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Two sides of four kingdoms and other problems of living things classifications
Alexey Shipunov University of Idaho


C a ro lu s L in n a e u s ( 1 7 3 5 )

His three kingdoms were based on physiological approach and located on successive manner, according to the "chain of being"­ "scala naturae"


C h a in o r b ra n c h e s ?
animals plants animals

3rd kingdom 3rd kingdom Branched classification

plants Successive classification


In the search of third kingdom
R.Owen (1860), introduced the third kingdom "Protozoa"; J.Hogg (1860) listed kingdoms Protoctista, Vegetabilia and Animalia. E.Haeckel (1866) called third kingdom "Protista". The emergence of concepts of evolution played a great role in the process of establishing the third kingdom of life. Th.Wilson and J.Cassin (1864) intentionally pointed that in the light of evolution "chain of being" should be disregarded.


Monera is the fourth kingdom
H.F.Copeland (1938, 1954) developed a four-kingdom classification of organisms which have been subsequently popularized by R.Whittaker (1957, 1969) and L.Margulis (1971, 1978), who added the fifth (fungal) kingdom. Their classification differ mostly in the place of "dissection" plants from algae. Monera (Prokaryotae) were added as successive step, and Fungi were added as the third branch.


Barrier is broken: multiple k in g d o m s
"Classic" example: the 19-kingdom classification of G.F.Leedale (1974). During the last 30 years, many multikingdom classifications appeared. The biggest example is probably the classification of A.L.Drozdov (2003) with 26 kingdoms.


Attempts to reduce kingdoms
Several attempts have been made for reduction of the number of kingdoms. F.J.R.Taylor (1978) introduced the type of mitochondrial cristae (flat or tubular) as the main character for distinguishing eukaryotes. Unfortunately, this character turned out to be unstable.

Tubulicristata Lamellicristata


A rc h a e a

C.R.Woese (1990­onwards) proposed another solution for small-number-of-kingdoms classification: just unite all eukaryotes, but separate Monera (prokaryotes) in two kingdoms ("domains"): Bacteria and new group Archaea, or Archebacteria. This mega-classification is the first based on phylogenetic trees obtained from DNA sequences.


"H y b r i d " a p p r o a c h e s
3 4 5 6 2

1

Six-kingdoms classification of Th.Cavalier-Smith (2004) is "hybrid": some parts are branches, but his kingdom Protozoa is just a step.


F o u r m a in b ra c h e s
The simplest tree-based classification may contain four main clades in accordance with hypothesis of Th.Cavalier-Smith and A.Stechmann (2003). / Pananimalia (/ Unikonta) / Panplantae (/ Bikonta)

/Archaea /Bacteria


F o u r m a in k in g d o m s
Vegetabilia The simplest space-based classification may contain four kingdoms which differ by levels of complexity. Animalia tissues and organs Protista "true" cells (eocytes) Monera

The concept of "Histonia", or multitissued organisms originated from R.Owen (1860) and developed in several publications of J.Corliss (1983-onwards).


Complementary approaches
Bacteria Archaea Panplantae Pananimalia

Monera

Vegetabilia

Protista

Animalia

These two classifications could be used together because they used two complementary "taxon designations" (Oskolsky, 2007): "taxon as class" (space-based classifications) and "taxon as place" (tree-based). For practical purposes, second is preferable where ranks are used, and first is preferable for rank-free classifications.


1. Paraphyly

M a in p ro b le m s o f mega-classification

T h is is m o s tly a p r o b le m o f c o m m u n ic a tio n b e tw e e n tr e e - a n d s p a c e b a s e d c la s s ific a tio n s . T h e s e c o n flic ts s h o u ld b e a v o id e d a s m u c h a s p o s s ib le .

2. Devalvation of ranks
W h e r e tr e e - b a s e d a p p r o a c h is te r m in a l ta x a o b ta in m u c h r e c e iv e th e r a n k o f o r d e r o r a n k - fr e e c la s s ific a tio n fo r u s e d , to n s o f r a n k s a r e n e e d e d a n d /o r lo w e r r a n k ( e .g ., flo w e r in g p la n ts c a n r e v e n fa m ily ) . T h e b e s t s o lu tio n is to u s e a ll tr e e - b a s e d c la s s ific a tio n s .

3. Rank designation
M a n y h ig h e r ta x a a r e th e u s e o f p r o p o s a r e o fte n q u ite d if d e s ig n a tio n s , lik e n o t ty p ifie d , b u t w h e n th e y fin a lly b e c a m e ty p ifie d , ed endings (like "-mycetidae", "-phytina", "-formes" fic u lt. T h e s o lu tio n is to u s e n u m b e r s fo r r a n k "5Felis" for Mammalia and "6Felis" for Chordata.


Main problems (contd.)
4. Inclusion of viruses
W h e th e r o r n o t in c lu d e v ir u s e s to th e c la s s ific a tio n o f liv in g th in g s i s u n c le a r s in c e th e ir d is c o v e r y . T h e s o lu tio n d e p e n d s fr o m w h a t w e c a ll " l iv in g " .

5. "Nanobacteria"
A u th o r s o f n a m e ( K a ja n d e r e t a l., 1 9 9 8 , 2 0 0 6 ) p r o p o s e th a t n a n o b a c te r ia ( p r o p a g a tin g c a lc ify in g n a n o p a r tic le s ) a r e m o r e p r im itiv e th a n prokaryotes and probably represent a "third branch of life". But even th e e x is te n c e o f th is o r g a n is m s is s till d o u b tfu l.

6. "Environmental" groups
T h e s e ta x a o r ig in a te d a r e ju s t b r a n c h e s fr o m e n v ir o n m e n ta l s e q u e n c e s tr e e s s o th e y la c k m o r p h o lo g ic a l d e s c r ip tio n s . M a y b e th e b e s t w a y is to a c c e p t o n ly w e ll- c h a r a c te r iz e d e n v ir o n m e n ta l g r o u p s ( lik e " P ic o b ilip h y ta " ) .


Main problems (contd.)
7. Tissues in protists
S o m e p r o tis ta n g r o u p s ( m e m b e r s o f R h o d o p h y ta , P h a e o p h y c e a e a n d p r o b a b ly s o m e fu n g i) h a v e tr u e tis s u e s . H o w e v e r , c o m p le x ity o f th e ir tis s u e s is in c o m p a r a b le w ith tis s u e s o f A n im a lia a n d V e g e ta b ilia ( C o r lis s , 1 9 8 4 ) . In a d d itio n , m a n y tr a n s itio n a l fo r m s a r e p r e s e n t th e r e .

8. Some protists do not belong to Pananimalia or Panplantae
T h e r e a r e s e v e r a l e x a m p le s : A p u s o m o n a d id a , C o llo d ic ty o n id a , B r e v ia te a a n d p ro b a b ly s o m e n o n -s e q u e n c e d o rg a n is m s lik e H e m im a s tig o p h o r e a . H o w e v e r , th e ir p o s itio n c o u ld b e r e s o lv e d e ith e r in P a n a n im a lia o r P a n p la n ta e .


Acknowledgements
·Alexei Oskolsky (Botanical Institute, S.-Petersburg) ·Yuri Tchaikovsky (Institute of the History of natural Sciences, Moscow) ·Igor Pavlinov (Zoological Museum, Moscow State University)

Web-site of the authors' classification: http://herba.msu.ru/shipunov/os