Evolutionary Ecology of the First Fungi

Abstract

The Fungi apparently originated about one billion years ago from a common ancestral, aquatic eukaryotic protist that derived its nutrition as a chemotrophic osmotroph. Evolutionary morphological trends within the kingdom have involved losses of swimming spores, and acquisition of life cycle adaptations for terrestrial colonization. These include an extensive filamentous growth habit, together with spore production, dispersal, and survival mechanisms for aerial dissemination; and evolutionary physiological trends that have involved nutritional mode shifts, and losses and gains by lateral gene transfer (LGT) in metabolic trophic attributes. This chapter, first, recapitulates the phylogenetic and geological history of the fungi inferred from morphological and molecular systematics. Second, it addresses an issue not covered mechanistically by phylogenetics, namely, what drove the evolutionary origins of the fungi. This is accomplished by addition of the dimension of nutritional trophic property to the conventional phylogenetic tree, with emphasis on eukaryotes in general, the fungi, and the alphaproteobacteria (the hypothetical ancient mitochondrial endosymbiont). Bioenergetic electron flow diagrams, which provide a visual, conceptually powerful means to identify evolutionary energy connections between the mitochondrial endosymbiont and fungi, form the basis for understanding and predicting biogeochemical forces driving organism growth and ecology. The results indicate that the fungi are closely related metabolically to the ancestral mitochondrial eukaryote, although the trophic relationships are not always in complete accord with phylogenetic placement, presumably because of LGT, or retention of primordial properties by some advanced lines.