Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings MACROEVOLUTION AND SPECIATION How did this flightless bird come to live on the isolated Galápagos Islands?

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Separation of the Species Macroevolution is best observed within the fossil record, Macroevolution is best observed within the fossil record, Requires the origin of species, also called speciation. Requires the origin of species, also called speciation. Speciation is the final result of changes in gene pool allelic and genotypic frequencies. Speciation is the final result of changes in gene pool allelic and genotypic frequencies. 2

Macroevolution: the origin of new taxonomic groups Speciation: the origin of new species 1- Anagenesis (phylogenetic evolution): accumulation of heritable changes 2- Cladogenesis (branching evolution): budding of new species from a parent species that continues to exist (basis of biological diversity)

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Species Definitions Evolutionary species concept distinguish species from one another based on: Evolutionary species concept distinguish species from one another based on: Morphological (structural) traits, Morphological (structural) traits, Biological species concept relies primarily on reproductive isolation rather than trait differences to define a species. Biological species concept relies primarily on reproductive isolation rather than trait differences to define a species. 4

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings What is a species? Biological species concept (ErnstMayr): a population or group of populations whose members have the potential to interbreed and produce viable, fertile offspring (genetic exchange is possible and that is genetically isolated from other populations) Biological species concept (ErnstMayr): a population or group of populations whose members have the potential to interbreed and produce viable, fertile offspring (genetic exchange is possible and that is genetically isolated from other populations)

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings How and why do new species originate? Species are created by a series of evolutionary processes Species are created by a series of evolutionary processes populations become isolated populations become isolated geographically isolated geographically isolated reproductively isolated reproductively isolated isolated populations evolve independently isolated populations evolve independently

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

PREZYGOTIC BARRIERS Reproductive Isolation (isolation of gene pools) Prezygotic barriers: impede mating between species or hinder the fertilization of the ova Habitat (snakes; water/terrestrial) Behavioral (fireflies; mate signaling) Temporal (salmon; seasonal mating) Mechanical (flowers; pollination anatomy) Gametic (frogs; egg coat receptors)

2 species of garter snake, Thamnophis, occur in same area, but one lives in water & other is terrestrial lions & tigers could hybridize, but they live in different habitats:  lions in grasslands  tigers in rainforest lions & tigers could hybridize, but they live in different habitats:  lions in grasslands  tigers in rainforest Habitat isolation: Species occur in same region, but occupy different habitats so rarely encounter each other Leopon awesome-hybrid-animals/

Temporal isolation: Species that breed at different times of the day, different seasons, or different years cannot mix their gametes Eastern spotted skunk (Spilogale putorius) Western spotted skunk (Spilogale gracilis) Eastern spotted skunk (R) & western spotted skunk (L) overlap in range but eastern mates in late winter & western mates in late summer

Behavioral isolation: Courtship rituals and other behaviors unique to a species are effective barriers Video: Blue-footed Boobies Courtship Ritual Video: Blue-footed Boobies Courtship Ritual Video: Giraffe Courtship Ritual Video: Giraffe Courtship Ritual Video: Albatross Courtship Ritual Video: Albatross Courtship Ritual Courtship ritual of blue- footed boobies

Mechanical isolation: Morphological differences can prevent successful mating Bradybaena with shells spiraling in opposite directions For many insects, male & female sex organs of closely related species do not fit together, preventing sperm transfer –lack of “fit” between sexual organs: hard to imagine for us… but a big issue for insects with different shaped genitals!

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Gametic isolation: Sperm of one species may not be able to fertilize eggs of another species Gametic isolation: Sperm of one species may not be able to fertilize eggs of another species Sea urchins Sea urchins release sperm & eggs into surrounding waters where they fuse & form zygotes. Gametes of different species— red & purple —are unable to fuse.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Postzygotic barriers prevent the hybrid zygote from developing into a viable, fertile adult: Postzygotic barriers prevent the hybrid zygote from developing into a viable, fertile adult: Zygote mortality (Reduced hybrid viability) Zygote mortality (Reduced hybrid viability) Hybrid Sterility (Reduced hybrid fertility) Hybrid Sterility (Reduced hybrid fertility) F2 Fitness (Hybrid breakdown) F2 Fitness (Hybrid breakdown) POSTZYGOTIC BARRIERS

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Zygote mortality (Reduced hybrid viability): Genes of the different parent species may interact and impair the hybrid development Ensatina hybrid

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Hybrid Sterility (Reduced hybrid fertility): Even if hybrids are vigorous, they may be sterile Donkey

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings F2 Fitness (Hybrid breakdown): Some first- generation hybrids are fertile, but when they mate with another species or with either parent species, offspring of the next generation are feeble or sterile Hybrid cultivated rice plants with stunted offspring (center)

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

REPRODUCTIVE ISOLATION REVIEW

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Speciation can take place with or without a geographic barrier Geographic speciation can occur in two ways : Geographic speciation can occur in two ways : Allopatric speciation Allopatric speciation Sympatric speciation Sympatric speciation (b) Sympatric speciation (a) Allopatric speciation

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Allopatric (Other Country) Speciation In allopatric speciation, gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations In allopatric speciation, gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations Evidence of Allopatric Speciation Regions with many geographic barriers typically have more species than do regions with fewer barriers

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Allopatric Speciation 23 Salmon that matured at Pleasure Point Beach do not reproduce with those that matured in the Cedar River. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lake female Lake male River male River female a. Sockeye salmon at Pleasure Point Beach, Lake Washingtonb. Sockeye salmon in Cedar River.The river connects with Lake Washington.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 24 Adaptive Radiation When members of a species invade several new geographically separate environments The populations become adapted to the different environments Many new species evolve from the single ancestral species This is an example of allopatric speciation Adaptive Radiation

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Sympatric (“Same Country”) Speciation In sympatric speciation, speciation takes place in geographically overlapping populations In sympatric speciation, speciation takes place in geographically overlapping populations Caused by chromosomal abnormalities….abnormal number of chromosomes Caused by chromosomal abnormalities….abnormal number of chromosomes Nonrandom mating (lowers gene flow) Nonrandom mating (lowers gene flow)

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Polyploidy Polyploidy is the presence of extra sets of chromosomes due to accidents during cell division Polyploidy is the presence of extra sets of chromosomes due to accidents during cell division Polyploidy is much more common in plants than in animals Many important crops (oats, cotton, potatoes, tobacco, and wheat) are polyploids

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Autopolyploidy

Allopolyploidy

Alloploidy 29 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. seeds polyploid banana diploid banana (2n) no seeds

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Allopatric and Sympatric Speciation: A Review In allopatric speciation, geographic isolation restricts gene flow between populations In allopatric speciation, geographic isolation restricts gene flow between populations Reproductive isolation may then arise by natural selection, genetic drift, or sexual selection in the isolated populations Reproductive isolation may then arise by natural selection, genetic drift, or sexual selection in the isolated populations Even if contact is restored between populations, interbreeding is prevented Even if contact is restored between populations, interbreeding is prevented

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Patterns in the Fossil Record The fossil record includes examples of species that appear suddenly, persist essentially unchanged for some time, and then apparently disappear The fossil record includes examples of species that appear suddenly, persist essentially unchanged for some time, and then apparently disappear Niles Eldredge and Stephen Jay Gould coined the term punctuated equilibrium to describe periods of apparent stasis punctuated by sudden change Niles Eldredge and Stephen Jay Gould coined the term punctuated equilibrium to describe periods of apparent stasis punctuated by sudden change The punctuated equilibrium model contrasts with a model of gradual change in a species’ existence The punctuated equilibrium model contrasts with a model of gradual change in a species’ existence

Fig (a) Punctuated pattern (b) Gradual pattern Time

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Speciation Rates The punctuated pattern in the fossil record and evidence from lab studies suggests that speciation can be rapid The punctuated pattern in the fossil record and evidence from lab studies suggests that speciation can be rapid The interval between speciation events can range from 4,000 years (some cichlids) to 40,000,000 years (some beetles), with an average of 6,500,000 years The interval between speciation events can range from 4,000 years (some cichlids) to 40,000,000 years (some beetles), with an average of 6,500,000 years

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 34 Principles of Macroevolution Macroevolution Evolution at the species or higher level of classification Occurs gradually Evolutionists support a gradualistic model Speciation occurs after populations become isolated Each group continuing its own evolutionary pathway The gradualistic model suggests that it is difficult to indicate when speciation occurred

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 35 Principles of Macroevolution Macroevolution Some paleontologists believe that Species can appear quite suddenly Remain essentially unchanged phenotypically during a period of stasis (sameness) until they undergo extinction. Based on these findings, they developed a punctuated equilibrium model to explain the pace of evolution.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 36 Developmental Genes and Macroevolution Genes can bring about radical changes in body shapes and organs. Gene Expression Can Influence Development A change in gene expression could stop developmental process or continue it beyond its normal time. Using modern technology researchers discovered genes whose differential expression can bring about changes in body shapes and organs.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 37 Pax6 Gene and Eye Development (Left): © Carolina Biological Supply/Photo Researchers, Inc.; (Center): © Vol. OS02/PhotoDisc/Getty Images; (Right): © Aldo Brando/Peter Arnold, Inc.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Evolution is not goal-oriented An evolutionary trend does not mean that evolution is goal-oriented. Surviving species do not represent the peak of perfection. There is compromise & random chance involved as well Remember that for humans as well! Evolution is not the survival of the fittest. Rather it is the survival of the just good enough.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings From Speciation to Macroevolution Macroevolution is the cumulative effect of many speciation and extinction events Macroevolution is the cumulative effect of many speciation and extinction events