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The Origin of Species: Understanding Speciation and the Formation of New Species

This chapter explores the concepts of microevolution and macroevolution, the biological definition of a species, prezygotic and postzygotic barriers that maintain reproductive isolation, different modes of speciation, and the impact of genetic factors on speciation. Learn how mutations, sexual recombination, genetic drift, gene flow, and natural selection contribute to macroevolution and the origin of new species.

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The Origin of Species: Understanding Speciation and the Formation of New Species

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  1. Chapter 24 The Origin of Species

  2. 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.

  3. 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

  4. Mutations + Sexual recombination + genetic drift +gene flow + natural selection! = Macroevolution: --the origin of new species, genera, families, orders, classes, phyla, and kingdoms Speciation—the origin of new species

  5. SPECIES “kind”-”appearance” – group of populations whose members can interbreed and produce fertile offspring; • A biological species is the largest set of populations in which genetic exchange is possible and is genetically isolated from other populations. Different Species Of HUMANS??? What is a species ? How does speciation occur ?

  6. Distinctions between species are not always clear. Subspecies have small differences from other subspecies and usually have geographical variation. C. hutchinsii hutchinsii C. canadensis canadensis

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

  8. 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

  9. 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

  10. Organisms of different species cannot interbreed for a number of reasons. • Prezygotic barriers- hinder fertilization • Habitat isolation—live in different places ex: water vs. terrestrial in garter snakes

  11. 2) behavioral isolation—respond only to members of the same species; ex: firefly flashes Prezygotic barriers hinder fertilization Ex. Firefly flashes, Bower Bird nest

  12. Prezygotic barriers hinder fertilization 3) temporal isolation—different breeding times (ex. W. and E. skunks) EASTERN- summer WESTERN - winter

  13. Prezygotic barriers hinder fertilization 4) mechanical isolation—anatomical incompatibility Ex. Damsel fly genitalia, flowers

  14. Prezygotic barriers hinder fertilization 5) gametic isolation—gametes may not be recognized by other species for fertilization (molecular recognition missing between egg and sperm)

  15. Postzygotic barriers - gametes can get together to make a zygote, BUT barriers prevent a zygote from developing properly

  16. Postzygotic barriers prevent a zygote from developing properly. • Reduced hybrid viability—development is aborted at some embryonic stage. Ex. frogs

  17. Postzygotic barriers prevent a zygote from developing properly. 2. Reduced hybrid fertility—hybrids are sterile—usually there is a failure of meiosis in these hybrids so they cannot produce viable (good) gametes

  18. Postzygotic barriers prevent a zygote from developing properly. 3) hybrid breakdown—first-generation hybrids may be fertile, but second-generation offspring are not viable. Ex. cotton

  19. Recipe to make a New Species: Need to create a barrier for gene flow within a population- that is a barrier for productive SEX Need to maintain this barrier (prezygotic/postzygotic) so that the two groups can continue accumulating differences through mutation/sexual recombination (acted upon by natural selection - of course you knew that!) And then PRESTO! You have a new species (give or take a million years!) Anagenesis = one species changes into another Cladogenesis = branching of a new species from a species that continues to exist

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

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

  22. 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

  23. Two main modes of speciation

  24. How do new species arise (barrier creation) • Allopatric speciation (“other homeland”) • Sympatric speciation (“together”)

  25. Two main modes of speciation:

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

  27. Allopatric Speciation --occurs when geographical barriers block gene flow *small populations are more likely to change enough to become a new species RING SPECIES

  28. HAWAIIN HONEYCREEPERS 'I'IWI - Vestiaria coccineaFound in 'ohi'a lehua forests.  Feeds on the nectar of 'ohi'a lehua flowers high in the forest canopy and from tubular blossoms in the understory. 'AMAKIHI - Hemignathus virensCommon in native forests above 2,000 feet.  Feeds more on insects and is less dependant on nectar.  Female is a darker, olive green color. PALILA - Loxioides bailleuiEndangered Found only in the dry forests on the slopes of Mauna Kea, Big Island, 6,000 to 9,000 feet. 'AKOHEKOHE - Palmeria dolei Crested honeycreeper - Endangered Found only in the rain forests of east Maui at elevations of 4,500 to 6,500 feet.

  29. 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

  30. Adaptive radiation— evolution of many different species from a common ancestor *common on islands*

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

  32. Sympatric Speciation --a new species can evolve without geographic isolation --genetic changes can prevent members of the same species from mating ex. Apple maggot flies, polyploid plants

  33. Sympatric Speciation --a new species can evolve without geographic isolation -- female lays egg where she grew up Apples (introduced to US by immigrants) Apple Maggot Flies Hawthorns (native to US)

  34. 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) Autopolyploid Speciation 2n 2n = 6 4n = 12 4n

  35. Allopolyploidy

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

  37. Polar Grizzly “Grolar” or “Pizzly”

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

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

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