Brown NAW et al. (2019), Plasticity in the antipredator behavior of the ...

ECB-ART-48735

Curr Zool 2019 Dec 01;656:685-695. doi: 10.1093/cz/zoy100.

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Plasticity in the antipredator behavior of the orange-footed sea cucumber under shifting hydrodynamic forces.

Brown NAW , Wilson DR , Gagnon P .

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Marine invertebrates that move too slowly to evade unfavorable environmental change may instead exhibit phenotypic plasticity, allowing them to adjust to varying conditions. The orange-footed sea cucumber Cucumaria frondosa is a slow-moving suspension feeder that is preyed on by the purple sunstar Solaster endeca. The sea cucumber''s antipredator behavior involves changing shape and detaching from the substratum, which might increase its probability of being displaced by water motion into an unsuitable environment. We hypothesized that sea cucumbers'' antipredator responses would be diminished under stronger hydrodynamic forces, and that behavioral strategies would be flexible so that individuals could adjust to frequent changes in water flows. In a natural orange-footed sea cucumber habitat, individuals lived along a pronounced hydrodynamic gradient, allowing us to measure antipredator behavior under different water flow strengths. We placed purple sunstars in physical contact with sea cucumbers living at various points along the gradient to elicit antipredator responses. We then repeated this procedure in a laboratory mesocosm that generated weak and strong hydrodynamic forces similar to those observed at the field site. Subjects in the mesocosm experiment were tested in both wave conditions to determine if their antipredator behavior would change in response to sudden environmental change, as would be experienced under deteriorating sea conditions. Antipredator responses did not covary with hydrodynamic forces in the field. However, antipredator responses in the mesocosm experiment increased when individuals were transplanted from strong to weak forces and decreased when transplanted from weak to strong forces. Overall, our results indicate environmentally induced plasticity in the antipredator behavior of the orange-footed sea cucumber.

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Genes referenced: LOC100887844

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	Figure 1. Procedure for experimental tests in the field. (A) An URSKI with weight and scale bar was placed close to a tagged orange-footed sea cucumber (Cucumaria frondosa). (B) After 40Â s of baseline video, a purple sunstar (Solaster endeca) selected haphazardly from a mesh bag containing 3 sunstars was placed gently on top of the sea cucumber. The sunstar stayed on the sea cucumber for 60Â s, untouched by divers. (C) The sunstar was removed. (D) 120Â s of post-predator video was recorded. Either the dive weight with orange tag attached or distinctive patches of red coralline algae carpeting the seabed (such as the patch to which the sea cucumber is attached in panel (C) were used as static reference points to correct body shape variability measurements (see the âMaterials and Methodsâ section for details).
	Figure 2. Setup for the mesocosm experiment. (A) Top-view schematic of the wave tank depicting the 2 sections, their dividers, and other components of the tank setup (see the âMaterials and Methodsâ section for details). (B) Sample video frame from the strongly agitated section. Darkly colored sea cucumbers are visible against the light tank. Small, numbered orange tags were attached to rocks and positioned directly next to each sea cucumber to keep track of their identities.
	Figure 3. Water flow acceleration by depth for 15 orange-footed sea cucumbers. Each open circle shows the median instantaneous acceleration at a given subjectâs location and the thick line shows the line of best fit among these points. The 2 thin solid lines are the lines of best fit for the 10th (lower line) and 90th (upper line) percentile values of the acceleration values calculated at each of the 15 subjectsâ locations, and the outermost dashed lines are the lines of best fit for the minimum (lower line) and maximum values at each of these locations. The closed circles are the median of the hourly mean flow accelerations at the 2 ends of the study site from the long-term data, and the associated error bars show the inter-quartile ranges (thick error bars) and ranges (thin error bars) for the long-term acceleration measurements.
	Figure 4. Effect of reciprocal transplants on the number of post-predator observation periods in which a subject detached from the substratum. Open squares connected by a dashed line represent subjects moved from strongly to weakly agitated conditions. Solid squares connected by a solid line represent subjects moved from weakly to strongly agitated conditions. Solid circles connected by a faded gray line represent control subjects moved to another location within the same environment (sham disturbance). Change in behavior (post-transplant â pre-transplant) was compared among the 3 transplant treatments with a 1-way ANOVA. Treatments with different letters are statistically different, as indicated by post-hoc, pairwise comparisons corrected for type I error (Holm 1979).

References [+] :

Adler, Inducible defenses, phenotypic variability and biotic environments. 1990, Pubmed