Zhao Z et al. (2023), Swing Regulates Movement Direction in the Sea C...

ECB-ART-52654

Animals (Basel) 2023 Nov 01;1321:. doi: 10.3390/ani13213388.

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Swing Regulates Movement Direction in the Sea Cucumber Apostichopus japonicus in the Presence of Food Cue: New Insights into Movement Patterns.

Zhao Z , Sun J , Yu Y , Ding P , Ding J , Chang Y , Zhao C .

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Regulating movement direction is essential in the locomotion of animals. Sea cucumbers, as eyeless animals, do not have eyes for the perception of the surrounding environment and food. They have a unique way of swinging their bodies when a food cue is detected, although they lack an important perceptual tool. The present study investigated the movement patterns of the sea cucumber Apostichopus japonicus in the absence of a food cue (experiment 1) and in the presence of a food cue (experiment 2). In experiment 1, we found that the movement of sea cucumbers was close to a linear motion (motion linearity 0.91 ± 0.01). In experiment 2, sea cucumbers most frequently adjusted the movement direction when being exposed to food (84 times/216 min), indicating that sea cucumbers adjusted the direction of movement in the swing state but not the motion state. In experiment 2, we found significantly lower time in the immobility state in the sea cucumbers in the presence of food cues compared to that of those without being exposed to food cues, and the frequency of the motion state in response to food cues was 1.6 times than that of those without food cue. This suggests that food cues cause the change in motion state in sea cucumbers. Swing frequency was 1.7 times higher in sea cucumbers exposed to food cues than that of those not exposed to food cues. Further, sea cucumbers in the presence of food showed significantly better performances in swing angle and swing velocity compared to those not exposed to food cues. This suggests that food cue significantly affects the swing state of sea cucumbers. Notably, the present study described the movement patterns of sea cucumbers when they detected food cues, and other factors (such as the detection of predators) need to be further studied. The present study provides new insights into the regulation of movement direction in eyeless organisms.

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References [+] :

Bracis, Memory Effects on Movement Behavior in Animal Foraging. 2015, Pubmed

	Figure 1. Schematic diagrams for experiments 1 (A) and 2 (B). A schematic representation of the path and three states of sea cucumbers (C).
	Figure 2. Duration of three states (A), movement speed (B), and displacement (C) of sea cucumbers in experiment 1. Duration of three states (D), movement speed (E), and displacement (F) of sea cucumbers in experiment 2. The asterisks * mean p < 0.05; The asterisks *** mean p < 0.001.
	Figure 3. Change in angle cosine between the front of sea cucumber and the center of food area during the foraging movement. The gray area represents the sea cucumber in the swing state, and the black solid point is the segmentation point of broken line (A). The linear distance represents the distance between sea cucumber and the center of food cue zone. The gray area represents that the sea cucumber is in the state of swing (B).
	Figure 4. The movement direction deviation angle of sea cucumbers was affected by motion state and swing state (A). The movement linearity in motion state and after swing state (B). Movement speed of the front body of sea cucumbers in experiments 1 and 2 (C). Swing angle of sea cucumbers in experiments 1 and 2 (D). Swing speed of sea cucumbers in experiments 1 and 2 (E). The asterisks * mean p < 0.05; The asterisks ** mean p < 0.01.