Adaptation to an acid environment in Chironomus riparius (Diptera, Chironomidae) from Smoking Hills, NWT, Canada

Abstract

The Smoking Hills in the North West Territories, Canada have burnt for centuries causing long term acidification of ponds in the vicinity. Chironomus riparius, a red chironomid larva dominated the bottom fauna in the ponds. It was investigated if it was the buffering capacity of the hemolymph rather than the oxygen binding capacity of its hemoglobin that gave these larvae a selective advantage and explained their high abundance. Canadian C. riparius larvae were compared with larvae of the same species from Sweden and with larvae of Chironomus plumosus and C. anthracinus also from Sweden. The Canadian strain of C. riparius survived 7 d exposure to pH 3.5 much better than the others. Titration curves on the hemolymph showed that the Canadian larvae had the highest buffering capacity. Within the pH range 6.0–7.0 it was 17–18 meq pH−1 1−1 as compared with 13–15 meq pH−1 1−1 for the others. The hemoglobin content of the Canadian larvae was found to be twice as high as that of the same species from Sweden.