Population and reproductive patterns of the Neotropical planarian Girardia capacivasa (Platyhelminthes, Tricladida), and the influence of seasonality on its life history

Abstract

The biology of Neotropical freshwater planarians (Platyhelminthes) is almost unknown compared with that of their Holarctic relatives. In this paper, we 1) studied the sequence of development of the reproductive system of Girardia capacivasa Sluys & Kawakatsu, 2005 (Dugesiidae), to estimate the onset of sexual maturity, applying the logistic regressions for the first time in flatworms; and 2) assessed reproductive and population patterns of this freshwater flatworm, and their responses to water temperature variation in a temperate Neotropical stream. These appraisals allowed us to test if the life history traits of freshwater planarians are similar in regions with marked temperature seasonality. According to the degree of development of the gonads and copulatory apparatus the development of the reproductive system was classified in five stages. The estimated size at the onset of sexual maturity was 12 mm. We found no relationship between the density of G. capacivasa and temperature, but planarians were more gregarious in warmer months. The largest planarians were recorded in cold months. The reproductive effort during the warm season was higher, but cocoons and juveniles were found throughout the study period, indicating continuous reproduction. Hence, the temperature variation recorded in the study area was not a limiting factor for breeding but influenced the body size and spatial distribution pattern of G. capacivasa.