Sexual reproduction is common in some groups of fungi but has never been observed in others. Many fungal species have two or more genetically distinct mating types. The sac fungi and club fungi share a dikaryotic condition, in which two genetically different haploid nuclei coexist in the same cell.
learning outcomes
You should be able to:
Compare and contrast sexual reproduction in fungi with that of plants and animals.
Summarize the parasitic life style of microsporidia.
Infer the likely ancestral habitat of chytrids based on chytrid features.
Compare and contrast the life cycles of zygospore fungi, sac fungi, and club fungi.
Explain the concept of mating types. How are they different from male and female sexes?
In mating types, there is no phenotypic distinction as exists between male and female sexes, and there are often more than two mating types. Mating types are morphologically indistinct, but within each species, each mating type is genetically different. Individuals within a species may not mate with another of the same mating type. In contrast, male and female sexes are defined by the relative size of their gametes. (Females have large gametes, and males have small gametes; reproduction requires the combination of a male and a female gamete.)
Describe how microsporidia infect the cells of their animal hosts.
Microsporidia are among the smallest eukaryotes known. They are obligate parasites on animals. The host cell is penetrated by a polar tube through which the contents of the spore are injected into the host. This sporoplasm then replicates within the host cell and produces new infective spores. In some insects, once an individual is infected, the microsporidian parasite may be transmitted from parent to offspring.
What feature of the chytrids suggests that the fungi had an aquatic ancestor?
Most chytrids possess flagellated gametes and reproduce in water (or at least in wet environments, such as moist soil).
What is the role of the zygospore in the life cycle of zygospore fungi?
The zygospore is the diploid phase of the zygospore fungi life cycle. It has a thick, multilayer cell wall and can serve as a resting stage that may remain dormant for months until environmental conditions are favorable for growth. At that time, its diploid nuclei undergo meiosis, and the zygospore produces a stalked sporangiophore, which bears from one to many sporangia. Each sporangium contains haploid spores, which are the products of meiosis.
What distinguishes the fruiting bodies of sac fungi from those of club fungi?
The haploid ascospores of sac fungi are contained in sacs known as asci. Many species of sac fungi bear these asci on cup-
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Fungi are of special interest to biologists because of the roles they play in interactions with other organisms, including humans. But they are also useful as tools for studying many kinds of biological problems and for finding solutions to those problems.