1. Chapter 24 ~The Origin of Species

2. Macroevolution: the origin of new taxonomic groups
Speciation: the origin of new species
1- Anagenesis (phyletic evolution): accumulation of heritable changes
2- Cladogenesis (branching evolution): budding of new species from a parent species that continues to exist (basis of biological diversity)

3. What is a species?
Biological species concept (ErnstMayr): a population or group of populations whose members have the potential to interbreed and produce viable, fertile offspring (genetic exchange is possible and that is genetically isolated from other populations)

4. 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

5. Reproductive Isolation (isolation of gene pools), I
Prezygotic barriers: impede mating between species or hinder the fertilization of the ova
Habitat (snakes; water/terrestrial)
Behavioral (fireflies; mate signaling)
Temporal (salmon; seasonal mating)
Mechanical (flowers; pollination anatomy)
Gametic (frogs; egg coat receptors)

6. Habitat isolation
Species occur in same region, but occupy different habitats so rarely encounter each other
reproductively isolated
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 rainforest

7. Temporal isolation
Species that breed during different times of day, different seasons, or different years cannot mix gametes
reproductive isolation
Eastern spotted skunk (L) & western spotted skunk (R) overlap in range but eastern mates in late winter & western mates in late summer

8. Behavioral isolation
Unique behavioral patterns & rituals isolate species
identifies members of species
attract mates of same species 
courtship rituals, mating calls
reproductive isolation
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

9. Mechanical isolation Plants
sympatric speciation?
Mechanical isolation
Morphological differences can prevent successful mating
reproductive isolation
Plants
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.

10. Mechanical isolation Animals
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

11. Gametic isolation
Sperm of one species may not be able to fertilize eggs of another species
mechanisms
biochemical barrier so sperm cannot penetrate egg
receptor recognition: lock & key between egg & sperm
chemical incompatibility
sperm cannot survive in female reproductive tract
Sea urchins release sperm & eggs into surrounding waters where they fuse & form zygotes. Gametes of different species— red & purple —are unable to fuse.

12. Gametic isolation
Sperm of one species may not be able to fertilize eggs of another species
mechanisms
biochemical barrier so sperm cannot penetrate egg
receptor recognition: lock & key between egg & sperm
chemical incompatibility
sperm cannot survive in female reproductive tract
Sea urchins release sperm & eggs into surrounding waters where they fuse & form zygotes. Gametes of different species— red & purple —are unable to fuse.

13. Reproductive Isolation, II
Postzygotic barriers: fertilization occurs, but the hybrid zygote does not develop into a viable, fertile adult
Reduced hybrid viability (frogs; zygotes fail to develop or reach sexual maturity)
Reduced hybrid fertility (mule; horse x donkey; cannot backbreed)
Hybrid breakdown (cotton; 2nd generation hybrids are sterile)

14. 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.

15. 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
Mules 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)
Mules have 63 chromosomes!

16. 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.

17. Modes of speciation (based on how gene flow is interrupted)
Allopatric: “other country” populations segregated by a geographical barrier; can result in adaptive radiation (island species)
Sympatric: “same country reproductively isolated subpopulation in the midst of its parent population (change in genome); polyploidy in plants; cichlid fishes

18. 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

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

20. 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
Time

21. 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.

22. Evolution is not goal-oriented
An evolutionary trend does not mean that evolution is goal-oriented.
Surviving species do not represent the peak of perfection. There is compromise & random chance involved as well
Remember that for humans as well!
Evolution is not the survival of the fittest. Rather it is the survival of the just good enough.

23. Categories of Evolution
Convergent evolution - acquisition of the same biological trait in unrelated lineages.
Leads to analogous structures

24. Parallel evolution is the development of a similar trait in related, but distinct, species descending from the same ancestor, but from different clades.lades
Cladogram (family tree) of a biological group. The red and blue boxes at right and left represent clades (i.e., complete branches). The green box in the middle is not a clade, but rather represents anevolutionary grade, an incomplete group, because the blue clade at left is descended from it, but is excluded.

25. Divergent evolution - accumulation of differences between groups which can lead to the formation of new species, usually a result of diffusion of the same species adapting to different environments