Aspectos reprodutivos de Limnodrilus hoffmeisteri Claparede, 1862 e Branchiura sowerbyi Beddard, 1892 (Oligochaeta: Tubificidae)

Abstract

The organisms of the Oligochaeta Class are very important for the aquatic ecosystems, because they both participated in the organic matter mineralization and mixed the sediment, transporting substances deep into the surface, making them available to the biota. Among the limnic oligochaetes, stands the family Tubificidae, in which several species are widely recognized as indicators of organic pollution in aquatic environments (eg. Tubifex tubifex, Limnodrilus hoffmeisteri and Branchiura sowerbyi). The biology of these species has been researched in many countries, but in Brazil, despite the reports of occurrence, there is a lack of studies on their biologies. Thus, the present work aimed to gather information about biological attributes of L. hoffmeisteri and B. sowerbyi from Brazilian aquatic environments. To this end, two experiments involving L. hoffmeisteri were conduced, the first for assess the influence of the temperature on the reproduction and the second the influence of the biomass body on the production of cocoons. In spite of these experiments, two 30-individual populations, cultured in two granulometric fractions of sand and kept at 25 ± 1°C, were observed, during 25 weeks for verify the time spent for reach the maturity, growth and reproduction rate, for the two types of substrate. For B. sowerbyi, a 52-week observation was made for a 30-individual population, aiming to verify the same objectives describes for the other species. From the results, verified that the temperature has great influence on the reproduction of L. hoffmeisteri, a great production of cocoons was recorded at high temperatures. For some authors, this fact could be used as a parameter to indicate thermal pollution in temperate regions. Besides the temperature, biomass body also had an influence on eggs production, which is directly proportional to the weight of the organisms. From the observations during the 25 weeks, it was possible to determine (for fine sand and medium sand, respectively): hatching time (8 to 12 days, for both sediments), the mean specific daily growth rate (2.14 ± 0.75 e 2.04 ± 0.42%), maturation time (7.17 ± 2.93 e 9.00 ± 2.00 weeks) and the mean number of cocoons laid per adult per day (0.37 ± 0.22 e 0.23 ± 0.24 cocoons) for of L. hoffmeisteri. According the results, it isn’t possible to affirm that this species develops better in one of the substrates types tested. B. sowerbyi, according the results of the 52 weeks of observation, shown two annuals reproductive cycles, the first been more expressive, in the number of cocoons, than the second, since the posture of cocoons was constant during all the first cycle and inconstant during the second one. The results of the present work revealed important aspects of the biological attributes of two tubificids species

(L. hoffmeisteri and B. sowerbyi), little studied in Brazil, that should be incorporated into futures ecologies researches.