Sex and the Microsporidia
In this chapter, the author brings the various types of evidence for sexuality and asexuality in the microsporidia, ranging from observations of life cycles under the light and electron microscope to population genetic analyses of recombination and surveys of whole genomes for sex-related genes. Sexual reproduction in fungi includes the three crucial steps: plasmogamy, karyogamy and meiosis that are common to most sexual multicellular organisms. Microsporidia are descended from fungal or fungal-like ancestors. Given that most major groups of fungi include sexual species and that asexual species tend to have reduced evolutionary potential, the most parsimonious hypothesis is that microsporidia are descended from an ancestor that reproduced sexually in a similar manner to existing sexual fungi. Various types of evidence suggest that some or all microsporidia reproduce sexually in a similar manner to fungi. Observations of microsporidian life cycles have identified putative meiotic structures and gametes in certain microsporidian species.
