AP Biology, Chapter 24
The Origin of Species

Summary
Introduction
	1. Distinguish between anagenesis and cladogenesis.
		a. Anagenesis: accumulation of changes within a species; one whole species evolves 
		into another
		b. Cladogenesis: branching evolution; original species gives rise to a branch

WHAT IS A SPECIES?
	Introduction
	The biological species concept emphasizes reproductive isolation
		2. Define biological species according to Ernst Mayr.
			a. Population or group of populations that can successfully interbreed in nature
	Prezygotic and postzygotic barriers isolate the gene pools of biological species
		3. Distinguish between prezygotic and postzygotic isolating mechanisms.
			a. Prezygotic barriers impede mating or fertilization
			b. Postzygotic barriers block after the formation of the zygote
		4. Describe five prezygotic isolating mechanisms and give an example of each.
			a. Habitat isolation
				i. Physical separation into two places
				ii. Parasites living in different hosts; squirrels divided by a canyon
			b. Behavioral isolation
				i. Mating signals don't match
				ii. Firefly blinking; meadowlark singing
			c. Temporal isolation
				i. Mating times don't match
				ii. Western and eastern spotted skunks; orchids
			d. Mechanical isolation
				a. Mating structures don't fit
				b. Pollinators match flower shapes
			e. Gametic isolation
				a. Sperm may die in female tract of separate species
				b. Fusion of sperm and egg may require species-specific signals
		5. Explain why many hybrids are sterile.
			a. Reduced viability because of genetic imbalance, uncoordinated development 
			b. Reduced fertility because chromosomes may not be able to synapse
		6. Explain how hybrid breakdown maintains separate species even if gene flow occurs.
			a. Offspring of hybrids may be weak or sterile
			b. Hybrids may maintain a presence but cannot become genetically independent
	The biological species concept does not work in all situations
		7. Describe some limitations of the biological species concept.
			a. Extinct forms cannot be tested
			b. Asexual forms are isolated, period
			c. Subspecies have a wide range of gene flow
	Other species concepts emphasize features and concepts that identify and unite 
	species members
		8. Define and distinguish among each of the following: ecological species concept, 
		pluralistic species concept, morphological species concept, and genealogical species 
		concept.
			a. Morphological: distinct structure only; the most-used
			b. Recognition: will they recognize each other and mate
			c. Cohesion or pluralistic: takes into account all isolating mechanisms
			d. Ecological: where they live and what they do instead of morphology
			e. Evolutionary or genealogical: recognizes separating groups or organisms

MODES OF SPECIATION
	Introduction
		9. Distinguish between allopatric and sympatric speciation.
			a. Allopatric: physical separation leads to divergence
			b. Sympatric: divergence in place due to intrinsic factors
	Geographical isolation can lead to the origin of species: allopatric speciation
		10. Explain the allopatric speciation model and describe the role of intraspecific variation 
		and geographic isolation.
			a. Explanation: one population becomes separated, populations diverge as they 
			adapt
			b. Gene pool of the new population may differ at the outset
			c. New population may drift, or select changes to new environment
		11. Define a ring species and describe an example found in salamanders.
			a. Ring species a spreading around a geographic barrier
			b. The farther around, the more divergent
		12. Describe examples of adaptive radiation in the Galapagos and Hawaiian 
		archipelagoes.
			a. Galapagos finches: one original colonist, many island environments
			b. Hawaii: many habitats, many thousand unique species
		13. Explain how reproductive barriers evolve. Describe an example of the evolution of a 
		prezygotic barrier and the evolution of a postzygotic barrier.
			a. Evolve by separation followed by selection and/or drift
			b. Prezygotic example: fruit flies adapted to different foods showed assortative 
			mating
			c. Postzygotic: monkeyflower hybrid fertility is inversely proportional to distance
	A new species can originate in the geographical midst of the parent species: 
	sympatric speciation
		14. Define sympatric speciation and explain how polyploidy can cause reproductive 
		isolation.
			a. Sympatric speciation: new species arise amidst parent population
			b. Polyploidy can interfere with chromosome separation in anaphase I
		15. Distinguish between an autopolyploid and an allopolyploid species and describe 
		examples of each.
			a. Autoployploids
				i. Multiple chromosome sets from one species
				ii. Primrose, 4n = 28
			b. Allpolyploids
				i. Hybrids having sets from two species
				ii. Three goatsbeard species were introduced to the US; various hybrids 
				are now known 
				iii. Bread wheat is a hybrid of an original wheat and goatgrass
		16. Describe an example of sympatric speciation in fish.
			a. Sexual selection, by color, in cichlids in Lake Victoria
	Genetic change in populations can account for speciation
	The punctuated equilibrium model has stimulated research on the tempo of 
	speciation
		17. List some points of agreement and disagreement between the two schools of thought 
		about the tempo of speciation (gradualism versus punctuated equilibrium).
			a. Agreement
				i. The fossil record shows stasis; long periods of no changes
				ii. The fossil record is incomplete; periods of change are undocumented
			b. Disagreement
				a. Divergence as continuous and gradual
				b. Punctuated equilibrium: bursts of rapid change followed by stasis 
				c. Gross morphological stasis is illusory

THE ORIGIN OF EVOLUTIONARY NOVELTY
	Introduction
		18. Explain why speciation is at the boundary between microevolution and 
		macroevolution.
			a. Microevolution is the change in allele frequencies
			b. Accumulation of gene pool changes gives new species
			c. Many speciation events constitute macroevolution
	Most evolutionary novelties are modified versions of older structures
		19. Define exaptation and illustrate this concept with an example.
			a. Exaptation involves a new adavantageous use for an old trait
			b. Example: originally feathers may have conserved heat/energy
	Genes that control development play a major role in evolutionary novelty
		20. Explain how the evolution of changes in temporal and spatial developmental 
		dynamics can result in evolutionary novelties. Define evo-devo, allometric growth, 
		heterochrony, and paedomorphosis.
			a. Relatively few genes control timing a proportions; small alterations have big 
			results
			b. Definitions
				i. Evo-devo: interface between developmental  and evolutionary biology 
				ii. Allometric growth: relative growth rates in different parts
				iii. Heterochrony: evolution of morphology from modifying allometric 
				growth
				iv. Paedomorphosis: retention of juvenile characteristics in the adult due 
				to altered timing of reproductive development
	An evolutionary trend does not mean that evolution is goal oriented
		21. Explain why extracting a single evolutionary progression from a fossil record can be 
		misleading.
			a. Lining up fossils out of context implies uninterrupted direct lineage
			b. A series of changes does not imply an ultimate goal
		22. Define and illustrate the concept of species selection. Explain why evolutionary trends 
		are not directional.
			a. Successful, long-lived, widespread species speciate more often
			b. The traits of the long-lived, fecund species appear as a trend in the fossil 
			record
			c. Traits making species fecund, like better dispersal, make it look like all the 
			species traits are important