1. The Origin of Species Mom, Dad… There’s something you need to know…
I’m a MAMMAL!

2. “That mystery of mysteries…”
Darwin never actually tackled how new species arose…
In the Galápagos Islands Darwin discovered plants and animals found nowhere else on Earth
Many questions remain concerning how long it takes for new species to form, or how many genes need to differ between species
Animation: Macroevolution
Speciation, the origin of new species, is at the focal point of evolutionary theory
Evolutionary theory must explain how new species originate and how populations evolve
Microevolution consists of adaptations that evolve within a population, confined to one gene pool
Macroevolution refers to evolutionary change above the species level
Both in space and time, we seem to be brought somewhat near to that great fact —that mystery of mysteries— the first appearance of new beings on this Earth.

3. So…what is a species? defined by Ernst Mayr
Biological species concept
defined by Ernst Mayr
population whose members can interbreed & produce viable, fertile offspring
Distinct species: songs & behaviors are different enough to prevent interbreeding
Humans re so diverse but considered one species, whereas these Meadowlarks look so similar but are considered different species.
Meadowlarks Similar body & colorations, but are distinct biological species because their songs & other behaviors are different enough to prevent interbreeding
Eastern Meadowlark
Western Meadowlark

4. Not the only “species”
Other species definitions: Morphological Ecological Paleological
Species is a Latin word meaning “kind” or “appearance”
Biologists compare morphology, physiology, biochemistry, and DNA sequences when grouping organisms
The biological species concept states that a species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; they do not breed successfully with other populations
Gene flow between populations holds the phenotype of a population together
The biological species concept cannot be applied to fossils or asexual organisms (including all prokaryotes)
Other species concepts emphasize the unity within a species rather than the separateness of different species
The morphological species concept defines a species by structural features
It applies to sexual and asexual species but relies on subjective criteria
The ecological species concept views a species in terms of its ecological niche
It applies to sexual and asexual species and emphasizes the role of disruptive selection
The phylogenetic species concept: defines a species as the smallest group of individuals on a phylogenetic tree
It applies to sexual and asexual species, but it can be difficult to determine the degree of difference required for separate species

5. How and why do new species originate?
Species are created by a series of evolutionary processes
populations become isolated
geographically isolated
reproductively isolated
isolated populations evolve independently
Isolation
allopatric
geographic separation
sympatric
still live in same area
In allopatric speciation, gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations
The definition of barrier depends on the ability of a population to disperse
Separate populations may evolve independently through mutation, natural selection, and genetic drift
Regions with many geographic barriers typically have more species than do regions with fewer barriers
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, speciation takes place in geographically overlapping populations
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

6. Allopatric speciation
Fig. 24-6
Allopatric speciation
A. harrisi
A. leucurus
Figure 24.6 Allopatric speciation of antelope squirrels on opposite rims of the Grand Canyon

7. Allopatric speciation
Fig. 24-7
Allopatric speciation
Mantellinae
(Madagascar only):
100 species
Rhacophorinae
(India/Southeast
Asia): 310 species
Other Indian/
Southeast Asian
frogs
100 80 60 40 20 1 2 3
Figure 24.7 Allopatric speciation in frogs
Regions with many geographic barriers typically have more species than do regions with fewer barriers
Millions of years ago (mya) 1 2 3
India
Madagascar
88 mya
65 mya
56 mya

8. Fig. 24-8
Reproductive isolation between populations generally increases as the distance between them increases
Allopatric speciation
2.0
1.5
Degree of reproductive isolation
1.0
0.5
Figure 24.8 Variation in reproductive isolation with distance between populations of dusky salamanders
Barriers to reproduction are intrinsic; separation itself is not a biological barrier 50
100
150
200
250
300
Geographic distance (km)

9. Allopatric speciation
Fig. 24-9
EXPERIMENT
Allopatric speciation
Initial population
Some flies
raised on
starch medium
Some flies
raised on
maltose medium
Mating experiments
after 40 generations
RESULTS
Female
Female
Starch
Starch
Starch
Maltose
population 1
population 2
Figure 24.9 Can divergence of allopatric populations lead to reproductive isolation?
Starch
population 1
Starch 22 9 18 15
Male
Male
Maltose 8 20 12 15
Starch
population 2
Mating frequencies
in experimental group
Mating frequencies
in control group

10. Polyploidy
Sympatric speciation
Polyploidy is the presence of extra sets of chromosomes due to accidents during cell division
An autopolyploid is an individual with more than two chromosome sets, derived from one species
Polyploidy is much more common in plants than in animals
Many important crops (oats, cotton, potatoes, tobacco, and wheat) are polyploids

11. Sympatric speciation 2n = 6 4n = 12 2n 4n Failure of cell
Fig
Sympatric speciation
2n = 6
4n = 12 2n 4n
Failure of cell
division after
chromosome
duplication gives
rise to tetraploid
tissue.
Gametes
produced
are diploid..
Offspring with
tetraploid
karyotypes may
be viable and
fertile.
Fig Sympatric speciation by autopolyploidy in plants

12. Sympatric speciation
An allopolyploid is a species with multiple sets of chromosomes derived from different species

13. Species B 2n = 4 Unreduced gamete with 4 chromosomes Unreduced gamete
Fig
Species B
2n = 4
Unreduced
gamete
with 4
chromosomes
Unreduced
gamete
with 7
chromosomes
Hybrid
with 7
chromosomes
Meiotic
error
Normal
gamete
n = 3
Viable fertile
hybrid
(allopolyploid)
2n = 10
Figure One mechanism for allopolyploid speciation in plants
Normal
gamete
n = 3
Species A
2n = 6

14. Habitat Differentiation
Sympatric speciation
Sympatric speciation can also result from the appearance of new ecological niches
For example, the North American maggot fly can live on native hawthorn trees as well as more recently introduced apple trees

15. Sexual selection can drive sympatric speciation
Sexual selection for mates of different colors has likely contributed to the speciation in cichlid fish in Lake Victoria

16. Fig
A hybrid zone is a region in which members of different species mate and produce hybrids
EUROPE
Fire-bellied
toad range
Hybrid zone
Fire-bellied toad,
Bombina bombina
Yellow-bellied
toad range
Yellow-bellied toad,
Bombina variegata
0.99
0.9
Fig A narrow hybrid zone for B. variegata and B. bombina in Europe
A hybrid zone can occur in a single band where adjacent species meet
Hybrids often have reduced fitness compared with parent species
The distribution of hybrid zones can be more complex if parent species are found in multiple habitats within the same region
Allele frequency (log scale)
0.5
0.1
0.01 40 30 20 10 10 20
Distance from hybrid zone center (km)

17. Hybrid Zones over Time
When closely related species meet in a hybrid zone, there are three possible outcomes:
Strengthening of reproductive barriers
Weakening of reproductive barriers
Continued formation of hybrid individuals

18. Isolated population diverges
Fig
Isolated population
diverges
Possible
outcomes:
Hybrid
zone
Reinforcement OR
Fusion
Gene flow
Hybrid OR
Figure Formation of a hybrid zone and possible outcomes for hybrids over time
The reinforcement of barriers occurs when hybrids are less fit than the parent species
Over time, the rate of hybridization decreases
Where reinforcement occurs, reproductive barriers should be stronger for sympatric than allopatric species
If hybrids are as fit as parents, there can be substantial gene flow between species
If gene flow is great enough, the parent species can fuse into a single species
Extensive gene flow from outside the hybrid zone can overwhelm selection for increased reproductive isolation inside the hybrid zone
In cases where hybrids have increased fitness, local extinctions of parent species within the hybrid zone can prevent the breakdown of reproductive barriers
Barrier to
gene flow
Population
(five individuals
are shown)
Stability

19. PRE-reproduction barriers
Obstacle to mating or to fertilization if mating occurs
geographic isolation
ecological isolation
temporal isolation
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
behavioral isolation
mechanical isolation
gametic isolation

20. Habitat isolation: Two species encounter each other rarely, or not at all, because they occupy different habitats, even though not isolated by physical barriers

21. Temporal isolation: Species that breed at different times of the day, different seasons, or different years cannot mix their gametes

22. Behavioral isolation: Courtship rituals and other behaviors unique to a species are effective barriers

23. Mechanical isolation: Morphological differences can prevent successful mating
Bradybaena with shells
spiraling in opposite
directions

24. Gametic isolation: Sperm of one species may not be able to fertilize eggs of another species

25. Postzygotic barriers prevent the hybrid zygote from developing into a viable, fertile adult:
Reduced hybrid viability
Reduced hybrid fertility
Hybrid breakdown

26. Reduced hybrid viability: Genes of the different parent species may interact and impair the hybrid’s development
Ensatina hybrid

27. Reduced hybrid fertility: Even if hybrids are vigorous, they may be sterile
Donkey
Mule (sterile hybrid)
Horse

28. Hybrid breakdown: Some first-generation hybrids are fertile, but when they mate with another species or with either parent species, offspring of the next generation are feeble or sterile
Hybrid cultivated
rice plants with
stunted offspring (center)

29. Figure 24.4 Reproductive barriers
Prezygotic barriers
Postzygotic barriers
Habitat Isolation
Temporal Isolation
Behavioral Isolation
Mechanical Isolation
Gametic Isolation
Reduced Hybrid Viability
Reduced Hybrid Fertility
Hybrid Breakdown
Individuals of
different
species
Mating
attempt
Viable,
fertile
offspring
Fertilization
(a)
(c)
(e)
(f)
(g)
(h)
(i)
(l)
(d)
(j)
(b)
Figure 24.4 Reproductive barriers
(k)

30. Rate of Speciation Current debate:
Does speciation happen gradually or rapidly?
Gradualism
Charles Darwin
Charles Lyell
Punctuated equilibrium
Stephen Jay Gould
Niles Eldredge
Niles Eldredge
Curator
American Museum of Natural History

31. Gradualism Gradual divergence over long spans of time
assume that big changes occur as the accumulation of many small ones

32. Punctuated Equilibrium
Rate of speciation is not constant
rapid bursts of change
long periods of little or no change
species undergo rapid change when they 1st bud from parent population

33. Stephen Jay Gould ( )
Harvard paleontologist & evolutionary biologist
punctuated equilibrium
prolific author
popularized evolutionary thought
Stephen Jay Gould (September 10, 1941 – May 20, 2002) was a New York-born American paleontologist, evolutionary biologist, and historian of science. He was the most influential and widely read writer of popular science of his generation. He served as a member of the faculty at Harvard University beginning in Toward the end of his life he served as the Alexander Agassiz Professor of Zoology at that university. He helped Niles Eldredge develop Eldredge's theory of punctuated equilibrium 1972, wherein evolutionary change occurs relatively rapidly in comparatively brief periods of environmental stress, separated by longer periods of evolutionary stability. According to Gould, this overthrew a key tenet of neo-Darwinism; according to most evolutionary biologists, the theory was an important insight but merely modified neo-Darwinism in a way fully compatible with what had been known before. Gould became widely known through his popular science essays in Natural History magazine, collections of essays like The Panda's Thumb and The Flamingo's Smile, and extended studies like Wonderful Life and others.Gould was an emphatic advocate of evolution and wrote prolifically on the subject, trying to communicate his understanding of contemporary evolutionary theory to a wide audience. A recurring theme in his writings is the history and development of evolutionary (and pre-evolutionary) thinking. His early research involved the study of the fossil record of snails (detailed in one of his essays). He was also an enthusiastic baseball fan and made frequent references to the sport (including an entire essay) and a very wide range of other topics.

34. 1. A biologist discovers two populations of wolf spiders whose members appear identical. Members of one population are found in the leaf litter deep within the woods. Members of the other population are found in the grass at the edge of the woods. The biologist decides to designate the members of the two populations as two separate species. Which species concept is this biologist most closely utilizing?
Ecological
Biological
Morphological
Pluralistic
genealogical
Answer: a
Source: Barstow - Test Bank for Biology, Seventh Edition, Question #28 34

35. 2. The formation of a land bridge between North and South America about three million years ago should have resulted in which of the following? I. allopatry of marine populations that were previously sympatric II. sympatry of marine populations that were previously allopatric III. sympatry of terrestrial populations that were previously allopatric
I only
II only
III only
I and II
I and III
Answer: e
Source: Barstow - Test Bank for Biology, Seventh Edition, Question #33 35

36. A. Geographical isolation B. Behavioral isolation
For each of the following situations, choose the best answer from the following types of isolating mechanisms:
A. Geographical isolation
B. Behavioral isolation
C. Mechanical isolation
D. Temporal isolation
E. Reproductive isolation
Two species of rats live on different islands.
Refers to all species that adhere to the biological definition.
Two species of fruit fly have different courtship rituals.
The pollen from a Dogwood tree can not penetrate the pine cone of a Douglas Fir.
3. A
4. E
5. B
6. C