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Listening for Love in the Darkness?

Publication Date: 31 July, 2014

 

Probably the most important decision in any animal’s life, including our own, is finding the best mate! If you make the wrong decision then this can have repercussions for generations. Your choice of mate enables the transfer and continuation of your genes and indeed can drive the evolution of a species. For humans, typically the first thing that attracts you to a potential mate are visual cues, how well or attractive a person looks. ‘Good-looks’ have shown to be indicative of ‘good-genes’ or better fitness, so this makes sense. Well imagine having to find a mate in total darkness? This is the ultimate challenge that bats face.

Of all mammals, bats are the hearing specialists. They use echolocation or sonar, to orient and detect prey in complete darkness, relying on the echo of their ultrasound calls to develop an acoustic image of their environment. Bat echolocation is considered to be one of the most fascinating yet least well understood modes of sensory perception. Unlike bird song, the primary role of echolocation in bats is for orientation and finding food. Little is known about its use in communication and mate choice. Indeed, only in the past decade has it been suggested that echolocation calls can actually encode information on sex, body size, age and its role in mate choice has never been tested.

In a novel integrative study led by Dr. Sébastien Puechmaille, University of Greifswald, Germany, Prof. Emma Teeling, University College Dublin, Ireland and PD Dr. Björn Siemers, Max Planck Institute for Ornithology, Germany to be published in PLOS ONE, the researchers tested the role of echolocation in mate choice. They showed for the first time that bats are indeed ‘listening’ for a good mate rather than ‘looking for one’. Combining ecology, genetics and behavioural observations of wild bats, this study showed that female Rhinolophus mehelyi horseshoe bats are using echolocation to choose a mate. The higher the frequency of the male’s call the more attractive the male is to the females. The higher the frequency of the male’s call the more, off-spring he will sire. Indeed, the male’s echolocation is like a ‘peacock’s tail’, the higher the frequency the more attractive the call. However, despite this sexual advantage, these higher frequency calls are considered to be less efficient for foraging, and ultimately are an ‘attractive’ handicap. The male might ‘sound’ better to females but he can’t hunt as optimally. It appears that the female’s preference for males with a higher echolocation call frequency may explain why this species echolocates at 30 kHz higher than expected, something that has puzzled scientists until now. This evolutionary ‘trade-off’ between efficiency and attractiveness moulds and constrains bat echolocation.

This study is the first to show the role of echolocation in mate choice and will become a reference for future studies. Its power comes from the integration of three different types of data, ecological, behavioural and genetics. These results highlight bats as a novel system in which to explore the role of sound in mate choice and the potential conflict between natural and sexual selection on specific traits in evolution.

This paper was published with Open Access in PLOS ONE on the 30th July 2014.

[Female mate choice can drive the evolution of high frequency echolocation in bats: a case study with Rhinolophus mehelyi; DOI: 10.1371/journal.pone.0103452]. It represents an Irish-German driven project, funded by an IRCSET-Marie Curie International Mobility Fellowships in Science, Engineering and Technology awarded to S.J. Puechmaille.