For bats, love is blind – and increasingly loud
A recent study of bat mating behaviour addresses the question of whether female sexual preferences for high-pitched calls can be bad for the males
Rhinolophus mehelyi in northeast Bulgaria: in a study, the males had echolocation calls 30 kilohertz higher than the range expected for bats of this size. Photograph: Sebastien Puechmaille
Love at first sight is nice when you want to find a partner, but pity the lovelorn bat. It has to find the love of its life in complete darkness and make a choice on the basis of sound alone.
This means bats aren’t looking for a good mate: they are listening for one, says Prof Emma Teeling, director of the Centre for Irish Bat Research at University College Dublin. She and colleagues in Germany recently provided the first hard evidence that bats use their echolocation systems as a way to find and identify suitable mates.
Teeling is a world authority on bat genetics but she relied on ecological and behavioural studies as well as genes to show that female bats were making choices on the basis of how a male sounds. The higher the pitch the more the females like it, according to the results of the study, published in Plos One of which Teeling was the senior author.
The work also highlights a possible evolutionary cul-de-sac, given that this sexual rather than natural selection has the potential to select male bats with higher- and higher-pitched calls rather than bats that are healthy and would make sound genetic partners, says Teeling.
This evolutionary change is apparently already under way in a colony of horseshoe bats, Rhinolophus mehelyi, the researchers studied in Bulgaria. The males have echolocation calls that are 30 kilohertz higher than the range expected for bats of this size.
“The bigger the bat, the lower the call, based on the size of vocal cords, but these guys were 30 kilohertz too high,” says Teeling. “We wanted to know what was driving that: was it female mate choice playing a role?”
In part, their determination to get to the bottom of this arose 10 years earlier when lead author of the new paper, Dr Sébastien Puechmaille of the University of Greifswald in Germany and she were studying bumblebee bat colonies in Thailand and Myanmar. The Myanmar bats had a much higher-pitched call, usually a clear sign that this was a distinct bat species, but they seemed identical to the Thailand colony.
They could find no direct genetic connection between the two, and it looked as though natural selection had made the pitch of the Myanmar bats go higher. But having a higher-frequency call was assumed to be a major disadvantage, something that natural selection should have worked against. “The problem is, echolocation calls are used by bats for finding food and navigating the environment they live in,” says Teeling.
The higher the frequency, the shorter the echolocation call range. “They need sound waves to go far, so lower frequency is better. Basically they can ‘see’ farther.
“We were driven a bit mad by this. Most of the data said that echolocation calls were playing a role in mate choice, but we had not been able to prove that.”
Until now, that is. Their work at the German field station in Bulgaria, which added the efforts of co-author Dr Björn Siemers of the Max Planck Institute for Ornithology, brought more technologies into play. They caught bats with higher-pitched calls and assessed them for fitness, showing that despite their high-pitched calls they were “big and strong”, says Teeling. “They were able to overcome the [high-pitch] handicap like a peacock and its large tail.”