Chapter 14 : The Origin of Species Evolution is the source of biological diversity Most changes are minor Definition of species: Linnaeus invented Genus species naming system But it is complicated Some species look alike but cant interbreed Some vary greatly but can interbreed Species Concepts Morphological Species Concept Ecological Species Concept Phylogenetic Species Concept Biological Species Concept Group of populations whose members have the potential to interbreed in nature and produce fertile offspring. - Ernst Mayer, 1942 Systematics and the Origin of Species Reproductive isolation pre-zygotic post-zygotic inviable or infertile offspring Emma Hickerson, NYTimes Speciation Allopatric Geographic barrier arrises Populations diverge genetically Genetic divergence accidentally causes reproductive isolation Reinforcement Controversial step If hybrids between 2 evolving species are less fit - inviable or infertile, it pays for females to be choosy about mates. =Direct selection to evolve pre- zygotic isolation Evidence Koopman (1950), Coyne and Orr (1989), Noor (1995) Speciation Sympatric no geographic barrier Polyploidy Speciation in one generation! 2N 4n Caused by failure of cell division after chromosome duplication Most common in plants auto vs allo-polyploidy Fig. 14-5a-1 Parent species 2n = 6 Tetraploid cells 4n = 12 1 Fig. 14-5a-2 Parent species 2n = 6 Tetraploid cells 4n = 12 1 Diploid gametes 2n = 6 2 Fig. 14-5a-3 Parent species 2n = 6 Tetraploid cells 4n = 12 1 Diploid gametes 2n = 6 2 Viable, fertile tetraploid species 4n = 12 Self- fertilization 3 Fig. 14-5b-1 Species A 2n = 4 Gamete n = 2 Species B 2n = 6 Gamete n = 3 Fig. 14-5b-2 Species A 2n = 4 Gamete n = Species B 2n = 6 Gamete n = 3 Sterile hybrid n = 5 Chromosomes not homologous (cannot pair) Fig. 14-5b-3 Species A 2n = 4 Gamete n = Species B 2n = 6 Gamete n = 3 Sterile hybrid n = 5 Chromosomes not homologous (cannot pair) Viable, fertile hybrid species 2n = 10 3 Fig. 14-6b Triticum monococcum (14 chromosomes) Hybridization AABB AB Sterile hybrid (14 chromosomes) 1 2 Cell division error and self-fertilization Wild Triticum (14 chromo- somes) AA BB DD Sterile hybrid (21 chromosomes) ABD Hybridization 3 4 Cell division error and self-fertilization T. tauschii (wild) (14 chromosomes) T. turgidum Emmer wheat (28 chromosomes) AA BB DD T. aestivum Bread wheat (42 chromosomes) Estimate that 80% of living plant species arose by polyploidy Many food crops Plant geneticists use chemicals that cause mitotic and meiotic errors to make more. Sympatric speciation in animals Polyploid occurs occasionally More likely through habitat differentiation sexual selection Genetics of Speciation 2 major genetic modes of speciation 1. Polyploidy 2. Modern Synthesis Modern Synthesis Darwins Paradox how to get through sterile stage? Dobzhansky-Muller Model (1930) the conflicting alleles never meet Does Natural Selection Cause Speciation? Evidence so far says: The genes are in a variety of classes Very rapidly evolving Evolving by selection! Reproductive barriers evolve Dodd experiment single genes multiple genes Fig. 14-7a Initial sample of fruit flies Maltose medium Starch medium Mating frequencies in experimental groups Starch Mating frequencies in starch control groups Maltose Mating experiments Results Female Starch Maltose Male Population Pop#1 Pop# Male #1 #2 Fig. 14-7b Hybrid Zones Coyne and Orr Cichlids Darwins finches Adaptive Radiation Evolution of many diverse species from one common ancestor. A few organisms colonize an unexploited area Or environmental changes cause extinctions Phylogeny for Greater Antillean Anolis lizards showing reconstruction of microhabitat specialization via maximum likelihood. Microhabitat divergence occurred relatively early in the radiation. Subsequent speciation events have been associated with differentiation along other resource axes.R. Glor Speciation Rates Punctuated Equilibrium SJ Gould and Eldridge Gradual