1. Chapter 24. The Origin of Species
“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.”
— Darwin
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2. What is a species? Biological species concept defined by Ernst Mayr
population whose members can interbreed & produce viable, fertile offspring
reproductively compatible
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3. Biological species concept
Eastern Meadowlark
Western Meadowlark
Similar body & colorations, but are distinct biological species because their songs & other behaviors are different enough to prevent interbreeding
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4. Diversity & Taxonomy The Tree of Life
species are the smallest unit at the ends of branches
basic unit for organizing & categorizing living things
smallest unit by which we measure diversity
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5. How and why do new species originate?
Reproductive isolation
biological barriers that impede members from producing viable offspring
before vs. after fertilization
pre-zygotic barriers
before the zygote
post-zygotic barriers
after the zygote
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6. displaying to attract females
Pre-zygotic barriers
Impede mating or hinder fertilization if mating occurs
habitat isolation
temporal isolation
behavioral isolation
mechanical isolation
gametic isolation
male Frigate bird
displaying to attract females
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7. Ecological isolation
Two species may occupy different habitats within same area so may encounter each other rarely
2 species of garter snake, Thamnophis, occur in same area, but one lives in water & other is terrestrial
lions & tigers could hybridize, but they live in different habitats:
lions in grasslands
tigers in forest
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8. Temporal isolation
Species that breed during different times of day, different seasons, or different years cannot mix gametes
Eastern spotted skunk (L) & western spotted skunk (R) overlap in range but eastern mates in late winter & western mates in late summer
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9. Behavioral isolation
Courtship rituals that attract mates & other unique behaviors to a species are effective reproductive barriers
The most comedic species of the Galapagos Islands is the Blue Footed Booby, what a ridiculous outfit and expression! Their name is in fact taken from the Spanish 'bobo' which means clown.
The Blue Footed Boobies above display part of their humorous courtship ritual whereby they raise their feet one at a time and then swivel their heads away from the prospective mate looking to the sky.
Other interesting Booby features are the highly evolved airbag systems in their skulls which allow them to dive bomb into the sea for fish from great height, and the egg and hatchling nesting boundaries they make which are rings of Boobie poop. They aren't the only Booby on the island — there are also Masked and Red Footed Boobies about.
Blue footed boobies mate only after a courtship display unique to their species
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10. Gray-Crowned Cranes engaged in courtship display, Kenya
What can you say?
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11. Mechanical isolation
Morphological differences can prevent successful mating
Even in closely related species of plants, the flowers often have distinct appearances that attract different pollinators. These 2 species of monkey flower differ greatly in shape & color, therefore cross-pollination does not happen.
The most comedic species of the Galapagos Islands is the Blue Footed Booby, what a ridiculous outfit and expression! Their name is in fact taken from the Spanish 'bobo' which means clown.
The Blue Footed Boobies above display part of their humorous courtship ritual whereby they raise their feet one at a time and then swivel their heads away from the prospective mate looking to the sky.
Other interesting Booby features are the highly evolved airbag systems in their skulls which allow them to dive bomb into the sea for fish from great height, and the egg and hatchling nesting boundaries they make which are rings of Boobie poop. They aren't the only Booby on the island — there are also Masked and Red Footed Boobies about.
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12. Mechanical isolation
For many insects, male & female sex organs of closely related species do not fit together, preventing sperm transfer
lack of “fit” between sexual organs: hard to imagine for us, but a big issue for insects with different shaped genitals!
The selection is intense because it directly affects offspring production -- it is affecting sex itself
Damsel fly penises
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13. Gametic isolation
Sperm of 1 species may not be able to fertilize eggs of another species
variety of mechanisms
chemical incompatibility
sperm cannot survive in female reproductive tract
biochemical barrier so sperm cannot penetrate egg
receptor recognition: lock & key between egg & sperm
Sea urchins release sperm & eggs into surrounding waters where they fuse & form zygotes. Gametes of different species—red & purple —are unable to fuse.
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14. Postzygotic barriers
prevent hybrid zygote from developing into a viable, fertile adult
reduced hybrid viability
reduced hybrid fertility
hybrid breakdown
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zebroid

15. Reduced hybrid viability
Genes of different parent species may interact & impair the hybrid’s development
Species of salamander genus, Ensatina, may interbreed, but most hybrids do not complete development & those that do are frail.
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16. Reduced hybrid fertility
Even if hybrids are vigorous they may be sterile
chromosomes of parents may differ in number or structure & meiosis in hybrids may fail to produce normal gametes
Mule are vigorous, but sterile
What’s wrong with having 63 chromosomes?
Odd number! Cannot pair up in meiosis.
Horses have 64 chromosomes
(32 pairs)
Donkeys have 62 chromosomes
(31 pairs)
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Mules have 63 chromosomes!

17. Hybrid breakdown
Hybrids may be fertile & viable in first generation, but when they mate offspring are feeble or sterile
In strains of cultivated rice, hybrids are vigorous but plants in next generation are small & sterile.
On path to separate species.
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18. Speciation Species are created by a series of evolutionary processes
populations become isolated
reproductively isolated
geographically isolated
isolated populations evolve independently
Isolation
allopatric
physical separation
sympatric
still live in same area
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19. Allopatric speciation
Allopatric = “other country”
geographic separation
migration
physical barrier
Harris’s antelope squirrel inhabits the canyon’s south rim (L). Just a few miles away on the north rim (R) lives the closely related white–tailed antelope squirrel
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20. Sympatric speciation Sympatric = “same country”
some type of isolation even though populations live in same area
what causes this isolation?
behavioral differences
non-random mating
physiological differences
chromosomal changes
polyploidy
mostly in plants: oats, cotton, potatoes, tobacco, wheat
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21. Adaptive radiation
Evolution of many diversely adapted species when introduced to various new environmental challenges & opportunities
Drosophila
Geospiza
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22. Adaptive radiation in plants
all descended from a common ancestor 5mya
Silversword alliance
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23. Adaptive radiation Many ecological niches open
Evolution of many diversely-adapted species from a common ancestor to fill niches
Darwin’s finches
mammals
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24. Review Speciation is a process populations become isolated
geographic isolation
different environmental conditions
food, predators, disease, habitat
different selection pressures
genetic drift
reproductive isolation
sexual selection
isolated populations evolve independently
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25. Current debate
Does speciation happen gradually or rapidly perhaps in response to environmental change
Gradualism
Charles Darwin
Charles Lyell
Punctuated equilibrium
Stephen Jay Gould
Niles Eldredge
Niles Eldredge
Curator
American Museum of Natural History
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26. Gradualism Gradual divergence over long spans of time
assume that big changes occur as the accumulation of many small ones
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27. Punctuated Equilibrium
Rate of speciation is not constant
species undergo most change when they 1st bud from parent population
as separate species, remain static for long periods of time
Time
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28. 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.
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30. Evolution is not goal-oriented
An evolutionary trend does not mean that evolution is goal oriented. The modern horse is the only surviving twig of an evolutionary tree with many divergent trends.
It does not represent the peak of perfection. There is compromise & random chance involved as well
Remember that for
humans as well!
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31. Some interesting evolutionary trends….
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32. Convergent evolution Flight evolved 3 separate times
evolving similar solutions to similar “problems”
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33. Australian Marsupials
Parallel Evolution
Fill similar niches; have similar adaptations, but are not closely related
Niche
Placental Mammals
Australian Marsupials
Burrower
Mole
Marsupial mole
Anteater
Numbat
Anteater
Nocturnal
insectivore
Marsupial mouse
Mouse
Climber
Spotted cuscus
Lemur
Sugar glider
Glider
Flying
squirrel
Stalking
predator
Tasmanian cat
Ocelot
Chasing
predator
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Wolf
Tasmanian “wolf”

34. Mimicry convergent evolution based on similar (protective) appearance
Monarch male
poisonous
Viceroy male
edible
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35. Coevolution Predator-prey relationships Parasite-host relationships
Flowers & pollinators
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36. Darwin Awards
Named in honor of Charles Darwin, the father of evolution, the Darwin Awards commemorate those who improve our gene pool by removing themselves from it.
The Darwin Awards salute the improvement of the human genome by honoring those who accidentally kill themselves in really stupid ways.
Of necessity, this honor is bestowed posthumously.
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37. Any Questions??
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