Download Powerpoint- Speciation

HOW does SPECIATION
occur?
Review:
What defines a species?
A species is defined by a population
that is able to reproduce FERTILE
offspring.
NOTE: A species is not defined by
variations (differences in color, size,
etc.), but variations may lead to
speciation.
SPECIES EXAMPLE
Homo sapiens: (scientific name for
humans)
Male and female homo sapiens with
any variation can mate to produce
children. These children can grow up to
reproduce with other humans as well.
SPECIES EXAMPLE
Red roses and white roses can
reproduce to make red, white or pink
roses. Their offspring can reproduce to
make more roses that can also
reproduce.
SPECIES NON-EXAMPLES
Any animals that cannot physically
mate.
Any animal that can physically mate,
but cannot reproduce offspring.
Any animal that physically mate, and
reproduce INFERTILE or Sterile
offspring.
SPECIES NON-EXAMPLE
A horse and donkey can mate and
produce the animal known as the mule.
A mule is a sterile animal that cannot
have offspring. Since the offspring of
the horse and donkey does not produce
fertile offspring, they are considered
separate species.
SPECIES NON-EXAMPLE
A lion and tiger can mate and produce
the animal known as the Liger. A Liger
is a sterile animal that cannot have
offspring. Since the offspring of the lion
and tiger does not produce fertile
offspring, they are considered separate
species.
SPECIATION
The proccess by which new species are
formed from an existing species.
How do You think speciation might
occur? What factors might lead to
speciation?
SPECIATION
Two major factors contribute to
speciation
Physical Barriers or Geographic
Isolation
Reproductive Isolation
Any ideas on what this looks like?
Geographic Isolation
A physical barrier divides a population
Examples:
Lava from volcanic eruptions
Canyon or mountain formation
Sea level change resulting in the creation
of islands
Flooding that may separate a population
through a stream or river
Geographic Isolation
If geographically isolated, the separate populations
can no longer breed and exchange genes; over
time, they will adapt to new environments through
natural selection and develop their own “gene
pool”.
Eventually the “gene pools” become so different
that the separated population can no longer
interbreed
Explain this illustration:
REPRODUCTIVE ISOLATION
Occurs as populations become more
distinct, one or all of the following can
happen
1) Populations can no longer mate and
make fertile offspring
2) Genetic material becomes so different that
fertilization cannot occur
3) Behavioral changes in mating occurs- mating
in fall versus summer
Reproductive Isolation example:
Lack of “fit” between sexual organs:
Hard to imagine, but a big issue in
insect speciation is variably-shaped
genitalia!
Reproductive Isolation example:
Mistakes happen during mitosis or
meiosis resulting in chromosome
abnormalities.
This can result in immediate speciation
Similar polyploids within a population
can reproduce to form a new species
Reproductive Isolation example:
Behavioral
A population of frogs usually mates in
the summer.
The population grows and due to the
environmental conditions, a subgroup of
the population begins mating in the fall.
The two groups are now reproductively
isolated.