Download Chapter 19: Speciation and Macroevolution

Chapter 19: Speciation and
Macroevolution
Biological Species Concept
• Species consist of 1+ populations whose
members are capable of interbreeding in
nature to produce fertile offspring and do not
interbreed with members of different species
• Sexual reproduction
• Reproductive isolation
Fig. 24-2
(a) Similarity between different species
(b) Diversity within a species
Reproductive Isolating
Mechanisms
• Prevent interbreeding between 2 species
• Preserve genetic integrity
• Gene flow is prevented
Reproductive barriers - prezygotic
• Prezygotic – prevent fertilization
• Interspecific zygote never made
• Types:
– Temporal
– Habitat
– Behavioral
– Mechanical
– gametic
Temporal
• Different times
• Day, season, year
• Ex:
– Fruit flies – afternoon vs. morning
– Frogs – late March vs. mid-April
Fig. 24-4e
(c)
Eastern spotted skunk
(Spilogale putorius)
Fig. 24-4f
(d)
Western spotted skunk
(Spilogale gracilis)
Habitat
• Same geographical area, different habitat
• Ex:
– Flycatchers
•
•
•
•
•
Open woods/farms
Deciduous forest
Wet thickets
Coniferous forest
Brushy pastures/ willow thickets
Fig. 24-4c
(a)
Water-dwelling Thamnophis
Fig. 24-4d
(b)
Terrestrial Thamnophis
Behavioral
• Courtship (signals before mating)
• Aka “sexual isolation”
• Ex:
– Nest decoration, dance, song, vocalizations
Fig. 24-4g
(e)
Courtship ritual of bluefooted boobies
Mechanical
• Incompatible structures of genital organs
• Ex:
– Flowers adapted for different insect pollinators
Fig. 24-4h
(f)
Bradybaena with shells
spiraling in opposite
directions
Gametic
• Egg and sperm incompatible after mating
• Ex:
– Aquatic animals – release egg and sperm at once;
egg and sperm protein bind to each other
Fig. 24-4k
(g)
Sea urchins
Reproductive barriers - Postzygotic
• Prevent gene flow when fertilization occurs
– Hybrid inviability
– Hybrid sterility
– Hybrid breakdown
Fig. 24-4l
(h)
Ensatina hybrid
Hybrid inviability
• Increased likelihood of reproductive failure
after fertilization
• Spontaneous abortion – genes do not interact
properly
Hybrid sterility
• Interspecific hybrid lives but can’t reproduce
• Incompatible courtship w/ either parent
species
• Gametes of hybrid abnormal during meiosis
– Different chromosome #’s
• Female horse – 64
• Male donkey – 62
• Mule - 63
Fig. 24-4m
(i)
Donkey
Fig. 24-4n
(j)
Horse
Fig. 24-4o
(k)
Mule (sterile hybrid)
Hybrid breakdown
• Inability of a hybrid to reproduce due to some
defect
• F2’s
• Ex:
– 2 sunflower species – 80% F2 can’t reproduce
Fig. 24-4p
(l)
Hybrid cultivated rice plants with
stunted offspring (center)
Reproductive isolation is the Key to
Speciation
• Speciation = evolution of a new species
• 2 patterns
– 1) Anagenic
– 2) Cladogenic
Anagenesis
• (phyletic evolution)
• Relatively small, progressive evolutionary
changes in a single lineage over long periods
• Enough time  conversion of 1 species to
another
• Sequence of species occurs over time without
an increase in the number of species
Cladogenesis
• (branching evolution)
• 2+ populations of an ancestral species split
and diverge, eventually forming 2+ new
species
• Clade = cluster of species derived from a
single common ancestor
• Over time  increase species richness
When has speciation occurred?
• Population is sufficiently different from its
ancestral species that no genetic exchange can
occur between them
• 2 ways:
– Allopatric
– Sympatric
Fig. 24-5
(a) Allopatric speciation
(b) Sympatric speciation
Allopatric Speciation
• Occurs when 1 population becomes
geographically separated from the rest of the
species and then evolves by natural selection
and/or genetic drift
• Most common
• Geographic isolation by:
– Changing of Rivers, glaciers, mountains, land bridges,
lakes
• Birds vs. rats
– Small population migrates or is dispersed
– Colonize new area
– Isolated gene pool  microevolution  new species
Fig. 24-6
A. harrisi
A. leucurus
Sympatric Speciation
• New species evolves within the same
geographical region as the parent species
• 2 ways:
– Change in
• Ploidy
• Ecology
Ploidy
• Polyploidy - 2+ chromosome sets
– Plants – rapid speciation
• Autopolyploid – multiple sets chromosomes
from a single species
• Allopolyploidy – multiple sets of chromosomes
from 2+ species
– Allopolyploid – diff # chromosomes from parents =
new species
• 1) extinct
• 2)coexist
• 3)replace parent species
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.
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
Allopatric and Sympatric
Speciation: A Review
• In allopatric speciation, geographic isolation
restricts gene flow between populations
• Reproductive isolation may then arise by natural
selection, genetic drift, or sexual selection in the
isolated populations
• Even if contact is restored between populations,
interbreeding is prevented
• In sympatric speciation, a reproductive barrier
isolates a subset of a population without
geographic separation from the parent species
• Sympatric speciation can result from polyploidy,
natural selection, or sexual selection
Ecology
• Parasitic insects
– Ex: fruit maggot flies
• Switched host from hawthorn tree fruits to domestic
apples
• Mutation  disruptive selection  different
ecological opportunity
Evolutionary Change – rapid or gradual?
2 models
• Punctuated Equilibrium – fossil record
accurately reflects evolution as it actually
occurs
– Long periods of stasis are punctuated by short
periods of rapid speciation triggered by changes in
the environment
– Speciation in “spurts”
– Short periods evolution, long periods stability
– Accounts for abrupt appearance of new species
with few intermediate forms
Fig. 24-17
(a) Punctuated pattern
Time
(b) Gradual pattern
• Gradualism – traditional view of evolution
– Evolution proceeds continuously over long periods
– Rarely observed, fossil record incomplete
– Populations slowly diverge from 1 another by the
gradual accumulation of adaptive characteristics
within each population
Macroevolution
• Dramatic changes that occur over long time
spans in evolution
• Attempts to explain large phenotypic changes
(novelties)
• Important aspects
– Evolutionary novelties
– Adaptive radiation
– Mass extinction
Macroevolution
Adaptive radiation
• Evolutionary diversification of many related
species from 1 or a few ancestors in a short
period
• Adaptive zones: new ecological opportunities
that were not exploited by an ancestor
• Islands – common – fewer species there
• Ex: Darwin’s finches, honeycreeper birds,
silversword plants
Extinction
•
•
•
•
End of lineage; last member of species dies
Permanent
Makes adaptive zones vacant
Background extinction
– Continuous, low-level
• Mass extinction
– Numerous species die at once
– Adaptive radiation follows
Extinction video
• Causes of mass extinction
– Climate change / Earth’s temp.
– Catastrophes
• Comet/asteroid  dust (block light)  food chain
disrupted, drop in temp.
– Competition
• Humans  animal / plant habitats
Microevolution vs. Macroevolution
• Genetics
• Well suited survive
• Chance events
• “lucky” to survive
• Right place, right time