Orienting and avoidance turning are precisely computed by the predatory sea-slugPleurobranchaea californicaMcFarland

Abstract

Computing the direction and amplitude of orienting and avoidance turns is fundamental to prey pursuit and risk avoidance in motile foragers. We examined computation of turns in the predatory sea-slug Pleurobranchaea californica, observing orienting and aversive turn responses to chemotactile stimuli applied to the chemosensory oral veil. We made seven observations: (1) the relation of turn angle/stimulus site on the oral veil was linear; (2) turn amplitudes increased with stimulus strength; (3) turn responses markedly overshot the target stimulus; (4) responses to two simultaneous stimuli at different loci were averaged to an intermediate angle; (5) stimuli could induce sequential turns in which the angles of the first and third turns were similar, a form of working memory; (6) turn direction was affected by appetitive state, so that animals with higher feeding thresholds tended to avoid appetitive stimuli; and (7) avoidance turns induced by mildly noxious stimuli were computed similarly to orienting, while differing in direction. These observations appear to outline a framework of behavior that could be employed for efficient tracking of odor trails, and which is regulated by decision mechanisms that integrate sensation, internal state and experience.

Putative lateral inhibition in sensory processing for directional turns

“…Chemotactile stimuli were prepared as gelatin pellets made with artificial seawater solutions of the appetitive stimulant betaine (trimethylglycine, Sigma-Aldrich; Gillette et al 2000) at concentrations of 0, 10 Ϫ3 , 10 Ϫ2 , and 10 Ϫ1 M; 10 Ϫ2 M was most often used, which elicits robust orienting turn responses in the intact animal (Yafremava et al 2007). A few drops of food coloring (Red #40) added to the gelatin improved visualization as in earlier behavioral experiments (Yafremava et al 2007). Gelatin pellets cut in 5-mm cubes were impaled on a Pasteur pipette for chemotactile stimulation of the oral veil.…”

“…Pellets were replaced after two or three applications. We aimed to simulate conditions of the behavioral experiments (Yafremava et al 2007), where pellets were placed immediately in front of the animal, which approached and touched the pellet with its oral veil. Here, animals were suspended immobile.…”

“…The computations for directional turns have been examined in invertebrates and vertebrates (Eaton and Emberley 1991;Ewert et al 1999;Levi and Camhi 2000;Murphey 1973;Teyke et al 1990;Yafremava et al 2007). However, intervening neural mechanisms of precisely directed orienting and avoidance remain for the most part to be described.…”

“…Elements of foraging and tracking were recently addressed in a study of turn behavior in the predatory sea slug, Pleurobranchaea californica, that tested the role of the anterior oral veil of the head (Yafremava et al 2007). It was found that the angle of the turn response to a punctate chemotactile stimulus on the animal's oral veil followed a linear relationship as the stimulus site was moved horizontally across, and increased with stimulus strength, similar to relations for turn angle/ stimulus site observed for directional behaviors in other invertebrates and vertebrates.…”

Animal escapology II: escape trajectory case studies

“…Iwasaki suggests that fleeing in a direction almost perpendicular to that of the attack may be more effective than fleeing away or towards the predator, because it may allow prey to get further away from the predator within a shorter time, and reduce the probability of a second attack (Iwasaki, 1993). In the sea slug Pleurobranchaea californica, appetitive or aversive chemotactile stimuli applied to the chemosensory oral veil triggered orienting and aversive turns, respectively, and the turn angles were linearly related to where the stimulus was applied to the animal's body (Yafremava et al, 2007). As in some other animals, e.g.…”