Egg development in the mayflies of a Swiss glacial floodplain

Abstract

The duration and timing of egg development is crucial to the survival of invertebrates in glacier-fed rivers. The relationship between egg development and environmental conditions was investigated in 3 mayfly species, Baetis alpinus, Rhithrogena nivata, and Ecdyonurus picteti, in an alpine glacier-fed alluvial system. Field-collected eggs were reared in the laboratory at temperatures representing field conditions (1.5, 3, 5, and 7°C). Egg-incubation period and degree-days demand (DD) were determined, and hatching in the field was predicted from field temperature records. Egg development and temperature relationships for B. alpinus and R. nivata were documented for the first time. Baetis alpinus had synchronous egg development and high hatching success. Faster development in warmer habitats enabled it to hatch during favorable autumnal conditions. Ecdyonurus picteti had a very long development time that decreased slightly at higher temperatures. However, the variation in DD was considerable. The observed long and delayed hatching would favor successful development in unpredictable habitats at the low temperatures experienced in these glacial conditions. Rhithrogena nivata, one of the most extreme cold-adapted mayfly species, had a long egg incubation period, and success in development largely depended on the timing of hatching and discharge conditions. This species could exploit extremely unstable and cold habitats where other species are limited by low water temperatures.