CICLO DE VIDA DE DERO (AULOPHORUS) COSTATUS MARCUS, 1944 (TUBIFICIDAE, OLIGOCHAETA) EN UN CUERPO DE AGUA CON VEGETACION FLOTANTE EN LOS TALAS, ARGENTINA

Abstract

The life cycle (March 1996-March 1997) of Dero (Aulophorus) costatus was studied in a vegetated pond located at Los Talas, Argentina. A change in the composition of the vegetation cover -developing Azolla sp- produced the displacement of Allonais lairdi by the species here studied. Inmature, mature and asexually reproductive specimens, forming chains of two zooids, were colected. Length, wet and dry weight (65 ° C, 24 h) of the organisms were registred. The spatial dispersion of the individuals, analyzed according to Morisita's Index, showed a random distribution. The population density fluctuated during the study (1.58 to 101.97 ind./g.d.w.vegetal.m2) due to an asexual reproduction, and two peaks of abundance were registred, in April, after a period of intense asexual reproduction and in December. The abundance was correlated with the water temperature (Pearson coefficient r = 0.5906, p< 0.05) and especially with the plant biomass (r = 0.9211, p< 0.001). The organisms sexually mature were found in spring and at the beginning of summer (from October to January), comprising a low proportion (4.86 %) of the population. Based on the sizes and weights of the individuals measured, the sucession of three cohorts was estimated: the first one developed from October to November (including the period of sexual maturation of the organisms), a second one from December to February and the last one in March.