Chapter 24 The Origin of Species Ways to define a species A natural and basic unit of classification Originally Latin for kind Morphological species is a set of organisms that LOOK alike o But looks may deceive Ecological species is a set of organisms adapted to a particular set of resources Niche useful in defining prokaryotes Phylogenetic species is the smallest distinct set of organisms that share a common ancestor cougars in north and south America BIOLOGICAL species is the member of all the populations that potentially interbreed in nature and do not successfully interbreed with other such groups It has been used since the Hardy Weinberg principle about 100 years Its focus is on reproduction Biological Species Concept Members of the same species Share the same gene pool o There is gene flow between populations it doesn t take much to count Are reproductively isolated from other species by natural barriers o Prezygotic is a natural feature that keeps a individuals from meeting and forming offspring o Postzygotic barriers keep the formed hybrid from reproducing Prezygotic Barriers prevent the formation of a hybrid Habitat ecological isolation distant or different ecosystem Temporal isolation different mating seasons frogs Behavior isolation applies only to animals courtship calls blue footed v red footed booby Mechanical isolation anatomy won t fit love bugs Gametic isolation gametes don t match zygote doesn t form Postzygotic Barriers act after the hybrid is formed Reduced hybrid viability embryo fails to develop or is weak Reduced hybrid fertility the hybrid survives but is sterile Hybrid breakdown the 2nd generation of hybrids are feeble or sterile Problems with the Biological Species Concept We cannot classify fossil species in this way and must use the morphological concept It does not take asexual reproduction into account Sometimes gene flow and the production of a viable hybrid happens How can new species form Speciation and Evolution Microevolution with gene flow can change the appearance of species over time BUT this does not make more species Speciation is the creation of new species from existing ones There are two ways allopatric and sympatric speciation Allopatric speciation Begins with the geological isolation of a population o The effectiveness of the geographical barrier depends on the species birds vs beetles Time and isolation allows for divergence through natural selection and genetic drift o Non Adaptive microevolution Requires the evolution of a reproductive barrier Ex Squirrels at the grand canyon Evidence o Reduced success in lab matings between allopatric salamanders o Fish from isolated populations prefer to mate with their own shape o Fruit flies adapted to different foods diverged enough to prefer like adapted mates o Endemic island species resemble the nearest mainland species cormorants If prezygotic barriers do NOT arise o The hybrids result at contact areas hybrid zone o Possible outcomes specific to allopatric Reinforcements gene pools separate further creating fewer hybrids Fusion gene pools merge no speciation occurs Stability hybrids continue to be formed but other factors keep the gene pool isolated Sympatric Speciation Speciation in the same geographic area o Gene pools are isolated in other ways o Much less common we think especially in animals Due to habitat differentiation o Population isolation by use of different resources o Ex Apple maggot fly fig wasp Due to sexual selection o Experiment 24 12 fish color patterns Due to polyploidy o New species with multiple sets of chromosomes 4n 6n etc o Arises from cell divergence errors o Occurs often in plants o Autopolyploidy from same species o Allopolyploidy polyploidy hybrid of 2 species o 30 70 of plants polyploidy very rare in animals Patterns in the fossil record Gradual small divergences and change over a long period of time Punctuated species are the same for a long time then there is rapid change o Ex trilobites ribs in the exoskeleton stay much the same after a new group appears How many genes make a species Amount of genetic variation varies 1 few or many genes may separate a species o Japanese snail one gene causes different spiral directions and thus mechanical isolation o Flower color one gene changes pollinator preference see book
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