Transcript Species
Ch. 23 Warm-Up Use the following information to help you answer the question below: Population = 1000 people AA = 160 Aa = 480 aa = 360 1. What are the genotypic frequencies? Allele frequencies? 2. Use directional, stabilizing or disruptive selection to answer the following: a) The mice in the Arizona desert have either dark or light fur. b) Birds produce 4-5 eggs per clutch c) Average human baby weighs 7 lbs. d) 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 populaitons. • 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 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 Sympatric Speciation “other” “homeland” “together” “homeland” Geographically isolated populations Overlapping populations within home range • Caused by geologic events or processes • Evolves by natural selection & genetic drift Gene flow between subpopulations blocked by: • polyploidy • sexual selection • habitat differentiation Eg. Squirrels on N/S rims of Grand Canyon 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) 2n = 6 2n 4n = 12 Autopolyploid Speciation 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) 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 1.3 Dubautia laxa million years KAUAI 5.1 million years MOLOKAI MAUI OAHU 3.7 LANAI million years Argyroxiphium sandwicense HAWAII 0.4 million years Dubautia waialealae Dubautia scabra Dubautia linearis Hybrid Zones • Incomplete reproductive barriers • Possible outcomes: reinforcement, fusion, stability Grizzly “Grolar” or “Pizzly” Polar Tempo of Evolution Gradualism • Common ancestor • Slow, constant change Punctuated Equilibium • Eldridge & Gould • Long period of stasis punctuated by short bursts of significant change