Transcript Geographic Isolation

Ch 24
 Speciation -As individuals are no longer able
to mate with each other, they are classified
as different species.
 This is caused by reproductive isolation.
This occurs when members of 2 populations
cannot interbreed with each other to
produce fertile offspring.
Types of Reproductive Isolation
(Count them: There’s 5!)

Behavioral Isolation – populations do not
breed because they have different mating
rituals or behavioral reproductive strategies

Ex: A fruit fly will only breed with another fruit
fly after recognizing a particular mating ritual
“dance” performed by the male. (PICTURE
FROM LAB BENCH)
Geographic Isolation – populations do not
breed because they are physically
separated from each other (by a river,
mountain range, etc)
•Temporal Isolation –
populations do not breed
because they reproduce
at different times
Ex: flowers opening up at
different times of day

Mechanical Isolation
 Anatomical incompatibility may prevent sperm
transfer when closely related species attempt to
mate.
EX: male dragonflies use a pair of special
appendages to clasp females during copulation.
When a male tries to mount a female of a different
species, he is unsuccessful. (male is on left)
Gamete Isolation
Gametes of different
species that meet rarely
fuse to form a zygote.
EX: For animals that use
internal fertilization, the
sperm of one species may
not be able to survive the
internal environment of the
female reproductive tract
of a different species.
 All of these previous isolations were
prezygotic (not able to make a fertilized egg)
 What if an egg is made?
 Postzygotic barriers= When prezygotic
barriers are crossed and a hybrid zygote
forms, hybrids may be (1) frail or unable to
survive to develop or (2) have different
chromosome numbers so meiosis cannot
happen normally so hybrid has no fitness
Two Types of Speciation…
 Allopatric Speciation= Speciation forms due
to geographic barrier.
 Sympatric Speciation- Formation of new
species within the range of parent
populations (no geographic barrier)
Early Earth---Ch 26
 Life on Earth began between 3.5 and 4.0
billion years ago.
 Earliest organisms were prokaryotes at
least 2 billion years ago before eukaryotes
arrived
 Stromatolites= banded domes of sediment
constructed by colonies of bacteria and
cyanobacteria currently living in salty
marshes (3.5 billion years ago!!, west
Austrailia and southern Africa)
The first cells…
 Little to no oxygen
 Lightning, volcanic activity, meteorite
bombardment, and intense UV light
 Earth’s crust had just solidified
First living organisms may have
been products of chemical evolution
in 4 stages…
 1. Abiotic synthesis and accumulation of
monomers
 2. Joining of monomers into polymers
 3. Formation of protobionts- droplets which
formed from aggregates of abiotically produced
molecules and were different from chemical
surroundings
 4. Origin of heredity during or before protobiont
appearance
Polymers
 …are made from dehydration synthesis
 Must have occurred without enzymes in
early Earth
 Clay must have been important because:
-monomers bind to charged sites in clay,
concentrating amino acids + monomers
-metal ions (iron, zinc) could catalyze
dehydration reactions
More on Protobionts
 They are molecules that can maintain an
internal environment different from
surroundings and have some life
properties such as metabolism +
excitability
 Experimental evidence for spontaneous
formation of these?
Yes. Example: Microspheres. Undergo
shrinking, swelling. Selectively permeable
membrane and have a potential energy in
the form of membrane potential.
Microspheres
It’s an “RNA WORLD” *
 Today’s cells transcribe DNA into
RNA…then to proteins BUT
 We hypothesize in primitive times, RNA
became before DNA. Evidence:
 RNA can self-replicate (in small amounts)
 RNA is autocatalytic as ribozymes have the
ability to act as catalysts
 RNA unfolds uniquely depending on
sequence (unlike DNA)
Debate about life continues…
 Panspermia- organic compounds may have
reached Earth by way of meteorites and
comets. Organic compounds were
recovered.
 Most researchers believe life appeared first
in shallow water or moist sediments. Some
believed life started on sea floor due to
harsh conditions on surface. This was
supported by discovery of sea vents.
Sea Vents
Tube Worms…have adapted to immense pressure,
total darkness, and proximity to super-heated water
that reaches 662 degrees F.