Chapter 22 Speciation (Biology PDF)

Chapter 22 Speciation What is species Maintaining Reproductive Isolation Geography of speciation Genetic Mechanisms of Speciation © 2017 Cengage Learning. All Rights Reserved. Two Closely Related Bird Species Two closely related bird species, purple martins (Progne...

Chapter 22 Speciation What is species Maintaining Reproductive Isolation Geography of speciation Genetic Mechanisms of Speciation © 2017 Cengage Learning. All Rights Reserved. Two Closely Related Bird Species Two closely related bird species, purple martins (Progne subis) and tree swallows (Tachycineta bicolor) perching together on a branch in Crane Creek, Ohio. © 2017 Cengage Learning. All Rights Reserved. Why It Matters… In 1927 Ernst Mayr identified 137 species of birds in New Guinea, based on differences in size, plumage, color, and other external characteristics In 1942 Mayr published Systematics and the Origin of Species, which describes the role of geography in the evolution of new species © 2017 Cengage Learning. All Rights Reserved. Ernst Mayer – the Darwin of the 20th century © 2017 Cengage Learning. All Rights Reserved. Bird of Paradise 35 species of birds of paradise are found only in New Guinea Each mountain Bruce Beehler/Science Source range Mayr explored was home to some species that lived nowhere else © 2017 Cengage Learning. All Rights Reserved. Species and Speciation The species is the fundamental unit of biodiversity and biological studies Species arise through microevolutionary processes that alter the gene pools and phenotypic variation between populations Speciation is the process of species formation © 2017 Cengage Learning. All Rights Reserved. The British biologist Thomas Henry Huxley (1825- 1895), best remembered for his active support of Charles Darwin's theory of evolution, asked: “In the first place, what is a species ?” 22.1 What Is a Species? Biologists have developed a variety of species concepts (32!!) Popular approaches: Morphological species concept Biological species concept Phylogenetic species concept © 2017 Cengage Learning. All Rights Reserved. Morphological species concept The idea that all individuals of a species share measurable anatomical traits that distinguish them from individuals of other species Example: Paleobiologists use morphological criteria to identify species of fossilized organisms © 2017 Cengage Learning. All Rights Reserved. Morphological Species Concept Relying exclusively on morphology can present problems when there is: much variability within a single species, or when two species are nearly identical in appearance (cryptic species) Closely related cryptic species are called sibling species © 2017 Cengage Learning. All Rights Reserved. Cryptic species © 2017 Cengage Learning. All Rights Reserved. Morphological Features of Warblers Yellow-throated warbler Myrtle warbler (Dendroica dominica) (Dendroica coronata) Diagnostic characters. Yellow-throated warblers and myrtle warblers can be distinguished by the colour of feathers on the throat and rump © 2017 Cengage Learning. All Rights Reserved. Biological Species Concept Emphasizes genetic cohesiveness of species. Populations of the same species experience gene flow, thus genetic material = mixed 2nd emphasizes genetic distinctness of each species. Populations of different species are reproductive isolated, they cannot exchange genetic information. © 2017 Cengage Learning. All Rights Reserved. Limitations of the BSC Species are groups of interbreeding natural populations that are reproductively isolated from other such groups (Mayr) Defined in terms of population genetics and evolution does not apply to forms of life that reproduce asexually, or to extinct organisms, e.g. fossils © 2017 Cengage Learning. All Rights Reserved. Phylogenetic Species Concept First uses morphological and genetic sequence data to reconstruct an organism’s evolutionary tree Defined as a cluster of populations that emerges from the same small branch (share recent evolutionary history) © 2017 Cengage Learning. All Rights Reserved. Phylogenetic Species Concept Because evolutionary histories have been described for relatively few groups, the phylogenetic species concept cannot be applied to all forms of life © 2017 Cengage Learning. All Rights Reserved. Geographical Variation Neighboring populations often share characteristics because they live in similar environments and some gene flow occurs Widely separated populations may live under different conditions, and gene flow is less likely to occur – gene pools and phenotypes often differ © 2017 Cengage Learning. All Rights Reserved. Subspecies When geographically separated populations of a species exhibit dramatic, easily recognized phenotypic variation, biologists may identify them as different subspecies Local variants of a species (sometimes called a “race”) Usually interbreed where geographical distributions overlap © 2017 Cengage Learning. All Rights Reserved. Five Ratsnake Subspesies (Elaphe obsoleta) E. o. lindheimeri Black rat snake - Eastern North (E. o. obsoleta) America differ in colour and in the presence or absence of stripes or Yellow rat snake (E. o. quadrivittata) blotches. Texas rat snake Gray rat snake Everglades rat snake (E. o. lindheimeri) (E. o. spiloides) (E. o. rossalleni) © 2017 Cengage Learning. All Rights Reserved. Patterns of Geographical Variation Ring species Plant and animal species with a ring- shaped geographical distribution surrounding uninhabitable terrain Adjacent populations exchange genetic material directly © 2017 Cengage Learning. All Rights Reserved.  Gene flow between distant populations occurs only through intermediary populations Example: Seven subspecies of lungless salamander around California’s hot, dry Central Valley differ in biochemical traits, color, size, and ecology © 2017 Cengage Learning. All Rights Reserved. Ring Species Oregon salamander (E. e. oregonensis) Subspecies often Painted salamander Sierra Nevada salamander interbreed where their Centr (E. e. picta) (E. e. platensis) geographical distributions al le Val overlap. However, the two y subspecies that nearly close the ring in the south Yellow-eyed salamander (E. e. xanthoptica) Yellow-blotched salamander (marked with an arrow), (E. e. croceater) the Monterey salamander Two subspecies in the southern and the yellow-blotched part of the distribution rarely salamander, Monterey salamander interbreed. Large-blotched rarely interbreed. (E. e. eschscholtzii) salamander (E. e. klauberi) © 2017 Cengage Learning. All Rights Reserved. Patterns of Geographical Variation Clinal variation A species distributed over a large, environmentally diverse area may exhibit a pattern of smooth/gradual variation in traits along a geographical gradient (cline) CV is usually the result from gene flow between adjacent populations adapting to slightly different conditions Example: Many birds and mammals in the northern hemisphere show clinal variation in body size © 2017 Cengage Learning. All Rights Reserved. Clinal Variation House sparrows exhibit clinal variation in overall body size Darker shading in the map indicates larger size © 2017 Cengage Learning. All Rights Reserved. Study Break 22.1 1. How do the morphological, biological, and phylogenetic species concepts differ? 2. What is clinal variation? © 2017 Cengage Learning. All Rights Reserved. 22.2 Maintaining Reproductive Isolation Reproductive isolation is central to the biological species concept Reproductive isolating mechanism A biological characteristic that prevents the gene pools of two species from mixing © 2017 Cengage Learning. All Rights Reserved. Two Categories of Reproductive Isolating Mechanisms Prezygotic isolating mechanisms ( premating ) Operate before production of a fertilized egg (zygote) Postzygotic isolating mechanisms ( postmating ) Operate after zygote formation Reduce the fitness of hybrid individuals © 2017 Cengage Learning. All Rights Reserved. Two Categories of Reproductive Isolating Mechanisms Reproductive isolating mechanisms are not mutually exclusive – two or more may operate simultaneously 5 mechanisms have been ID that can prevent production of hybrid offspring [see table 22.1] © 2017 Cengage Learning. All Rights Reserved. Prezygotic Mechanisms (5) Ecological isolation Species live in different habitats in the same region Example: Asian lions (open grassland) and tigers (dense forest) of India © 2017 Cengage Learning. All Rights Reserved. Temporal isolation Species breed at different times of day or year. Examples: fruit flies (time of day); pine trees (time of year) D. perimilis Morning P. radiata Feb D. psudoobscura Afternoon P. muricata April © 2017 Cengage Learning. All Rights Reserved.  Photographer’s Choice/ Behavioral Gail Shumway/ Getty Images isolation 1 Signals of one 3 species are not 7 4 recognized by 8 another Examples: Birds 9 5 (song, colour), KEY 1 P. consimilis 4 P. collustrans frogs (song), 7 P. ignitus fireflies (light 2 P. brimleyi 5 P. marginellus 8 P. pyralis 3 P. carolinus 6 P. consanguineus 9 P. granulatus Bioluminescence patterns of 9 sp. flashes) © 2017 Cengage Learning. All Rights Reserved. Prezygotic Mechanisms (cont'd.) Mechanical isolation Differences in structure of reproductive organs or other body parts physically prevent mating Example: Monkey-flowers adapted to different pollinators © 2017 Cengage Learning. All Rights Reserved. Mechanical Isolation: Monkey-Flowers Purple monkey-flower Scarlet monkey-flower (Mimulus lewisii) (Mimulus cardinalis) Design Pics/Michael Interisano/Getty Images FLPA/Larry West/Age Fotostock attracts bumblebees attracts hummingbirds. © 2017 Cengage Learning. All Rights Reserved.  Gametic isolation Species have non-matching receptors on gametes Examples: Marine invertebrates, fruit flies, flowering plants © 2017 Cengage Learning. All Rights Reserved. Postzygotic Mechanisms (3) Hybrid inviability Hybrid offspring do not complete development-die as embryo or early age Example: Sheep and goats © 2017 Cengage Learning. All Rights Reserved.  Hybrid sterility Hybrid offspring cannot produce functional gametes, although they develop into healthy vigorous adults. Example: Horse and donkey (mules) Hybrid Sterility: Zebroids Horses and zebroids (hybrid offspring of horses and zebras) run in a mixed herd. Zebroids are usually sterile. © 2017 Cengage Learning. All Rights Reserved. Postzygotic Mechanisms Hybrid breakdown Hybrid offspring have reduced survival or fertility Line of descent does not pass the F2- generation Example: Fruit flies © 2017 Cengage Learning. All Rights Reserved. Isolating Mechanisms © 2017 Cengage Learning. All Rights Reserved. Study Break 22.2 1. What is the difference between prezygotic and postzygotic isolating mechanisms? 2. When a male duck of one species performed a courtship display to a female of another species, she interpreted his behavior as aggressive rather than amorous. What type of reproductive isolating mechanism does this scenario illustrate? © 2017 Cengage Learning. All Rights Reserved. 22.3 The Geography of Speciation Biologists define three modes of speciation based on the degree of geographical connectedness of populations as they become reproductively isolated: Allopatric speciation (allo = different, patria = homeland) Parapatric speciation (para = beside) Sympatric speciation (sym = together) © 2017 Cengage Learning. All Rights Reserved. Allopatric Speciation Takes place when a physical barrier subdivides a large population, or when a small population becomes separated from a species’ main geographical distribution Common mode of speciation in large animals © 2017 Cengage Learning. All Rights Reserved. Allopatric Speciation Allopatric speciation occurs in two stages: Two populations become geographically separated, preventing gene flow between them Accumulated genetic differences isolate them reproductively © 2017 Cengage Learning. All Rights Reserved. Allopatric Speciation and Secondary Contact 1 At first, a population is 2 A geographical change distributed over a large separates the original geographical area. population, creating a barrier to gene flow. © 2017 Cengage Learning. All Rights Reserved.  3 In the absence of gene flow, 4 When another geographical the separated populations change allows individuals of evolve independently and the two species to come into diverge into different species. secondary contact, they do not interbreed. Parapatric speciation Small peripheral populations may become isolated at the edge of a species’ geographical distribution Once a small population is isolated, genetic drift and limited gene flow from the parent population, increase differentiation (gene pool and phenotypic) © 2017 Cengage Learning. All Rights Reserved. Accumulated genetic differences may lead to reproductive isolation © 2017 Cengage Learning. All Rights Reserved. Populations on Oceanic Islands The founder effect (genetic drift) makes populations on oceanic islands genetically distinct On oceanic archipelagos (Galápagos, Hawaiian islands) individuals from one island may colonize nearby islands, founding populations that differentiate into distinct species © 2017 Cengage Learning. All Rights Reserved. Populations on Oceanic Islands Species cluster Group of closely related species recently descended from a common ancestor © 2017 Cengage Learning. All Rights Reserved. Evolution of a Species Cluster on an Archipelago Letters (A-D) ID 4 islands in hypothetical A archipelago, coloured 1 A few individuals of a species from dots represent different the mainland B C arrive on isolated species. Ancestor of all islands A and B. D the sp. is represented by black dots on the mainland. At end of the process, islands A and B are each 2 Over time, they differentiate into A occupied by 2 sp., and new species on these islands. The islands C and D are purple species then colonizes islands B C occupied by 1 sp, all of C and D. D which evolved on islands © 2017 Cengage Learning. All Rights Reserved. Secondary Contact Secondary contact between allopatric populations occurs when a geographical barrier is eliminated or breached, and the two populations reestablish contact If their gene pools did not differentiate much, the populations will interbreed and merge via species fusion © 2017 Cengage Learning. All Rights Reserved. Secondary Contact If the populations have differentiated enough to be reproductively isolated, they have become separate species © 2017 Cengage Learning. All Rights Reserved. Evolution of a Species Cluster on an Archipelago (cont’d.) 3 Over time, the A populations on islands C and D differentiate into B C two new species. D 4 Some time A later, the blue species colonizes island A, and the B C orange species colonizes island B, D establishing secondary contact. © 2017 Cengage Learning. All Rights Reserved. Secondary Contact (cont'd.) If prezygotic reproductive isolation is incomplete, individuals of two populations may mate in narrow hybrid zones If postzygotic isolating mechanisms cause hybrid offspring to have lower fitness, natural selection will promote evolution of prezygotic isolating mechanisms that enhance reproductive isolation (reinforcement) © 2017 Cengage Learning. All Rights Reserved. Hybrid Zones Bullock’s oriole (Icterus bullockii) Baltimore oriole (Icterus galbula) KEY Robert L Kothenbeutel/Shutterstock.com Bullock’s oriole iStockphoto.com/lightstalker Hybrid zone Baltimore oriole Males of the Bullock’s oriole and Baltimore oriole differ in color and courtship song. Populations have maintained a hybrid zone for 100’s years, and were considered subspecies of the same species. American Ornithologists’ Union recognized them as separate species in 1997. Hybridize less frequently than they once did, leading some researchers to suggest that their reproductive isolation evolved recently. © 2017 Cengage Learning. All Rights Reserved. Sympatric Speciation Sympatric speciation Reproductive isolation evolves between distinct subgroups that arise within one population Populations are neither geographically nor environmentally separated as their gene pools diverge © 2017 Cengage Learning. All Rights Reserved. Sympatric Speciation Example: Insects that feed on just one or two plant species Host plant choice may be genetically determined A mutation may result in some individuals feeding on different plants and mating on them In this way they become reproductively isolated and over time evolve into a new species © 2017 Cengage Learning. All Rights Reserved. Study Break 22.3 1. What are the two stages required for allopatric speciation? 2. Why might insects from different host races be unlikely to mate with each other? © 2017 Cengage Learning. All Rights Reserved.  NEXT LECTURE Online Chapter Description 2 Sept 20 [457-475] Evolutionary thinking 9 Sept 21 [476-499] Microevolution 16 Sept 22 [501-511, Speciation 518-519] 23 Sept 23 [521-549] Macroevolution