Hatchability of gemmules of two Neotropical freshwater sponges (Porifera: Spongillida)

Eclosão de gêmulas em duas esponjas dulciaquícolas neotropicais (Porifera: Spongillida) em diferentes águas continentais.

ABSTRACT

Inland waters experience extreme environmental conditions determining the evolution of several adaptive strategies of the fauna to these variable conditions. Freshwater sponges produce resisting bodies called gemmules that contain totipotent cells and specialized spicules (gemmuloscleres). Completely formed gemmules exhibit low metabolic rates and may become dormant during periods of environmental stress. Until now, few species had their hatchability tested against different environmental conditions. The purpose of the present study was to test the capacity of hatching gemmules of two freshwater sponge species (Heteromeyenia cristalina Batista, Volkmer-Ribeiro & Melão, 2007 and Radiospongilla inesi Nicacio & Pinheiro, 2011) from inland waters from different localities. Five assays were tested (A): A1 (water of sponge collection site); A2 (Pirangi River water); A3 (Araraquara Pond water); A4 (mineral water) and A5 (A1 after drying gemmules). For each assay, three replicates with 30 gemmules were used. The gemmules were observed daily during 30 days. Data analysis was performed using ANOVA and a posteriori Tukey test. Results showed that gemmules from both species submitted to A3 have not hatched, probably due to its very high conductivity. There was a significant difference between assays (A1, A2 and A4) and between species (F_{2, 12} = 77.2; P < 0.001). Comparison between A1 and A5 showed significant differences between both assays and species (F_{1, 8} = 27.5; P < 0.001). Radiospongilla inesi presented high hatching rate at all assays, while H. cristalina had a high hatching rate only on A1 and A5. Results clearly show that each species has a different capacity of hatching.

KEYWORDS
Dormancy; freshwater sponges; hatching; Spongillidae