Meeting Abstract
Diploid populations of Lumbriculus we have collected from the littoral regions of lakes and sloughs in the upper Midwest states of Minnesota, Iowa, Wisconsin, and Montana demonstrate a sexual mode of reproduction during the summer months. From mid-April through mid-August, collected worms have reproductive structures including atria, testes, ovaries, sperm sacs, male and female funnels, and spermatheca and produce cocoons containing viable embryos. Histological sections of the worms stained with hematoxylin/eosin show the presence of sperm in spermatheca, suggesting that cross-fertilization is occurring in these hermaphrodites. To obtain more direct evidence of outcrossing, worms showing reproductive structures were incubated with Hoechst 33342. This DNA stain penetrated into the worms, labeling a variety of cells including sperm. Uptake of the stain by sperm heads was verified using tissue sections of worms embedded in gelatin/albumin. Fluorescently labeled sperm were observed in sperm sacs, testes, and atria. Labeled worms were then incubated with unlabeled worms for 2-5 days. Some pairings resulted in formation of cocoons containing viable embryos, indicating that the labeling with Hoechst stain did not disrupt the ability of the sperm to fertilize eggs. Detection of labeled sperm in homogenates from unlabeled worms following their incubation with labeled worms suggested that outcrossing had occurred. To substantiate these results, tissue sections are being examined to determine if the transferred, labeled sperm are localized within the spermatheca of recipient worms.
