Download Evolution Lecture Part 2

Ch 23 Part II, Ch 24
Evolution : Mechanisms
Natural Selection (only one that consistently leads to
adaptive evolution)
Genetic Drift
Genetic Flow
Alleles drift but how does that look?
• Survival of the fittest?
• Adaptive advantage can lead to greater
relative fitness
• Relative fitness: contribution an individual
makes to the gene pool of the next
generation
• PHENOTYPE DIRECTLY
Fig. 23-13
Original population
Original
Evolved
population population
(a) Directional selection
Phenotypes (fur color)
(b) Disruptive selection
(c) Stabilizing
selection
Sexual Selection
• Likelihood of mating
• Can result in sexual dimorphism
– Intrasexual selection : mostly males
competing physically with each other
– Intersexual selection: usually females choose
Fig. 23-16
EXPERIMENT
Female gray
tree frog
SC male gray
tree frog
LC male gray
tree frog
SC sperm  Eggs  LC sperm
Offspring of Offspring of
SC father
LC father
Fitness of these half-sibling offspring compared
RESULTS
Fitness Measure
1995
1996
Larval growth
NSD
LC better
Larval survival
LC better
NSD
Time to metamorphosis
LC better
(shorter)
LC better
(shorter)
NSD = no significant difference; LC better = offspring of LC males
superior to offspring of SC males.
What preserves genetic variation?
• (Tendency of directional and stabilizing selection is to reduce
variation)
• Mechanisms to preserve variety:
• Diploidy (“hide” recessive)
• Balancing Selection
– Heterozygote advantage
– Frequency dependent selection: fitness of a
phenotype decreases if it becomes too
common
• Neutral variation: no affect on protein fxn
Why Can’t We Be Perfect?
• 1. Selection can only act on existing
variations (may not be ideal)
• 2. Evolution is limited by historical
constraints (bats, birds from walking)
• 3. Adaptations are often compromises
• 4. Chance, natural (founders effect does
not ensure fit alleles in new pop)
selection,and the environment interact
Fig. 23-19
Ch 24 Origin of Species
• Biological Species concept
– Populations
– Reproductively compatible
– Gene flow even over long distances can hold
gene pool together ( if NS or drift =
divergence)
– *emphasizes separateness of species
Types of Isolation
• Reproductive isolation: barriers will isolate
a gene pool
– Prezygotic barriers
– Postzygotic barriers
Fig. 24-4
Prezygotic barriers
Habitat Isolation
Temporal Isolation
Individuals
of
different
species
(a)
Postzygotic barriers
Behavioral Isolation
Mechanical Isolation
Gametic Isolation
Mating
attempt
(c)
(d)
(e)
(f)
Reduced Hybrid Viability
Reduced Hybrid Fertility
Hybrid Breakdown
Viable,
fertile
offspring
Fertilization
(g)
(h)
(i)
(j)
(b)
(k)
(l)
3 types of species concepts unity
within a species
• morphological species concept: body
shape and other structural features
(sexual and asexual, most used method)
• Ecological species concept: niche,
interaction with enviro. Disruptive selection
• Phylogenetic species concept: smallest
group that share a common ancestor
Sympatric vs Allopatric speciation
• Allopatric: gene flow is
interrupted by a
geographic barrier cuts a
population off from the
main
• Colonists
• Evidence: frogs, squirrels,
highly subdivided regions
tend to have more
species than areas with
fewer barriers
• Reproductive isolation
increases with distance
• Sympatric: speciation
occurs in populations that
live in same geography
• Less common
• Gene flow is reduced by
– polyploidy, (plants)
– habitat differentiation
– sexual selection
Fig. 24-7
Mantellinae
(Madagascar only):
100 species
Rhacophorinae
(India/Southeast
Asia): 310 species
Other Indian/
Southeast Asian
frogs
100
60
80
1
2
40
20
0
3
Millions of years ago (mya)
1
3
2
India
Madagascar
88 mya
65 mya
56 mya
Fig. 24-5
(a) Allopatric speciation
(b) Sympatric speciation
Polyploidy
• A species may originate from an accident during
cell division that results in extra sets of
chromosomes
• Autopolyploid: extra sets of chromosomes
derived from a single species
– Ex, failure in cell division
– Tetraploid offspring tend to be less fertile
– Can produce fertile offspring with self fertilization or
with other tetrapods
– One generation can be reproductively isolated
Fig. 24-10-3
2n = 6
4n = 12
Failure of cell
division after
chromosome
duplication gives
rise to tetraploid
tissue.
2n
Gametes
produced
are diploid..
4n
Offspring with
tetraploid
karyotypes may
be viable and
fertile.
Allopolyploid
• Two different species interbreed and have
infertile offspring
• Propagate asexually
• Plants more tolerant of meiotic and mitotic errors
• After several generations a sterile hybrid can
become fertile with each other not the parent
species
• Frog (occasionally in animals)
• 80% plant species may have formed this way)
Fig. 24-11-4
Species B
2n = 4
Unreduced
gamete
with 4
chromosomes
Meiotic
error
Species A
2n = 6
Normal
gamete
n=3
Hybrid
with 7
chromosomes
Unreduced
gamete
with 7
chromosomes
Normal
gamete
n=3
Viable fertile
hybrid
(allopolyploid)
2n = 10
Habitat Differentiation & Sexual
Selection
• Apple maggot fly(slow
hawthorn tree vs
apple tree)
– Temporal isolation and
post zygotic (helpful
alleles in one tree,
harmful in the other)
– Habitat or food source
not used by parent
population
• Female driven
selection of male
coloration patterns in
cichlids
Fig. 24-12
EXPERIMENT
Normal light
P.
pundamilia
P. nyererei
Monochromatic
orange light
Speciation can occur rapidly or
slowly and can result from changes
in many or a few genes
• Punctuated Equilibria: periods of apparent
stasis punctuated by sudden change
– Relatively rapidly
• Gradualism
• Adaptive Radiation
Fig. 24-17
(a) Punctuated pattern
Time
(b) Gradual pattern
Adaptive Radiation
• Over the last 250 my diversity of life has
increased in the fossil record
• Periods of evolutionary change in which
groups of organisms form many new
species whose adaptations allow them to
fill different ecological roles or niches
• Large scale after each of the 5 mass
extinctions
• Seed plants, mammals etc..
Predator genera
(percentage of marine genera)
Fig. 25-16
50
40
30
20
10
0
Paleozoic
Mesozoic
Era
D
C
P
C
E
O S
J
Tr
Period
359
488 444 416
542
299 251
200
145
Time (millions of years ago)
Cenozoic
P
65.5
N
0
Fig. 25-17
Ancestral
mammal
Monotremes
(5 species)
ANCESTRAL
CYNODONT
Marsupials
(324 species)
Eutherians
(placental
mammals;
5,010 species)
250
200
100
150
Millions of years ago
50
0
Fig. 25-18
Close North American relative,
the tarweed Carlquistia muirii
Dubautia laxa
KAUAI
5.1
million
years
MOLOKAI
OAHU
3.7 LANAI
million
years
1.3
MAUI million
years
Argyroxiphium sandwicense
HAWAII
0.4
million
years
Dubautia waialealae
Dubautia scabra
Dubautia linearis
New roles in community lead to
radiations
• Rise of photosynthetic prokaryotes
• Evolution of large predators in the
Cambrian explosion
• Colonization of land by
– plants, (stems, waxy coat)
– insects
– Tetrapods
The radiation of plants stimulated radiation of
insects