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CHAPTER 24
THE ORIGIN OF SPECIES
Different Species Of Japanese
Ants!!!
What is a species ? How does
speciation occur ?
Mutations + Sexual recombination + genetic drift +gene flow
+ natural selection! =
Macroevolution:
--the origin of new species, genera,
families, orders, classes, phyla, and
kingdoms
Speciation—the origin of new species
SPECIES “kind””appearance” –
group of populations
A biological species is the whose members can
largest set of populations
interbreed and
in which genetic exchange produce fertile
is possible and is
offspring;
genetically isolated from
other populations.
Different Species Of HUMANS???
What is a species ? How does
speciation occur ?
Distinctions between species are not
always clear.
Subspecies have small differences from
other subspecies and usually have
C. hutchinsii hutchinsii
geographical variation.
C. canadensis canadensis
Concepts of species:
1. Biological species concept—reproductive isolation
2. Morphological species concept—measurable
anatomical differences between species
3. Ecological species concept— based on the ‘niche’
– environment and organisms’ role in using it
4. Pluralistic species concept—cohesion of (2) and (3)
Situation:
2 populations that are microevolving (different p,q)
-what will make them 2 species?
-not having fertile offspring!
a) Prezygotic barriers
b) Post zygotic barriers
Organisms of different species cannot
interbreed for a number of reasons.
Prezygotic barriers- hinder fertilization
1) Habitat isolation—live in different places
ex: water vs. terrestrial in garter snakes
Prezygotic barriers hinder fertilization
2) behavioral isolation—respond only to
members of the same species; ex:
firefly flashes
•
•
Ex. Firefly flashes, Bower Bird nest
Prezygotic barriers hinder fertilization
3) temporal isolation—different
breeding times (ex. W. and E. skunks)
EASTERNsummer
WESTERN winter
Prezygotic barriers hinder fertilization
4) mechanical isolation—anatomical
Ex. Damsel fly genitalia, flowers
incompatibility
•
Prezygotic barriers hinder fertilization
5) gametic isolation—gametes may not
be recognized by other species for
fertilization (molecular recognition
missing between egg and sperm)
Postzygotic barriers - gametes can get
together to make a zygote, BUT barriers
prevent a zygote from developing
properly
Postzygotic barriers prevent a zygote
from developing properly.
1. Reduced hybrid viability—development
is aborted at some embryonic stage.
Ex. frogs
Postzygotic barriers prevent a zygote
from developing properly.
2. Reduced hybrid fertility—hybrids are
sterile—usually there is a failure of
meiosis in these hybrids so they
cannot produce viable (good) gametes
Postzygotic barriers prevent a zygote
from developing properly.
3) hybrid breakdown—first-generation
hybrids may be fertile, but secondgeneration offspring are not viable. Ex.
cotton
SUMMARY
RecipeAnagenesis
to make a New
= Species:
one species changes
1) Need
intotoanother
create a barrier for gene flow within a
population- that is a barrier for productive SEX
2) Need to maintain this barrier
(prezygotic/postzygotic)
Cladogenesis =
so that the two groups can
continue
branching
accumulating
of a new differences through
mutation/sexual
species from recombination
a
(acted upon by
natural
species
selection
that - of course you knew that!)
3) Andcontinues
then PRESTO!
to
You have a new species (give
or take
exista million years!)
How do new species arise (barrier creation
• Allopatric speciation (“other homeland”)
• Sympatric speciation (“together”)
Allopatric Speciation
--occurs when geographical barriers
block gene flow
*small populations are more likely to
change enough to become a new
species
RING
SPECIES
HAWAIIN HONEYCREEPERS
'I'IWI - Vestiaria coccinea
'AMAKIHI - Hemignathus virens
Found in 'ohi'a lehua
Common in native forests above 2,000
forests. Feeds on the nectar of
feet.
PALILA
Feeds -more
Loxioides
on insects
bailleui
and is less
'ohi'a lehua flowers
'AKOHEKOHE
- Palmeria
high in thedolei
dependant
Endangered
on nectar. Female is a darker,
forest canopy
Crested
honeycreeper
and from- Endangered
tubular
olive
Found
green
only
color.
in the dry forests on the slopes
blossoms
Found
only
in in
thethe
understory.
rain forests of east Maui of Mauna Kea, Big Island, 6,000 to 9,000
at elevations of 4,500 to 6,500 feet.
feet.
Adaptive
radiation—
evolution of
many
different
species from
a common
ancestor
*common
on islands*
1. gene pool at the edge is probably different
Peripheral isolate = small population at
(founder
effect)
the fringe of a larger population’s range
for speciation
2.--good
until the candidate
peripheral population
becomes larger,
genetic drift will occur
3. natural selection may be different in the fringe
environment
Sympatric Speciation
--a new species can evolve without
geographic isolation
--genetic changes can prevent members
of the same species from mating
ex. Apple maggot flies, polyploid plants
Sympatric Speciation
--a new species can evolve without
geographic isolation
-- female lays egg where she grew up
Apples
(introduced
to US by
immigrants)
Apple Maggot Flies Hawthorns
(native to
US)
One species=autopolyploid
Tetraploid plants can’t
interbreed with normal
plantspostzygotic barrier
2 different species form an allopolyploid hybridthese
usually propagate asexually (sympatric or allopatric?)
Wheat evolved from 2 meiotic errors.
•
What type of
speciation is this?
Speciation is at the boundary
between microevolution
(population allelle frequency
change) and macroevolution
(accumulation of change over
millions of years).
Rate of Speciation -Gradualism vs.
Punctuated Equilibrium
Gradualism—species diverge gradually
over a long period of time
Punctuated equilibrium—species diverge
in spurts of relatively rapid change
--long periods of equilibrium punctuated
by short periods of speciation
Development genes are important in
macroevolution.
Allometric growth—
difference
in relative rates of
growth of
various parts of the
body
Paedomorphosis—adult retains features
that were juvenile structures in its
ancestors.
ex. some salamanders retain gills
•Heterochrony, an evolutionary
change in the rate or timing of
developmental events.
Temporal changes in development that
differ between species--heterochrony
Homeosis = alteration in
basic body design
controlled by small sets
of gene in
development—homeotic
genes (Hox complex)
Evolution is not goal-oriented--species selection
produces an evolutionary trend