Senses & Sensibility: Predator-Prey Experiments Reveal How Fish Perceive & Respond to Threats

Abstract

The predator-prey relationship is one of the most recognizable and well-studied animal relationships. One of the more striking aspects of this relationship is the differential natural selection pressure (Table 1) placed on predators and their prey. This differential pressure results from differing costs of failure, the socalled life-dinner principle (Dawkins & Krebs, 1979). If a predator fails to catch a prey item, it simply goes hungry; if a prey item fails to escape a predator, its life is usually over. This strong selection pressure on prey has led to a diversity of defensive adaptations, such as camouflage, poison, and armoring. Here we describe a two-part laboratory experiment (developed as part of Vassar College's Neuroscience and Behavior program curriculum) designed to examine two putative defensive adaptations in an aquatic predator-prey system: multimodal predator detection systems and the fast-start escape response. Aquatic prey species have multiple senses available to them with which to detect the presence and activity of predators. One of these, the lateral line system, is mechanosensory and allows fish to detect objects moving near them in the water; this system, however, offers limited information about who or what is causing the water to move. Fish have a keen sense of vision that is used in a variety of contexts, including foraging, mating, and predator identification and avoidance; however, vision has limited utility at long distances underwater, due to water's physical properties. Fish also have acute chemosensory abilities. A fish's sense of smell is useful at longer distances than a fish's visual sense and in a wider array of situations, such as murky water or other low-light conditions. By documenting a prey individual's response to threatening stimuli under a variety of contexts, we can explore how fish respond to multiple sensory inputs and which senses take precedence in a given situation. Once a predator has been detected, prey species offer an array of behavior responses. One of the best-studied prey responses is predator inspection. In both wild and laboratory conditions, researchers have observed that, somewhat counter-intuitively, prey fish species tend to move towards predators. The presumption is that individuals are attempting to gain information about potential threats (Magurran & Seghers, 1990; Dugatkin & Godin, 1992). Inspection tendency varies by group size, predator identity, and on geographic location in the wild (e.g., high versus low-predation regions). Another prey response is the fast-start escape response, which is a rapid burst of movement away from a negative or threatening stimulus, such as an attacking predator. The fast start is displayed by an extraordinary diversity of fish species (Hale et al., 2002) and its kinematics, neurophysiology, and biomechanics have been well studied (e.g., Wakeling & Johnston, 1998; Domenici & Blake, 1997). As a consequence, this escape behavior presents an excellent platform for the simultaneous study of many aspects of animal biology. Here we describe a two-part experiment. The first part of the experiment examines three phenomena: * how prey detect the presence of a predator * how prey respond to the presence of a predator * whether prey response to predator presence is dependent on which sensory system the prey uses to detect the predator. The second part of this experiment examines, using highspeed videography: * the importance of the fast-start escape response in escaping threatening stimuli * whether the speed of the fast-start escape response differs with differing levels of threat. Study Organisms & Statistical Context The Trinidadian guppy (Poecilia reticulata) and the pike cichlid (Crenicichla alta) represent an ideal species dyad for classroom or laboratory studies of predator-prey interactions. First, the ecological and evolutionary interactions between the two species are well documented (Reznick & Endler, 1982; Magurran et al. …