Interacting effects of sex and age on immune responses in a polygynous bat with male-biased mortality

Bats have attracted considerable recent interest for their extraordinary longevity and ability to withstand infection by a range of pathogens without major harm. However, few studies have examined immune responses as a function of age, sex, or social status. We investigated sources of individual immune variation by comparing whole-blood transcriptomes of wild greater spear-nosed bats, Phyllostomus hastatus, before and after ex vivo exposure to lipopolysaccharide, a membrane component of gram-negative bacteria. This species exhibits an extreme harem-polygynous mating system, which has pervasive consequences on life history traits, including male-biased mortality. We observe clear differences in immune responses, with males and older bats each mounting stronger inflammatory responses. Males also show steeper patterns of age-related variation in immune profiles, suggesting their earlier mortality is associated with accelerated immunosenescence. We did not detect largescale differences in immune responses between males of different social status, suggesting that--unlike in many primates--immune variation is not strongly influenced by social adversity. Our findings support recent calls for a more nuanced approach to understanding immune adaptations in bats that considers the diverse ways in which species and individuals differ in ecology, resource allocation, and selection.