Voortplanting by Eudrilus eugeniae (Oligochaeta) en die invloed van dieldrien op aspekte daarvan

Abstract

REPRODUCTION OF E. EUGENIAE (OLIGOCHAETA) AND THE INFLUENCE OF DIELDRIN.

The reproductive organs of the tropical vermicomposting earthworm species Eudrilus eugeniae was investigated. The ovaries and oviducts contain sperms, thus making it highly probable that fertilisation is internal. Spermatogenesis was studied at the ultrastructural level. Spermatogonia, spermatids and mature sperm are described. The general steps of spermatogenesis in E. eugeniae are basically similar to those found in many other annelids. An ultrastructural study of the mature sperm of E. eugeniae showed an elongated sperm cell, typical of the Oligochaeta. From SEM studies could be seen that the sperm possesses a very long, well developed flagellum with a typical "corkscrew" head. TEM studies showed the presence of a characteristic vesicle-type acrosome, cylindrical nucleus and spirally curved mitochondrion with six lobes. The flagellum have a typical 9+2 micro-tubule arrangement. During the present study the influence of the organochlorine, dieldrin, on the reproduction of E. eugeniae was investigated. This was done by exposing adult, clitellate specimens to the toxin. The contact filter paper method was used, and a number of replicates of the worms were exposed for 48 hours to concentrations of 0,154; 0,462; 0,77 and 1,54μg/cm-2 of dieldrin. The exact amounts of dieldrin which had penetrated the bodies of the worms were determine by means of gas chromatography. In comparison to the "normal" spermatosoa of the control group, no changes in sperm morphology in specimens exposed to 0,154 or 0,462μg/cm-2 were observed. In the sperm from the higher concentration exposures, however, the TEM work showed definite damage to the nuclei of a number of sperm (up to 10% in the case of the 1,54μg/cm-2 exposure). Under the SEM the sperm from the two lowest concentrations also appeared normal, but an abnormal curling and folding of the sperm flagella was observed in a number of spermatosoa of the worms exposed to the higher concentrations of dieldrin. The gross damage observed in the nuclei of some of the spermatosoa might directly damage the genetic material within the spermatosoa and this could seriously influence reproduction or cause malfunctions in offspring if these sperm remained viable. The effect of malfunction of the flagella on the other hand could have an effect on fertilization. Further experimental work is, however, needed to determine the effect of dieldrin on these processes of reproduction.