The Origin of Species

2. The Origin of Species Chapter 14

3. Rapid Speciation Does Occur • Evolution has generally been thought of as a very gradual process • However, examples of rapid evolution have been observed • One example of rapid evolution occurred among mosquitoes who migrated into the London underground • This species evolved into a different species due to a different environment

4. Rapid Speciation • In less than 150 years, Culex pipiens evolved into a new mosquito species, Culex molestus • The origin of new species is called speciation • Adapted mating strategy, breeding strategy, and feeding habits, and due to their isolation from the other species, they evolved rapidly

5. What is a species?

6. Taxonomy • Taxonomy the branch of biology concerned with naming and classifying the forms of life • Linnaeus developed a binomial system of naming organisms which is still in use • Defined each species he saw based on physical appearance • Similarities between some species and variation within a species can make defining species difficult

7. The Biological Species Concept • The biological species concept defines a species as • a population or group of populations whose members can interbreed and produce fertile offspring • If members of one species do not mate with members of another species, the offspring will not be fertile • If they can mate they are not a separate species, if they cannot they are a separate species

8. Ring Species • Ring Species- species whose distribution forms a ring as it extends its range around some geographic barrier • Populations that have been separated the longest and diverged most in their evolutions eventually meet where the ring closes • Only those organisms which are farthest away on the ring and who do not interbreed are classified as different species

9. 1 OREGON POPULATION SierraNevada 2 Yellow-blotched Yellow-eyed INLANDPOPULATIONS COASTALPOPULATIONS Gap in ring Large-blotched Monterey 3 Ring Species

10. The biological species concept is not applicable to fossils or asexual organisms • Most organisms are classified based on observable phenotypes • The morphological species concept • The genealogical species concept defines a species as a cluster of organisms representing a specific evolutionary lineage • Use molecular data • The ecological species concept defines a species by its ecological role • Focuses on adaptation and roles in community

11. Reproductive Barriers • Geographic barriers can lead to reproductive barriers • But not all species are separated by geographic barriers • Reproductive Barrier a biological feature of the organisms themselves that prevent mingling of the gene pool • There are two types of reproductive barriers aside from geographic barriers; Prezygotic barriers and Postzygotic barriers

12. Reproductive Barriers • Prezygotic barriers actually prevent mating or fertilization between species • Species are breeding at different times • Species live in the same general area, but not in the same types of places • Species display no sexual attraction between male and females of different species • Species male and female sexual organs are not compatible • Species gametes do not unite to form a zygote

13. + Reproductive Barriers • Postzygotic Barriers operate after the zygote has already formed • The genes of the parents are incompatible and the offspring does not survive • Offspring reaches maturity, but the hybrid is sterile • Offspring reaches maturity and is fertile, but its children are feeble or sterile

14. Geographic Isolation • When a population is cut off from its parent stock, species evolution may occur • An isolated population may become genetically unique as its gene pool is changed by natural selection, genetic drift, or mutation • This species can follow its own evolutionary course • This is called allopatric speciation

15. On the Galápagos Islands, repeated isolation and adaptation have resulted in adaptive radiation of 14 species of Darwin’s finches Islands as Living Laboratories

16. Islands as Living Laboratories • Islands are often far enough apart to permit populations to evolve in isolation, but close enough to allow occasional dispersions to occur • By studying the Galapagos chain of islands Darwin was able to surmise that all of the finch species all evolved from a small population of ancestral birds that colonized one of the islands

17. 1 Species Afrom mainland 2 B A B 3 B B 4 C C C C D C D 5 • Migration from the mainland may have caused the founder species to change and become a new species • Part of species on island moves to next island and evolves to suit this environment • Island species may migrate back to founder island • Second island population may migrate back to first island or back to the founder island

18. Adaptive Radiation • This process is called adaptive radiation • The emergence of numerous species from a common ancestor introduced to new and diverse environments • The species in the Galapagos islands colonized and speciated repeatedly on many of the islands in the chain • Those species that are on more isolated areas do not evolve into as numerous species because they do not have the opportunities to colonize

19. Parent species Zygote Meioticerror Self-fertilization Offspring maybe viable andself-fertile 2n = 6Diploid 4n = 12Tetraploid Unreduced diploid gametes New Species Within the Same Geographic Area • Sympatric Speciation when reproductive isolation develops and new species arise without geographic separation • A failure in meiosis can produce diploid gametes • Self-fertilization can then produce a tetraploid zygote

20. AA BB WildTriticum(14 chromo-somes) Triticummonococcum(14 chromosomes) AB Sterile hybrid(14 chromosomes) Meiotic error andself-fertilization AABB DD T. turgidumEMMER WHEAT(28 chromosomes) T. tauschii(wild)(14 chromosomes) ABD Sterile hybrid Meiotic error andself-fertilization AA BB DD T. aestivumBREAD WHEAT(42 chromosomes) Many Plants are Polyploid • Many plants are polyploid • 25-50% of plants • They are the products of hybridization • Many species are believed to have come about because of polyploid formation • Bananas, coffee • The modern bread wheat is an example

21. Tetraploid and Polyploid Plants • Are able to self fertilize to produce other tetraploid plants • Able to breed with other tetraploids • Can breed with a diploid plant but the result will be a triploid which is infertile • Can arise from the doubling of the same plant or by hybridization

22. Evolution of Reproductive Barriers • Prezygotic barriers- a behavior obstacle to interbreeding • Different mating strategies • Different diets • Geographic isolation- isolation geographically can alter the population rapidly and create reproductive barriers

23. The Tempo of Speciation • According to the gradualist model of the origin of species • new species evolve by the gradual accumulation of changes brought about by natural selection • However, few gradual transitions are found in the fossil record

24. The Tempo of Speciation • The punctuated equilibrium model suggests that speciation occurs in spurts • Rapid change occurs when an isolated population diverges from the ancestral stock • Virtually no change occurs for the rest of the species’ existence