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Biology Chapter 14 Outline

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Biology Chapter 14 Outline Introduction:  Species – group of organisms whose members can breed and produce fertile offspring  Speciation – emergence of new species 14.1:  Each time speciation occurs, diversity of life increases  New species often resembles its parent species  Macroevolution traces large-scale changes in history of life 14.2:  Taxonomy – branch of biology that names and classifies species and groups them into broader categories  Biological species concept – defines species as a group of populations with potential to interbreed and produce fertile offspring  Reproductive isolation – prevents gene flow and maintains gap between species  There is no way to determine whether fossils were able to interbreed  BSC cannot be used for prokaryotes since prokaryotes produce asexually  Morphological species concept – classification is based on observable and measurable physical traits and features of morphology  This can be used for asexual organisms and fossils, however relies on subjective criteria  Ecological species concept – identifies species in terms of ecological niches, focus on unique adaptations to particular roles  Phylogenetic species concept – species is the smallest group of individuals that share a common ancestor and form one branch  Trace phylogenetic history by comparing differences in morphology or DNA sequences  Determining amount of difference to distinguish species is issue 14.3:  Reproductive barrier – biological feature of organism that prevents individuals of closely related species from interbreeding  Prezygotic barriers – prevent mating or fertilization  Temporal isolation – species live in same area but breed at different times  Habitat isolation – species live in same general area but not same kinds of places preventing the species from meeting  Behavioral isolation – no sexual attraction between species  Mechanical isolation – female and male sex organs of species are not compatible  Gametic isolation – male and female of differing species may copulate but gametes do not form zygote or do not unite  Postzyogtic barriers – operate after hybrid zygotes are formed  Hybrids result from union of gametes of two different species  Reduced hybrid viability – hybrid offspring do not survive because they do not develop properly or they never mature  Reduced hybrid fertility – hybrid offspring reaches maturity but are sterile  Hybrid breakdown – first generation of hybrid offspring are fertile but once the hybrids mate then the offspring of hybrids are week and/or sterile 14.4:

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Key event in origin of species is the separation of a population with its gene pool from other populations of the same species With gene pool isolated, new population can follow own evolutionary course Initial block to gene flow is a geographic barrier Allopatric speciation – arise of new species by separation of species with geographical barrier, isolation that blocks gene flow Ability of organisms to move affects the size of geographic barrier and how big the barrier is to start allopatric speciation Likelihood of allopatric speciation is greater when population small and isolated Small population is less likely to have gene pool reflecting parent population Geographic isolation does not always lead to creation of new species Speciation only occurs when gene pool undergoes changes that establish new reproductive barriers

14.5:  Sympatric speciation – new species arises within same geographic area as parent species  Sympatric speciation occurs when mating and gene flow between populations are reduced by polyploidy, habitat differentiation and sexual selection  Polyploid – cells that have more than two sets of chromosomes  Polyploid arising: failure in division after chromosome duplication leads to production of diploid gametes  Self-fertilization of plants can use tetraploid zygotes and produce fertile tetraploid offspring by self-pollination or mating with other tetraploid individuals  Tetraploid plants cannot form fertile offspring with parent plants  Triploid individuals are always sterile  New species from tetraploid plants are produced in one generation  Most polyploid species arise from hybridization of two different species  Hybrid may reproduce asexually or have errors in cell division that allow for production of fertile polyploidy species  Sympatric speciation for animals is more likely with habitat differentiation and sexual selection  Adaptations for a specific environment or habitat would make mating between two specializing populations rare and thus isolate the gene pool  Sexual selection also isolates populations and gene pools amongst specific sexually desired individuals, leading to arise in new species 14.6:  80 percent of living plant species are descendants of polyploid ancestors  Hybridization provides adaptive advantage of diverse amount of genes  Wheat occurs as 20 different species  Bread wheat has 42 chromosomes  Plant geneticists can create new polyploids by using chemicals that induce mitotic and meiotic errors to produce new hybrids 14.7:  Both types of speciation require restriction of gene flow between populations and the emergence of reproductive barriers  Dodd- tested with fruit flies on different food sources for reproductive barriers

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Reproductive barriers evolve as by-products of changes in populations as they adapt to different environments Reproductive isolation occurs as allopatric populations become further adapted Reproductive isolation can come from change in single gene Change in single gene can affect reproduction such as with behavioral isolation Some other organisms have speciation linked to changes in larger number of genes and gene interactions

14.8:  Hybrid zones – regions in which members of different species meet and mate  Formation of hybrid zone: four populations meet by gene flow, one population becomes isolated, speciation occurs, gene flow is reestablished in the hybrid zone  Natural selection reinforces reproductive barriers when hybrids are less fit  Allopatric individuals look much more similar to parent than sympatric  When reproductive barriers between two species are weak and the species come together in a hybrid zone then fusion may occur as speciation is reversed and the different species fuse to become one species  Many hybrid zones end up stable as hybrids continue to be produced 14.9:  Grants work with finches to study variation in small isolated populations  Interbreeding between finches can occur when males pick up mating song of differing species  Hybrids of finches have intermediate beak length and can only eat small seeds  When hybrids breed with parent species, introduce new genes on which natural selection can act  Severe selection – during drought years, populations of finch species are reduced as the food supply dwindles and hybrids die off 14.10:  Adaptive radiation – evolution of many diverse species from a common ancestor  Adaptations of species allow them to fill new habitats and niches within community  Adaptive radiation occurs when few organisms colonize new areas or when mass extinctions occur and open up new opportunities for survivors  Colonizers can undergo multiple speciations to form completely new species  Adaptive radiation linked to new opportunities 14.11:  Many fossils appear in a strata suddenly and then disappear just as quick in later strata  Punctuated equilibria – long periods of little change punctuated by abrupt episodes of speciation among species  Other fossils diverge gradually over long periods of time, differences gradually evolve in populations as they become adapted to environments  Punctuated pattern indicates speciation occurred rapidly  Gradual change cannot be determined for when species was formed  Rapid speciation occurs rarely  Time between speciation averages 6.5 million years and did not take less than 1 million  Vast amounts of time must be taken for life on Earth to evolve  Cumulative effects of speciation and extinction shape the fossil record

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