Friday, February 6, 2015

Evolution of Echolocation in Bats: An Antagonistic Interplay between Natural and Sexual Selection

Date:  July 30, 2014

Source:  PLoS ONE

Institutions Involved:  Max Planck Institute for Ornithology, University College Dublin, Tabachka Bat Research Station, MTA-ELTE-MTM Ecology Research Group, Naturalia environnement, Tunis Superior Institute for Biological Applied Sciences, and Max Planck Institute for Evolutionary Biology

Summary:  Research suggests that sexual selection plays a role in the evolution of high frequency echolocation in bats, possibly against natural selection, according to a study published on July 30, 2014 in the open-access journal PLoS ONE by Sebastien J. Puechmaille and his colleagues. 

Animals generally use echolocation, or acoustic signals, as a means of communication.   Unlike bird songs or frog calls, bats are very interesting when studying the evolution of signaling systems because echolocation is used for both foraging (food detection) and communication.  While it was common belief that echolocation is influenced by ecology through natural selection alone, Puechmaille et al. investigated the role of echolocation calls with regards to sexual selection in bats. 

This study was conducted using 90 Rhinolophus mehelyi or Mehely’s horseshoe bat (75 females and 15 males) collected at two caves in North-Eastern Bulgaria.  This bat species was an ideal choice because unlike other species of the Rhinolophidae family that produce lower frequencies as they increase in body size, R. mehelyi differ greatly by producing frequencies higher than expected given their size.  Attributing this piece of information to sexual selection, researchers hypothesized that an individual’s echolocation peak frequency should be related to its body size and condition, and therefore indicate mate quality.  They predicted that females should prefer males with high frequency calls during the mating season.  As a result, males with high peak frequency should have a higher reproductive success, and therefore have higher relatedness with other members of the colony (more relatives). 

The experiments were performed in a one cubic meter box, lined with sound-absorbing foam.  The bat was placed on a listening perch (wooden basket) at an equidistant position from the two compartments, with each containing a speaker.  The set-up was also equipped with infrared light, and an infrared-sensitive camera to monitor the activity of the bat.  The assignment of low or high frequency playback to the left or right speaker was randomized before testing each individual. 

The data demonstrated that echolocation peak frequency is representative of body size and body condition, with the larger and heavier individuals have higher frequencies.  It was found that the female bats are more attracted to males with higher peak frequency during the mating season.  This result is in accordance with the theory of sexual selection that females prefer to mate with good quality males to produce fitter offspring.  Along with female mate choice, the researchers had observed a significant positive correlation between relatedness and peak frequency in male bats. 

The combination of behavioral, ecological, and genetic studies provided researchers with the first documented evidence that female bats indeed choose their mate based on echolocation frequency.  The ability of bats to precisely locate the source of acoustic signals even in complete darkness further establishes the idea that echolocation is essential for mating.  

Citation:

Puechmaille, S.J., I.M. Borissov, S. Zsebok, B. Allegrini, M. Hizem, S. Kuenzel, M. Schuchmann, E.C. Teeling, and B.M. Siemers. 2014.  Female Mate Choice Can Drive the Evolution of High Frequency Echolocation in Bats: A Case Study with Rhinolophus mehelyi. PLoS ONE 9(7): e103452. 

3 comments:

  1. I found it interesting how bats produce higher frequencies with increasing body size and weight. It was also fitting how you mentioned at the end that this study is supported since bats find mates in the dark.

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  2. I found it interesting that echolocation is used by bats as a measure of fitness. In fact, the parallel between natural selection and sexual selection related to echolocation is one that I have never read up on prior to this summary.

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  3. I found this study and write-up really interesting because it related to the main idea of the paper I researched, which is the sometimes antagonistic correlation between natural and sexual selection. I was also really fascinated in this particular study by the correlation between frequency and body size/weight. I had no idea that the two were related, but after reading your write-up, it makes sense that the two traits would go hand-in-hand, seeing as bigger bats might be considered the healthier and fitter kind, traits that a female would want to pass on to her offspring and also seeing as these bigger bats are the ones producing the higher frequencies that attract the females, proving -- like you said -- that echolocation is essential for bat mating.

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