Behavioral evidence for cone-based ultraviolet vision in divergent bat species and implications for its evolution

ABSTRACT

We investigated the reactions of four bat species from four different lineages to UV light Hipposideros armiger (Hodgson, 1835) and Scotophilus kuhlii Leach, 1821, which use constant frequency (CF) or frequency modulation (FM) echolocation, respectively; and Rousettus leschenaultii (Desmarest, 1820) and Cynopterus sphinx (Vahl, 1797), cave and tree-roosting Old World fruit bats, respectively. Following acclimation and training involving aversive stimuli when exposed to UV light, individuals of S. kuhlii and C. sphinx exposed to such stimuli displayed conditioned reflexes such as body crouching, wing retracting, horizontal crawling, flying and/or vocalization, whereas individuals of H. armiger and R. leschenaultii, in most cue-testing sessions, remained still on receiving the stimuli. Our behavioral study provides direct evidence for the diversity of cone-based UV vision in the order Chiroptera and further supports our earlier postulate that, due to possible sensory tradeoffs and roosting ecology, defects in the short wavelength opsin genes have resulted in loss of UV vision in CF bats, but not in FM bats. In addition, Old World fruit bats roosting in caves have lost UV vision, but those roosting in trees have not. Bats are thus the third mammalian taxon to retain ancestral cone-based UV sensitivity in some species.