Lecture #11 Date ________Lecture #11 Date ________

• Chapter 24 ~ Chapter 24 ~ The Origin of The Origin of SpeciesSpecies

TodayToday• Look at the definition of speciesLook at the definition of species• How do new species ariseHow do new species arise• What are ways organisms can be What are ways organisms can be

reproductively isolatedreproductively isolated• Allopatric vs sympatric speciationAllopatric vs sympatric speciation• Gradualism vs punctuated equilibriumGradualism vs punctuated equilibrium

ReminderReminder

• Test WednesdayTest Wednesday– Multiple choiceMultiple choice

– Essays (1-2)Essays (1-2)

Macroevolution: Macroevolution: the origin of new taxonomic groupsthe origin of new taxonomic groups

• Speciation: Speciation: the origin of new speciesthe origin of new species

• Microevolution – a change in allelic Microevolution – a change in allelic frequencies (p and q) within a frequencies (p and q) within a population over timepopulation over time

• Macroevolution – broad pattern of evolution over long periods of time (involves speciation)

What is a species?What is a species?

• Biological species concept Biological species concept (Mayr):(Mayr): a population or group a population or group of populations whose members of populations whose members have the potential to interbreed and have the potential to interbreed and produce viable, fertile offspring produce viable, fertile offspring (genetic exchange is possible and (genetic exchange is possible and that is genetically isolated from that is genetically isolated from other populations)other populations)

Other definitions of speciesOther definitions of species

• Morphological – can include Morphological – can include asexual organismsasexual organisms

• EcologicalEcological

• PhylogeneticPhylogenetic

Reproductive Isolation (isolation of gene pools), IReproductive Isolation (isolation of gene pools), I

• Prezygotic barriers:Prezygotic barriers: impede mating impede mating between species or hinder the fertilization between species or hinder the fertilization of the ovaof the ova

• Habitat (snakes; water/terrestrial)Habitat (snakes; water/terrestrial)

• Behavioral (fireflies; mate signaling)Behavioral (fireflies; mate signaling)

• Temporal (salmon; seasonal mating)Temporal (salmon; seasonal mating)

• Mechanical (flowers; pollination Mechanical (flowers; pollination anatomy)anatomy)

• Gametic (frogs; egg coat receptors)Gametic (frogs; egg coat receptors)

VideosVideos

Reproductive Isolation, IIReproductive Isolation, II• Postzygotic barriers: Postzygotic barriers: fertilization occurs, but fertilization occurs, but

the hybrid zygote does not develop into a the hybrid zygote does not develop into a viable, fertile adultviable, fertile adult

• Reduced hybrid viability (frogs; zygotes Reduced hybrid viability (frogs; zygotes fail to develop or reach sexual maturity)fail to develop or reach sexual maturity)

• Reduced hybrid fertility (mule; horse x Reduced hybrid fertility (mule; horse x donkey; cannot backbreed)donkey; cannot backbreed)

• Hybrid breakdown (cotton; 2nd Hybrid breakdown (cotton; 2nd generation hybrids are sterile)generation hybrids are sterile)

Liger

Zebroid

Zonkey

Zetland

Beefalo

Geep

Leopon

Cama

Pumapard

Ocelot/Puma

Jaglion

Modes of speciation Modes of speciation (based on how gene flow is interrupted)(based on how gene flow is interrupted)

• Allopatric:Allopatric: populations segregated by a populations segregated by a geographical barrier; can geographical barrier; can result in result in adaptive radiationadaptive radiation (island species)(island species)

• Sympatric:Sympatric: reproductively isolated reproductively isolated subpopulation in the midst of subpopulation in the midst of its parent population (change its parent population (change in genome); polyploidy in in genome); polyploidy in plants; cichlid fishesplants; cichlid fishes

SpeciationSpeciation• Allopatric speciation – geographic Allopatric speciation – geographic

isolationisolation

• Sympatric speciation – polyploidy Sympatric speciation – polyploidy in plants, habitat differentiation in plants, habitat differentiation (clines), sexual selection(clines), sexual selection

Cline – a graded change in a Cline – a graded change in a character along a geographic character along a geographic

axisaxis• Along a mountainside (changing Along a mountainside (changing

temperature, elevation, precipitation)temperature, elevation, precipitation)

• In aquatic environments (changing In aquatic environments (changing temps., pressure, O2 concentration)temps., pressure, O2 concentration)

Allopatric speciationAllopatric speciation

• http://wps.prenhall.com/esm_freeman_biosci_1/7/1951/499633.cw/index.html

Hybrid ZonesHybrid Zones

• Reinforcement – hybrids are less Reinforcement – hybrids are less fitfit

• Fusion – gene pools become Fusion – gene pools become similar (cichlids)similar (cichlids)

• Stability – continued production of Stability – continued production of hybrid individualshybrid individuals

Patterns of evolutionPatterns of evolution

Punctuated equilibriaPunctuated equilibria

• Tempo Tempo of speciation:of speciation: gradual vs. divergence in gradual vs. divergence in rapid bursts; Niles Eldredge rapid bursts; Niles Eldredge and Stephen Jay Gould and Stephen Jay Gould (1972); helped explain the (1972); helped explain the non-gradual appearance of non-gradual appearance of species in the fossil recordspecies in the fossil record

Adaptive Adaptive Radiation/Mass Radiation/Mass

extinctionsextinctions

Divergent evolution / Divergent evolution / homologous evolutionhomologous evolution

Convergent evolution Convergent evolution /Analogous Structures/Analogous Structures