In this chapter, we will give you an overview of the organisms that make up Kingdom Fungi. We’ll try to emphasise a more ecosystem-oriented approach because we want to avoid rambling taxonomy-driven species lists. However, there may be as many as 3.8 million species currently present on Earth (see section 1.7 above), so we need to know some by name and understand the natural classification of fungi. A natural classification is the arrangement of organisms into groups based on their evolutionary relationships.

When early humans gave up their nomadic hunter-gatherer existence and turned to agriculture to solve their food problem they would quickly have been challenged by the fungi. Early farmers must have learned very rapidly that crops are very uncertain resources, prone to variations in weather, fire, floods, weeds, insect pests and those troubles that came to be referred to collectively as ‘blights’ which were due to various sorts of plant disease.

Sexual reproduction is a nearly universal feature of eukaryotes and its core features are conserved throughout each group within the eukaryotic tree of life. This is taken to imply that sexual reproduction evolved once only and was present in the Eukaryote Last Common Ancestor (ELCA). Studies of the fungal kingdom have revealed novel and unusual patterns of sexual reproduction, which we will discuss in this chapter.

In this chapter, we examine the biotechnology that uses intact living organisms to produce commercially important products. In the main this means fungal fermentations in submerged liquid cultures, so we describe in detail the essential aspects of cultivating fungi: media, oxygen demand and supply, and fermenter engineering. We describe fungal growth pattern in liquid cultures, fermenter growth kinetics, growth yield, the stationary phase and growth as pellets.

Chapter 4 deals with investment in reproduction by organisms, first considering the destiny and care of the products of reproduction and the alternative between oviparity and viviparity, followed by a brief mention of the forms of parental care given to the offspring by one or other parent, or both. Some energetic and metabolic aspects of reproduction, in particular vitellogenesis in animals and the formation of endosperm in flowering plants, are also considered, concluding with a short section on the various strategies of parental investment, including different fecundity/fertility levels, considered against different environmental contexts.

Chapter 3 covers the natural history of reproduction. A first section on asexual reproduction deals with the different forms of cell division in unicellular prokaryotes and eukaryotes. A short interlude introduces the notion of sex and describes sexuality phenomena uncoupled from reproductive processes, both in prokaryotes and in unicellular eukaryotes. The main types of sexual reproduction (gametogamy, gamontogamy, autogamy) are described, as are the distinction between sexes and mating types and the different ways in which sexual roles can be distributed within the population. Short paragraphs are devoted to secondary sex characters and to conditions such as aneuploidy, gynandromorphism and intersexuality. Attention is then shifted to the reproductive organs of the metazoans and the morphology of eggs and spermatozoa, and also to the reproductive organs of the plants and the morphology of their gametes. Finally, the fate of gametes is described, both in typical biparental reproduction, with particular regard to its ecological context, and in uniparental sexual reproduction (self-fertilization, parthenogenesis, gynogenesis, androgenesis and hybridogenesis).

Chapter 5 deals with the genetics and cytogenetics of reproduction, starting again from asexual reproduction. Genetic variation due to new mutations, recombination, stochastic segregation or epigenetic causes is discussed. Moving to sexual reproduction, we discuss mechanisms of genetic exchange in the prokaryotes, but eventually focus more closely on sexual reproduction in the eukaryotes. First, the various sources of genetic variation (independent assortment of chromosomes and chromatids, crossing over and gene conversion at meiosis, syngamy) are discussed, thus addressing the genetics of hereditary transmission through different modes of sexual reproduction (amphigony, self-fertilization, meiotic and ameiotic parthenogenesis, gynogenesis, hybridogenesis, androgenesis). The last paragraphs of this chapter are devoted to sexual leakage and some special cases of sex in eukaryotes (conjugation in ciliates, parasexual cycle in fungi, chimerism).

Chapter 7 presents an overview of the reproductive phenomena that occur in the different phyla.

Chapter 6 discusses the determination of sex and mating type, considering both chromosomal or genetic systems of sex determination and those dependent on environmental factors such as temperature or interactions with conspecific individuals, to end with cases of maternal determination of sex and so-called mixed sex-determination systems. We devote only brief notes to sexual differentiation, to conclude with the mating types of fungi and protists.

A cat gives birth to her kittens, two earthworms mate and exchange sperm, a bee brings the pollen collected from the stamens of a buttercup to the pistils of another buttercup – diverse scenes from the same biological phenomenon, reproduction.

Chapter 1 introduces some fundamental concepts, starting with a tentative definition of reproduction that will be revised and enriched in the following chapters and with the traditional distinction between sexual and asexual reproduction. We address the delicate issues relating to the notions of biological individual, generation and life cycle (but we refrain from discussing these topics from a philosophical perspective). We also deal with the not always clearly defined relationship between reproductive and developmental processes, in particular those related to regeneration.

We have come to the end of this excursion through the phenomena of reproduction. It was not a short trip, but the reader will certainly have realized that it could have been much longer. In every taxonomic group, reproduction involves a range of very different biological processes: from the creation of new genotypes to social behaviour, from resisting adverse environmental conditions to migration. Reproduction borders on these ‘other aspects’ of an organism’s biology and often trespasses into them. So what is it that is common to all these reproductive phenomena? In other words, what exactly, in the end, is reproduction?

Chapter 2 is devoted to the relationships between reproduction and life cycle. We start by illustrating the classical division of life cycles on the basis of the alternation of nuclear phases (haplontic, diplontic, haplodiplontic). Then we move on to the alternation between sexual and asexual generations (metagenetic cycles), amphigony and parthenogenesis (heterogonic cycles), gonochoric and hermaphroditic (heterogenic cycles), solitary and colonial, unicellular and multicellular, to conclude with short sections on the alternation of generations dependent on seasonal polyphenism and the different ways in which different reproductive phases can be distributed within one generation.