leptonycteris yerbabuenae is linked to the gut microbiota in a sex-specific manner

The immune system and gut microbiota are interconnected components that play a key role in host health. The nature of this relationship in wildlife is under-explored, especially in migratory animals, which are exposed to diverse microorganisms that can impact their immune system, microbiota and health. This study explored the relationship between constitutive humoral immunity (bacterial killing-ability, BKA, and total immunoglobulin G concentration, tIgG) and the diversity and composition of gut microbiota (16S rRNA gene amplicons) in the lesser long-nosed bat Leptonycteris yerbabuenae. Males of this bat form resident populations whereas some females migrate to complete their reproductive cycle. Each sex harbored a distinctive fecal microbiota, yet no significant relationships were found between BKA and microbiota diversity, but tIgG was negatively correlated with Shannon's and Simpson's inverse indices in females and positively with the Shannon's index in males. Humoral immunity in both sexes was significantly related to fecal bacterial genera known to harbor immunostimulatory species, species linked to intestinal mucosa integrity, and infection-associated species. Other free-living and unclassified bacterial genera were associated with immunity in a sex-specific manner, highlighting the importance of novel and uncommon bacteria for immune activity in wildlife. These findings suggest that gut microbiota composition, and to a lesser extent diversity, are linked to constitutive humoral immunity in L. yerbabuenae. The distinct relationship exhibited by each sex suggests that migration and other sex-associated traits may be crucial to understanding the natural variation of immunity in wildlife.