Chapter 17 Speciation= process that produces splits among lineages in tree of life◦ divergence of biological lineages◦ emergence of reproductive isolation between lineages  Morphological species concept: individuals “look” alike Cryptic species:two or more species that morphologically same but do not interbreed Reproductive isolation:two groups of organisms can no longer exchange genes Biological species concept:species interbreed and can produce offspring ◦ concept does not apply to asexually reproducing organisms lineage species concept: tree of life◦ one species to two or more daughter species Speciation requires interruption of gene flow More genetic divergence= more reproductive isolation Allopatric speciation:population divided by physical barrier ◦ geographic barrier◦ divergence of sub population◦ establishment of reproductive barrier(s) (species diverge and cannot reproduce)◦ new species Sympatric speciation:speciation without physical isolation ◦ may occur with disruptive selection (preference for distinct microhabitats where mating takes place)◦ takes place mostly in plants( meitoc errors in plants cause sympatric speciation)◦ common means of sympatric speciation is polyploidy(duplication of sets of chromosomes within individuals▪ autopolyploidy:chromosome duplication in single species▪ allopolyploidy:combining of two different species  Prezygotic isolating mechanisms prevent hybridization ◦ Temporal isolation: breeding seasons◦ Mechanical isolation: inability to breed due to reproductive organs◦ Behavioral isolation: preference for mate◦ Gametic isolation: sperm cannot attach to egg◦ Habitat isolation: species evolved due to habitat and no contact with other species Postzygotic isolating mechanisms:reduce fitness of hybrid offspring◦ Low hybrid zygote viability: zygotes do not mature ◦ Low hybrid adult viability: hybrid offspring has low survivability◦ hybrid infertility:infertile adults Adaptive radiation:formation of many related species from single common ancestor  Sexual reproduction= new combos of genes and produces gene variety◦ Disadvantages:meiosis, males, and mating◦ Advantages:sexual selection, escape from parasites, changing