Speciation occurs through various mechanisms that result in populations becoming reproductively isolated. The main types of speciation are allopatric, parapatric, and sympatric speciation. Allopatric speciation involves geographic isolation of populations which then evolve independently. Parapatric speciation occurs when mating is more likely between nearby individuals, reducing gene flow. Sympatric speciation can arise from pre-mating or post-mating isolation within a population due to traits like habitat, seasonality, behavior, or hybrid inviability/sterility.

1. Name:
Tanvir ul hassan
Topic:
speciation
presented to:
madam Razia

2. speciation
• THE FORMATION OF NEW SPECIES
• Occurs when sub_population are
prevented from interbreeding

3. Ways
Waysofspeciation
Allopatric speciaton
Parapatric speciation
Sympatric speciation

4. Allopatric speciation
• Sub_population geographically isolated
• May be mountain range or river etc
• No longer mating between seperated population
• Different population adapted to different environment
• Not mate successfully even if experimentally reunite
• Most common type of speciation
• Separating small population more susceptible to
genetic drift, gene flow, founder effect and mutation

5. Explanation
• Diane Dodd examined effect of geographical
isolation on fruit flies
• Parent species divide into two group
• Sm and Sf feed with starch
• M,m and Mf feed with maltose
• When re_collect Sm prefer Sf for mating
• Mm prefer the Mf for mating

6. Example

7. parapatric speciation
• The population does not mate randomly
• Individuals are more likely to mate with their
geographic neighbors than with individuals in
a different part of the population’s range
• Reduced gene flow within the population

8. • Two species of crows,
Corvus corone and
Corvus cornix, meet
along a line in central
Europe. Along that
line they produce
hybrids. Speciation is
incomplete.

9. Sympatric Speciation
• Occurs due to reproductive isolation within a
population due to polymorphism
• It has two types of reproductive isolation
• Post mating isolation
• Pre mating isolation

10. How does reproductive isolation evolve?
Premating or prezygotic mechanisms:
a) Ecological or habitat isolation
b) Seasonal or temporal isolation
c) Sexual or ethological isolation
d) Mechanical isolation
e) Isolation by different pollinators
f) Gametic isolation
Postmating or zygotic mechanisms:
a) Hybrid inviability
b) Hybrid sterility
c) Hybrid breakdown

11. Different mechanisms prevent
reproduction between
individuals of different species.
These may occur premating or
postmating, as illustrated here
with two species of salamander.

12. The green lacewings, Chrysoperla carnea and Chrysoperla downesi may
illustrate an example of sympatric speciation.

13. C. Carnea is light green in spring and early
summer, changing to brown in the fall. C.
downesi is a darker green year round.
Their color is adapted to their habitat. C.
carnea lives in fields and meadows in the
summer and moves to deciduous trees in
the fall. C. downesi lives mainly on
conifers. Their ranges are sympatric. The
species are separated by breeding season
as well as habitat. C. carnea breeds in
winter and again in summer. C. downesi
breeds only in the spring.

14. The evolution of different mating
location, mating time, or mating
rituals:
• Genetically-based changes to these aspects of
mating could complete the process of
reproductive isolation and speciation
• Bowerbirds (shown below) construct
elaborate bowers and decorate them with
different colors in order to woo females. If two
incipient species evolved differences in this
mating ritual, it might permanently isolate
them and complete the process of speciation

15. Different species of bowerbird construct elaborate bowers and decorate them with
different colors in order to woo females. The Satin bowerbird (left) builds a channel
between upright sticks, and decorates with bright blue objects, while the MacGregor’s
Bowerbird (right) builds a tall tower of sticks and decorates with bits of charcoal.
Evolutionary changes in mating rituals, such as bower construction, can contribute to
speciation.

16. Lack of “fit” between sexual organs
• Hard to imagine for us, but a big issue for
insects with variably-shaped genitalia

17. Offspring inviability or sterility
• All that courting and mating is wasted if the
offspring of matings between the two groups
do not survive or cannot reproduce.
• Mule etc