Bioaccumulation of photoprotective compounds in copepods: environmental triggers and sources of intra-specific variability.

29. ZAGARESE, HE., GARCÍA, PE, DIÉGUEZ, MC & FERRARO M A.

San Francisco

Simposio; AGU Fall Meeting; 2012

AGU

Investigaciones Científicas y Técnicas (CONICET), Bariloche, Río Negro, Argentina. ABSTRACT BODY: Ultraviolet radiation (UVR) and temperature are two globally important abiotic factors affecting freshwater ecosystems. Planktonic organisms have developed a battery of counteracting mechanisms to minimize the risk of being damaged by UVR, which respond to three basic principles: avoid, protect, repair. Copepods are among the most successful zooplankton groups. They are highly adaptable animals, capable of displaying flexible behaviors, physiologies, and life strategies. In particular, they are well equipped to cope with harmful UVR. Their arsenal includes vertical migration, accumulation of photoprotective compounds, and photorepair. The preference for a particular strategy is affected by a plethora of environmental (extrinsic) parameters, such as the existence of a depth refuge, the risk of visual predation, and temperature. Temperature modifies the environment (e.g. the lake thermal structure), and animal metabolism (e.g., swimming speed, bioaccumulation of photoprotective compounds). In addition, the relative weight of UVR-coping strategies is also influenced by the organism (intrinsic) characteristics (e.g., inter- and intra­specific variability). The UV absorbing compounds, mycosporine-like amino acids (MAAs), are widely distributed among freshwater copepods. Animals are unable to synthesize MAAs, and therefore depend on external sources for accumulating these compounds. Although copepods may acquire MAAs from their food, for the few centropagic species investigated so far, the main source of MAAs are microbial (most likely prokaryotic) organisms living in close association with the copepods. Boeckella gracilipes is a common centropagic copepod in Patagonian lakes. We suspected that its occurrence in different types of lakes, hydrologically unconnected, but within close geographical proximity, could have resulted in different microbial-copepod associations (i.e., different MAAs sources) that could translate into intra-specific differences in the accumulation of MAAs when experimentally exposed to different combinations of radiation exposure and temperature. We exposed B. gracilipes individuals from two lakes (Verde: high elevation, fishless; Morenito: piedmont, with fish) to two radiation conditions (PAR+UVA vs. darkness) crossed with five temperatures (5, 8, 12, 16 and 20 C) for periods of 10 days. DNA fingerprinting (DGGE) revealed the existence of differences in microbial composition between the two copepod populations. The two populations differed in initial total MAAs concentration and composition. Exposure to PAR+UVR stimulated the accumulation of MAAs in individuals from lake Morenito and to a lesser extent in those from lake Verde. There were significant differences in the rates of MAAs accumulation between the two populations. More specifically, individuals from lake Morenito had a higher propensity to lose and gain MAAs that those from Lake Verde, which maintain a more stable MAA concentration regardless of the experimental conditions. Temperature affected the concentration of MAAs in individuals maintained in darkness. As expected, the individuals tended to lose MAAs at higher temperatures. Unexpectedly however, the lower temperatures stimulated the accumulation of MAAs, even when the copepods were in the dark. Thus, low temperature by itself may induce MAA accumulation.