Feeding Patterns of Pelusios Castaneus (Chelonia: Pleurodira)

Abstract

The aim of this study is to describe the feeding patterns of the pleurodiran West African mud turtle Pelusios castaneus. The kinematics of feeding were studied for two types of prey (fish, snail) to provide a description of the feeding cycle and to determine whether kinematic patterns can be altered in response to prey size and type. High-speed film recordings (250 frames/s) of feeding cycles were evaluated. Five variables were measured and four velocities were calculated. The feeding cycle was divided into five phases: preliminar head fixation, final head fixation, final head approach, grasp followed by manipulation and a transport phase, and suction end position which is followed by swallowing. The turtle has the ability to modulate the feeding kinematics depending on prey type. Furthermore, two types of suction were distinguished, compensatory suction and inertial suction. While compensatory suction is used mainly for prey capture, inertial suction is needed during the manipulation and transport phase, and becomes more important the longer these phases last. A Ram-Suction-Index was used to show the relation between the ram and the suction component during the different phases of the feeding cycle. The results show that the smaller and less agile the prey, the more the turtles enhance the suction component of their feeding patterns. Hydrodynamically induced kinematic similarities in aquatic feeding of fish, larval aquatic salamanders and turtles were found, as well as differences that result from the fundamentally different morphological design of the feeding apparatus.