Production of new evlutionary lineages

1. Production of new evolutionary
lineages
By
N.Arulselvan
I Ph.D. Entomology

2. Speciation is the evolutionary process by
which reproductively isolated biological
populations evolve to become distinct species.
Orator F. Cook (coined the term speciation)
Production of new evolutionary lineages is termed
as speciation

3. How does speciation occur?
• Speciation is the origin of new species
• It is the keystone process of macroevolution
• The theory of evolution must explain the
origin of new species
• Speciation can occur by
Anagenesis
Cladogenesis

4. Anagenesis and Cladogenesis
• Anagenesis is a type of phyletic evolution,
which occurs only within a single species
• Whereas cladogenesis is a type of branching
evolution.
• In other words, in anagenesis, one gene pool
is converted into another gene pool.
• In contrast, in cladogenesis, a single gene pool
is split into several gene pools.

5. What is Anagenesis
• Anagenesis is an evolutionary change of a single lineage
where one taxon is replaced by another without branching.
• Anagenesis is called phyletic evolution or progressive
evolution.
• Anagenesis occurs due to the specialization of individuals in
a particular species in response to stimuli of the external
environment.
• Natural selection promotes the adaptations of the
individuals in relation to the existing conditions.
• The increase of the complexity and the perfection of the
adaptations is a biological process, which occurs
continuously, promoting a particular species to a higher
level.

6. Characteristics of Anagenesis
• The increased complexity and the
rationalization of organs to improve the
function
• The division of labour in body parts

7. The increased length of the neck in
giraffe is an example of anagenesis

8. Anagenesis
Anagenesis - Phyletic evolution
 Tachytely - very rapid Anagenesis
 Horotely - moderate speed of evolution
 Bradytely - A very slow rate of anagenesis which normally
occurs in stable environmental conditions in isolated pockets

9. What is Cladogenesis
• Cladogenesis is an evolutionary change of a
particular species in which new species are
branched off from a common ancestral species.
• Most common mode of speciation in response to
the changes in the conditions of the
environment.
• more than one species are produced from a
single species during cladogenesis, cladogenesis
brings biological diversity to the environment.
• active evolutionary process than anagenesis. also
called the branching evolution.

10. Both anagenesis and cladogenesis are
shown in figure

11. The three types of cladogenesis classified based on the speed
of the process are:
• Tachyschizia,
• Rapid splitting of lineages, which occurs due to
their invasion of a new habitat or due to the extinction of
competitors. When new opportunities are available for the
population to increase their number in a particular habitat,
they rapidly diversify to adapt to that environment.
• Horoschizia
• cladogenesis occurs at a moderate rate when the
environmental conditions are not very harsh.
• Bradyschizia .
• The bradyschizia occurs very slowly.

12. Mechanism of Speciation
• A single population may have two or more
different species
• These population no longer interbreed
• No gene flow between populations
• If conditions experienced by the two
populations, differ significantly, the two may
eventually evolve to become distinct species.

13. Three general ideas on speciation
1. Form
a. Phyletic speciation
The species formed in this manner is called successional, allochronic or paleo
Species. The species which have become extinct is called taxonomic
Extinction (Wiley, 1981).
Criticism:
Never actually demonstrated
Speciation occurred without splitting of lineages

14. b. Additive speciation
Phyletic evolution can and does occur between nodes or speciation events.
The type of evolution forms the basis of the important concepts
of apomorphic (derived) characters of a Recent species or synapomorphic
(shared-derived) characters that were inferred to be possessed by
an ancestral species to a monophyletic group.
May also take the form of reticulate speciation where
additional diversity evolves from hybridization between
different species, producing a separate, independent
lineage. The parental species remain extant. This is
often involves allopolyploids and uniparental lineages

15. C. Reductive Speciation
Theoretically possible and there is some indication that this actually occurs
(compilospecies). Involves fusion of two previously independent lineages
through hybridization between parental species wherein their identities are
fused and a new identity is created. You essentially get the "swamping" of
two species into one over entire ranges
Here Z and X go extinct and are merged into the new lineage and have the new identiy of Y.

16. 2. Tempo
a. Phyletic gradualism
Gradual accumulation of evolutionary novelties. Sometimes referred to as
microevolution. This has been hypothesized to occur in populations and lead
to uniform divergence.
b. Punctuated Equilibrium.
Divergent species appear suddenly in the fossil record without transitional forms;
persist for a long time without displaying any morphological (or other) changes and
then there is a rapid change.

18. Four main geographic modes of speciation in nature
• Allopatric
• Sympatric
• Parapatric
• Peripatric
Speciation may also be induced artificially through
laboratory experiments
3. Modes of speciation

19. Allopatric Speciation (alios— other, patria—
native land):
• A part of the population becomes
geographically isolated from the main
population.
• The population becomes entirely
separated and finally constitutes a new
species.
• Thus geographic isolation brings about
allopatric speciation.

21. Sympatric Speciation (sym— together, patria—
native land):
• A small segment of the original
population becomes isolated
reproductively.
• As the isolating mechanism comes
into force, a new subspecies
emerges.
• In due course of time a new species
is formed.

23. Example of Sympatric speciation
• Host switching is one mechanism by which sympatric
speciation can occur
• Rhagoletis pomonella
• Originally fed on Hawthorn
• Apple was introduced in 1600s
• Some populations shifted to apple in 1800s (Bush,1969)
apple maggot flies
hawthorns
apples

24. Gene flow has been reduced between flies that feed on
different food varieties, even though they both live in the
same geographic area

25. Parapatric Speciation:
Separates adjacent population
Takes place when a population of a species
enters a new niche or habitat.
Occurs only at the edge of the parent species
range.
Occupancy of a new niche results as a barrier
to gene flow between the population of new
niche.
Two species are produced due to reproductive
isolation from single one.

26. Anthoxanthum odoratum
Although continuously distributed, different flowering
times have begun to reduce gene flow between metal-
tolerant plants and metal-intolerant plants.

27. Peripatric
• In this form, new species are
formed in isolated peripheral
populations
• One of the populations is much
smaller than the other.
• Geographically widespread
ancestral species
becomes paraphyletic, thereby
becoming a paraspecies.
• Peripatric speciation was
originally proposed by Ernst
Mayr

28. Double disaster Rare genes survive
Gene frequencies drift
More changes Speciation

29. Stasipatric speciation
Formation of new species as a result of
chromosomal rearrangements giving
homozygotes which are adaptively superior in
a particular part of the geographical range of
the ancestral species.
Allo – parapatric speciation
Population initially separated but then
secondarily come into contact with
subsequent parapatric population is allo
parapatric speciation.

30. Artificial Speciation
• Artificial speciation is the form of speciation that
can be achieved by the input of human influence.
• By separating populations, and thereby
preventing breeding, or by intentionally breeding
individuals with desired morphological or
genotypic traits, humans can create new, distinct
species.
• This is also known as ‘artificial selection’; most
modern domesticated animals and plants have
undergone artificial selection.

31. Artificial speciation
Rice and Elen E. Hostert (1993)
Allopatric speciation

32. • Artificial selection has been demonstrated most
effectively in species of Fruit Fly (Drosophila
melanogaster).
• Experiments in which flies are placed into
environments which contain different resources
or habitats show the changes that occur when
the flies adapt to each environment.
• After several generations, the flies are removed
from the experimental zone and are allowed to
cohabitate, although the populations are unable
to mate due to the reproductive isolation process
that occurred while in isolation.

33. Conclusion
• Speciation is likely to have happened in
different modes
• The organisms continue to speciate as a result
of changing needs