Transcript Macroevolution - Hatboro

Macroevolution
•A change of one species into an entirely
new species!
**Macroevolution
encompasses the grandest
trends and transformations in
evolution, such as the origin of
mammals
Speciation
Formation of new species
Allopatric Speciation- When speciation
occurs do to geographic isolation
Sympatric Speciation- When speciation
occurs do to reproductive isolation
What Is a Species?
• How can you determine whether a group
of plants or animals belong to the same
species?
• Appearance isn’t sufficient.
Let’s take a look…
What Is a Species?
These happy face spiders look different,
but since they can interbreed, they are
considered the same species:
Theridion grallator.
What Is a Species?
BIOLOGICAL SPECIES CONCEPT
• a group of organisms that can reproduce
in nature and produce fertile offspring
(meaning the offspring are also capable of
mating and producing offspring)
• members of one species cannot
successfully interbreed with members of
other species.
How New Species Form
ALLOPATRIC SPECIATION (“different country”)
GEOGRAPHIC ISOLATION
• Separation of population as a result of geological change
or dispersal to a remote location.
• Example – harris’ antelope squirrel and the white tailed
squirrel – opposite rims of the Grand Canyon
(Ammospermophilus)
• Causes: Emergence of mountain range, slow moving
glacier, colonization of an island
This is a simplified model of
speciation by geographic isolation
• The scene: a population of wild fruit flies
minding its own business on several
bunches of rotting bananas, cheerfully
laying their eggs in the mushy fruit...
• Disaster strikes: A hurricane washes the bananas and
the immature fruit flies they contain out to sea. The
banana bunch eventually washes up on an island off the
coast of the mainland. The fruit flies mature and emerge
from their slimy nursery onto the lonely island. The two
portions of the population, mainland and island, are now
too far apart for gene flow to unite them. At this point,
speciation has not occurred—any fruit flies that got back
to the mainland could mate and produce healthy
offspring with the mainland flies.
• The populations diverge: Ecological
conditions are slightly different on the
island, and the island population evolves
under different selective pressures and
experiences different random events than
the mainland population does.
Morphology, food preferences, and
courtship displays change over the course
of many generations of natural selection.
• So we meet again: When another storm
reintroduces the island flies to the mainland,
they will not readily mate with the mainland flies
since they’ve evolved different courtship
behaviors. The few that do mate with the
mainland flies, produce unviable eggs because
of other genetic differences between the two
populations. The lineage has split now that
genes cannot flow between the populations.
How New Species
Form
SYMPATRIC SPECIATION (“Same country”)
REPRODUCTIVE ISOLATION
• The inability of two different species to
successfully interbreed in nature.
How New Species Form
CAUSES OF REPRODUCTIVE ISOLATION
• Timing - two similar species may have
different breeding seasons
• Ex: Great Plains – western spotted skunks
breed in fall, eastern spotted skunks breed
in late winter (coexist on great plains)
How New Species Form
CAUSES OF REPRODUCTIVE ISOLATION
• Behavior - two similar species may have
different courtship or mating behaviors.
• Ex. Eastern vs. western meadowlarks –
identical in shape, coloring, habitat –
ranges in US overlap – but have different
songs to attract mates
How New Species Form
CAUSES OF REPRODUCTIVE ISOLATION
• Habitat (niche) - Some species remain
reproductively isolated because they are adapted
to different habitats in the same general location.
• Ex. lakes in Canada, contain two different species
of three-spine stickleback fish. One species is
adapted to living along the lake bottom, feeding on
small snails.
• Fish of the other species spend most of their lives
in the open water, filtering plankton (small floating
organisms). The two species' preferences for
different habitats help maintain their isolation.
How New Species Form
CAUSES OF REPRODUCTIVE ISOLATION
 Incompatibility - two seemingly similar
species may be unable to mate because
their reproductive structures are physically
incompatible.
Ex. Not showing you this one!
How New Species Form
CAUSES OF REPRODUCTIVE ISOLATION
 Death of hybrid - the offspring of two
different species may die or may mature
into infertile adults. (Remember that the
definition of a species requires that its
members be able to produce fertile
offspring.)
 Ex: Horses and donkeys remain separate
species because their hybrid offspring
(mules) are infertile
Rate of Speciation
GRADUALISM = long term gradual change
in species – slow, progressive change of
one species into another
Rate of Speciation
PUNCTUATED EQUILIBRIUM – some species
remained unchanged for millions of years and
then underwent periods of very rapid, major
change
Major environmental changes in predation
pressure, food supply, climate, long droughts,
major volcanic eruptions, beginning and end of
ice ages
Mutations in regulator genes can provide radically
new variations in the organization of the body