Predator Chemical Cue Effects on the Diel Feeding Behaviour of Marine Protists

Abstract

We have assessed the effect of copepod chemical cues on the diel feeding rhythms of heterotrophic and mixotrophic marine protists. All phagotrophic protists studied exhibited relatively high diurnal feeding rates. The magnitude of the diel feeding rhythm, expressed as the quotient of day and night ingestion rates, was inversely related to the time that phagotrophic protists were maintained in the laboratory in an environment without predators. In the case of the recently isolated ciliate Strombidium arenicola, the rhythm was lost after a few months. When challenged with chemical alarm signals (copepodamides) from the copepod Calanus finmarchicus at realistic concentrations (0.6-6 pM), S. arenicola partially re-established diurnal feeding.Conversely, the amplitude of the diel feeding rhythm for the ciliate Mesodinium rubrum was not affected by copepodamides, although the 24 h integrated food intake increased by approximately 23%. For the dinoflagellates Gyrodinium dominans and Karlodinium armiger, copepodamides significantly reduced the amplitude of their diel feeding rhythms; significant positive effects on total daily ingestion were only observed in G. dominans. Finally, the dinoflagellate Oxyrrhis marina, isolated >20 years ago, showed inconsistent responses to copepodamides, except for an average 6% increase in its total ingestion over 24 h. Our results demonstrate that the predation risk by copepods effects the diel feeding rhythm of marine protists and suggests a species-specific response to predation threats.

Mixoplankton interferences in dilution grazing experiments

“…We noticed that irrespective of the light conditions, all species exhibited a diurnal feeding rhythm ( R. salina panels in Figs. 2 and 3 ), which is in accordance with earlier observations on protists (e.g., 29 , 57 , 58 ). The presence of light typically increased the ingestion rates.…”

“…Ideally, incubations would be started at different times of the day to capture the intricacies of the community dynamics on a diel cycle. Nevertheless, should the segmented analysis be impossible, we argue that the right time to begin the incubations would be during the night, as this is the time where ingestion rates by protozooplankton are typically lower (e.g., 29 , 57 , 58 , this study) and would, consequently, reduce their quota of Chl a in the system.…”

Thermal Acclimation and Adaptation in Marine Protozooplankton and Mixoplankton

“…Therefore, we cannot expect wild protists to behave the same way as our cultures. Clear evidence of this is the results of Arias et al (2021) , who found the ciliate S. arenicola lost its diel feeding rhythm after prolonged periods of laboratory cultivation and partially recovered it when exposed to predators chemical cues.…”

Predator cues target signaling pathways in toxic algal metabolome

“…Nevertheless, copepodamides might passively diffuse through phytoplankton cell membranes without causing substantial cell leakage, activating signaling pathways from within rather than via a membrane‐bound GPCR. The femtomolar‐to‐nanomolar sensitivity of phytoplankton to copepodamides (Selander et al 2015, 2019; Arias et al 2021) supports the involvement of signal amplification via secondary messengers.…”

“…However, only some zooplankton predators trigger particular defensive phenotypes (Senft‐Batoh et al 2015; Lundholm et al 2018) suggesting species‐specific recognition of predator cues. In the case of predatory copepods, a suite of taurine lipid‐derived metabolites called copepodamides (Selander et al 2015) appear to be the primary cue leading to induced resistance in various phytoplankton prey (Selander et al 2019; Arias et al 2021). The particular cocktail of copepodamide molecules produced by copepods varies based on their species and diet (Grebner et al 2019).…”