Mutually exclusive muscle designs: the power output of the locomotory and sonic muscles of the oyster toadfish (Opsanus tau)

Animals perform a vast array of motor activities. Although it has generally been accepted that muscles are well suited to the function that they must perform, specialization for performing one function may compromise their ab ility for carrying out another. We examined this principle in the toadfish muscular system: slow-twitch red and fast-twitch white myotomal muscles are used for powering swimming at relatively low frequencies, while the superf ast swimbladder muscle powers mating calls by contracting at 100 Hz. We mea sured muscle power output over a wide range of frequencies. The red and whi te locomotory muscles could not generate power over ca. 2.2 and 12 Hz, resp ectively and, hence, could not power sound production. In contrast, the swi mbladder muscle has many specializations that permit it to generate power a ( frequencies in excess of 100 Hz. However, these specializations drastical ly reduce its power output at low frequencies: the swimbladder muscle gener ated only one-twentieth of the power of the red muscle and one-seventh of t he power of the white muscle at the frequencies used during swimming. To ge nerate the same total power needed for swimming would require unfeasibly la rge amounts of swimbladder muscle that could not fit into the fish. Hence, the designs of the swimbladder and locomotory muscles are mutually exclusiv e.