vinutha seminar 2008

8/4/2019 Vinutha Seminar 2008

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Contents

i)Introductiona)Stages in taxonomy.b) Importance of taxonomy.

ii) Basic components of systematic.

1) Classification.2) Identification.3) Description.4) Nomenclature.5) Phylogeny.

iii) Species concept.

1) Salient feature of species.2) Types of species concept.

a) Morphological species concept.b)Biological species concept.c)Evolutionary/Ecological species

concept.


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Sl no. contents Pageno.

i Introduction

a)Stages in taxonomy.b)Importance of taxonomy

ii Basic components of systematic1) Classification.2) Identification.

3) Description.4) Nomenclature.5) Phylogeny.

iii Species concept.1) Salient feature of species.2) Types of species

concepts.a) Morphological speciesconcept.

b)Biological species concept.c)Evolutionary/Ecologicalspecies concept.

IV Summary.

v Reference.


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Introduction

Linnaeus

The diversity of life on earth is overwhelming, the total number of living species generally

range from 10 to 100 million. Too many species exist today and throughout the fossil record

for us to remember and communicate about each one individually. For centuries, humans

have attempted to organize, or classify, organisms into categories that make sense. The most

famous system of classification, developed by Linnaeus in the 1700s and still used today, is

the binomial nomenclature system. There are two important features of this system. First each
http://en.wikipedia.org/wiki/File:Carl_von_Linn%C3%A9.jpg


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species has a two-part name: genus and species. Second, the system classifies species into

hierarchical groupings, in which groups are nested within larger groups. Similar species are

grouped into a genus. Similar genera are grouped into a family, and so on. In short, organisms

are classified together because they are similar.

Charles Darwin made an extremely important observation about classification: organisms

are

Classified together because they are similar; they are similar because they stem from a

common ancestor. This point cannot be emphasized enough. The foundation of taxonomy is

evolutionary relatedness; classification reflects the history of species. This idea forms the

basis of modern systematics. The main goal of modern systematics is to make biological

classification reflect evolutionary history.

Systematics was initially recognized as a more inclusive field of study

concerned with the diversity of animal and their naming, classification and

evolution. Simpson (1961) defined systematics as a scientific study of kinds

and diversity of organisms, and its relationships between them. The scope of

taxonomy has, however, been enlarged in recent years to make taxonomy and

systematics synonymous. Some authors prefer to differentiate between them,giving systematics a broader definition and restricting taxonomy to the study of

classification .A broader definition (Stace , 1980) of taxonomy to coincide with

systematics recognise it as the study and consequences of this variation, and

the manipulation of the data obtained to produce a system of classification.

Taxonomy now is thus a broadened field for the study of nomenclature,

classification, identification and phylogeny. Taxonomy is the science of

describing, naming, and classifying living and extent organisms. In the year

1813, Prof A P Candolle coined the word Taxonomy. Taxonomy is the study

of principles and practices of classification, which is nothing but the ordering of

animal in to groups, on the basis of their relationships i.e of association of

animals by contiguity, similarity or both (Simpson, 1961). Black welder

(1967) defined classification as the arrangement of individuals into groups

(Taxa) and the groups into a system in which the data about the kinds determine

their position in the system and there after are reflected by the position. Mason

(1950) define Taxonomy as the synthesis of all the facts about organisms into a

concept and expression of interrelationships of organism. Heslop Horrison

(1953) explain Taxonomy as the study of principle and practices of classification

in particular method. Simpson (1961) defined taxonomy as theoritical study of

classification including its basic principles, procedures and rules. Davis

Heywood (1963) consider Taxonomy as the way of arranging and interpreting

information. Black welder (1967)explain Taxonomy as day today practice of


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handling different kind of organisms which include collection and identification of

specimens, The publication of data , the study of literature and the analysis of

variation show by the specimens. Johnson (1974) say, it is a science placing

biological forms in order. Christoffersen (1995) define Taxonomy as the

practice of recognising, naming and ordering taxa into a system of words

consistant with any kind of relationships among taxa that investigation has

discovered in nature. Taxonomy is the most basic activity in biology dealing

excusely with discover, ordering and communication of patterns of biological

taxa thus. Taxonomy includes classification and nomenclature but recently

depend mainly on systematic for its concepts.

STAGES IN TAXONOMY

Theoritically it is now well understood that, the taxonomy of a given group

passes through different stages. They are 1) Alpha or Analytical phase-is the

level at which species are characterised and named.2) Beta or Synthetic phase-refers to the arrangement of species in to a natural system of lower and higher

categories.3) Gama or Biological phase-which is the analysis of interspecific

variation and evolutionary studies. i.e the study of speciation. But practically it is

rather too difficult to separate these different stage .As they overlap and they

are integrated. In majority of the groups, the taxonomical work is still at Alpha

and Beta levels, where as only some Vertebrates. Specially, Aves and few

Insects (belonging to Order Lepidopeter) are examples where taxonomy has

reached up to Gama level.

IMPORTENCE OF TAXONOMYEach species of animals occur in nature in many different forms like sexes,

larvae, nymphs, pupae, seasonal forms etc. Taxonomy helps up to know about

all these living thing present around in nature.1.5 million species have been

discovered and it is estimated that about 30 million species still await discovery.

In order to understand over all biology of organisms, it is necessary to put such

large number of species into definite groups so the extent of their harmful and

useful properties are established.

Theoretically systematics has helped us in knowing structure of species andevolutionary role of peripheral population. It is only the taxonomist reaffirmed

role of natural selection as evolutionary factor in contrast to mutation theory of

Mendel. Mimicry and other evolutionary areas have also been clearly

understood through taxonomy. It also played important role in the development

of behavioural science. It is key to study of ecology. Practically the applied

biologists are heavily dependent on taxonomy for laying accurate proof

experiments and getting quick useful results. For example-Chemical control of

pest using insecticides is only a short term need. The appearance of insecticide

resistant strains of pest and the problem of hazards residues in food, water, air

etc. have led to the conclude that, the best and perhaps the only way to save ourcrops from insects is to organise and IPM (Integrated pest management.) in


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which different control methods with the use of chemical with the use of

resistant plant verities, predators and parasites, pheromones, hormones and

lethal gene are all integrated. All these methods (expect the use of insecticides)

are highly species specific and can only succeed if the identity of the pests or

pest is accurately determined through taxonomical studies. In the following

areas also taxonomy plays an impotent role in biological control, in public health,

wildlife management , mineral prospecting through paleontological studies by

taxonomists of the fossils present in the sedimentary rocks in national defence,

environmental problems especially pollution study, indicator organisms, soil

fertility etc.

BASIC COMPONENTS OF SYSTEMATICS:Various systematic activities are directed toward the singulargoal of constructing an ideal system of classification that

necessitates the procedures of identification, description,nomenclature and constructing affinities.

1)CLASSIFICATION

No discussion of evolution and systematics would be complete withoutconsidering classification. Classification refers to a system of organizingand naming living (or once living) things. What rules should we use forclassifying organisms? By now, the usefulness of identifying phylogeneticrelationships among species and clades should be clear evolutionary

processes structure the diversity of life and phylogenetic methods may beused to reconstruct the pattern of evolution. For this reason, it is mostinformative to name groups of species on the basis of their phylogeny.Recall that phylogenies are hierarchical and clades are interested. Namingsuccessively more inclusive clades, or groups of species that sharecommon ancestry, reflects the process of descent with modification.Not all classifications are organized according to patterns of phylogeneticrelationships, however. In fact, the system of classification that biologistsand palaeontologists use today was established before evolution wasrecognized as the process structuring patterns of phylogeny. In the

eighteenth century, a Swedish biologist named Carl Linn developed asystem for naming groups of species (higher taxa) and ranking them in aparticular hierarchy. He arranged in a hierarchy with the largest group,the kingdom at the top of the hierarchy, the categories that Linnaeus usedword kingdom, phylum, class, order, family genus and species. Eachcategory is a unit and is also called taxon. So the principles governing thegrouping of species in to higher taxa are based fundamentally onevolution. Systematics classify organisms will be based on trulyevolutionary criteria.

Phylum Chordata

Subphylum Vertebrata


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Class Mammalia

Subclass Theria

Infraclass Eutheria

Order Primates

Family Hominidea

Genus Homo

Species sapiens

2) IDENTIFICATION

Identification or determination is recognising specimen with an alreadyknow taxon, and assigning a correct rank and position in an extentclassification.

3) DESCRIPTION

The description of a taxon involves listing its features by recordingappropriate character states. A shortened description consisting of only

those taxonomic characters which help separate a taxon from closelyrelated taxa, from diagnosis, and the characters are termed diagnosticcharacters.

4) NOMENCLATURE

Nomenclature deals with determination of a correct name for a taxonusing rules and recommendations of the International Code of ZoologicalNomenclature (ICZN). Updated every six years or so, the Code helps inpicking up a single correct name out of numerous scientific names

available for a taxon, with a particular circumscription, position and rank.To avoid inconvenient name changes for certain taxon, a list of conservednames is provided in the code.

5) PHYLOGENYContinued speciation will generate groups of closely related species. Aclade is a group of species that includes an ancestral species and all of itsdescendants. Clade (also called monophyletic groups), like species, areformed by the process of descent with modification. A phylogeny is apattern of common ancestry reflecting this evolutionary process. We callour own "family phylogeny" a family tree or a genealogy; the all these

terms refer to the same type of pattern generated at different scales bythe evolutionary process of common descent.


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Phylogenetic Inferencespecies and clades originate over evolutionary time scales, by the splittingor branching process inherent in reproductive isolation), we cannotobserve their origination directly. Instead, we must infer the relativetiming of origin of species by comparing features that they possess. How

do we decide which species are closest? And especially how do we decidewhich species branched off from which? We use special methods ofphylogenetic inference, developed over the last several decades, tocompare features present in a given group of species to allow us to figureout how they are related to one another. These methods are based on thesame simple principle that we use unconsciously to guess at humanfamily relationships. Closely related individuals tend to share a largernumber of similar features than do distantly related individuals, as a resultof their shared common ancestry.

Is a whale more closely related to a human or a shark? Even though

whales and sharks both share certain features of overall body form, byfollowing phylogenetic methods of observation and comparison (discussed


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in more detail below), we conclude that whales and humans actually havemany more detailed features in common than do whales and sharks. Thiscan be explained by the fact that whales share a more recent commonancestry with humans than they do with sharks. We predict that theircloser relationship means that they share more features in common, and

the evidence supports this prediction. Similarities between whales andsharks are largely superficial and result from their common aquatichabitat, not from their descent from a common ancestor. Phylogeneticsystematics is the name of the field of study in which genealogicalrelationships among species and clades are discovered. Systematistspractice systematic methods of reconstructing phylogenies in order tounderstand the pattern and process of evolution.

Cladograms and Phylogenetic TreesPhylogenetic patterns generated from branching processes may be

represented in at least two different ways: cladograms and phylogenetictrees. Cladograms are branching diagrams that illustrate patterns ofphylogenetic relationships. The pattern of branching itself is the focus of acladogram; the relative lengths of branches in cladograms have no specialsignificance. Time is included in cladograms only in a relative sense, inthe internested structure of the cladogram itself. For example, we see thatsharks originated before whales, but cannot tell from the cladogram howlong before. Phylogenetic trees are branching diagrams that illustrateboth branching patterns and time; branch lengths have meaning in thesense that longer branches imply longer periods of time. We can think ofboth cardiograms and trees as phylogenetic maps. Both express

hypotheses about a phylogeny a pattern of evolution

Examining Characters

There are two types of characters in phylogenetic inference homologous characters "tell the truth" about phylogeny and homoplasticcharacters are deceptive about phylogenetic relationships. Homologouscharacters share common ancestry and for this reason they are useful in

reconstructing phylogeny. They are often, but not always, similar to oneanother in appearance. Homology of two states can be tested bycomparing the development and location of the features on organisms.Hair, for example, develops in the same manner, from the same kind ofcells in the skin in all mammals. Hair is homologous in cows, bats,humans, and all other mammals.

Homoplastic (analogous) characters may also be similar in appearance,but have actually evolved from different ancestors. Homoplasticcharacters can distort patterns of relationship indicated by homologouscharacters because they are often in conflict with them. Octopus eyes and

human eyes are homoplastic; they develop very differently and haveevolved independently in two remotely related groups of animals. Body


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form in whales and fishes is homoplastic and relates to their aquatic modeof life. Wings in birds and bats have evolved separately in each group;these features are homoplastic as wings. However, they are homologousas forearms, because they evolved in each case from the front limbs.Characters change from one state to another through the process of

evolution. The initial (old) state is said to be ancestral (or plesiomorphic);the new or novel state is derived (or apomorphic) relative to the ancestralstate. For example, brain to body size ratios increased in humanevolution. Relatively smaller brains are ancestral, relatively larger brainsare derived. Closely related organisms share derived features, such asfeathers shared by birds. Characters shared through common ancestry(homologues) and derived relative to a former state are called sharedderived characters or synapomorphies. Species and clades are defined bythese new features because they are more informative than sharedancestral characters.

Character Polarity.The direction of character change in evolution, from ancestral to derived,is referred to as character polarity. It is not always obvious whichcharacter states are derived and which ancestral. Some criteria fordetermining the direction of character change in evolution must beestablished. Ancestral and derived states are always identified as such bycomparison to a frame of reference. Of several possible character states(e.g., hair present, hair absent), the ancestral state is the one present in aclosely related species outside the group of interest (outgroup criterion),or the one appearing lower in the stratigraphic record (paleontological

criterion), or earlier in development (ontogenetic criterion). Becauseancestral and derived states are determined relative to some referenceframe, their status changes if the frame of reference changes. Hair isderived for mammals (relative to other [non-mammalian] vertebrates),but ancestral for humans, because the closest relatives to humans,gorillas and chimps, also have hair. Consider whales, which have veryminimal hair. Does their apparent lack of hair mean that whales are notmammals? No. Because of many other shared derived characters ofmammals that whales possess (for example, giving birth to live young andnursing their young), we conclude that whales are mammals that nolonger need much hair for their fully aquatic mode of life. Loss of hair isthus a derived feature for whales, among the mammals.

All living things are related to each other, more closely or more distantly.This relative pattern of relationships can be expressed in a vast, nestedhierarchy the hierarchy of life represented in a series of internestedcladograms. The possession of certain features (homologues) can helplocate the position of an individual in the hierarchy of life. Closely relatedindividuals tend to share a larger number of similar features than dodistantly related individuals as a result of their shared common ancestry.Establishing the pattern of character distribution among individuals and

among species and higher taxa can therefore reflect and reveal theprocess of common descent with modification the process of evolution.


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Species concepts

Species is the basic or lowest unit in the classification of animals. Species

is a group of genetically similar individuals with mate with each other

Salient features of species.

1) A species is a Mendelion population or a biological unit.

2)The members of species possess distinct morphological characters.

3)The member possess identical genes.

4)The members of a species are tied together by bonds of mating.

5)The members interbreeding among themselves.

6)They are reproductively isolated from other species.

7)They share a common gene pool.

8) A species is an isolated pool of genes flowing through space and

time, constantly adapting itself to changes in its environment aswell as to the new environment.


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9) Each species is an isolated pool of gene which interconected by

gene flow.

10) Each species fills an ecological niche not exactly utilized by

another species.

11) Each species posses a set of isolating mechanisms that

indirectly or directly prevent exchange of genes with other species.

12) Each species has the capacity to give rise to new species.

There are numerous species concepts at the research and practical

level in the scientific literature. A recent count put the number of

different species concept at more than 24. All species concept are

united by basic principles of evolution. Some organisms diverged more

recently than others and thus more closely related.

1. Agamospecies*

Asexual lineages, uniparental organisms (parthenogens and apomicts), that cluster

together in terms of their genome. May be secondarily uniparental from biparental

ancestors . Quasispecies are asexual viruses or organisms that cluster about a "wild-type"

due to selection. Cain (1954), Eigen (1993, for quasispecies).

2. Autapomorphic species

A phylospecies conception. A geographically constrained group of individuals with some

unique apomorphous characters, the unit of evolutionary significance (Rosen 1979); simply

the smallest detected samples of self-perpetuating organisms that have unique sets of

characters (Nelson and Platnick 1981); the smallest aggregation of (sexual) populations or

(asexual) lineages diagnosable by a unique combination of character traits (Wheeler and

Platnick 2000). Nelson and Platnick (1981); Rosen (1979).

3. Biospecies*

Defined by John Ray, Buffon, Dobzhansky (1935); Mayr (1942). Inclusive Mendelian

population of sexually reproducing organisms (Dobzhansky 1935, 1937, 1970);

interbreeding natural population isolated from other such groups (Mayr 1942, 1963, 1970;Mayr and Ashlock 1991). Depends upon endogenous reproductive isolating mechanisms.

4. Cladospecies

Set of organisms between speciation events or between speciation event and extinction

(Ridley 1989), a segment of a phylogenetic lineage between nodes. Upon speciation the

ancestral species is extinguished and two new species are named. Hennig (1950; 1966);

Kornet (1993).

5. Cohesion species

Evolutionary lineages bounded by cohesion mechanisms that cause reproductive

communities. Templeton (1989).


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6. Compilospecies

A species pair where one species "plunders" the genetic resources of another via

introgressive interbreeding. Harlan (1963); Aguilar and others (1999).

7. Composite Species

All organisms belonging to an internodon and its descendents until any subsequent

internodon. An internodon is defined as a set of organisms whose parentchild relations

are not split (have the INT relation). Kornet and McAllister (1993).

8. Ecospecies*

A lineage (or closely related set of lineages) which occupies an adaptive zone minimally

different from that of any other lineage in its range and which evolves separately from all

lineages outside its range. Simpson (1961); Sterelny (1999); Turesson (1922); Van Valen

(1976).

9. Evolutionary species*

A lineage (an ancestraldescendent sequence of populations) evolving separately from

others and with its own unitary evolutionary role and tendencies. Simpson (1961); Wiley

(1978, 1981).

10. Evolutionary significant unit

A population (or group of populations) that (1) is substantially reproductively isolated from

other conspecific population units, and (2) represents an important component in theevolutionary legacy of the species. Waples (1991).

11. Genealogical concordance species

Population subdivisions concordantly identified by multiple independent genetic traits

constitute the population units worthy of recognition as phylogenetic taxa. Avise and Ball

(1990).

12. Genic species

A species formed by the fixation of all isolating genetic traits in the common genome of

the entire population.

13. Genetic species*

A group of organisms that may inherit characters from each other, a common gene pool, a

reproductive community that forms a genetic unit. Dobzhansky (1950); Mayr (1969);

Simpson (1943).

14. Genotypic cluster

Clusters of monotypic or polytypic biological entities, identified using morphology or

genetics, forming groups that have few or no intermediates when in contact. Mallet

(1995).


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15. Hennigian species

A phylospecies conception. A tokogenetic community that arises when a stem species is

dissolved into two new species and ends when it goes extinct or speciates. Hennig (1950,

1966); Meier and Willman (1997).

16. Internodal species

Organisms are conspecific in virtue of their common membership of a part of a

genealogical network between two permanent splitting events or a splitting event and

extinction. Kornet (1993).

17. Least Inclusive Taxonomic Unit (LITUs)

A taxonomic group that is diagnosable in terms of its autapomorphies, but has no fixed

rank or binomial. Pleijel (1999); Pleijel and Rouse (2000).

18. Morphospecies*

Defined by Aristotle and Linnaeus, and too many others to name, but including Owen,

Agassiz, and recently, Cronquist. Species are the smallest groups that are consistently and

persistently distinct, and distinguishable by ordinary means. Contrary to the received

view, this was never anything more than a diagnostic account of species. Cronquist

(1978).

19. Non-dimensional species

Species delimitation in a non-dimensional system (a system without the dimensions of

space and time). Mayr (1942, 1963).

20. Nothospecies

Species formed from the hybridization of two distinct parental species, often by

polyploidy. Wagner (1983).

21. Phenospecies

A cluster of characters that statistically covary; a family resemblance concept in which

possession of most characters is required for inclusion in a species, but not all. A class of

organisms that share most of a set of characters. Beckner (1959); Sokal and Sneath

(1963).

Phylospecies

The smallest unit appropriate for phylogenetic analysis, the smallest biological entities

that are diagnosable and monophyletic, unit product of natural selection and descent. A

geographically constrained group with one or more unique apomorphies (autapomorphies).

There are two versions of this and they are not identical. One derives from Rosen and is

what I call the autapomorphic species conception. It is primarily a concept of diagnosis

and tends to be favored by the tradition known as pattern cladism. The other is what I call

thephylogenetic taxon species conception, and tends to be favored by process cladists.

Cracraft (1983); Eldredge and Cracraft (1980); Nelson and Platnick (1981); Rosen (1979).


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22. Phylogenetic Taxon species

A phylospecies conception. A species is the smallest diagnosable cluster of individual

organisms within which there is a parental pattern of ancestry and descent Cracraft

(1983); Eldredge and Cracraft (1980); the least inclusive taxon recognized in aclassification, into which organism are grouped because of evidence of monophyly

(usually, but not restricted to, the presence of synapomorphies), that is ranked as a

species because it is the smallest important lineage deemed worthy of formal recognition,

where "important" refers to the action of those processes that are dominant in producing

and maintaining lineages in a particular case Nixon and Wheeler (1990); Mishler and

Brandon (1987).

23. Recognition species

A species is that most inclusive population of individual, biparental organisms which share

a common fertilization system. Paterson (1985).

24. Reproductive competition species

The most extensive units in the natural economy such that reproductive competition

occurs among their parts. Ghiselin (1974).

25. Successional species

Arbitrary anagenetic stages in morphological forms, mainly in the paleontological record. S

George (1956); Simpson (1961).

26. Taxonomic species*

Specimens considered by a taxonomist to be members of a kind on the evidence or on the

assumption they are as alike as their offspring of hereditary relatives within a few

generations, Whatever a competent taxonomist chooses to call a specie Blackwelder

(1967), but see also Regan (1926); Strickland and others (1843).

Out of these many species concept, I am going to discusses some of the

following species concept,which are at almost importence and may be acceptable from

zoologist point of view:

1) Morphological species concept (MSC)

Taxonomists defined species on the basis of morphological characterstics.

According to Tade Ragan a species is a community or a number of related

communities having distinctive morphological character.

Biologists describe new species on the basis of visible anatomical characteristics,

a process that dates back to Linnaeus classification of organisms in the

seventeenth century. This approach is based on the morphological species

concept, the idea that all individuals of a species share measurable traits that

distinguish them from individuals of other species.


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The morphological specie concept has many practical applications. For example,

paleobiologists use morphological criteria to identify the species of fossilized

organisms. And because we can observe the external traits of organisms in

nature, field guide to plants and animal list diagnostic physical characters that

allow us to recognise them.

Nevertheless, relying exclusively on a morphological approach can present

problems. Consider the variation in the shells of Cepaea nemoralis. How could

anyone imagine that so variable collection of shell represents just one species of

snail? Moreover, morphology does not help us distinguish some related species

that are nearly identical in appearance. Finally, morphological species definitions

tell us little about the evolutionary processes that produce new species.


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2) Biological species concept (BSC)

Species ias a sexually interbreeding or potentially interbreeding group ofindividuals normally separated from other species by the absence of genetic

exchange. Dobzhansky (1937) has defined species as the stage in the

evolutionary process at which the once actually or potentially interbreeding array

of forms become segregated into two or more separate arrays which are

physiologically incapable of interbreeding. In brief, acording to Dobzonsky

species are the Mendelian Population, which share common gene pool.

Mendelian population is defined as a community of similar individuals living

within a particular area and particular time and capable of interbreeding. Mayr

(1942) states that species is a group of actually or potentially interbreeding

population that is reproductively isolated from other such groups, the definition

given by Dobzhasky and Mayr are widely accepted.

Species is composed of populations whose members mate with each other and

produce fertile offspring or would be so if they came into contact. Conversely,

population whose members do not mate with each other or who cannot produce

fertile offspring are said to be reproductively isolated and thus members of

different species.

Reproductive isolation results organisms cannot interbreed or cannot produce

fertile offspring they clearly belong to different species. However, so populations

that are considered separate species can interbreed and produce fertile

offspring, but they ordinarily do not do so under natural conditions. They are still

considered reproductively isolated in that gene from one specie generally will

not be able to enter the gene pool of the other species. Such barrier is

reproductive isolating mechanisms. Because they prevent genetic exchange

between species .We will discuss examples of these, beginning with those that

prevent the formation of zygotes, which are called prezygotic isolating

mechanism. postzygotic isolating mechanisms prevent the proper functioning of

zygotes after they form.

Species maintain their genetic distinctiveness through barrier to reproduction.

Prezygotic isolating machanisms, postzygotic isolating mechanisms operate to

help to species retain their identities.

a) Geogrophic isolation-

Species occur in different area, which are often separated by a physical barrier

such as a river or mountain range.


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b) Ecological isolation-

Ecological isolation occurs when different species live in the same geographic

area but occupy different habitats within that area. These barriers are

byproducts of different adaptation to local environment. Under these

circumstances, individuals of different species do not hybridize simply because

they rarely encounter one another.

For example, until recently, the natural ranges of lion and tigers in India

overlapped. However, these two species have different habitats; lion live andbreed in the open grassland While, tiger generally stay in the forest. Thus, even

though lions and tiger technically can mate and produce viable offspring, this is

rarely if ever occurs in natural setting.

c) Temporal isolation

Many species of closely related amphibians have different breeding seasons that

prevent hybridization between the species. For example, five species of frog of

the Rana occur together in most of the Eastron USA, but hybrids are rare

because the peak breeding time is different for each of them.

d) Mechanical isolation

Structural difference prevent mating obvious features as size, the structure of

the male and female copulatory organs many be incompatible. In many insects

and other arthropod groups, the sexual organs, particularly those of the male,

are so diverse that they are used as primary basis for distinguishing species.

e) Prevention of gamete fusion.

In gametes directly in to water, egg and sperm derived from different species

many not attract one another. Many land animals may not hybridize successfully


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because sperm of one species function so poorly within the reproductive tract of

another that fertilization never takes place.

Postzygotic isolating mechanisms.

Postzygotic isolating mechanisms are those in which hybrid zygotes fail to

develop or develop abnormally, or in which hybrids cannot become established

in nature.

Example: In Leopard frog Rana pipiens, Rana blairi, Rana sphenocephala,

Rana berlandieris. These four species resemble one another closely in their

external feature. Their status as separate species was first suspect, when hybrids

between some pairs of these species were found to produce defective embryos

in the laboratory.

Geographic variation within species.

Population change in response to shifting environment and separate populations

of species frequently differ both genetically and phenotypically. Neighbouring

populations often have shared characteristics because they live in similar

environment, exchange individuals and experience compare patterns of

selection. Widely separated population, by contrast many live under different

condition and experience different patterns of selection; because gene flow is

less likely to occur between distant populations, their gene pools and

phenotypes often differ.

When geographically separate population of a species exhibit dramatic, easily

recognized phenotypic variation, biologists many identify them as differentsubspecies, which are local variation have provided great insight into the

speciation process. Two of the best studied patterns are ring species and clinal

variation.

Ring species-Some plant animal species have a ring shaped geographical

distribution that surrounds uninhabitable terrain. Adjacent populations of these

so called ring species.These species can exchang genetic material directly but

gene flow between distinct populations occurs only through the intermediary

populations.

The lungless salamander Ensatina eschscholtzii is an example of ring species,

it is widely distributed in the Coast mountains and the Sierra Nevoda of

California, but cannot survive in the hot dry central valley. Seven subspecies of

differ in biochemical trait, color, size and ecology. Individuals from adjacent

subspecies often interbreed where their geographical distributions overlap and

intermediate phenotype are fairly common. But at Southern end of the central

valley, adjacent subspecies rarely interbreed. Apparently they have exchange

genetic material directly.

Clinal variation-When a species is distributed over a large environmentally

diverse area, trait may exhibit a cline, a pattern of smooth variation along ageographical gradient. Clinal variation usually result from gene flow between


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adjacent population that are each adapting to slightly different conditions .For

example, many birds and mammals in the northern hemisphere show clinal

variation in body size and the relative length of their appendages. In general,

population living in colder environments have larger bodies and shorter

appendages, a pattern that is usually interpretd as a mechanism conserve heat ,

if a cline extends over a large geographic gradient, populations at the opposite

ends many be very different.

Although the biological species concept has wide following it faces some

problems, when applied to certain group of animals. The species are mainly

determined from their visible characteristics, and in some cases such

characteristics are either imperceftible and in some cases poorly developed. In

such cases one has to depend on visible or less convenient characters because

the species do exist irrespective being visibly express or not following are the

hurdles:

1. Asexual or apomictic groups: Apomicti are the animals are plants

produced by a process called apomixes in which the reproduction has

the superficial appearance of ordinary sexual reproduction(amthimixis)

but occurs without fertilization and meiosis. These asexually reproducing

forms do not fulfill the criteria the interbreeding which is the important

characteristics of biological species concept. In asexual reproduction all of

the following is lacking meiosis, gametes production, fertilization, transfer

of genetic material between individuals and parthenogenesis.-Which is

nothing but development of an unfertilized gamete (egg cell) into new

individuals. Asexual and parthenogenesis are basis of natural cloning

Thalyto is a form of animal of parthenogenesis is the common cause of

male haploidy, as males are either very rare effectively without a genetic

role are entirely absence. There are about 1000 Thalytokus animals from a

large number of taxa only about 25 [4 fish, 2 Salamandres and about 19

Lizards] are vertebrates. Such cases pose great problems to a taxonomists

. Mayr 1940 gave a good reasoning about such groups in being

descendents of single sexual species as a collective species including all

strains arising due to mutation except polyploids all these are likely to

terminate sooner or later either by extintion or fusion with another line

through a sexual process.

2. Sibling or species: Sibling species are very clearly related species differing

only in minor respects or appearing identical but in fact reproductively

isolated. In these species classification depends upon cytological

techniques such use of DNA probes[in which a defined and fairly short

labeled DNA sequence 5 propagated by gene manipulation and introduced

to DNA from a different taxon in order to detect complementary DNA

hybridization] species also one freely or not at all separated

morphologically.

3. Gradual speciation or anagenesis: Is a process by which characters change

during evolution within species by natural selection or genetic drift or any


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non branching speciation in which species originate along a single line of

descent yet only one species represents the linage aafter any speciation is

not possible within the biological species concept for reproduction

isolation never comflcted between ancestral and descendent species.

Moreover, we still do not have any sure method designating an entity as a

subspecies or species therefore, this criterion at this movement soly

depends upon the knowledge of an experienced taxonomists.

4. Ring species or rings of races: Ring species are characterized by circular or

looped goegraphical distribution adjacent population interbreeding on the

two arms of the loops but not where arms over lap .

Transitivity is the relational propants of populations interbreeds

with is transitive if when population A interbreeds with population B, and

population A interbreeds with population C, then population B interbreeds

with population C. Ring species indicates that interbreeds with is not

transitive at the population level and so cannot job with demands of it.

These ring species are good species like the allopatric ones not related by

intergrading populations. It intermediate population are taless into account

each such populations irrespective of differences sometimes interbreeds with

the members of populations on each side of their own populations under such

cases, it becomes very difficult for biologists to regard such end-populations

of different species or the same species on the basis of reproductive isolation.

The problem s also arises, if one takes into the account the reproductive

criterian following the theory of evolution explaining the fact the all organismshave descended from relatively few initial individuals. In majority of such cases

the parent and offspring generation can potentially interbreed producing

temporal chain races except asexually reproducing form. If the principle of

interbreeding is applied on these cases one vwill be force to believe all nearly all

animals both of the past and present,belong to the same species their

theoretically; of one insistes on depending on to critarian of interbreeding

reproductive isolation biological species concept will be forced to arrive at some

decision which may be arbitory with regard to reproductive creterian.

Hybrid complexes: Hybrid complex are progeny relating from a cross between

the genetically non identical individual parents of a hybrid have a little

chromosome homology particularly where these have different chromosome

number hybrid offspring will be sterile through failure of chromosome to pair

during meiosis although one offspring sex may be partially or completely fertile.

This hybrid sterility is one factor maintaining species boundary and selection

against hybrids is a major factor in through of speciation. The BSC fails to give

satisfactory answer when applied to these hybrid complexes, which are also

called Synganon(Lotsy 1925) Mayr (1940) have redefined hybrids as the one

which reflects the some total of species similar species linked buy frequent or

occasional hybridization


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3) evolutionary/ecological species concept. (ESH)

As studied earlier BSC fails when applied to uniparental organism. Where

absolute self fertilization renders interbreeding impossible there by suppressingthe physical link which is a most for individuals of same species, thus Grant


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supports BSC, but only for sexual reproducing forms which is also the view of

Megalitsch (1984 ),Simpson (1964) then defines an evolutionary species as a

lineage-ancestral descendent sequence of population evolving separately from

others and with its own unitary evolutionary role and tendencies. The ESC of

Grant is based on this fact and is applicable not only asexual reproducing

population, but also fossil lineages. Wikey (1978) reconsidered this ESC andconcluded that a species is a single lineage of ancestral decendent population of

organism. Which maintain its own evolutionary tendencies and historical fate.

Willis (1981) on contrary believes that each species is an internally similar part

of phylogenetic tree. A species may be branched or not; it originated and

perhaps ended at some intermediate plane in case of allopatric species. i.e a

parent spacies becomes physically separated in to daughter population by

geography restricting or eliminating gene flow between overlapping population.

In case of sympatric speciation at a plane across the base of a branch a parent

species differentiates in to leniages in the absence of any physical restrictions or

gene flow.

Thus recently fever has developed for ecological and evolutionary species

concepts. The ecological species concept fix a classification to independently

existing environmental states are niches; difficult to isolate independently of the

organism, which occupy them equating speciation with niche change (is one

niche one species) but living open the exact of change required the latter stress

on the genealogical uniqueness of species useful in asexual tytotokous form, but

emphasize the cladistic(branching) nature of speciation at the expense of

gradual anagensis.

Summary.

Taxonomy is essential to identifying species that are important for human health

and food production and for the protection, conservation and maintenance of

functioning ecosystem. It also provides the evidence for naming organisms,

which is the basis of all scientific all scientific and popular communication about

organisms. Systematic guides the search for useful biological product, biological

control agents and potential food crop species. Systematic have both Taxonomy

and evolution.

The most basic category of biological classification is species. The biologicalspecies concept is one of the widely used and accepted way of delimiting

species. Biological species concept has limitations, which have led to the

proposal of alterative species concept, which are evolutionary/ecological species

concept, phylogenetic species concept.

University of Mysore

Department of studies in zoology


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Manasagangotri,

Mysore-560006.

Seminar topic:

Systematic and species concept.

Submitted to: prof. Sadananda

yamakanamaradi

Dos in zoology.

Submitted by: vinutha Patil.

IV semester, DOS in zoology.

Manasagangothri.

Reference:

Arumugam N.2009, Organic Evolution,

7th Edition. Saras publication,

Kanyakumari. PP 255-261.

Simpson.1961, Principal of AnimalTaxonomy, Oxford Bocle company.

NewDelhi.PP 02-33.


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Raven P.H ,2005, Biology. 7th Edition,

Tata Mograw Hill Publishing company

Limited, New Delhi. PP 471-488.Russell P.J 2008, Ecology, 1th Edition.

Cengage learning India Pvt htd., New

Delhi PP 78-95.

Mark Ridley. 1996, Evolution, 2th Edition.

Black Well science, Cambridge. PP 398-

424.


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vinutha seminar 2008

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