The evolutionary development of modern-day butterflies was so profoundly influenced by insect-eating bats that they could be credited with "inventing" day-flight in butterflies, suggests one University of Toronto researcher.
In a paper to be published in the Jan. 20 edition of Nature, Carleton University biology post-doctoral student Jayne Yack and University of Toronto at Mississauga zoology professor James Fullard studied ultrasonic hearing in nocturnal butterflies. They then examined the anatomies and behaviours of day-flying butterflies. The scientists suggest that bats have had such an impact on day- and night-flying butterflies that their defence and communication systems have specifically evolved to protect them from these natural predators.
"Bats are major predators of night-flying insects, and this research points to the intense pressure on all nocturnal insects to evolve methods of detecting and avoiding insect-eating bats," says co-author Fullard. "With respect to butterflies, the majority of them switched their activity from night to day, thereby avoiding bats altogether. But for some rare species of nocturnal butterflies, the evolution of ultrasound-sensitive ears means that these insects have developed and been able to use this sensory defence to stay alive during the night."
On Barro Colorado Island in Panamá, Yack and Fullard found night-flying butterflies that possess ears on their wings that detect calls used by bats to locate and track prey. When the researchers exposed the nocturnal butterflies to simulated ultrasonic stimulus - such as the type given off by bats - the insects exhibited bat-evasion flight manoeuvres characterized by steep dives, climbs or up- or down loops and spirals. Until now, it was believed that ultrasonic hearing was a common defence and communication mechanism for moths and other nocturnal insects but not butterflies.
"The discovery of ultrasonic hearing in this species of night-flying butterflies in Panamá is quite remarkable," says Fullard. "Clearly, bat predators imposed a great selection pressure on the evolution of ears in this type of butterfly."
By and large, butterflies are predominantly day-flying, say the researchers. It was thought that the daytime behaviour of butterflies was enough to protect them from bats. However, day butterflies have evolved highly developed visual systems for communication and to detect other types of predators that hunt during the day.
This study was funded by the Natural Sciences and Engineering Council of Canada.
CONTACT:
Prof. James Fullard
U of T at Mississauga Dept. of Zoology
(905) 828-5416
jfullard@credit.erin.utoronto.ca
Journal
Nature