Evidence of hermaphroditism and sex ratio distortion in the fungal feeding nematode Bursaphelenchus okinawaensis.
Bottom Line: B. okinawaensis males successfully mated only with sperm-depleted old hermaphrodites, and the spermatid sizes of males were almost the same as those of hermaphrodites.B. okinawaensis is phylogenetically distant from established model nematodes such as C. elegans and is more closely related to some economically relevant parasitic nematodes.This newly discovered hermaphroditic nematode has great potential for evolutionary and parasitological research.
Affiliation: Howard Hughes Medical Institute and Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California 91125 Department of the Environmental Biology, College of Bioscience and Biotechnology, Chubu University, Kasugai 487-8501 Japan.Show MeSH
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Mentions: Oocytes stored in the proximal gonad of Bursaphelenchus okinawaensis each had a single germinal vesicle containing six sister chromatids (Figures 1, A and B). After the oocyte moved through the spermatheca to the uterus, the two pronuclei were reconstructed (Figures 1, C and D) and the fertilized egg was laid soon thereafter (after approximately 20 min). At this time, one pronucleus appeared at one pole of the embryo and the other pronucleus emerged at a lateral position (Figure 2A). The first and second polar bodies were extruded from the pronucleus at a lateral position (Figures 3, A and B). This result suggested that the pronucleus at the lateral position was oocyte-derived while the other pronucleus was sperm-derived. After the oocyte pronucleus completed meiosis, the two pronuclei migrated toward each other (Figure 2B and Figure 3, C and D). After the pronuclei met, they moved to the center of the embryo and rotated 30° to 90° (Figure 2, C and D and Figure 3, E and F) and then fused (Figure 2E and Figure 3G). At this time, the number of chromosomes was restored from six to 12 (Figure 3G). Subsequently, first and second cleavages occurred (Figures 2, F–H and Figures 3, H–J). No significant differences in the process of pronuclear fusion were observed between three B. okinawaensis isolates (only the images from SH1 are shown in Figure 1).
Affiliation: Howard Hughes Medical Institute and Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California 91125 Department of the Environmental Biology, College of Bioscience and Biotechnology, Chubu University, Kasugai 487-8501 Japan.