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How a single species changes through time? WHY Speciation matters? 4 • • • • To understand how evolution has produced the diversity of life, we need to study two fundamental processes: • • • • To understand how evolution has produced the diversity of life, we need to study two fundamental processes: • How a single species changes through time? • • • • To understand how evolution has produced the diversity of life, we need to study two fundamental processes: • How a single species changes through time? • How a single species becomes two or more species? = speciation SPECIES changes through time How a single species changes through time? anagenesis - evolution within a species lineage Ponctuated EQUILIBRIUM Punctuated equilibrium Niles Eldredge & Steven J. Gould (1972). Punctuated equilibrium: An alternative to phyletic gradualism. pp. 82-115. In: T. J. M. Schopf (ed.) Models in Paleobiology, Freeman, Cooper & Co.,San Francisco. • Speciation modes and tempo • • Speciation modes and tempo • • Speciation modes and tempo • • Speciation modes and tempo • • Speciation modes and tempo • • Speciation modes and tempo • • Speciation modes and tempo • • Speciation modes and tempo • How a single species becomes two or more species? “... it is probable that the periods, during which each [species] underwent modification, though many and long as measured by years, have been short in comparison with the periods during which each remained in an unchanged condition.” Charles Darwin, from the final 6th edition (1872) of On the Origin of Species Punctuated equilibrium predicts that a lot of evolutionary change takes place in short periods of time tied to speciation events. How a single species becomes two or more species? How a single species becomes two or more species? Punctuated equilibrium predicts that a lot of evolutionary change takes place in short periods of time tied to speciation events. How a single species becomes two or more species? How a single species becomes two or more species? How a single species becomes two or more species? How a single species becomes two or more species? How a single species becomes two or more species? How a single species becomes two or more species? How a single species becomes two or more species? • • • • To understand how evolution has produced the diversity of life, we need to study two fundamental processes: • How a single species changes through time? • How a single species becomes two or more species? = speciation Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids Prezygotic Isolation Individuals of different species Barriers to REPRODUCTION Habitat isolation Behavioral Isolation Mechanical Isolation ATTEMPT MATING Postzygotic Gametic Isolation Reduced Hybrid Viability FERTILIZATION Reduced Hybrid Fertility Hybrid Breakdown VIABLE, FERTILE OFFSPRING Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids Reproductive Isolating Mechanisms Prezygotic barriers o Habitat/Geographic isolation o Behavioral isolation o Temporal isolation o Mechanical isolation o Gamete isolation Prezygotic BARRIERS Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids Geographical Isolation Prezygotic Barriers Habitat Individuals of different species Temporal Behavioral Mechanical ATTEMPT MATING Gametic FERTILIZATION Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids Habitat Isolation Sciurus aberti kaibabensis Sciurus aberti Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids Habitat Isolation Water-dwellinggarter snake Thamnophis Terrestrial Thamnophis Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids Temporal Isolation Breeds Jan - March Temporal Isolation Breeds late March - May Bufo americanus Eastern spotted skunk (Spilogale putorius) Western spotted skunk (Spilogale gracilis) mates in late summer mates in late winter Bufo fowleri • • • • 17 Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids Behavioral isolation Courtship Ritual Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids Vocalization 22 Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids Mechanical Isolation Genital openings are not in alignment Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids Mechanical Isolation Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids Marine invertebrates and other organisms that lack mating behavior: species recognition occurs between egg and sperm Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids Bindin egg surface ❚ Bindin is an adhesive protein that binds sperm to the egg surface. Without this, fertilization does not occur. ❚ Rapid change of bindin proteins creates barriers to fertilization between species. Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids Chromosome evolution in animals Postzygotic BARRIERS Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids Postzygotic Barriers Reduced Hybrid Viability Reduced Hybrid Fertility Hybrid Breakdown Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids Reproductive Isolating Mechanisms VIABLE, FERTILE OFFSPRING Postzygotic barriers o Reduced Hybrid Viability o Reduced Hybrid Fertility o Hybrid Breakdown Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids Reduced Hybrid Viability Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids Reduced Hybrid Fertility Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids Hybrid Breakdown • Speciation modes and tempo • Modes of speciation Speciation modes have been also classified historically by the geographical arrangement of populations undergoing the process, a classification that focuses on the inhibitory effects of gene flow on the evolution of reproductive isolation. Modes of SPECIATION Allopatry and sympatry • Speciation modes and tempo • • Speciation modes and tempo • Evidence for two types of speciation ❚ It is thought that most speciation has been allopatric ❚ Sympatric speciation is thought to occur often among flowering plants (2-4% of species formed through this process) The classic scenario of an ecological speciation event, from beginning to end. Reproductive isolation builds in allopatry (green) as an incidental byproduct of adaptation to alternative environments (by-product mechanism). Reinforcement of pre-mating isolation, driven by reduced hybrid fitness, completes the speciation process during the sympatric phase (blue). The timing of secondary contact is flexible (indicated by arrows at the boundary between the allopatric and sympatric phases). Schluter 2001. TREE • Speciation modes and tempo • How a single species becomes two or more species? The Process of Speciation One species (set of interbreeding organisms) Genetic variant spreads through part of the species; bearers of this variant must mate only with other bearers of the same variant Two species. Further phenotypic, behavioural and ecological differences may evolve • Speciation modes and tempo • • Speciation modes and tempo • Speciation is a 2-part process Initially identical populations must diverge Reproductive isolation must evolve to maintain these differences • Speciation modes and tempo • Most species form when geographic barriers block genetic exchange • Speciation modes and tempo • Allopatric Peripatric Parapatric Sympatric (allo = other, patric = place) (peri = near, patric = place) (para = beside, patric = place) (sym = same, patric = place) • Speciation modes and tempo • • Speciation modes and tempo • Isolated island population of kingfishers Isolated island population of kingfishers Mainland population of kingfishers NEW GUINEA PACIFIC OCEAN Isolated island population of kingfishers • Speciation modes and tempo • Mainland population of kingfishers • Speciation modes and tempo • • Speciation modes and tempo • • Speciation modes and tempo • Adaptive Radiation Character Displacement 13 15 • Speciation modes and tempo • Adaptive Radiation: Character Displacement: • “Closely related • “Natural selection species that have favors those recently evolved individuals that use from a common resources not used ancestor by by other species” adapting to different parts of the environment” ALLOPATRY Vicariance Ancestral population Geographic isolation Speciation The geography of speciation • Speciation modes and tempo • 1.A geographic barrier creates isolation between two or more portions of a population The descendant populations diverge genetically (due to drift and selection) The reproductive isolation is completed 2. 3. Allopatric speciation through “dispersal and colonization” • Speciation modes and tempo • Isthmus of Panama closed ~ 3.1 MYA Split ~150 “geminate” (twin) species Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids A. formosus • Speciation modes and tempo • A. nuttingi P6 Knowlton et al.(1993) created a phylogeny of Pacific (P) and Caribean (C) species pairs of Alpheus P6 C6 P3 In 6 out of 7 cases, the closest relative of a species was on the other side of the Isthmus Atlantic Ocean C3 C3 P5 C5 Isthmus of Panama P4 C4 Pacific Ocean P1 C1 P2 C2 Allopatric speciation in snapping shrimp Alpheus – sibling species P7 P7 A. panamensis A. millsae 53 • Speciation modes and tempo • ALLOPATRY A model for adaptive radiation on island chains Vicariance Ancestral population Geographic isolation Speciation Testing hypothesis in biogeography ALLOPATRY Dispersal Species A’ Ancestral population Geographic isolation Testing hypothesis in biogeography Species B Speciation Testing hypothesis in biogeography • Speciation modes and tempo • • Speciation modes and tempo • • Speciation modes and tempo • Examples Frequency of alternative alleles Diagnosing Models of Speciation from Clinal Variation • Speciation modes and tempo • • Speciation modes and tempo • The descendant populations diverge genetically due to: D. heteroneura D. silvestris • Speciation modes and tempo • drift and selection (unrelated to interbreeding) selection against hybridization (reinforcement) • Speciation modes and tempo • How much isolation and for how long is needed for allopatric speciation? The reproductive isolation is completed this occurs after “secondary contact” between allopatric populations a crucial step, why? secondary contact is common without complete reproductive barriers, species will re-fuse Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids Secondary contact and reinforcement Secondary contact - contact between two populations that have been isolated from each other and have been diverging genetically for a while. Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids Secondary contact and reinforcement Secondary contact - contact between two populations that have been isolated from each other and have been diverging genetically for a while. What happens after secondary contact depends on whether reproductive isolating mechanisms have developed or not. Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids Secondary contact and reinforcement Secondary contact - contact between two populations that have been isolated from each other and have been diverging genetically for a while. What happens after secondary contact depends on whether reproductive isolating mechanisms have developed or not. Reinforcement - the ways in which distinctness between populations is maintained so as to prevent hybridization. eg. lowered fitness of hybrid phenotypes. Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids • Speciation modes and tempo • • Speciation modes and tempo • Species concepts • Isolating mechanisms • Speciation modes and tempo • Hybrids Reinforcement example • Speciation modes and tempo • Populations become sympatric again and interbreed. Populations become sympatric again but do not interbreed. Speciation has not occurred. Speciation has occurred. 106 • Speciation modes and tempo • Sympatric speciation no geographic barrier much rarer shows how ecology can drive speciation by selecting for assortative mating • Speciation modes and tempo • • Speciation modes and tempo • • Speciation modes and tempo • Variation in Lake Malawi and Lake Tanganyika Cichlids New species - through sexual selection? color polymorphism fixation of color genes through assortative mating interruption of gene flow population differentiation ⇓ species • Speciation modes and tempo • Peripatric Speciation Peri and Parapatry An example of this is the London Underground mosquito, a variant of the mosquito Culex pipiens, which entered in the London Undgerground in 19th century. Evidence for its speciation includes genetic divergence, behavioural differences, and difficulty in mating. 111 • Speciation modes and tempo • Examples Parapatric Speciation Although continuously distributed, different flowering times have begun to reduce gene flow between metal-tolerant plants and metal-intolerant plants. Human Human Human Human Human Human