Different species concept by Saurav Jyoti Roy

1. STATUS OF ‘SPECIES CONCEPT’ IN
PROKARYOTES (Bacteria)
SAUROV JYOTI ROY
M.Sc. 1st Sem (Botany) / Roll no 09
Gauhati University
Under guidance of Prof. Dr. D. Narzary

2. Species Concept
• There are a wide range of approaches to define how we
identify species and how species function in nature, each
approach is known as a species concept.
• The number and types of species concepts which exist are
constantly changing time to time, but there are at least 26
recognized species concept.
• There are four main types of species concept.
1. Biological species concept
2. Phylogenetic species concept
3. Ecological species concept
4. Morphological species concept

3. Biological species concept
• Biological species concept is the
most widely accepted species
concept. It defines species in
terms of interbreeding.
• Biological species concept was
defined by ERNST MAYR.
• Biological species concept states
that species are groups of
interbreeding natural populations
that are reproductively isolated
from other such groups and can
produce viable offspring.

4. Biological Species Concept
Limitations of Biological species concept-
• The biological species concept cannot be applied
to asexual organisms.
• It not applicable for fossils.
• Its is also not applicable for the organisms about
which little known regarding their reproduction.

5. Morphological (Phenetic) species concept
• Morphological species concept defines species as
a group of organisms sharing a unique
combination of physical characteristics.(Simpson,
1961)
• A species may be morphologically diverse (e.g.,
dogs) or distinct species may be morphologically
indistinguishable (“cryptic species”).

6. Ecological species concept
• According to the ecological species concept the more similar two organisms
are that the more are likely to overlap the need and will compete over
resources such as food and shelter. That is they share the share the exact
same ecological niche. ( Zoological point of view) (Valen, 1975)
• Ecological niche is not followed in case of plants.

7. Phylogenetic Species
Concept
• It defines a species as a
group of organisms that
shares a common
ancestor and can be
distinguished from other
organisms that do not
share that ancestor.
• Phylogenetic species
concept asserts that on
the tree of life, species
are the distal twigs.

8. Prokaryotes characters
• Prokaryotes are single celled
(unicellular) organisms.
• Well defined nucleus is absent.
• Membrane bound organelles are
absent. Example mitochondria etc.
• Locomotion through flagella.
• Prokaryotes contain cell wall
(absent in Mycoplasma) Fig. Bacterial cell

9. BACTERIA CHARACTERS
• Bacteria are prokaryotic in nature.
bacteria lacks prominent nucleus.
• Cell wall contains peptidoglycan (
absent in mycoplasma). They may
be motile(flagella) or non motile.
• Bacteria posses variety of shapes
in them. example - they may be rod
shaped (bacilli), spherical (cocci)
etc.
• They are cosmopolitan in
distribution i.e., their habit is
diversified.
• Reproduction by asexual method.
the sexual reproduction mean here
by the recombination of different
dna fragments.

10. Strains
• A strain is a subset of a bacterial species i.e.,
it is a low-level taxonomic rank, usually at
intraspecific level (within a group) differing
from other bacteria of the same species by
some minor but identifiable difference and
different functions.
• Strains refer to the small changes in bacterial
genotypes. Genotypes list only genes that are
mutated in the bacterial strains.

11. Prokaryotes(Bacteria) does not satisfy the
criteria for species concept
• Bacteria's are morphologically identical but physiologically they
are different.
• They keep on changing their genetical composition.
• They can easily acquire the characteristics of other bacteria. By
taking their genetic material.
• They are very flexible at releasing and picking the genes of other
bacteria.
• They lack true sexual reproduction but it occurs through another
process known as Recombination.
• Their biochemical functions are totally different even the
individuals belong to the same genus.

12. Examples
Lactobacillus Bacillus thuringiensis
Salmonella typhi (pathogenic)Escherischia coli (non-pathogenic)

13. Conclusion
• From the points mentioned it is clear that prokaryotes
(bacteria) does not fit into the species concept and could
not maintain the species concept criteria's.
• And for that reason it is not clear that whether bacteria
should be called as species or a strain.
• Several scientists are still in doubt in this serious matter
of debatable topic. As it is very difficult to speak out the
correct term for the prokaryotes as well as for bacteria.