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Week 4 Notes

by: Raquel Notetaker

Week 4 Notes BIOL 1010

Raquel Notetaker
GPA 3.5
Introduction to Biology

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About this Document

evolution 1.6 Speciation and Extinction
Introduction to Biology
Class Notes
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This 0 page Class Notes was uploaded by Raquel Notetaker on Thursday February 18, 2016. The Class Notes belongs to BIOL 1010 at Rensselaer Polytechnic Institute taught by in Spring 2016. Since its upload, it has received 25 views. For similar materials see Introduction to Biology in Biology at Rensselaer Polytechnic Institute.


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Date Created: 02/18/16
Speciation and Extinction Biological Species Concept 0 quotSpecies are groups of interbreeding natural populations that are reproductiver isolated from other such groupsquot Ernst Mayr It follows that 0 Each species has a unique set of alleles that forms that species gene pool 0 Each species gene pool is isolated from other gene pools for example alleles do not ow between species Reproductive Isolation Cornerstone of the BSC 0 Reproductive isolation results from genetic changes causing prezygotic or postzygotic barriers to reproduction Speciation is the attainment of reproductive isolation How we recognize speciation in nature Depends on de nition of what a species is Problems with the BSC 0 Application of BSC to many groups problematic because of hybridization between clearly delimited species BSC doesn t apply and hence of no help in delimiting species in asexual populations eg rotifers eugenoids some green algae diatoms self pollinating plants and Daphnia 0 Each individual and its descendents are isolated gene pools so is each lineage a separate species 0 In practice BSC can t be applied to delimit species breeding experiments are de nitive test of species membership and such tests often impossible with wild populations 0 No widely accepted concept of species for prokaryotes de nitions based on DNA rRNA sequence differences gt70 DNA gt987 rRNA How many species Mammals 5000 5100 Birds 10000 10500 Reptiles 7000 7500 Amphibians 5500 5000 Fish 20000 22000 Insects 1000000 710 million Chelicerata spiders etc 80000 800000 Nematodes 20000 400000 Fungi 50000 1500000 Plants 300000 350000 Eubacteria l Archaea 7000 250 million fetal 2000000 10100000000 Mechanisms of speciation North rim Kaibab squirrel South rim Abert s squirrel Ancestral population divided by formation of Grand Canyon Reduced gene ow between separated populations Allopatric Speciation o Speciation in geographically isolated populations 0 Some type of barrier exists that preventsreduces gene ow 0 Effectiveness of barrier varies with species Barriers in Allopatric Speciation 0 Mountain ranges o Oceans and bodies of freshwater 0 Land especially freshwater species 0 Glacial masses 0 Vaeys Parapatric Speciation o Adjacent populations evolve into distinct species 0 Maintain contact aong common border 0 Often hybridize aong contact zone Speciation in Rhagoletis iesSympatric speciation o 1862 farmer in Hudson River valley notices Rhagoletis larvae eating his apples 0 Prior to 1862 only known food source was fruit of hawthorns o Rhagelotis had begun exploiting a completely new food source for its arvae Differentiation of Races 0 Chemical sensing of hose altered by a mutation 0 Second mutation enhanced arva survival on apples 0 Genes promoting earier emergence also selected for l Apple Fruiting Season l Hawthorn Fruiting Season Apple Hawthom Race Race Emergence Enlargmca a E W E m E E l l Mme air1 25 5 115 25 5 15 is 115 25 5 151125 5 115 Jul AME Sap Out New Speciation in Prog ress Apple and hawthorn races have evolved reproductive barriers Adults mate and oviposit on their birth fruit Apple race emerges 3 weeks earlier Leads to limited interbreeding These differences between races mark early stages of sympatric speciation Sympatric Speciation quotThe divergence of a single interbreeding population of one species into two reproductiver isolated populations without any barriers to gene owquot Formerly dismissed by biologists especially Ernst Mayr But compelling evidence for existence and importance of sympatric speciation since 1960s study of Rhagoletis by Guy Bush Sympatric Speciation in Progress Blue indigobird lays eggs in nests of African re nch and Blackbellied re nch Baby indigobirds learn songs of their respective quotfosterquot nches and have developed two races Females prefer males who know same nch song as they do and pass preferences on Female indigobirds that grow up in African re nches nests lay eggs in African re nch nests rather than Blackbellied re nch nest Adaptive Radiation A burst of speciation and evolutionary divergence Single lineage ves rise to man new species New species ll vacant quotadaptive zonesquot Adaptive zone is a new set of niches or quotways of lifequot Mass Extinctions El nEllen min Epnreanh a nigmn aj LE Six major mass extinctions have occurred over past 600 million years mum all imam ll Cretaceous Extinction lridium much more common in asteroids and meteors than Earth rocks Iridium layer at KT boundary in soil fossil layer marks and separates age of reptiles and age of mammals After several year search geologists found quotsmoking gunquot huge Chicxulub crater 120 miles in diameter 810 miles deep 0 Controversy over what caused other mass extinctions Recovery from Extinction Over time species diversity recovers 3 models 0 A recovery starts immediately lasts few million years 0 B recover has time lag then rapid adaptive radiation trough feedback new species and niches create more and more opportunities for more species 0 C recovery starts and builds slowly following Sshaped logistic curve 0 Extensive fossil data for marine species favor model b 0 Time lag is about 10 million years The Greatest Mass Extinction Over past 300 years Homo sapiens responsible for 100s of thousands of extinctions Extinction rates now 1001000 times background or normal levels of about 12 species per year o If increased rate continues we are headed towards greatest mass extinction in Earth s history


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