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The role of male forearm crust odour in fringe-lipped bats (Trachops cirrhosus)


Chemical signals can play important roles in communication, and this is especially true for social mammals such as bats. Male fringe-lipped bats (Trachops cirrhosus) produce an odorous substance on their forearm, called forearm crust. Only adult males with descended testes produce forearm crust. This is thus a sexually dimorphic odour, which suggests that it is a sexually selected trait. Since males lack a specific gland on their forearm we sought to identify the source of the forearm crust. Our second aim was to test female and male preference for this trait. Based on gas chromatography and mass spectrometry analyses we tentatively identified several compounds that were exclusive to the forearm crust. We found that the chemical composition of the forearm crust was not mainly composed of chest gland secretions or urine. We conducted a y-maze odour preference experiment to test whether adult females and reproductive males preferred the odour of a male with forearm crust compared to the odour of a male without forearm crust. Contrary to our prediction we found that females did not approach the scent of a male with forearm crust more frequently than the scent of male without forearm crust. We found that males with forearm crust, however, preferred the odour of males without forearm crust. Overall our results suggest that in this Neotropical bat species, reproductive males could use odorous signals in the forearm crust to mediate interactions between reproductive males and potentially avoid costly competition for mates or aggression. In sum, our results shed light on the role that chemical mediated signals can play in mammalian social behaviour.