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

MODENUTTI, BEATRIZ E.; WOLINSKI, LAURA; SOUZA, MARIA S.; BALSEIRO, ESTEBAN G.

LIMNOLOGY AND OCEANOGRAPHY

AMER SOC LIMNOLOGY OCEANOGRAPHY

Año: 2018 vol. 63 p. 939 - 950

0024-3590

Diel vertical migration (DVM) is a commonbehavior in zooplankton to avoid visual predation as well as potentiallyhazardous light wavelengths. In deep transparent lakes of Patagonia, the darkpigmented mixotrophic ciliate Stentoraraucanus inhabits the upper layers of the epilimnion and is resistant toultraviolet radiation (UVR). The cyclopoid copepod Mesocyclops araucanus also inhabits these lakes and can feed on theciliate. Here we investigated if the ciliate pigment called stentorin increasesoxidative stress in its predators. We studied the DVM behavior of M. araucanus and the presence ofstentorin in field-collected copepods and evaluated in the laboratory the rateat which the copepod releases stentorin. We conducted feeding experiments withthis ciliate and an alternative prey without stentorin, subsequently exposingboth sets to different light treatments. We determined that S. araucanus has a C:P ratio ~ 170(atomic), which is one half of that of the bulk seston of the studied lake. Thismeans that, on an elemental basis, Stentorwould be a very good food source in a system with very low food quality. Whenfeeding on S. araucanus, the copepodsuffered high oxidative stress (as indicated by high glutathione S-transferaseactivity). Reduced glutathion levels showed that oxidative status of thecopepod fed on Stentor increased fromdark to visible and ultraviolet radiation. However, we also determined that exposureto only visible light was sufficient to cause oxidative stress. In the field, weobserved that M. araucanus displays alarger amplitude DVM than other crustaceans, while the ciliate Stentor remained in the upper levels ofthe epilimnion. The fact that Mesocyclopscan move along the water column via DVM protects the copepods from stentorin-inducedoxidative stress during daytime. Our findings are the first to show that acompound of a zooplankton prey item can influence the vertical behavior ofpredators in order to minimize the negative effect.