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.

Chromosome polymorphism and complements in populations of Girardia species (Platyhelminthes, Tricladida, Paludicola) from southern Brazil

“…The body size differences that were observed in the present study between diploids and total or partial triploids are notorious at the first glance. The specimens with total or partial triploidy cannot be differentiated merely by their external morphology, which is in agreement with the results of a quantitative analysis done by Knakievicz et al (2006). Aside from ploidy, no variability in the chromosome morphology was detected.…”

Polyploidy as a chromosomal component of stochastic noise: variable scalar multiples of the diploid chromosome complement in the invertebrate species Girardia schubarti from Brazil

“…G. schubarti and G. tigrina). The positive correlations of body criteria measurements of a group of specimens from Salvador do Sul with PV disagree with results of previous research for G. schubarti also from southern Brazil (Knakievicz et al, 2006) but are commensurate with research findings in other parts of the Americas (Gregory et al, 2000). The 2n chromosomal aggregate for G. schubarti was treated as 2n, 3n and 2n/3n mosaic with no consideration of any possible specific PV values for the mosaics.…”

“…Previous studies for this region, analyzing correlations of anatomic criteria with ploidal multiplicity (Knakievicz et al, 2006), employed specimens of two species (i.e. G. schubarti and G. tigrina).…”

Estado do conhecimento dos macroturbelários (Platyhelminthes) do Brasil

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