Transcript THE ORIGIN OF SPECIES

THE ORIGIN OF SPECIES
Chapter 24
Origin of Species
• Macroevolution – the origin of
new taxonomic groups
• Speciation – the origin of new
species
Figure 24.1 Two patterns of speciation
SPECIES
• Species - population(s) whose
members interbreed in nature
and produce fertile offspring
Figure 24.2a The biological species concept is based on interfertility rather than
physical similarity
Figure 24.2b The biological species concept is based on interfertility rather than
physical similarity
Barriers that prevent different
species from interbreeding:
1.Prezygotic – impede mating
between species by
hindering the fertilization
of ova
2.Postzygotic – impede
mating between species by
preventing the zygote from
developing into a viable,
fertile adult
Figure 24.5 A summary of reproductive barriers between closely related species
PREZYGOTIC BARRIERS
a. Habitat Isolation – living in
different habitats within same
area
• Example: snakes in water vs. land
b. Behavioral Isolation – special
signals to attract mates (probably
most important barrier)
• Example: fireflies using
different blinking signals
Figure 24.3 Blue-footed boobies: Males high step as part of a courtship ritual.
This creates a behavioral barrier between species
c. Temporal Isolation – breeding during
different seasons or years
• Example: skunks mating in summer vs. late
winter
d. Mechanical Isolation – cannot mate due to
anatomical differences
• Example: Snails
e. Gametic Isolation – gametes unable to fuse
together to make zygote
• Example: sperm not surviving vaginal
environment
POSTZYGOTIC BARRIERS
a. Reduced Hybrid Viability –
zygotes/embryos aborted (miscarriage)
• Example: frogs (Ranus)
b. Reduced Hybrid Fertility – offspring end
up being mostly sterile
• Example: horses mating with donkeys to
make sterile mules
c. Hybrid Breakdown – offspring are fertile,
but next generation is sterile
• Example: cotton
FAULTS WITH THE BIOLOGICAL
SPECIES CONCEPT
• Extinct organisms
• Asexual organisms
• Too rigid: dogs and coyotes
• Gene flow through subspecies
OTHER SPECIES CONCEPTS
• Morphological – physical features
• Recognition – mating adaptations
• Cohesion –phenotype (genes and
adaptations)
• Ecological – live and do (niches)
• Evolutionary – sequence of
ancestral and descendant
populations
SPECIATION
1. Allopatric – a geographic
barrier isolates populations
blocking gene flow
2. Sympatric – intrinsic factors
alter gene flow
Figure 24.6 Two modes of speciation
ALLOPATRIC SPECIATION
Geographical barriers – mountains
forming, canyons forming, climate
changing land
Example: pupfishes
(Cyprinodon) in springs of
Death Valley CA and OR (drying
caused separated “pools” in
which speciation occurred)
Figure 24.7 Allopatric speciation of squirrels in the Grand Canyon. On left is
Antelope squirrel (A. harris) and on right White-tailed antelope squirrel (A. leucurus)
Figure 24.8 Has speciation occurred during geographic isolation?
Conditions Favoring Allopatric
Speciation
• Peripheral isolate already
different from original
population (ex. Phenotypic
extremes)
• Genetic drift at work because
smaller population size
• Different natural selection in
new environment
ADAPTIVE RADIATION
• Evolution of many diversely
adapted species from a
common ancestor
– Example: Hawaiian islands
and the finches of Galapagos
Islands
Figure 24.11 A model for adaptive radiation on island chains
Figure 24.10 Long-distance dispersal
SYMPATRIC SPECIATION
• Polyploidy – extra set of
chromosomes (common in
plants)
• Autoploidy –more than 2
chromosome sets from same
original
• Allopolyploid – two different
species contribute to the
polyploidy hybrid
Figure 24.13 Sympatric speciation by autopolyploidy in plants
Figure 24.16 Mate choice in two species of Lake Victoria cichlids: females chose
mates that have same color as themselves. Under monochromatic light, females
chose both colors equally because they look the same. (Nonrandom mating causes
sympatric speciation)
POPULATION GENETICS
LEADING TO SPECIATION
• Adaptive divergence – when 2
populations adapt to different
environments, they
accumulate differences in
their gene pools
– Reproductive barriers may
evolve coincidentally causing
the populations to
differentiate into 2 species
OUTCOMES OF DIVERGENCE
• Two populations get back together
and interbreed = no new species
• Two populations get back together
and do not interbreed = 2 new
species
• Hybrid Zone = where 2 populations
get back together and interbreed
to make hybrids only around the
region where they overlap
PUNCTUATED EQUILIBRIUM
• Species diverge in spurts of
relatively rapid change,
instead of slowly and gradually
– Species undergo most of
their changes as they first
bud from parent species
Figure 24.17 Two models for the tempo of speciation
Punctuated
Gradualism
SUMMARY
• Evolution is a response to
interactions between
organisms and their current
environment. Evolution does
not imply some intrinsic drive
toward a preordained state.
Figure 24.24 The branched evolution of horses