Persistence of Chironomids in Metal Polluted Andean High Altitude Streams: Does Melanin Play a Role? Raú l A. Loayza-Muro,* ,†,‡ Jenny K. Marticorena-Ruiz, † Edwin J. Palomino, § Camille Merritt, ‡ Milo L. De Baat, ‡ Maarten Van Gemert, ‡ Rudo A. Verweij, ∥ Michiel H. S. Kraak, ‡ and Wim Admiraal ‡ † Laboratory of Ecotoxicology, Faculty of Sciences and Philosophy, Universidad Peruana Cayetano Heredia, Av. Honorio Delgado 430, P.O. Box 4314, Lima 31, Peru ‡ Institute for Biodiversity and Ecosystem Dynamics, Faculty of Science, University of Amsterdam. Science Park 904, 1098 XH, Amsterdam, The Netherlands § Faculty of Environmental Sciences, Universidad Nacional ‘Santiago Antú nez de Mayolo’, Av. Centenario 200, Huaraz, Peru ∥ Department of Animal Ecology, Institute of Ecological Sciences, VU University Amsterdam, De Boelelaan 1085, 1081 HV, Amsterdam, The Netherlands * S Supporting Information ABSTRACT: In high altitude Andean streams an intense solar radiation and coinciding metal pollution allow the persistence of only a few specialized taxa, including chironomids. The aim of the present study was therefore to determine the mechanisms underlying the persistence of chironomids under these multiple stress conditions, hypothesizing that melanin counteracts both the adverse effects of solar radiation and of metals. Melanin was determined in chironomids from reference and metal polluted streams at 3000 and 4000 m altitude, being 2-fold higher at 4000 m compared to 3000 m, and 2-fold higher in polluted streams than in reference streams at both altitudes. The field observations were experimentally verified by assessing the combined effects of Cu and UV-B on the survival and melanin concentration in larvae of the model species Chironomus riparius (Chironomidae, Diptera). In laboratory exposures, the highest melanin concentrations were found in larvae surviving toxic Cu concentrations, but not in those exposed to the highest UV-B radiation. Pre-exposure to UV-B decreased the sensitivity of the larvae to UV-B and to Cu+UV-B. It is concluded that in the field, melanin may protect chironomids partially against both elevated metal concentrations and solar radiation, allowing them to persist under the harshest conditions in high altitude streams. ■ INTRODUCTION The tropical Andes encompass vast areas with altitudes above 4000 m, creating harsh environmental conditions, such as variable water temperatures, low oxygen levels, and a blistering solar radiation, that challenge the survival and persistence of aquatic biota. 1−3 Metal pollution may add further stress to life at high altitude, since in the Andes metals are continuously released by acid mine drainage and natural weathering of metal- rich bedrock. 4,5 The few studies evaluating the effects of increased acidity and metal concentrations in high altitude tropical 5,6 and temperate streams 7 have shown a reduction of invertebrate abundance and sensitive taxa richness, and a significant shift in community composition toward more tolerant taxa. 8 Andean high altitude streams above 3500 m are also exposed to intense ultraviolet radiation, due to a naturally thinner ozone layer over low latitudes and the more direct solar light incidence near the equator. 9 Especially UV-B (280−320 nm) influences the structure and functioning of aquatic communities by inhibiting plant production, 9 and altering the abundance 10 and distribution of sensitive invertebrate species, either directly or indirectly by influencing trophic interactions. 11 The effects of UV-B are especially prominent during summer months, when clear skies and low water levels render benthic communities more vulnerable to solar radiation. Benthic macroinvertebrates have evolved several defense strategies to reduce the damage caused by solar UV-B, including the accumulation or synthesis of photoprotective pigments, such as melanin, carotenoids and mycosporine-like amino acids. 12−15 Melanin is a broad spectrum pigment, produced de novo by animals, which absorbs UV-B directly and releases the excess of energy as harmless heat. 15,16 Recently, it was discovered that in vitro melanin has the capacity to sequester reactive metal cations, such as copper, zinc, and iron, 17−19 which are also key regulatory factors for its Received: July 10, 2012 Revised: November 28, 2012 Accepted: November 28, 2012 Published: November 28, 2012 Article pubs.acs.org/est © 2012 American Chemical Society 601 dx.doi.org/10.1021/es302779b | Environ. Sci. Technol. 2013, 47, 601−607