Comparison of the filtration structures in South American Daphnia

Abstract

The third and fourth filtering limbs were studied in 16 Daphnia populations from South American lakes using scanning electron microscopy. The mesh sizes of the juvenile and adult Daphnia ranged from 100 to 1270 nm. Daphnia pulicaria from Ecuadorian lakes had the widest intersetular distances. In contrast, D. laevis, D. peruviana and D. obtusa from eutrophic ponds exhibited the narrowest adult mesh sizes, less than 300 nm. Three species from oligothrophic lakes exhibited narrow (100-436 nm) distances between the setulae. The filter area was measured by direct and indirect methods, the largest filtration area was found in Daphnia commutata (3.33 mm 2 ). Species from oligotrophic lakes had larger filter areas but all species showed a strong correlation between the increasing body size and filter area. Two clear types of relationships between filtering area and mesh size were recognized.