CASE 7 PREDATOR–PREY: A GAME OF LIFE AND DEATH

A notable feature of most animal nervous systems is that nervous system tissue, including specialized sense organs such as eyes, becomes concentrated at one end of the body. For example, the paired ganglia and eyespot of the flatworm are located at one end of its body, as are the brain and sense organs of the earthworm, squid, and insect, as shown in Fig. 35.3. The concentration of nervous system components at one end of the body, defined as the “front,” is referred to as cephalization. Cephalization is a key feature of the body plan of most multicellular animals, including all vertebrates.

Cephalization evolved independently multiple times in different animal groups and is therefore thought to confer certain advantages. Cephalization is thought be an adaptation for forward locomotion because it allows animals to take in sensory information from the environment ahead of them as they move forward. In addition, the nearness of the sensory organs to central ganglia or the brain makes it possible to process this information quickly to enable a suitable behavioral response. As the quality and amount of sensory information taken in increased, brain size and complexity increased. Cephalization is also considered to be an adaptation for predation, allowing animals to better detect and capture prey.

Although cephalization is a feature of many animals, it has been particularly well studied in vertebrates. In vertebrates, the brain, many sense organs, and mouth are all located in the head. Vertebrates also evolved several novel features, including a jaw, teeth, and tongue. These are all thought to be adaptations for predation, or more generally the acquisition and processing of food.

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As a result of evolutionary selection for enhanced sensory perception and the ability to respond to important cues in the environment, the brain, sensory organs, and nervous system of many animals are complex in their organization. These are linked to more sophisticated abilities that allow for a broad range of behaviors. These abilities are critical to the success of both predators and prey and underlie the complex interactions that occur among members of a species when they mate, reproduce and disperse, and care for their young.