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 Phenetics/taxometrics/taximetrics: an attempt to classify organisms based on overall similarity, usually in morphology or other observable traits, regardless of their phylogeny or evolutionary

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(1)

PARALLELISM

CONVERGENCE AND

CONVERGENCE

(2)

Two modern trends in taxonomy:

 Phenetics/taxometrics/taximetrics: an attempt to classify organisms based on overall similarity, usually in morphology or other observable traits, regardless of their phylogeny or evolutionary

relation.

relation.

This method is largely based on principles and

methods of ‘Numerical Taxonomy’, pioneered

by Peter Sneath and Robert R. Sokal.

(3)

 In phenetics, organisms are grouped on the basis of mathematically calculated similarity.

 Groups so obtained are termed as ‘phenons’.

 Clustering of Phenons are often depicted in the

 Clustering of Phenons are often depicted in the form of a dendrogram, known as ‘phenogram’.

 Constituents of a particular phenon are morpho- logically or otherwise similar, but they are not

necessarily phylogenetically or evolutionarily related.

(4)
(5)

 Cladistics: This term was first coined by E. Mayr in 1969. The credit of founding the subject goes to W. Hennig (1950 & 1966).

This is a methodology that attempts to analyse phylogenetic data objectively to produce an

phylogenetic data objectively to produce an

objective phylogenetic classification.

(6)

Some important terms:

Cladistics has its own vast array of terminology.

A few of them are explained here.

Principle of parsimony: Parsimony literally means

‘extreme care in spending money, reluctance to spend money unnecessarily’.

spend money unnecessarily’.

The principle of parsimony states that ‘the shortest hypothetical pathway of changes that explains the present phenetic pattern is the most likely

evolutionary route’.

(7)

Plesiomorphous character state: Primitive, a character state that is inherited from parent population.

Apomorphous character state: Advanced or derived character state. A character state that is not present in parent population but appears in progeny.

in parent population but appears in progeny.

Symplesiomorphy: Possession of plesiomorphous character states in common by a group of taxa.

Synapomorphy: Possession of apomorphous

character states in common by a group of taxa.

(8)

 The groups obtained as a result of cladistic analysis are known as ‘clades’.

 The organisms comprising a clade are believed to

be the evolutionary descendants of a common ancestor.

 The organisms comprising a clade are essentially similar

 The organisms comprising a clade are essentially similar phylogenetically but not necessarily morphologically or

in other respects (cf. phenone)

 Diagrammatic representation of phylatic relationship

among clades constitutes ‘cladogram’ (cf. phenogram)

(9)
(10)
(11)

CONVERGENCE

B C

A

P Q

"possession of similar

characteristics in two or more groups without an immediate common

ancestor"

Thus the groups showing convergence are genetically different.

Convergence is the result of adaptations to similar

type of environment or similar reproductive biology.

(12)

Examples:

Euphorbia obesa

E. avasmontana

Astrophytum asterias

Stenocereus thurberi

E. tescorum Hylocereus setaceous

(13)

Camelina sativa

Linum usitatissimum

(14)

Phalaenopsis sp.

Calotropis procera

(15)

SOME MORE EXAMPLES

Presence of C4 pathway is such unrelated groups as grasses, sedges, members of Amaranthaceae, Chenopodiaceae,

Asteraceae and Euphorbiaceae.

 Evolution of CAM photosynthetic pathway in at least 20

unrelated families such as, Crassulaceae, Cactaceae, Bromeliaceae and Orchidaceae and recently in Clusiaceae.

(16)

 Evolution of parasitic mode of life in such distantly related taxa as Cuscuta (Convolvulaceae/Cuscutaceae),

Striga (Scrophulariaceae), Viscum (Loranthaceae/Santalaceae), Pilostyles (Apodanthaceae) is another example.

Pilostyles aethiopica Cuscuta reflexa Viscum album

(17)

PARALLELISM

A B C

" possession of similar

characteristics by two or more groups which have evolved

through different clades but have a common ancestor, in which

those characteristics are absent“ q

those characteristics are absent“

As the parallel groups have a common ancestors, therefore, they are genetically much similar.

Convergence is relatively easily detectable than the parallelism.

P q

(18)

EXAMPLES:

The two species Ranunculus tripartitus and R. hederacea have a similar aquatic habit and dissected leaves and have acquired these characters by parallel evolution.

The development of vessels in Gnetales and dicotyledons also represents a case of parallelism.

Presence of double fertilization in Ephedra and flowering plants Presence of double fertilization in Ephedra and flowering plants

(19)

DISJUNCTION AND VICARIANCE

(20)

DISJUNCTION

Occurrence of SAME taxon in two or more regions that are separated, such as the southern beech trees in the genus Nothofagus, found in South America and across the

Pacific Ocean in Australia, New Guinea and New Zealand.

Distributional patterns which are interrupted by

considerable areas from which the taxon is absent.

(21)

PACIFIC

Subgenus Lophozonia

and Nothofagus Subgenus Fuscopora

Subgenus Brassopora

PACIFIC

(22)

Australia

South America

(23)

Disjunct distribution of a liverwort, Chiloscyphus campanulatus Steph.

(Bhattachrya et al., 2011)

(24)

Geographic distribution of Sarraceniaceae

Darlingtonia (A) western North America; Sarracenia (B) eastern North America; and Heliamphora (C) northern South America

(25)

Clethra alnifolia Clethra alnifolia

 Species of the genus Clethra occur in in eastern and southeastern Asia, Malesia, North and South America, and one species (C.

arborea) on the island of Madeira.

Tecophilaeaceae have a disjunct distribution in California, Chile and southern and tropical mainland Africa.

 Sisyrinchium bermudiana ---Ireland and eastern North America.

 Convolvulus boissieri– southern Spain & eastern Balkans

(26)

Types of disjunction 1. Diffuse

Several isolated populations

2. Bipartite

Two isolated populations in the same

N

Two isolated populations in the same hemisphere

3. Bipolar

One population in each hemisphere

(27)

ORIGIN OF DISJUNCTION:

1. Long range dispersal: The presence of coconut on a great number of far-distant Pacific islands.

2. Relics of former widespread distribution: Currently disjunct taxon was widely and continuously distributed in past. Areas between

current patches became depopulated due to changed environment.

Occurrence of alpine species on isolated mountain ranges in Europe (Alps, Pyrenes, and Sierra Nevada).

3. Stepping stone bridges: In past Present disjunct areas might have 3. Stepping stone bridges: In past Present disjunct areas might have been connected by a series of islands etc. (stepping stones) which facilitated exchange of biota. These stepping stones have now

disappeared. Disjunct populations

(28)

4. Divergent Migration from a third area

Migration/Dispersal

Disjunct

Parent population Migration/Dispersal

Disjunct

Parent population disappeared

(29)

5. Polytopic origin: Evolution of a taxon at two or more separate places from same ancestral population.

6. Vicariance events: Geological events leading to formation of barriers: formation of mountains, seas and continental drift etc.

(30)
(31)

VICARIANCE (= splitting in the range of a taxon)

Two or more SIMILAR taxa occupying separate geographical or ecological areas are known as VICARIANTS or VICARIADS, and the

phenomenon is known as VICARIISM.

phenomenon is known as VICARIISM.

The geographical separation of a population, typically by a physical barrier such as a mountain range or river, resulting in evolution of a pair of CLOSELY RELATED species.

(32)

Example:

Cedrus as a genus is a disjunct as THE SAME TAXON occurs in four separate areas:

1. Atlas mountains of Morocco and Algeria 2. Cyprus

3. Lebanon, Syria and south-eastern Turkey 4. Western Himalayas

But at species level it shows vicariance, because four different But at species level it shows vicariance, because four different species occupy these areas:

1. Atlas mountains of Morocco

and Algeria………..………..………. C. atlantica 2. Cyprus………..………C. brevifolia 3. Lebanon, Syria and south-eastern Turkey….….C. libani 4. Western Himalayas……….……C. deodara

(33)

1

2

4

C. atlantica

C. brevifolia

C. deodara

1

3

C. atlantica

C. libani

(34)

A number of taxa found in mountains of southern

Spain and those of eastern Balkan peninsula , but not in areas between them.

Viola cazorlensis………..Mountains of Spain Viola delphinantha……….Greece and Bulgaria Convolvulus lanuginosus………….southern France &

Spain

Convolvulus calvertii………..Crimea south western

Asia

(35)

Viola cazorlensis Viola delphinantha

Convolvulus lanuginosus Convolvulus calvertii

(36)

Origin of vicariants/vicariads

All hypotheses propounded to explain ‘disjunction’ are valid for vicariance also.

But here the process of population break is followed by further evolution and at least one or all of the new fragments

evolve into new species.

Newly evolved taxa

Parent population,

possibly now extinct Parent population, extant or extinct

Newly evolved taxon VICARIANCE DISJUNCTION

(37)

FALSE VICARIANCE

Two or more taxa in different areas may undergo convergent evolution to give rise to superficially similar taxa.

VICARIANCE BIOGEOGRAPHY/ CLADISTIC BIOGEOGRAPHY The concept was introduced in late 1970s. Donn Eric Rosen (1929- 1986, icthyologist at American Museum of Natural History),was the chief architect of the theory and methodology of vicariance

biogeography.

biogeography.

Vicariance biogeography utilizes the principles and techniques of

‘cladistic analysis’ to interpret the distribution patterns.

In this approach vicariance describes the formation of vicariant patterns: how the populations became physically separated before evolving into new taxa?

(38)

How it works?

First, a cladogram of vicariant taxa under consideration are constructed.

 As seen earlier a cladogram depicts evolutionary history: which taxon is evolutionarly oldest and which is youngest.

 Names of taxa at branch ends are substituted by the areas in

which the occurred, now we get what is known as ‘area cladogram’

( a combined picture of pylogeny and biogeography).

Area cladogram of chironomids

(39)

Brundin reconstructed the phylogeny of these

chironomid midges and prepared area cladogram.

If the successive splits in the phylogeny were driven by successive break-ups of the land, the area cladogram may suggest following sequence of continental drift.

The common ancestor of the modern forms would have occupied a large area made up of all their modern distributional zones----the

Gondwanaland.

Gondwanaland.

• South Africa splits from a combination of Australia, New Zealand, and South America;

• then New Zealand splits from South America and Australia;

• and finally Australia splits from South America.

Latter geological evidences support this hypothesis

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