Reproductive modes and life cycles of freshwater planarians (Platyhelminthes, Tricladida, Paludicula) from southern Brazil

Abstract

Abstract. Life cycles, ploidy levels, reproductive modes, and regeneration capacities of laboratory populations of the southern Brazil freshwater planarians Girardia tigrina and Girardia schubarti were studied. The mating behavior and life cycle of different populations from both species were analyzed regarding their karyotype, body size, modes of reproduction, and regeneration potential. Reproduction was evaluated according to fecundity, fertility, and fissiparity indices. In both species we observed that diploid planarians are ∼25% larger than triploid or mixoploid ones and that sexually reproducing populations have more offspring than asexual ones. Cocoon incubation time was shorter for G. tigrina, and G. schubarti showed a higher frequency of spontaneous malformations. G. tigrina was both more fecund (produced more cocoons) and more fertile (produced more hatchlings) than G. schubarti. The effects of alternative food sources (liver or egg yolk), demographic density, and water–salt concentration were evaluated in different populations of both species. All evaluated environmental factors had effects on fecundity and fertility indices and were more prominent for G. schubarti than for G. tigrina. Our data suggest that the populations of G. schubarti were more sensitive to environmental factors, and thus may be useful as bioindicators.