Life cycle shifts in Baetis rhodani (Ephemeroptera) in the Norwegian mountains

Abstract

The life cycle of the widely distributed mayfly, Baetis rhodani, was investigated in Øvre Heimdalen, in the Jotunheimen Mountains of central southern Norway. B. rhodani displayed a shift in life cycle from univoltine below the lake, Øvre Heimdalsvatn (1090 m a.s.l.) to a two-year life cycle in the inflowing stream, Brurskardbekken (1100–1300 m a.s.l.). The day degree sum for the univoltine life cycle was 950 compared to 1500–1550 for the two-year life cycle. Larvae of B. rhodani grew rapidly during the ice-free period (June–October) with growth rates of 2.1–8.1% (mg/day), while growth rates were low during winter (0.3–0.5%). There was a positive correlation between growth (mg/day) and temperature (r 2 = 0.34, p = 0.02). Although larval growth and voltinism were influenced by water temperature, other factors such as food resources are likely to be important in mountain areas. The life cycle plasticity exhibited by B. rhodani has undoubtedly contributed to its success in colonising a wide range of running water habitats throughout Europe.