The Dynamics of Nematode Movement

Abstract

An important factor in the survival of animals is their ability to disperse and migrate in order to find a habitat in which their physiological charac­ teristics can function best, to locate and catch their food, and to find a mate. Animals accomplish such objectives by various types of locomotion such as swimming, crawling, flying, walking, and running, according to their anatom­ ical structure and the habitat in which they live. This review attempts to show how nematodes, particularly the plant-parasitic species, move in the various situations and environments they encounter during their life cycle. With a few exceptions (23, 41), nematodes move by undulatory propul­ sion in which a train of dorso-ventral waves is passed from the head to the tail. The waves are formed by the coordinated contraction and relaxation of the longitudinal muscles on the dorsal and ventral side of the body. The study of nematode movement may be considered as an exercise in how an animal equipped with such morphological and physiological properties can solve the numerous mechanical problems that face it during its life. Such a deliberately teleological approach allows useful questions to be asked, e.g., how does a nematode propel itself around in the egg before hatching? How does it vacate the egg? How does it migrate through the soil pore spaces and through thin water films? How does it penetrate the host? How does it move through the host's tissues? In all such activities the nematode has to push backwards against external resistances in order to exert force in a forward direction. Some animals can exert forces on external resistances in a variety of ways by using their limbs but without moving over the ground. Nematodes on the other hand, because of their morphological simplicity and lack of ap­ pendages, can exert a force against external objects in only one way, by undulatory propulsion. The locomotion of nematodes in any environment, or the exertion of pressure against barriers such as the egg shell during hatching, or the epidermis of the root during feeding or invasion, are thus basically the same process. The pattern of this behaviour may vary according to the environment, and, although the end results may be very different, the mecha­ nism is the same.