When eating a prey is risky: Implications for predator diel vertical migration

Abstract

Diel vertical migration (DVM) is a common behavior in zooplankton to avoid visual predation as well as potentially hazardous light wavelengths. In deep transparent lakes of Patagonia, the dark pigmented mixotrophic ciliate Stentor araucanus inhabits the upper layers of the epilimnion and is resistant to ultraviolet radiation (UVR). Here, we investigated if the ciliate pigment called stentorin increases oxidative stress in its predators. We studied the DVM behavior of Mesocyclops araucanus and the presence of stentorin in field‐collected copepods and evaluated in the laboratory the rate at which the copepod releases stentorin. S. araucanus has a C : P ratio ∼ 170 (atomic), which is one half of that of the bulk seston of the lake resulting in a very good food source in a system with very low food quality. Compared to an alternative prey without stentorin, when feeding on Stentor, the copepod suffered high oxidative stress (increased glutathione S‐transferase activity) and the reduced glutathion levels increased from dark to visible and ultraviolet radiation. However, we also determined that exposure to only visible light was sufficient to cause oxidative stress. In the field, we observed that M. araucanus displays a larger amplitude DVM than other crustaceans, while the ciliate Stentor remained in the upper levels of the epilimnion. The DVM protects the copepods from stentorin‐induced oxidative stress during daytime. Our findings are the first to show that a compound of a zooplankton prey item can influence the vertical behavior of predators in order to minimize the negative effect.

Associations between Optical Properties and Mixotrophic Ciliates Abundances Using Remote Sensing Techniques in Two North Patagonian Lakes (Villarrica and Caburgua, 38ºS, Araucania, Chile)

“…Similar results about the same mixotrophic ciliates species abundances and trophic interactions, has been described for Argentinean north Patagonian lakes [6,7,[30][31][32]. The Argentinean lakes has more studies about interactions between bacteria and pyco-phytoplankton, for these lakes have descriptions of pyco-cianobacteria that are abundant in metalimnion zones [33] and other kind of bacteria [34,35].…”

Short term fluctuating temperature alleviates Daphnia stoichiometric constraints

“…All experiments were conducted in water baths in growth chambers at the selected temperature and subject to a photoperiod of 12:12 (light:dark) with dim light (4 µmol photon m −2 s −1 ). We used this light level for the illuminated phase of the experimental day cycle because during the day D. commutata migrating individuals are located in the hypolimnetic deep cold water, around the 1% surface irradiance 41 , 42 . All experiments began using neonates (< 12 h old) from adult females fed with algae grown in P-limited media according to each experiment.…”

“…In particular, D. commutata growth rates were negatively affected when C:P was higher than 350 36 and C:P over 550 limited their distribution 41 . The species displayed wide DVM (> 20 m) during which D. commutata experienced 10 °C of changing temperature (from 7 to 18 °C) 41 , 42 .…”

Mixotrophic ciliates in North-Patagonian Andean lakes: stoichiometric balances in nutrient limited environments

“…3) there is a strong photoinhibition for autotrophs (Villafañe et al, 2004) that causes low photosynthetic efficiency (Callieri et al, 2007). In addition, due to the UVR effect, plankton avoid upper layers during daytime (Alonso et al, 2004;Balseiro et al, 2007;Modenutti et al, 2018) with the exception of the pigmented ciliate S. araucanus (Modenutti et al, 1998;Modenutti et al, 2005). However, as a counterpart, light is not limiting for autotrophs at least up to ~30-40 m of the water column, and implies the development of deep chlorophyll maxima (DCM) located mainly in the metalimnion (Modenutti et al, 2013a).…”