Concept of Different Conventional and Newer Aspects of Biosystematics

Earlier approaches of biosystematics were mainly based exclusievely on observed characters without going into the question of infraspecific differences. Many of the species are, therefore, known by single or a few specimens. The old morphological concept now includes ecological, genetical, biochemical and other characters.

A brief account of current approaches in biosystematics is given below -

1. Population approach: -

Study of population structure of a species leads to the study of population continuam. Population continuam is segregated by geographical isolation and ultimately new species may be formed due to the complete reproductive isolation.

Fig: Population approach

2. Morphological approach: -

Old morphological approach enters into the modern ultramorphology, ie. relative morphometrics (proportionate measurement of all organs during developement) micro- morphology (3D image of SEM) and other characters like genitilia, antennae, wings, integument etc. may be taxonomically studied with accuracy of SEM (Scanning Electron Microscope).

3. Embryological approach: -

Comparision wth the life history stages with adult leads to correct identification. In some species allometric (unproportionate growth) variability of growth in certain body parts is seen which required study for correct identification.

The whole classification of white flies (Homoptera : Aleurodidae) is primarily based on the structure of their pupa.

4. Ecological approach or Eco-taxonomy: -

Each species has its own niche in nature differing from its close relatives in habitat, food preferences, breeding and in various physical factors.

Eg.

A. Habitat – Drosophila persimilis – Higher altitude.

D. pseudobscura – lower altitude

B. Food – Galapagos, Finch sp. I – Seed on ground tree.

II – Nest on rocks.

C. Breeding – Europian Cormoent – Nest on tree.

North Atlantic Cormorent – Insect on tree.

D. Ecological characters of six sibling species Anopheles maculipenis.

5. Ethological approaches – Ethotaxonomy:

The use of behavioural characteristics into the systematic is very useful in separating the closely related species.

Eg.

A. Drinking habits among Pigeons.

B. Dust bathing among Passer.

C. Nature of webbing of Spider.

D. Sound spectrogram to distinguish Passer and other species of Birds, frog , cricket and other insects.

E. Length and frequency of light flashes in firely.

6. Cytological approach – Cytotaxonomy:

The cytological differences and its analysis help the taxonomists to differentiate closely related species. It includes -

I. Genome and Plasmon method: - It is known that the amount of DNA per chromosome set is species specific and the structure of cytoplasmic DNA is same in same species.

- Genome – (DNA of nucleus)

- Plasmon – (DNA of cytoplasmic organellies)

II. Karyological method (Karyotaxonomy): -

Study of chromosome or karyotaxonomy is quite useful both in determining the phylogenetic relationships of the taxa as well as in the segregation of sibling species or cryptic species. The number, shape and size of chromosomes are species specific.

Patterson and Stone (1952) differentiated 16 species of genus Drosophila on the basis of number and shape of the chromosomes. Kiatu (1968) was able to demonstrate the phylogenetic relationship among the various families of of the order Tricoptera on the basis of number of chromosome. Grewal (1982) separated some important species of fruitfly by karyological method.

Chromosome banding technique: -

The metaphasic chromosomes can be identified by using certain staining technique and it is called chromosome banding technique. The parts of the chromosome which take darker stain are visualized as continuous series of dark bands. G, Q, and R bands are distributed along the length of the chromosome. C band is restricted to the centromere and nuclear organizer region. G band and R band are most commonly used technique for chromosome identification. Comparisions of chromosome banding pattern can confirm evolutionary relationship between species.

Limitation of cytotaxonomy:

Cytotaxonomy alone cannot be the sufficient to solve all systematic problems. It can be used in selective cases. Cytotaxonomists should be very careful in case of geographical races, individual abnormalities, clines, polymorphic morphss and seasonal morphs. However karyological data can be better utilized in combination with other aspects of taxonomy.

7. Biochemical approach or chemotaxonomy: -

It is also called protein taxonomy or molecular taxonomy. It is classification of plants and animals based on similarities and differences in biochemical composition. It includes –

I. Species can be differentiated on the basis of amino acid sequences in the proteins of the organisms and differences between them are found in different organisms.

II. Changes in the enzyme structure can also help in the discovery of new species.

III. On the basis of quantitative analysis of ascorbic acid Basu and Chatterjee (1969) demonstrated phylogenetic relationships among various orders of birds.

IV. The occurance of specific pheromones can also help to differentiate the certain groups of organisms.

V. The similarities and differences of colour pigments, toxins and other specific compounds such as venom, alkaloids etc. of organisms also help to distinguish the taxonomic relationships among organisms.

Diffeent methods of biochemical analysis:

I. Immunological: - Proteins of one species will react strongly with antibodies to the proteins of closely related species than the distant one.

II. Cromatographical: - Paper cromatographical methods used to compare amino acids and peptides among different species.

III. Electrophoresis: - It is based upon on the electrical potential differences among the different complex compounds. Electrophoresis shows that insulin of of ox, horse and sheep are different. Analysis of egg proteins help to distinguish different species of Mollusc of the genus Bulinus.

IV. Infra red spectrophotometry: - It is based on the principle on the principle of absorption of infra red light by biological materials. This approach is mainly applied to micro organisms. Micks and Benedict (1953) applied this technique in the identification of mosquitoes.

V. Histochemical study: - It involves staining reactions, use of cryostat microscope and above all electron microscopes have made such studies more meaningful.

Histology of tissue may be same in the related species, but their histological composition will be different in different species.

Limitation of cytotaxonomy: -

Though cytotaxonomy is quite helpful in solving many taxonomic problems but it is not sufficient for all cases.

I. Biochemical study is possible for extant species, so it cannot aid in tracing the evolutionary relationships for aparticular taxon.

II. Like morphological characters, chemical characters too are variable. Hence, proper proper understanding of taxonomic relationship among organisms demands comparision of a number of biochemical characters in comnation with one another to reveal the biodiversity of biochemical patterns rather than a single biochemical characters

8. Numerical taxonomy: - (or taximatrics/ taximetry/taxonometrics)

Maximum number of characters with equal weight are analysed for correlation among different species/groups. Closer on similarities and distant on dissimilarities are constructed among the species. Character number may vary from 60 to 1000 in insect. It does not help in identification of new species but establishes correlation among different species. It is mostly used in insect. Now a day computer and numerical taxonomic programmers are standard resources in every museum and systematic library.