Download Adaptation and speciation slide show

Adaptation
• Adaptation – describes any trait that enhances
an organisms fitness or increases its chance of
survival.
• While adaptations are products of natural
selection, variations within a species are the
raw material upon which natural selection
acts.
• Exaptation – an adaptation that evolved for
one function that could also be used for
another purpose.
Limbs on a lungfish
Types of Adaptations
• 1. Structural (anatomical) Adaptations – these
may include external or internal changes
within an individual, or even mimicry and
cryptic colors can be considered physical.
• 2. Physiological adaptations – changes within
the function of the organism.
– Enzymes
– Chemical defenses
• 3. Behavioral adaptations – how an organism
responds to the environment.
– Migration
– courtship
• Is evolution perfect????????
Speciation
• WHAT IS SPECIATION?
– The formation of a species (a reproductively
compatible population , ie. a population that can
interbreed and produce viable offspring)
• There are two pathways that lead to new
species: transformation vs. divergence pg 708
– For species to remain distinct, they must remain
reproductively isolated, or prevent breeding
between closely related species lines.
How to accomplish speciation?
• GEOGRAPHIC BARRIERS or ISOLATION
• REPRODUCTIVE (Biological ) BARRIERS or ISOLATION
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Geographic Isolation
• Nature has frequently
provided geographical
barriers that prevent
individuals from
interbreeding.
• Given sufficient time and
generations new species
may emerge.
Biological Barriers
• Even when individuals live in the same region
factors may exist that prevent interbreeding:
– Pre-zygotic Barriers – impede the mating process
or prevent the egg from becoming fertilized
– Post-zygotic Barriers – if sperm from one species
is capable of fertilizing the egg of another species.
There are mechanisms to prevent this hybrid
individual from developing.
Types of Pre-Zygotic Barriers
• Behavioural Isolation – a species may have
special signals or rituals that is species
specific.
– Eg. Songs of birds, pheromones etc…
• Habitat Isolation – two species can live the
same region but occupy different habitats.
– Eg. Garter snake lives near water where most
other snakes prefers open areas.
Pre- Cont.
• Temporal Isolation- species may be isolated
due to the time or season they are active or
are reproductively viable.
• Mechanical Isolation- related species may
attempt to mate but are anatomically
incompatible.
Pre- Cont.
• Gametic Isolation – even if gametes from
different species do meet, rarely will a zygote
form.
– Sperm from one species can not survive in the
female reproductive tract of another species.
Post- Zygotic Barriers
• Hybrid Inviability – development of the hybrid
zygote is stopped at some stage during
embryonic development.
• Hybrid Sterility – when two different species
can mate but the offspring is sterile.
– Horse + Donkey = Mule (sterile)
• Hybrid Breakdown – when first generation
hybrids are viable and fertile but if these
hybrids are mated, the next generation are
sterile or weak.
Again Not Perfect
• The biological definition of a species does not
work in all instances… (discuss)
• Other models include:
– Morphological species concept (physical or
phenotype characteristics)
– Cohesion species concept
– Ecological species concept
– Evolutionary species concept
PATTERNS OF SPECIATION?
How does it occur?
Two Modes Of Speication: (Pg. 714)
1. Sympatric Speciation: when reproductive isolation happens
when species are not geographically isolated.
2. Allopatric Speciation (geographical speciation): when speciation
happens in species that are geographically separated.
• GRADUALISM
• PUNCTUATED EQUILIBRIUM
Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.
Adaptive Radiation
• The creation of new species that have radiated from a
common ancestral species that have adapted differently
to their various environments.
• DIVERGENT EVOLUTION and CONVERGENT EVOLUTION
Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.
Divergent Evolution
• The Pattern of evolution
where species that
were once similar to an
ancestral species
diverge, or become
increasingly distinct.
ADAPTIVE RADIATION – AN EXAMPLE OF
DIVERGENT EVOLUTION
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Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.
Convergent Evolution
• Similar traits arise independently in species to
adapt and survive in similar environmental
conditions. They DO NOT share a common
ancestor.
CONVERGENT EVOLUTION – WHAT IS AN
EXAMPLE?
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Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.
Comparing the anatomy of organisms indicates a
common ancestry because of:
• homologous structures - structures having a
common ancestry but with different uses in
various species.
– Eg. Similar bone structure of the forelimb of
a bat, whale, horse and human suggests
these different species have a similar
evolutionary origin. Page 113,114 & 664
• - analogous structures - body parts of
organisms that do not have a common
evolutionary origin but perform similar
functions.
–Eg. insect wings and bird wings are
similar in function but not in structure.
Page 665
- vestigial organs - small or incomplete organs ( or bones )
that have no apparent function in one organism but do
have a function in another species. This indicates
evolutionary origin from a common ancestor. Page 665
– Eg. Human ear muscles, Human appendix, Hip bones
in whales, Human tail bone, Leg bones in snakes, and
Forelimbs in the flightless ostrich
Co-Evolution – the evolution of
species together so that both find
ways to adapt and survive.