SUMMARY: Sexual reproduction is often murky in parasites because it’s difficult to observe at times. There are two other ways to determine if an organism has sex: differences in genomes and genes for meiosis. However, in parasites, there are exceptions to this rule in that some organisms may have the genes, but not use them unless under special circumstances. Parasites in this article (and their sexual and life cycles) are divided into three different phylogenetic groups: apicomplexan, kinetoplastid, and entamoeba. Apicomplexans have very clear and necessary sexual stages while kinetoplastids and Entamoebas have more ambiguous ones. Understanding when and how parasites go through sexual reproduction helps researchers figure out better ways to target the life cycles of these microorganisms when developing treatments.
LESSON COMMENTS: The three markers for sexual reproduction in this article are a good place to start asking students questions. The answer may be obvious for large organisms, but this article points out the importance of sexual reproduction and how ambiguous it can sometimes be. Another good question that comes from this article is, “Why do some organisms only have sex when times are stressful?”
If teachers are doing a lab looking at pond protozoa, students can observe paramecia and other ciliates in conjugation as oxygen supplies run low (usually about 3-4 days after collection).
Weedall, G. D., & Hall, N. (2015). Sexual reproduction and genetic exchange in parasitic protists. Parasitology, 142 Suppl 1(Suppl 1), S120-7.