Abstract
BackgroundEven subtle changes in environmental factors can exert behavioral effects on creatures, which may alter interspecific interactions and eventually affect the ecosystem. However, how changes in environmental factors impact complex behaviors regulated by neural processes is largely unknown. The freshwater planarian Dugesia japonica, a free-living flatworm, displays distinct behavioral traits mediated by sensitive perception of environmental cues. Planarians are thus useful organisms for examining interactions between environmental changes and specific behaviors of animals.ResultsHere we found that feeding behavior was suppressed when the concentration of ions in the breeding water was low, while other behaviors were unaffected, resulting in differences in population size. Notably, the decline in feeding behavior was reversed in an ion-concentration-dependent manner soon after the planarians were moved to ion-containing water, which suggests that ions in environmental water rapidly promote feeding behavior in planarians. Moreover, the concentration of ions in the environmental water affected the feeding behavior by modulating the sensitivity of the response to foods. Finally, we found that calcium ions in the aquatic environment were required for the feeding behavior, and exposure to higher levels of calcium ions enhanced the feeding behavior, showing that there was a good correlation between the concentration of calcium ions and the responsiveness of planarians to foods.ConclusionsEnvironmental calcium ions are indispensable for and potentiate the activity level of the feeding behavior of planarians. Our findings suggest that the ions in the aquatic environment profoundly impact the growth and survival of aquatic animals via modulating their neural activities and behaviors.
Highlights
Even subtle changes in environmental factors can exert behavioral effects on creatures, which may alter interspecific interactions and eventually affect the ecosystem
The results showed that planarians cultured in Kanatani water, tap water, and 0.05% artificial seawater (ASW) ingested substantial amounts of foods, the food intake of planarians grown in 0.005% ASW and 0% ASW/pure water was much lower (Fig. 1a)
Comparison of the feeding indexes indicated that a low concentration (0.005% ASW) or the absence (0% ASW/pure water) of ions significantly reduced the food intake, there were no significant differences among planarians in the other breeding waters examined (Fig. 1b)
Summary
Even subtle changes in environmental factors can exert behavioral effects on creatures, which may alter interspecific interactions and eventually affect the ecosystem. Planarians are well known for their remarkable regenerative ability [4,5,6] Due to their unique physiological traits and phylogenetic position, planarians have been extensively used as experimental animals in the laboratory for investigations in a wide variety of biological fields, such as regenerative (2019) 5:31 machinery, dynamics of stem cells, organogenesis, neuroscience, reproductive strategy, and animal evolution. The degree of this lithium-induced malformation is modulated by the competitive effects of sodium and potassium ions in the water in which planarians live [15] These findings suggest that ions in the environmental water may impact planarian physiology; how ions in the aquatic environment affect planarian behaviors subject to neural regulation remains obscure
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