Transcript While adaptations are products of natural selection, variations within

 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
 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????????
 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.


GEOGRAPHIC BARRIERS or ISOLATION
REPRODUCTIVE (Biological ) BARRIERS or ISOLATION
http://evolution.berkeley.edu/evolibrary/home.ph
Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.
 Nature
has frequently
provided geographical
barriers that prevent
individuals from
interbreeding.
 Given sufficient time and
generations new species
may emerge.
 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.
 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.
 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.
 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.
 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.
 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