Ch. 23 Warm-Up Use the following information to help you answer the question below: Population = 1000 people AA = 160 Aa = 480 aa = 360 What are the genotypic frequencies? Allele frequencies? Use directional, stabilizing or disruptive selection to answer the following: The mice in the Arizona desert have either dark or light fur. Birds produce 4-5 eggs per clutch Average human baby weighs 7 lbs. Darwin's finches and beak size during drought

Chapter 24 The Origin of Species

What You Need to Know: The difference between microevolution and macroevolution. The biological concept of a species. Prezygotic and postzygotic barriers that maintain reproductive isolation in natural populations. How allopatric and sympatric speciation are similar and different. How autopolyploid or an allopolyploid chromosomal change can lead to sympatric speciation. How punctuated equilibrium and gradualism describe two different tempos of speciation.

Speciation = origin of species Microevolution: changes within a single gene pool Macroevolution: evolutionary change above the species level cumulative effects of speciation over long periods of time

HHMI Video Clip: Reproductive Isolation and Speciation Running Time: 2:38 min

Biological Species Concept Species = population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring Reproductively compatible Reproductive isolation = barriers that prevent members of 2 species from producing viable, fertile hybrids

Types of Reproductive Barriers Prezygotic Barriers: Impede mating/fertilization Types: Habitat isolation Temporal isolation Behavioral isolation Mechanical isolation Gametic isolation Postzygotic Barriers: Prevent hybrid zygote from developing into viable adult Types: Reduced hybrid viability Reduced hybrid fertility Hybrid breakdown

Types of Reproductive Barriers REDUCED HYBRID VIABILITY REDUCED HYBRID FERTILITY HYBRID BREAKDOWN

Types of Reproductive Barriers REDUCED HYBRID VIABILITY REDUCED HYBRID FERTILITY HYBRID BREAKDOWN

Other definitions of species: Morphological – by body shape, size, and other structural features Ecological – niche/role in community Phylogenetic – share common ancestry, branch on tree of life

Two main modes of speciation

Two main modes of speciation: Allopatric Speciation “other” “homeland” Geographically isolated populations Caused by geologic events or processes Evolves by natural selection & genetic drift Eg. Squirrels on N/S rims of Grand Canyon Sympatric Speciation “together” “homeland” Overlapping populations within home range Gene flow between subpopulations blocked by: polyploidy sexual selection habitat differentiation Eg. polyploidy in crops (oats, cotton, potatoes, wheat)

Allopatric speciation of antelope squirrels on opposite rims of the Grand Canyon

Sympatric Speciation by Polyploidy Autopolyploid: extra sets of chromosomes Failure of cell division (2n  4n) Eg. Strawberries are 4n, 6n, 8n, 10n (decaploid)! Allopolyploid: 2 species produce a hybrid Species A (2n=6) + Species B (2n=4)  Hybrid (2n=10) 2n = 6 4n = 12 4n 2n Autopolyploid Speciation

Allopolyploidy

Adaptive Radiation Many new species arise from a single common ancestor Occurs when: A few organisms make way to new, distant areas (allopatric speciation) Environmental change  extinctions  new niches for survivors Eg. Hawaiian archepelago Founding Parents

Adaptive Radiation: Hawaiian plants descended from ancestral tarweed from North America 5 million years ago KAUAI 5.1 million years OAHU 3.7 HAWAII 0.4 1.3 MAUI MOLOKAI LANAI Argyroxiphium sandwicense Dubautia linearis Dubautia scabra Dubautia waialealae Dubautia laxa N

Hybrid Zones Incomplete reproductive barriers Possible outcomes: reinforcement, fusion, stability

Grizzly Polar “Grolar” or “Pizzly”

Tempo of Evolution Gradualism Common ancestor Slow, constant change Punctuated Equilibium Eldridge & Gould Long period of stasis punctuated by short bursts of significant change

HHMI Short Film: Lizards in an Evolutionary Tree Topic: Adaptive Radiation Running Time: 17:50 min