Our paper showing that increased water temperature delays late-season phenology of mayfly was accepted today in Scientific Reports. In short, alternated regime of water temperature in rivers distunes insects inner clock. The larvae molted into subimago in late(er) autumn on the heated river. However, in late autumn temperature of water is already pretty low. Since cold temperatures prevent insects from emerging from water surface, they stayed there and most likely die….
Our parallel study (article in preparation) showed that these insects end up in stomachs of fish foraging near the water surface….
Conclusion: the projections of increases in global temperatures reach even 6.4 C degrees. Thus,reported mechanisms will potentially also occur in non-transformed watercourses, likely harming multivoltine insects populations.
Here is the abstract of the work, stay tuned for the full-text.
We analyzed the impact of increased water temperature on the late-season phenology of the mayfly (Baetis liebenauae). The River Gwda, unlike two other examined rivers (controls), has reservoirs along its length and thus, higher water temperature. Elevated water temperature prolonged summer diapause of the mayfly and shifted its life cycle to the later autumn: the last generation of mayflies started development later in the Gwda than in the control rivers. This translated into terrestrial stages (subimagos) of the insect being more abundant at water surface in the late autumn in the Gwda river than in the control rivers. The low water temperature in the late autumn hampered subimagos emergence from the water surface. Thus, the altered insect phenology at Gwda resulted in largely lost generation. However, the effect of reservoirs on the river water temperature was context-dependent, with the heating effect (and the impact on mayfly phenology) weaker in the year with lower average air temperature. In summary, warming blurred the environmental cue used by mayflies to tune their phenology, which resulted in a developmental trap. Since the projections of increases in global temperatures reach even 6.4oC, reported mechanisms will potentially also occur in non-transformed watercourses.