1. Speciation and Macroevolution
Divergent Evolution
Convergent Evolution

2. Evolutionary change of a species over time
Creation of new groupspeciation  diversity of living things.

3. Speciation & Macroevolution
Microevolution = evolution on small scale
changes in allele frequency in a population over time
Speciation = formation of new species
Bridges micro and macro-evolution
Macroevolution = large scale evolution
broad patterns of evolutionary change; species formation and larger

4. What is a species? biological species concept:
A group of individuals (i.e., multiple pops.) that have the potential to interbreed in nature and produce viable, fertile offspring.
Based on reproductive compatibility and isolation
Weakness of this def:
Other species definitions:
Morphological species concept: based on structure
Ecological species concept: based on niche (i.e., role in ecosystem)
Phylogenetic species concept: based on common ancestor (evolutionary relationship)
More…..

5. Reproductive Isolation
Reproductive isolation : inability to mate and produce viable, fertile offspring
Classification/Types of Isolation:
Prezygotic Barriers
Pre-mating attempt
Post-mating attempt
Post-zygotic Barriers

6. Figure 24.13-2 Isolated population diverges. Gene flow Population
Barrier to
gene flow
Figure Formation of a hybrid zone and possible outcomes for hybrids over time (step 2)
Figure

7. Mating doesn’t occur
Gametes don’t unite
Offspring doesn’t survive or can’t perpetuate species

8. Prezygotic barriers block fertilization from occurring by
Impeding different species from attempting to mate
Preventing the successful completion of mating
Hindering fertilization if mating is successful
Postzygotic barriers prevent the hybrid zygote from developing into a viable, fertile adult
Reduced hybrid viability
Reduced hybrid fertility
Hybrid breakdown

9. Two forms of Speciation:
Allopatric: speciation with geographic separation
Non-overlapping populations
“Barrier” is relative to dispersal ability of organism
Even if contact is restored, interbreeding is prevented
Sympatric: speciation within the same geographic location/area
Overlapping

10. Allopatric Speciation: A tale of two fuzzy animals

11. Experiment
Reproductive barriers can develop when laboratory populations are experimentally isolated and subjected to different environmental conditions
Initial population
of fruit flies
(Drosophila
pseudoobscura)
Some flies raised on starch medium
Some flies raised on
maltose medium
Mating experiments
after 40 generations
Results
Female
Female
Starch
population 1
Starch
population 2
Starch
Maltose
population 1
Starch
Starch 22 9 18 15
Figure 24.7 Inquiry: Can divergence of allopatric populations lead to reproductive isolation?
Male
Male
population 2
Starch
Maltose 8 20 12 15
Number of matings
in experimental group
Number of matings
in control group
Figure 24.7

12. Figure 24.6 (a) Under high predation (b) Under low predation
Figure 24.6 Reproductive isolation as a by-product of selection
(a) Under high predation
(b) Under low predation
Females from each pop show strong preference for their own body shape in mate selection
Figure 24.6

13. Sympatric Speciation Mechanisms for sympatric speciation
Habitat differentiation
Sexual selection
Polyploidy

14. A “tale” of two squirrels

15. I love a man with a red nose Orange noses are dreamy
Sexual Selection
Preference for specific traits (e.g., morphological or behavioral) by subset of females can lead to reproductive isolation.
E.g. Sexual selection for mates of different colors has likely contributed to speciation in cichlid fish in Lake Victoria
I love a man with a red nose
Orange noses are dreamy

16. Monochromatic orange light P. pundamilia P. nyererei
Figure 24.11
Experiment
Monochromatic
orange light
Normal light
P. pundamilia
Figure Inquiry: Does sexual selection in cichlids result in reproductive isolation?
P. nyererei

17. Polyploidy
Polyploidy is the presence of extra sets of chromosomes due to accidents during cell division
Polyploidy can produce new biological species in sympatry within a single generation
Autopolyploid: from a single species
Allopolyploid: from hybrids of two species

18. An autopolyploid is an individual with more than two chromosome sets, derived from a single species
Cell
division
error
Tetraploid cell 4n
2n = 6 2n
Meiosis
New species
(4n)
Gametes produced
by tetraploids
Autopolyploid speciation
Figure 24.UN02

19. Species A
2n = 6
Normal gamete
n = 3
n = 2
Species B
2n = 4
Sterile hybrid with
5 chromosomes
Mitotic or meiotic error
doubles the chromosome
number.
New species:
viable, fertile hybrid
(allopolyploid)
2n = 10
An allopolyploid is a species with multiple sets of chromosomes derived from different species
Figure

20. Figure 24.10 T. dubius (12) Hybrid species: T. miscellus (24)
T. mirus
(24)
Figure Allopolyploid speciation in Tragopogon
T. pratensis
(12)
T. porrifolius
(12)

21. Rate of speciation
It can happen quickly (punctuated equilibrium model)
It can happen slowly (gradualism)
The interval between speciation events can range from 4,000 years (some cichlids) to 40 million years (some beetles), with an average of 6.5 million years
(a) Punctuated model
Time
(b) Gradual model
Figure 24.16

22. Speciation Rates
The punctuated pattern in the fossil record and evidence from lab studies suggest that speciation can be rapid
For example, the sunflower Helianthus anomalus originated from the hybridization of two other sunflower species

23. Studying the Genetics of Speciation
How many genes change when a new species forms?
As few as a single gene or in other cases many genes
For example, in Japanese Euhadra snails, the direction of shell spiral affects mating and is controlled by a single gene
In monkey flowers (Mimulus), two loci affect flower color, which influences pollinator preference
Pollination that is dominated by either hummingbirds or bees can lead to reproductive isolation of the flowers
In other organisms, speciation can be influenced by larger numbers of genes and gene interactions

24. Figure 24.19 68x more hummmingbrid visits than wild-type M. lewisii
Preferred by bumblebees
(a) Mimulus lewisii
(b)
M. lewisii with
M. cardinalis allele
74x more bumblebee visits than wild-type M. cardinalis
Figure A locus that influences pollinator choice
Preferred by hummingbirds
Figure 24.19
(c) Mimulus cardinalis
(d)
M. cardinalis with
M. lewisii allele

25. Convergent Evolution
When similar selective forces cause similarities (similar traits) in unrelated species
E.g., body shape of aquatic organism (shark and dolfins)
Similar structure of desert plants cacti & euphorbs