In a fluctuating environment, organisms have to face and adapt to multiple threats acting simultaneously. One way to deal with a multiple threat scenario is to have traits that are only induced when needed. We focus on how common zooplankton (Crustaceae) handle and adjust pigmentation level in response to two simultaneously acting threats: predation and ultraviolet (UV) radiation. We quantify the fitness costs in using pigments (carotenoids, melanin) and other types of photo-protective compounds like MAAs (mycosporine-like amino acids) and if there are optimal choices in selecting different UV protection strategies. These aspects are studied under mechanistic lab. conditions and in lakes of temperate regions (southern Sweden; low UV threat/high predation) and in sub-arctic regions (northern Sweden, high UV threat/variable predation).

Results/Conclusions

We show different response among zooplankton where cladocerans mainly migrate vertically and copepods mainly change their content of photo-protective compounds (carotenoids, MAAs). Furthermore the blend of carotenoids and MAAs in the zooplankton is correlated to the present UV and predation threats. In a broader context the project will reveal knowledge about organisms with inducible plasticity in pigmentation and if they are less sensitive to large-scale environmental changes than their competitors and predators. We aim at disentangle mechanisms suggesting which organisms will dominate in future systems and, thereby, how biodiversity of aquatic systems may evolve.