The life cycle ofEphydatia fluviatilisinvolves obligatory gemmule formation, a process strongly related to environmental conditions. A comparative investigation carried out on three populations of this species distributed along a climatic gradient, besides confirming a link between occurrence of gemmules and the severity of the habitat, evidences that gemmulation may be triggered even by endogenous stimuli. Indeed, in the northern area (Torrente Scrivia, Liguria), subjected to ice‐up and notable thermic and water‐flow fluctuations, the sponges hibernate for a long period and show shorter summer activity. In the southern area (Canale Tagliavla, Sicily), with a summer dry‐up, the active sponges are present during the winter, while the quiescence coincides with an aestivation. The persistence of this rhythm over the years is discussed, also in consideration of a speciation trend which points to a physiological reproductive barrier between these metapopulations. By contrast, in the intermediate area (Rio Bunnari, Sardinia), notwithstanding the lack of a summer dry‐up, the population shows a short summer quiescence. This life cycle, not depending on environmental factors, supports the hypothesis of an intrinsic rhythm inducing the quiescence ofE. fluviatilis.