Can the hatchability of gemmules in differing environments explain the distribution of freshwater sponges?

Freshwater sponges produce gemmules, asexual structures that serve as dispersal propagules and resting bodies. However, the relationship between the physiology of gemmules hatching and the distribution of species has yet to be investigated. In this study, we tested whether the distribution of Radiospongilla inesi (found in different freshwater habitats) and Rosulaspongilla alba (restricted to mixohaline environments) could be related to the hatchability of their gemmules in different environmental conditions. Gemmules from both species were tested under 3 treatments: T1—water from the collection site of R. inesi; T2—mineral water; and T3—water from the collection site of R. alba. The generalized linear model with a quasibinomial distribution indicated significant differences among treatments and between species. Gemmules of R. inesi hatched in all treatments, whereas those of R. alba hatched only in T1 and T3. The gemmules of R. inesi developed into juvenile sponges in T1 and T2, and gemmules of R. alba only in T3. These findings suggest that the gemmules of the 2 species exhibit a distinct adaptive plasticity to cope with different types of waters. Although R. alba is cosmopolitan, in Brazil it is limited to mixohaline waters, indicating that gemmule adaptation to the physicochemical characteristics of the water plays an important role in determining species distribution.