How to survive and persist in temporary freshwater? Adaptive traits of sponges (Porifera: Spongillida): A review

Spongillida (Porifera) colonized temporary freshwater bodies at the global level. To enhance colonization, survival, long-term persistence, and dispersal, most continental sponges display cryptobiosis as dormancy of resting bodies, i.e. asexual gemmules, 0.25–1 mm in diameter, containing staminal cells protected by a collagenous theca usually armed by siliceous skeletal spicules. High plasticity of body plan, physiology, life cycle, and reproductive modes are the key adaptive strategies of these sponges. The life cycle rhythm is characterized by the alternation of vegetative (active sponges) and cryptobiotic phases (dormant clones of gemmules). Hibernation or aestivation occurs cyclically according to the species and the environmental constraints of local hydrographic and climatic regimes. Ontogenetic constraints, e.g. chronic morphogenesis and clonal strategy by staminal cells, support a metamorphic process transforming the mother sponge functional body into gemmules (gemmulation) and vice versa (regeneration of the active sponge). During dormancy, the majority of these sponges are represented only by gemmules adhering to hard substrata, floating at the water surface, resting in the silty/sandy bottoms, or dispersing by flooding, animal carriers, and wind. A double functional role is performed by clonal gemmules to persist in situ and for dispersal in discontinuous continental water both in time and space.