The collapse of the two-kingdom system, the rise of protistology and the founding of the International Society for Evolutionary Protistology (ISEP)

Abstract

This paper provides a brief summary of the rise and acceptance of protistology as a modern, realistic approach to the evolutionary relationships and classification of unicellular eukaryotic organisms as well as the origins of the multicellular groups. The apparent reasons for the renaissance of this 19th-century concept in the 1970s are reviewed, with electron microscopy considered to be the key factor, strongly reinforced by molecular phylogenetic studies in the 1980s and 1990s. The foundation of the International Society for Evolutionary Protistology in 1975 accompanied this major alteration in the view of biological diversity. The current status of protistology relative to protozoology and phycology is discussed. Introduction: unity, dualism and pluralismDuring the latter part of the 20th century, several important 'paradigm shifts' occurred in our view of cell evolution. Perhaps the most obvious of these, because it was so hotly contested, was the symbiotic origin of mitochondria and chloroplasts. It was an old idea, with roots in the late 19th century, whose successful revival was championed by Margulis (1970). Ironically, although the symbiotic origin for these organelles has been generally accepted, her additional hypothesis of a symbiotic origin of the '9+2' organelles (centrioles/basal bodies and derivative structures) as an origin for the eukaryotic mitotic process (Sagan, 1967) has not been supported by convincing evidence. Never one to quit, symbiotic spirochaete involvement is still espoused in her latest publication (Margulis & Sagan, 2002). The formulation of a theory that incorporated hypotheses for the symbiotic origin of mitochondria and plastids sequentially was dubbed the 'serial endosymbiosis theory ' (SET;Taylor, 1974) in a paper that also introduced the now widely used concepts of primary and secondary symbiosis that are particularly relevant to plastid acquisition.A less obvious but equally important major paradigm shift was the resurrection and development of another 19th-century concept: the protistological view of the basal nexus and radiation of unicellular eukaryotes preceding and giving rise to plants, animals and fungi but also many lineages independent of these multicellular groups. This replaced the long-held subdivision of all eukaryotes, and even prokaryotes, into the classical plant and animal kingdoms.The dualistic Plant-Animal view had its roots in Aristotle and his teacher Plato, in the Academy in Athens almost 2500 years ago (ca. 360 BC). Two living supergroups were formalized in 1735 by Carl von Linné in his monumental Systema Naturae as the Kingdoms Plantae and Animalia, into which all organisms were placed. By the 12th, and last, edition (Linnaeus, 1766), he had added a third kingdom of the natural world, Lapides (for 'rocks'; solid bodied, not living, not 'sentient', i.e. not having 'senses', a trait shared with plants in his scheme). This division of the living world was reflected in the disciplines of Botany and Zoology, housed in their own separate academic Departme...

An estuarine species of the alga Vaucheria (Xanthophyceae) displays an increased capacity for turgor regulation when compared to a freshwater species

“…In this study, we investigate turgor regulation in Vaucheria (yellow green alga, Xanthophyceae). The oomycetes and xanthophyceans share a relatively recent common ancestor, as shown by shared synapomorphic characters of compound flagellate cells and phylogenetic analysis of DNA sequences (Potter et al 1997, Taylor 2003. Both belong to a wider group of protists called the Stramenopila.…”

Contemporary issues, current best practice and ways forward in soil protist ecology

“…We here provide an overview of terms that we believe should be used in soil protist studies with reasons why. First of all, the term protist * (including all eukaryotes that do not evolve multicellularity through embryonic development, therefore excluding animals, plants and fungi (sometimes also included as protists) (Adl et al, 2005; Taylor, 2003)) should consistently be used rather than protozoa * (best referred to as heterotrophic protists). Arguably being a semantic discussion, the term protist is less problematic than protozoa as often discussed by experts, but still having missed the entire field of scientists who shifted towards or included protists in their research (Figure 1).…”

Why the World Needs Protists!1

“…Sogin et al (1996), Ancestral relationships of the major eukaryotic lineages; F.J.R. Taylor (1987b), An overview of the status of evolutionary cell symbiosis theories; F.J.R. Taylor (2003), The collapse of the two‐kingdom system, the rise of Protistology and the founding of the International Society of Evolutionary Protistology (ISEP); W.…”