Transcript File - Biology with Radjewski

17
Speciation
Concept 17.1 Species Are Reproductively Isolated
Lineages on the Tree of Life
Speciation—divergence of biological lineages
and emergence of reproductive isolation
between lineages.
Species—groups of organisms that mate with
one another.
Concept 17.1 Species Are Reproductively Isolated
Lineages on the Tree of Life
Linnaeus described
species based on their
appearance—the
morphological
species concept.
Members of species look
alike because they
share many alleles.
He originated the
binomial system of
nomenclature.
Kingdom, Phylum, Class, Order,
Family, Genus, Species
Classification
Figure 17.1 Members of the Same Species Look Alike—or Not (Part 1)
Limitations: members of the
same species don’t always look
alike (e.g., male and female
wood ducks).
Concept 17.1 Species Are Reproductively Isolated
Lineages on the Tree of Life
Biological species concept: “Species are
groups of actually or potentially interbreeding
natural populations which are reproductively
isolated from other such groups.” Ernst Mayr
Reproductive isolation: two groups of
organisms can no longer exchange genes.
Reproductive isolation is necessary for lineages to
remain distinct over evolutionary time.
It is also responsible for morphological
differences—mutations that result in
morphological changes cannot spread between
reproductively isolated species.
Concept 17.1 Species Are Reproductively Isolated
Lineages on the Tree of Life
Lineage species concept: species as branches
on the tree of life.
A lineage is an ancestor–descendant series of
populations followed over time.
How can one lineage ever split
into two reproductively isolated
species?
Concept 17.2 Speciation Is a Natural Consequence
of Population Subdivision
Not all evolutionary changes result in new
species.
Speciation requires interruption of gene flow.
Concept 17.3 Speciation May Occur through
Geographic Isolation or in Sympatry
Allopatric speciation—when populations are
separated by a physical or geographic barrier.
Barriers can form when continents drift, sea
levels rise and fall, glaciers advance and
retreat, or climates change.
The populations evolve through genetic drift and
adaptation to different environments in the two
areas.
Concept 17.3 Speciation May Occur through
Geographic Isolation or in Sympatry
Some members of a population may cross an
existing barrier and establish an isolated
population.
Finch species in the Galápagos Islands evolved
from a single South American species that
colonized the islands.
The islands are far apart, and have different
environmental conditions.
Figure 17.7 Allopatric Speciation among Darwin’s Finches
Concept 17.3 Speciation May Occur through
Geographic Isolation or in Sympatry
Sympatric speciation—
speciation without physical
isolation.
May occur with disruptive
selection—individuals with
certain genotypes prefer
distinct microhabitats
where mating takes place.
This appears to be taking place with
apple maggot flies. One group prefers
to lay eggs on hawthorne fruits, the
other group lays eggs on apples. They
are partially reproductively isolated.
Concept 17.4 Reproductive Isolation Is Reinforced
When Diverging Species Come into Contact
Mechanical isolation—differences in sizes and
shapes of reproductive organs.
Temporal isolation—species may breed at
different times of year or different times of
day.
Behavioral isolation—individuals reject or
fail to recognize mating behaviors of other
species
Concept 17.4 Reproductive Isolation Is Reinforced
When Diverging Species Come into Contact
Habitat isolation—when two closely related
species evolve preferences for living or mating
in different habitats.
Gametic isolation—sperm and eggs of
different species will not fuse. Important for
aquatic animals that release gametes into
the water.