Abstract
Behavioral plasticity in animals allows for moment-by-moment behavioral adjustments to biotic and abiotic uncertainties in the environment. For most aquatic animals, reproduction involves gonadal development and other physiological changes, causing increasing demands in nutrients and energy for females. The aim of this report was to determine how the female sea cucumber, Apostichopus japonicus, accommodates increasing energy demands during reproduction by adopting a behavioral energy conservation strategy. Dynamic changes in feeding activity, total body mass, locomotor activity, energetic condition, and metabolic performance of the females were measured from the non-breeding stage up to the mature stage. Routine metabolic rate analysis showed that reproduction caused a significant increase in energy demands in the adult. However, reproduction also suppressed the appetite of adults resulting in decreased energy intake. Interestingly, combining time-lapse camera and behavioral analysis software, the results showed that sea cucumbers down-regulated their locomotor activities in order to conserve energy effectively. Energy budget analysis and unchanged cortisol level revealed that the reduction in motility offset the increased energy demand for reproduction while helping to maintain energy homeostasis in the maternal body. Altogether, our study suggests that plasticity in the locomotor behavior allows sea cucumbers to cope with the high energy demands of reproduction.
Highlights
Reproduction is one of the most important events of all organisms
Our study provides new insights into the interaction of locomotor behavior and energetic physiology during reproduction in sea cucumber
The total body mass of A. japonicus showed a continuous increase during reproduction (Figure 1A; Kruskal–Wallis test: H4 = 71.557, P < 0.001)
Summary
Reproduction is energetically costly (Speakman, 2008). Gonadal development, metabolic maintenance, behavioral thermoregulation, and brood care require the expenditure of considerable amounts of energy in many aquatic animals (Baeza and Fernández, 2002; Fossette et al, 2012; McBride et al, 2015; Duisan et al, 2021). Maintaining energy homeostasis is critical for development, growth, reproduction, and survival (Unniappan et al, 2020). As a response to variations in energy or nutrient demands at different life stages (i.e., reproduction), animals have evolved the capacity to adjust their behavioral and physiological functions in order to accommodate changing energy demands (Nie et al, 2015). Plasticity in physiological adjustment involves remodeling gut structure, and adjusting digestive strategy to increase digestive and absorptive efficiency (Krockenberger and Hume, 2007; Reiff et al, 2015). Behavioral adjustments may involve expanding the home range, increasing foraging time, and shifting prey choice to increase energy intake (Barclay, 1989; Rodríguez et al, 2010; Sokolov et al, 2014)
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