Combined effects of Cu and UVR on survival and melanin synthesis in Chironomus riparius larvae

The tropical Andes encompass vast areas with altitudes above 4000 m, where the combination of high UV radiation and metal pollution creates environments that challenge the survival and persistence of aquatic life. Since the pigment melanin counteracts the negative effects of
UVR, and has the additional ability to sequester metal cations, it has been hypothesized that melanin plays an important role in the ability of benthic invertebrates to persist under these harsh conditions. The aim of the present study was therefore to determine the combined effects of Cu and UVR on survival and melanin synthesis in Chironomus riparius larvae, by mimicking the extreme environment of high altitude Andean streams under laboratory conditions. It was observed that melanin production was induced by lethal Cu concentrations in the water as well as by exposure to UVR. The detrimental effects of Cu and UVR added up to multistress. Ninety-six hour pre-exposure to UVR decreased the sensitivity of the larvae to UV, but this was not due to an increase in melanin in the larvae. The observed responses to Cu and UVR may explain the persistence of chironomids under the most extreme metal and UV-B conditions in high altitude Andean streams.