Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Click to edit Master subtitle style 1/12/13 Chapter 13The origin of species1/12/13 Species are independently evolving lineages•General lineage species concept: species are metapopulations that exchange alleles frequently enough to comprise the same gene pool1/12/13 Ways to identify species•Biological species concept: species are groups of interbreeding populations that are reproductively isolated from other such groups•Phylogenetic species concept: smallest possible group descending from a common ancestor and recognizable by unique, derived traits1/12/13 Speciation involves barriers to reproduction1/12/13 Isolating barriers•Geographic: extrinsic properties of landscape that prevent gene flow–Allopatry•Reproductive: features of organisms that prevent interbreeding–Barriers effective even in sympatry1/12/13 Elk and red deer: two species?1/12/13 Premating barriers: timing of reproduction1/12/13 Premating barriers: pollinator isolation1/12/13 Premating barriers: mismatched morphology1/12/13 Postmating-prezygotic barriers: •Gametic incompatibility: sperm or pollen from one species fails to penetrate and fertilize the egg of another species1/12/13 Postzygotic barriers•Hybrids are produced but have low fitness–Hybrid inviability–Hybrid sterility–Ecological inviability–Behavioral sterility1/12/131/12/13 Key Concepts•Geographic barriers to gene flow physically separate populations–Important for all species concepts•Reproductive barriers are intrinsic features of organisms that reduce likelihood of interbreeding•Geographic barriers are most common1/12/13 Key Concepts•Separation of populations in space and time reduces interbreeding–Habitat preference–Timing of reproduction•Divergent floral traits can cause pollinator isolation and reduce interbreeding•Molecular incompatibilities between gametes can prevent interbreeding•Genetic incompatibilities that reduce hybrid fitness can be important barriers to gene flow1/12/13 Allopatric speciation1/12/13 Phylogenetic signature of allopatric speciation1/12/13 Islands provide opportunity for allopatric speciation1/12/13 Colonization leads to speciation1/12/13 Ring speciesRing species: populations at ends can no longer interbreed1/12/13 Ring species example1/12/13 Sympatric speciation in RhagoletisEcological speciation: evolution of reproductive barriers due to adaptation to divergent environments1/12/13 Ecological speciation in stickleback1/12/13 Ecological speciation in Darwin’s finches1/12/13 Key Concepts•Populations become allopatric when new geographic barriers arise•New species can form when geographic barriers arise•Isolation by distance occurs because individuals tend to mate with individuals from the same or nearby populations•Ring species demonstrate how species can form even with some gene flow1/12/13 Key Concepts•Reproductive isolation can arise even in sympatry because individuals in different subpopulations rarely interbreed•Ecological speciation can lead to speciation in sympatry•Reproductive isolation can arise as a by-product of adaptation to divergent environments1/12/13 The speed of speciation1/12/13 Allopolyploidy can lead to extremely rapid speciation1/12/13 Key Concepts•The speed of speciation depends on genetic architecture of organisms–Genome duplication common in plants1/12/13 Genetic data reveals cryptic diversity in giraffes1/12/13 Cryptic diversity in skipper butterflies1/12/13 Bacterial species often defined by specific adaptationsSome scientists criticize this method1/12/13 Horizontal gene transfer makes classification difficult1/12/13 Horizontal gene transfer in E. coliCore genome includes 993 genesPan-genome includes 15,741 genes1/12/13 Horizontal gene transfer is common1/12/13 Key Concepts•Ultimately, species concepts are human artifacts–Methods for recognizing species continue to