Life at the edge: Benthic invertebrates in high altitude Andean streams

High altitude Andean streams harbor a quite diverse benthic community represented by the major groups of invertebrates. Evidence is provided that abundant insect species have not been described taxonomically and that unique genotypes occur, probably as a result of the geological history of the Andes and the strong selection for high altitude tolerance. Cuticular pigmentation of larvae is demonstrated to form an inducible sunscreen against scorching UV radiation, but the pigment melanin is also effective in mitigating metal stress. Thus a single trait of the fauna enables species to cope with the combined stressor UV radiation and metal exposure from leaching rock. The only species from the stress tolerant chironomids that survives the most harsh condition of a metal-rich, UV blasted site is a non-identifiable chironomid, characterized as a new haplotype. The vertical zonation of insect fauna on the slopes of the Andes is strong and I identify multiple stress factors such as the mountainous oxygen regime, high UV radiation and metal leaching as drivers of the composition of benthic assemblages in high altitude Andean streams. It is concluded that selection is strong at all altitudes in the Andes, but is most evident at high altitude and high metal exposure: at ‘the edges of life’.