Motor control of tongue movement during prey capture in plethodontid salamanders

Abstract

Four species of salamander of the family Plethodontidae were examined using electromyographic (EMG) recording during prey-capture behavior to test the hypotheses that the tongue retractor, tongue protractor and jaw depressor muscles are activated simultaneously and in a stereotyped pattern, as was found in other salamanders, and to determine whether species with different tongue morphologies and tongue protraction abilities exhibit different motor control strategies. The results show that sequential activation was observed far more frequently than simultaneous activation; the jaw depressor muscle was activated first, followed by the tongue protractor and then the tongue retractor. Species with short, attached tongues (Desmognathus quadramaculatus and Plethodon jordani) showed simultaneous activation more often than species with long, free tongues (Pseudotriton ruber and Hydromantes supramontis), which showed strongly non-simultaneous activation. Most EMG variables showed no effect of prey-capture success, suggesting that sensory feedback is not involved in modulating the motor pattern during the prey-capture strike. Hydromantes supramontis was examined for modulation of its motor pattern in response to prey distance, and several EMG variables were found to be positively correlated with tongue protraction distance. The motor pattern of strongly non-simultaneous activation of antagonistic tongue muscles has evolved along with the evolution of long, free tongues in plethodontids. The variable motor patterns observed provide further evidence that amphibian feeding in general is not as highly stereotyped as has been previously thought.