Thomas Cavalier-Smith

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Thomas Cavalier-Smith
Born (1942-10-21) 21 October 1942 (age 81)
Nationality British
Institutions King's College London, University of British Columbia, University of Oxford
Alma mater Gonville and Caius College, Cambridge King's College London
Thesis  (1967)
Notable awards Fellow of the Royal Society (1998)
International Prize for Biology (2004)
The Linnean Medal (2007)
Frink Medal (2007)
Website
www.zoo.ox.ac.uk/people/view/cavaliersmith_t.htm

Thomas (Tom) Cavalier-Smith, FRS, FRSC, NERC Professorial Fellow (born 21 October 1942), is a Professor of Evolutionary Biology in the Department of Zoology, at the University of Oxford.[1] He was presented with the International Prize for Biology (a prize of 10 million yen) in 2004.[2]

Life

He was educated at Norwich School, Gonville and Caius College, Cambridge (MA) and King's College London (PhD). He was under the supervision of Sir John Randall for his PhD thesis between 1964-1967; his thesis was entitled 'Organelle Development in Chlamydomonas reinhardii'.[3]

From 1967 to 1969, he was a guest investigator at Rockefeller University. He taught in the biophysics department of King’s College London. In 1989 he taught botany at the University of British Columbia. In 1999, he joined the University of Oxford.[4]

He won the 2007 Frink Medal of the Zoological Society of London.

Classification of life

Cavalier-Smith has published extensively on the classification of protists. One of his major contributions to biology was his proposal of a new kingdom of life: the Chromista, although the usefulness of the grouping is questionable given that it is generally agreed to be an arbitrary (polyphyletic) grouping of taxa. He also proposed that all chromista and alveolata share the same common ancestor, a claim later refuted by studies of morphological and molecular evidence by other labs. He named this new group the Chromalveolates. He also proposed and named many other high-rank taxa, like Opisthokonta (1987), Rhizaria (2002), and Excavata (2002). Together with Chromalveolata, Amoebozoa (he amended their description in 1998), and Archaeplastida (which he called Plantae since 1981) the six form the basis of current taxonomy of eukaryotes. Prof. Cavalier-Smith has also published prodigiously on issues such as the origin of various cellular organelles (including the nucleus, mitochondria), genome size evolution, and endosymbiosis. Though fairly well known, many of his claims have been controversial and have not gained widespread acceptance in the scientific community to date. Most recently, he has published a paper citing the paraphyly of his bacterial kingdom, the origin of Neomura from Actinobacteria and taxonomy of prokaryotes.

According to Palaeos.com:

Prof. Cavalier-Smith of Oxford University has produced a large body of work which is well regarded. Still, he is controversial in a way that is a bit difficult to describe. The issue may be one of writing style. Cavalier-Smith has a tendency to make pronouncements where others would use declarative sentences, to use declarative sentences where others would express an opinion, and to express opinions where angels would fear to tread. In addition, he can sound arrogant, reactionary, and even perverse. On the other [hand], he has a long history of being right when everyone else was wrong. To our way of thinking, all of this is overshadowed by one incomparable virtue: the fact that he will grapple with the details. This makes for very long, very complex papers and causes all manner of dark murmuring, tearing of hair, and gnashing of teeth among those tasked with trying to explain his views of early life. See, [for example], Zrzavý (2001) [5] [and] Patterson (1999).[6][7][8] Nevertheless, he deals with all of the relevant facts.[9]

Cavalier-Smith's eight kingdoms model

The first two kingdoms of life: plants and animals

The use of the word "kingdom" to describe the living world dates as far back as Linnaeus (1707–1778) who divided the natural world into three kingdoms: animal, vegetable, and mineral.[10][11] The classifications "animal kingdom" (or kingdom Animalia) and "plant kingdom" (or kingdom Plantae) remain in use by modern evolutionary biologists.

By 1910 the animal kingdom had been subdivided into twelve phyla:

The protozoa were originally classified as members of the animal kingdom.[12] Now they are classified as multiple separate groups.

Zoology is the study of animals while botany is the study of plants. While zoologists divided the animal kingdom into phyla, botanists carved the plant kingdom into "divisions". By 1940, five divisions were recognized:

Fungi and bacteria were included within the plant division thallophyta.[12] Today, bacteria are no longer classified as plants and fungi are known to be more closely related to animals than to plants.

The third kingdom: protists

File:Anemone monterey madrabbit.jpg
The sea anemone is an animal that resembles a plant.

By mid-nineteenth century, microscopic organisms were generally classified into four groups:

In 1858, Richard Owen (1804–1892) proposed that the animal phylum Protozoa be elevated to the status of kingdom.[13] In 1860, John Hogg (1800–1869) proposed that protozoa and protophyta be grouped together into a new kingdom which he called "Regnum Primigenum". According to Hogg, this new classification scheme prevented "the unnecessary trouble of contending about their supposed natures, and of uselessly trying to distinguish the Protozoa from the Protophyta". In 1866, Ernst Haeckel (1834–1919) proposed the name "Protista" for the Primigenum kingdom and included bacteria in this third kingdom of life.[11]

The fourth kingdom: fungi

Japanese popular mushrooms, clockwise from left, enokitake, buna-shimeji, bunapi-shimeji, king oyster mushroom and shiitake.

Fungi are more closely related to animals than to plants. By 1959, Robert Harding Whittaker (1920–1980) proposed that fungi, which were formerly classified as plants, be given their own kingdom. His four kingdoms of life were:

Whittaker subdivided the Protista into two subkingdoms:

The fifth kingdom: bacteria

Bacteria are fundamentally different from the eukaryotes (plants, animals, fungi, amebas, protozoa, and chromista). Eukaryotes have cell nuclei, bacteria do not. In 1969, Robert Whittaker elevated the bacteria to the status of kingdom. His new classification system divided the living world into five kingdoms:

  • plants,
  • animals,
  • protists (excluding bacteria),
  • fungi, and
  • Monera (the kingdom bacteria).[15]

Note: the word "protist" is ambiguous.

Eunucleata = single celled eukaryotes
Before 1959: protist = prokaryotes + Eunucleata + sponges
From 1959 to 1969: protist = prokaryotes + Eunucleata
Since 1969: protist = Eunucleata

The sixth kingdom and the three domains of life

Phylogenetic tree based on Woese et al. rRNA analysis in 1990 [16]

The kingdom Monera can be divided into two distinct groups: eubacteria and archaebacteria. In 1977 Carl Woese and George E. Fox proposed that eubacteria and archaebacteria both be elevated to the status of super-kingdom.[17] In 1990, Woese further elevated the status of bacteria by dividing life into three domains:

eukaryotes = plants + chromista + animals + fungi + Eunucleata
prokaryotes = Monera = eubacteria + archaebacteria

Note: the modern use of the word "bacteria" is ambiguous. It may refer either to eubacteria (as in the above phylogenetic tree) or prokaryotes (as in reference to the kingdom Monera).

The seventh kingdom: chromista

The brown algae are a member of the kingdom Chromista.

By 1981, Cavalier-Smith had divided the domain Eukaryota into nine kingdoms.[18] By 1993, he reduced the total number of eukaryote kingdoms to six. He also classified the domains Eubacteria and Archaebacteria as kingdoms, adding up to a total of eight kingdoms of life:

  1. Plantae,
  2. Animalia,
  3. Protozoa,
  4. Fungi,
  5. Eubacteria,
  6. Archaebacteria,
  7. Chromista, and
  8. Archezoa.

Cavalier-Smith's new classification scheme retained the plant, animal and fungal kingdoms from the traditional five kingdom model. It also split the kingdom Monera into the two groups, eubacteria and archaebacteria, as proposed by Woese and Fox. In addition it split the kingdom protists into three new kingdoms: archezoa, protozoa, and chromista.

Most chromists are photosynthetic. This distinguishes them from most other protists. In both plants and chromists photosynthesis takes place in chloroplasts. In plants, however, the chloroplasts are located in the cytosol while in chromists the chloroplasts are located in the lumen of their rough endoplasmic reticulum. This distinguishes chromists from plants.[13]

The eighth kingdom: archezoa

Cavalier-Smith's eighth kingdom, Archezoa [19] is now defunct. He now assigns former members of the kingdom Archezoa to the phylum Amoebozoa.[20]

Kingdom protozoa sensu Cavalier-Smith

Cavalier-Smith referred to what remained of the protist kingdom, after he removed the kingdoms Archezoa and Chromista, as the "kingdom Protozoa". In 1993, this kingdom contained 18 phyla as summarized in the following table:[13]

# Phylum Assigned to: Characteristics Fate
1 Percolozoa subkingdom Adictyozoa lacks Golgi dictyosomes  
2 Parabasalia subkingdom Dictyozoa
branch Parabasalia		 has Golgi dictyosomes
lacks mitochondria		  
3 Euglenozoa subkingdom Dictyozoa
branch Bikonta
infrakingdom Euglenozoa		 has Golgi dictyosomes mostly with mitochondria
with trans-splicing of

miniexons

  
4 Opalozoa (flagellates) subkingdom Dictyozoa
branch Bikonta
infrakingdom Neozoa
parvkingdom Ciliomyxa		 has Golgi dictyosomes tubular mitochondrial cristae with cis-spliced introns
predominantly ciliated,
no cortical alveoli		  
5 Mycetozoa (slime molds) subkingdom Dictyozoa
branch Bikonta
infrakingdom Neozoa
parvkingdom Ciliomyxa		 has Golgi dictyosomes tubular mitochondrial cristae
with cis-spliced introns

predominantly ciliated,
no cortical alveoli

  
6 Choanozoa (choanoflagellates) subkingdom Dictyozoa
branch Bikonta
infrakingdom Neozoa
parvkingdom Ciliomyxa		 has Golgi dictyosomes flattened mitochondrial cristae
with cis-spliced introns
predominantly ciliated,
no cortical alveoli		  
7 Dinozoa (Dinoflagellata and Protalveolata) subkingdom Dictyozoa
branch Bikonta
infrakingdom Neozoa
parvkingdom Alveolata		 has Golgi dictyosomes tubular mitochondrial cristae
with cis-spliced introns
with cortical alveoli		 Reassigned to Miozoa in Alveolata.[21]
8 Apicomplexa subkingdom Dictyozoa
branch Bikonta
infrakingdom Neozoa
parvkingdom Alveolata		 has Golgi dictyosomes tubular mitochondrial cristae
with cis-spliced introns
with cortical alveoli		 Reassigned to Miozoa in Alveolata.[21]
9 Ciliophora subkingdom Dictyozoa
branch Bikonta
infrakingdom Neozoa
parvkingdom Alveolata		 has Golgi dictyosomes tubular mitochondrial cristae
with cis-spliced introns
with cortical alveoli		 Reassigned to Alveolata.[21]
10 Rhizopoda (lobose and filose amoebae) subkingdom Dictyozoa
branch Bikonta
infrakingdom Neozoa
parvkingdom Neosarcodina		 has Golgi dictyosomes usually with tubular cristae
with cis-spliced introns		  
11 Reticulosa (foraminifera; reticulopodial amoebae) subkingdom Dictyozoa
branch Bikonta
infrakingdom Neozoa
parvkingdom Neosarcodina		 has Golgi dictyosomes usually with tubular cristae
with cis-spliced introns		  
12 Heliozoa subkingdom Dictyozoa
branch Bikonta
infrakingdom Neozoa
parvkingdom Actinopoda		 has Golgi dictyosomes mostly with mitochondria
with cis-spliced introns
has axopodia		  
13 Radiozoa subkingdom Dictyozoa
branch Bikonta
infrakingdom Neozoa
parvkingdom Actinopoda		 has Golgi dictyosomes mostly with mitochondria
with cis-spliced introns
has axopodia		  
14 Entamoebia subkingdom Dictyozoa
branch Bikonta
infrakingdom Neozoa
parvkingdom Entamoebia		 has Golgi dictyosomes
with cis-spliced introns
no mitochondria, peroxisomes, hydrogenosomes or cilia transient intranuclear centrosomes		  
15 Myxosporidia subkingdom Dictyozoa
branch Bikonta
infrakingdom Neozoa
parvkingdom Myxozoa		 has Golgi dictyosomes
with cis-spliced introns endoparasitic, multicellular spores, mitochondria,
and no cilia		 Reclassified as animals in 1998.[22]
16 Haplosporidia subkingdom Dictyozoa
branch Bikonta
infrakingdom Neozoa
parvkingdom Myxozoa		 has Golgi dictyosomes
with cis-spliced introns endoparasitic, multicellular spores, mitochondria,
and no cilia		 Reclassified as animals in 1998.[22]
17 Paramyxia subkingdom Dictyozoa
branch Bikonta
infrakingdom Neozoa
parvkingdom Myxozoa		 has Golgi dictyosomes
with cis-spliced introns endoparasitic, multicellular spores, mitochondria,
and no cilia		 Reclassified as animals in 1998.[22]
18 Mesozoa subkingdom Dictyozoa
branch Bikonta
infrakingdom Neozoa
parvkingdom Mesozoa		 has Golgi dictyosomes
with cis-spliced introns
tubular mitochondrial cristae multicellular with no collagenous connective tissue		 Reclassified as animals in 1998.[22]

The phylum Opalozoa was established by Cavalier-Smith in 1991.[23]

Cavalier-Smith's six kingdoms models

By 1998, Cavalier-Smith had reduced the total number of kingdoms from eight to six: Animalia, Protozoa, Fungi, Plantae (including red and green algae), Chromista and Bacteria.[22]

Five of Cavalier-Smith's kingdoms are classified as eukaryotes as shown in the following scheme:

Eukaryotes are divided into two major groups: unikonts and bikonts. Uniciliates are cells with only one flagellum and unikonts are descended from uniciliates. Unikont cells often have only one centriole as well. Biciliate cells have two flagella and bikonts are descended from biciliates. Biciliates undergo ciliary transformation by converting a younger anterior flagellum into a dissimilar older posterior flagellum. Animals and fungi are unikonts while plants and chromista are bikonts. Some protozoa are unikonts while others are bikonts.

The Bacteria (= prokaryotes) are subdivided into Eubacteria and Archaebacteria. According to Cavalier-Smith, eubacteria is the oldest group of terrestrial organisms still living. He classifies the groups which he believes are younger (archaebacteria and eukaryotes) as neomura.

His 1998 model

Kingdom animalia

In 1993, Cavalier-Smith classified Myxozoa as a protozoan parvkingdom. By 1998, he had reclassified it as an animal subkingdom. Myxozoa contains three phyla, Myxosporidia, Haplosporidia, and Paramyxia, which were reclassified as animals along with Myxozoa. Likewise, Cavalier-Smith reclassified the protozoan phylum Mesozoa as an animal subkingdom.

In his 1998 scheme, the animal kingdom was divided into four subkingdoms:

He created three new animal phyla:

and recognized a total of 23 animal phyla.[22]

Kingdom protozoa

Under Cavalier-Smith's proposed classification system, protozoa share the following traits:

  • they have or are descended from organisms with mitochondria
  • they have or are descended from organisms with peroxisomes
  • they lack collagenous connective tissue
  • they lack epiciliary retronemes (rigid thrust-reversing tubular ciliary hairs)
  • they lack two additional membranes outside their chloroplast envelope

Organisms that do not meet these criteria were reassigned to other kingdoms by Cavalier-Smith.

His 2003 model

Kingdom protozoa

In 1993, Cavalier-Smith divided the kingdom Protozoa into two subkingdoms and 18 phyla.[13] By 2003 he used phylogenic evidence to revise the total number of proposed phyla down to 11: Amoebozoa, Choanozoa, Cercozoa, Retaria, Loukozoa, Metamonada, Euglenozoa, Percolozoa, Apusozoa, Alveolata, Ciliophora, and Miozoa. [21]

Unikonts and bikonts

Amoebas (AmE: amebas) do not have flagella and are difficult to classify as unikont or bikont based on morphology. In his 1993 classification scheme, Cavalier-Smith incorrectly classified amoebas as bikonts. Gene fusion research later revealed that the clade Amoebozoa, was ancestrally uniciliate. In his 2003 classification scheme, Cavalier-Smith reassigned Amoebozoa to the unikont clade along with animals, fungi, and the protozoan phylum Choanozoa. Plants and all other protists where assigned to the clade Bikont by Cavalier-Smith.[21]

Cavalier-Smith's 2003 classification scheme:

Cladogram of life

By September 2003, Cavalier-Smith's tree of life looked like this:[24]

Eubacteria

Neomura

Archaebacteria


Eukarya
Bikonts

Apusozoa

Cabozoa

Excavata

Rhizaria

Retaria


Cercozoa





Kingdom Plantae

Chromalveolata

Kingdom Chromista


Alveolata




Unikonts

Amoebozoa

Opisthokonts


Choanozoa


Kingdom Animalia




Kingdom Fungi








In the above tree, the traditional plant, animal, and fungal kingdoms, as well as Cavalier-Smith's proposed Chromista kingdom, are shown as leaves. The leaves Eubacteria and Archaebacteria together make up the Bacteria kingdom. All remaining leaves together make up the protozoa kingdom.

By 2010 new data emerged that showed that Unikonts and Bikonts, originally considered to be separate because of an apparently different organization of cilia and cytoskeleton, are in reality more similar than previously thought. As a consequence, Cavalier-Smith revised the above tree and proposed to move its root to reside in between the Excavata and Euglenozoa kingdoms.[25]

Rooting the tree of life

In 2006, Cavalier-Smith proposed that the last common ancestor to all life was a non-flagellate negibacterium with two membranes.[26]

Work (samples)

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Footnotes

  1. ↑ http://www.cavali.net/cavali/default.asp?menuitemID=131
  2. ↑ The Committee on the International Prize for Biology of Japan Society for the Promotion of Science awards the 2004 International Prize for Biology in the field of "Systematic Biology and Taxonomy" to Prof. Thomas Cavalier-Smith, Department of Zoology, University of Oxford, UK. Retrieved December 9, 2006.
  3. ↑ Lua error in package.lua at line 80: module 'strict' not found.[page needed][non-primary source needed]
  4. ↑ http://www.cifar.ca/thomas-cavalier-smith[full citation needed]
  5. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  6. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  7. ↑ Apusomonadida
  8. ↑ Eukarya.
  9. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  10. ↑ Dan H. Nicolson. Animal, Vegetable or Mineral?. Proceedings of a Mini-Symposium on Biological Nomenclature in the 21st Century held at the University of Maryland on 4 November 1996. Edited by James L. Reveal
  11. ↑ 11.0 11.1 11.2 Lua error in package.lua at line 80: module 'strict' not found.
  12. ↑ 12.0 12.1 Lua error in package.lua at line 80: module 'strict' not found.
  13. ↑ 13.0 13.1 13.2 13.3 Lua error in package.lua at line 80: module 'strict' not found.
  14. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  15. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  16. ↑ 16.0 16.1 Lua error in package.lua at line 80: module 'strict' not found.
  17. ↑ Gert Korthof, (2007). Carl Woese: from scientific dissident to textbook orthodoxy. Cited February 11, 2009.
  18. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  19. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  20. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  21. ↑ 21.0 21.1 21.2 21.3 21.4 Lua error in package.lua at line 80: module 'strict' not found.
  22. ↑ 22.0 22.1 22.2 22.3 22.4 22.5 Lua error in package.lua at line 80: module 'strict' not found.
  23. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  24. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  25. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  26. ↑ Lua error in package.lua at line 80: module 'strict' not found.

Further reading

Peter H. Raven and Helena Curtis (1970), Biology of Plants, New York: Worth. [Early presentation of five-kingdom system.]

External links

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