October 30, 2013
Convergent Evolution Provided Bats And Whales With Surprisingly Similar Echolocation Abilities
[ Watch the Video: Echolocation Frequencies Similar In Bats And Whales ]
April Flowers for redOrbit.com - Your Universe OnlineWhat could a 50 ton whale and a one gram bat have in common? They share a success story - both have developed the ability to use echolocation, a type of biological sonar, for hunting. A new study from Aarhus University and the University of Southern Denmark reveals that the biosonar of toothed whales and bats share surprisingly many similarities - even though they live in very different environments and vary extremely in size.
Out of all of nature's specializations, echolocation is one of the most successful. Approximately 25 percent of all living species of mammals, including 1,100 species of bats and roughly 80 species of toothed whales, use echolocation. But why have such vastly different animals developed the same technique? Bats and whales are no more closely related to each other than all other mammals descended from the same land vertebrates 200 million years ago, so the answer does not lie in kinship.
Rather, the answer is in the theory of convergent evolution - when almost identical features or developments happen in different species. Bats and toothed whales have developed the same functional characteristics through convergent evolution.
The research team studied the acoustic properties of the mechanism behind echolocation in bats and whales in the wild. Prior research into their ability to locate and catch prey has been based on laboratory tests, for the most part. Studies conducted in the wild provide a much more realistic picture of how the animals use echolocation so successfully.
"Our studies have shown that the sounds of bats and toothed whales are surprisingly similar. This is due to two things: First, all mammalian ears are developed in quite similar ways, and second, - which is the most surprising – the contradicting physical conditions in air and water along with the differences in size of the animals even out the differences, that you would expect in the sound frequency”, says Professor Annemarie Surlykke from University of Southern Denmark.
Bats are much smaller than whales. Accordingly, their prey is much smaller as well, meaning the bat needs to produce sounds with a very high frequency in order to achieve the same capacity to determine the direction and size of its prey. The effect of this higher frequency is partially cancelled by the fact that the sound is transported five times more slowly than it would be in water, and the sound waves are correspondingly five times shorter.
The research team found that toothed whales and bats produce echolocation signals in the same frequency range, from 10 to 200 kHz.
The whale has an advantage, operating in water instead of air, because the whale's "acoustic field of vision" is up to six times larger than the bat's. The area where an animal can "see" using echolocation is the acoustic field of vision - a sperm whale can echolocate prey nearly 1500 feet away, while a bat can locate pray only 6 to 30 feet away.
Each species has advantages. Bats fly fast and cover nearly one echolocation distance per second. This means they often spend less than a second detecting and catching their prey. In contrast, whales have a much greater echolocation distance and move much slower - giving them more time to pick up information and select their prey more carefully. The researchers say that this might explain why bats do not seem picky with their prey, while toothed whales are very selective. The bat simply does not have time to choose, so it selects the fast, easy choice.
Both whales and bats emit a series of buzzing sounds as they approach their prey in the last part of the hunting phase. These buzzing sounds are weak and short sounds that pulse at very short intervals, in a way similar to strobe lights. Scientists do not yet fully understand this complex mechanism. When the animal emits sounds and listens for the resulting echo, they exert a tight control so that they can adjust these sounds exactly to their and their prey's speed. If the buzzing sounds are emitted too fast, they will not have time to listen for the echoes - if they emit the buzzing too slowly, they risk hitting obstacles on the fly.
"The mechanism must play a key role but we do not yet know exactly which one," says Professor Peter Teglberg from Aarhus University. "There is a need for further studies and fortunately new technologies make it possible to track animals in the wild, study their behavior and compare these results with the knowledge we have from the laboratory”.
The results of this study were published in the journal Physiology.