title: An Intermediate in the evolution of superfast sonic muscles.
abstract: BACKGROUND
  Intermediate forms in the evolution of new adaptations such as transitions from water to land and the evolution of flight are often poorly understood. Similarly, the evolution of superfast sonic muscles in fishes, often considered the fastest muscles in vertebrates, has been a mystery because slow bladder movement does not generate sound. Slow muscles that stretch the swimbladder and then produce sound during recoil have recently been discovered in ophidiiform fishes. Here we describe the disturbance call (produced when fish are held) and sonic mechanism in an unrelated perciform pearl perch (Glaucosomatidae) that represents an intermediate condition in the evolution of super-fast sonic muscles.
  
  
  RESULTS
  The pearl perch disturbance call is a two-part sound produced by a fast sonic muscle that rapidly stretches the bladder and an antagonistic tendon-smooth muscle combination (part 1) causing the tendon and bladder to snap back (part 2) generating a higher-frequency and greater-amplitude pulse. The smooth muscle is confirmed by electron microscopy and protein analysis. To our knowledge smooth muscle attachment to a tendon is unknown in animals.
  
  
  CONCLUSIONS
  The pearl perch, an advanced perciform teleost unrelated to ophidiiform fishes, uses a slow type mechanism to produce the major portion of the sound pulse during recoil, but the swimbladder is stretched by a fast muscle. Similarities between the two unrelated lineages, suggest independent and convergent evolution of sonic muscles and indicate intermediate forms in the evolution of superfast muscles.
authors: Institute of Marine Biology and Asia-Pacific Ocean Research Center, National Sun Yat-sen University, Kaohsiung 80424, Taiwan.
authors: Hin-Kiu
authors: HK
authors: Mok
authors: Laboratoire de Morphologie Fonctionnelle et Evolutive, Institut de Chimie, Université de Liège, - B6C, 4000 Liège, Belgium.
authors: Eric
authors: E
authors: Parmentier
authors: Institute of Marine Biology and Asia-Pacific Ocean Research Center, National Sun Yat-sen University, Kaohsiung 80424, Taiwan.|Department and Graduate Institute of Aquaculture, National Kaohsiung Marine University, 142 Hai-chuan Rd. Nan-tzu, Kaohsiung 81157, Taiwan.
authors: Kuo-Hsun
authors: KH
authors: Chiu
authors: Institute of Marine Biology and Asia-Pacific Ocean Research Center, National Sun Yat-sen University, Kaohsiung 80424, Taiwan.
authors: Kai-En
authors: KE
authors: Tsai
authors: Institute of Marine Biology and Asia-Pacific Ocean Research Center, National Sun Yat-sen University, Kaohsiung 80424, Taiwan.
authors: Pai-Ho
authors: PH
authors: Chiu
authors: Department of Biology, Virginia Commonwealth University, Richmond, VA 23284-2012, USA.
authors: Michael L
authors: ML
authors: Fine