Persistence of bat defence reactions in high Arctic moths (Lepidoptera)

We investigated the bat defence reactions of three species of moths (Gynaep hora groenlandica, Gynaephora rossi (Lymantriidae) and Psychophora sabini ( Geometridae)) in the Canadian Arctic archipelago. Since these moths inhabit the Arctic tundra and, therefore, are most probably spatially isolated fro m bats, their hearing and associated defensive reactions are probably usele ss and would therefore be expected to disappear with ongoing adaptation to Arctic conditions. When exposed to bat-like ultrasound (26 kHz and 110 dB s ound pressure level root mean square at 1 m) flying male Gynaephora spp. al ways reacted defensively by rapidly reversing their flight course. They cou ld hear the sound and reacted at least 15-25 m away. Psychophora sabini wal king on a surface froze at distances of at least 5-7 m from the sound sourc e. However, two out of three individuals of this species (all males) did no t respond in any way to the sound while in flight. Hence, we found evidence of degeneration of bat defence reactions, i.e. adaptation to the bat-free environment, in P. sabini but not in Gynaephora spp. Some Arctic moths (Gyn aephora spp.) still possess defensive reactions against bats, possibly beca use the selection pressure for the loss of the trait is such that it declin es only very slowly (perhaps by genetic drift) and there may not have been enough time for the trait to disappear. One possible reason may be that Arc tic moths have long generation times.