DOCSLIB.ORG

Allopatric Speciation

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Allopatric Speciation Lecture 22 Speciation “These facts seemed to me to throw some light on the origin of species — that mystery of mysteries”. C. Darwin – The Origin What is speciation? • in Darwin’s words, speciation is the “multiplication of species”. What is speciation? • in Darwin’s words, speciation is the “multiplication of species”. • according to the BSC, speciation occurs when populations evolve reproductive isolating mechanisms. What is speciation? • in Darwin’s words, speciation is the “multiplication of species”. • according to the BSC, speciation occurs when populations evolve reproductive isolating mechanisms. • these barriers may act to prevent fertilization – this is prezygotic isolation. What is speciation? • in Darwin’s words, speciation is the “multiplication of species”. • according to the BSC, speciation occurs when populations evolve reproductive isolating mechanisms. • these barriers may act to prevent fertilization – this is prezygotic isolation. • may involve changes in location or timing of breeding, or courtship. What is speciation? • in Darwin’s words, speciation is the “multiplication of species”. • according to the BSC, speciation occurs when populations evolve reproductive isolating mechanisms. • these barriers may act to prevent fertilization – this is prezygotic isolation. • may involve changes in location or timing of breeding, or courtship. • barriers also occur if hybrids are inviable or sterile – this is postzygotic isolation. Modes of Speciation Modes of Speciation 1. Allopatric speciation 2. Peripatric speciation 3. Parapatric speciation 4. Sympatric speciation Modes of Speciation 1. Allopatric speciation 2. Peripatric speciation 3. Parapatric speciation 4. Sympatric speciation Modes of Speciation 1. Allopatric speciation Allopatric Speciation ‘‘The phenomenon of disjunction, or complete geographic isolation, is of considerable interest because it is almost universally believed to be a fundamental requirement for speciation.’’ Endler (1977) Allopatric Speciation Large ground finch Small ground finch Modes of Speciation 1. Allopatric speciation Allopatric speciation is the outcome of isolation and divergence. – Isolation is created by reductions in gene flow. – Divergence is created when mutation, genetic drift, and selection act on populations separately. Modes of Speciation 1. Allopatric speciation Allopatric speciation is the outcome of isolation and divergence. – Isolation is created by reductions in gene flow. – Divergence is created when mutation, genetic drift, and selection act on populations separately. Isolation may be caused by dispersal or vicariance. Geographic isolation can rise from dispersal or vicariance Modes of Speciation 1. Allopatric speciation • reproductive isolation occurs in complete geographic isolation (no gene flow). Example: Hawaiian Drosophila Hawaiian Drosophila Speciation by island-hopping Modes of Speciation 2. Peripatric speciation Modes of Speciation 3. Parapatric speciation Modes of Speciation 3. Parapatric speciation • reproductive isolation occurs without complete geographic isolation (some gene flow). Modes of Speciation 3. Parapatric speciation • reproductive isolation occurs without complete geographic isolation (some gene flow). Example: greenish warblers (Himalayas) Trevor Price Ring species – evidence for parapatric speciation Modes of Speciation 3. Parapatric speciation • reproductive isolation occurs without complete geographic isolation (some gene flow). Example: ring species of salamanders (Ensatina) in CA Ensatina salamanders Ring species – evidence for parapatric speciation Modes of Speciation 4. Sympatric speciation Modes of Speciation 4. Sympatric speciation • reproductive isolation evolves with complete geographic overlap. Requirements for sympatric speciation 1. Sympatric distribution 2. History of allopatry is unlikely 3. Monophyletic sister taxa 4. Reproductive isolation 5. Pre-zygotic isolation Diploid parent Tetraploid parent (Two copies of (Four copies of each chromosome) Meiosis each chromosome) Mating Haploid gametes Diploid gametes (One copy of each chromosome) (Two copies of each chromosome) Triploid zygote Meiosis (Three copies of each chromosome) When these gametes combine, most offspring have incorrect number of chromosomes. Soapberry bug Beak length correlates with fruit size. Balloon vine Flat-podded (native species) golden rain tree (non-native species) Short-beaked population 12 growing on non-native Long-beaked population plants growing on native plants 8 4 0 2 3 6 7 8 9 10 11 12 Beak length (mm) Frequency 8 Non-native plant Native plant 4 (small fruit) (large fruit) 0 2 3 6 7 8 9 10 11 12 Fruit radius (mm) Barluenga et al. Nature 439, 719 Nicaragua Cichlids Barluenga et al. Nature 439, 719 Nicaragua Cichlids What evolutionary processes are involved in speciation? What evolutionary processes are involved in speciation? 1. Natural selection What evolutionary processes are involved in speciation? 1. Natural selection • driven by different abiotic conditions (e.g., temperature, altitude) and biotic conditions (e.g., competitors, parasites). Next generation sequencing – RAD tags Local adaptation – loci under selection 3000 Histogram of Fst_2Fst outliers – 7471 loci 600 500 400 300 Frequency 3 Sdev. 200 216 loci 100 0 0.0 0.2 0.4 0.6 0.8 1.0 FstFst_2 Island of Speciation Selected locus Sea level = upper limit of expected neutral divergence Tightly- linked neutral loci (Fst) Sea floor = purely neutrally evolving regions Genetic divergence Genetic Loosely- linked neutral loci Trenches = loci under balancing selection 5. Adaptation What evolutionary processes are involved in speciation? 1. Natural selection • driven by different abiotic conditions (e.g., temperature, altitude) and biotic conditions (e.g., competitors, parasites). 2. Sexual selection What evolutionary processes are involved in speciation? 1. Natural selection • driven by different abiotic conditions (e.g., temperature, altitude) and biotic conditions (e.g., competitors, parasites). 2. Sexual selection • both female choice and male-male competition can promote rapid divergence (e.g., Hawaiian Drosophila). What evolutionary processes are involved in speciation? 1. Natural selection • driven by different abiotic conditions (e.g., temperature, altitude) and biotic conditions (e.g., competitors, parasites). 2. Sexual selection • both female choice and male-male competition can promote rapid divergence (e.g., Hawaiian Drosophila). • antagonistic sexual selection too! Male-male competition in Hawaiian Drosophila What evolutionary processes are involved in speciation? 3. Random genetic drift What evolutionary processes are involved in speciation? 3. Random genetic drift • may involve founder effects and genetic bottlenecks. What evolutionary processes are involved in speciation? 3. Random genetic drift • may involve founder effects and genetic bottlenecks. • alleles that are neutral in one environment may not be neutral in another! Ecological speciation in sticklebacks Ecological speciation in sticklebacks Dolph Schluter Ecological speciation in sticklebacks Ecological speciation in sticklebacks Ecological speciation in sticklebacks 1. Colonization by marine stickleback ~10,000 years ago Ecological speciation in sticklebacks 1. Colonization by marine stickleback ~10,000 years ago 2. Adaptation to freshwater environment Ecological speciation in sticklebacks 1. Colonization by marine stickleback ~10,000 years ago 2. Adaptation to freshwater environment 3. Secondary invasion by marine stickleback Ecological speciation in sticklebacks 3. Secondary invasion by marine stickleback Ecological speciation in sticklebacks 3. Secondary invasion by marine stickleback 4. Evolution of limnetic and benthic sticklebacks Evidence for secondary invasion hypothesis Evidence for secondary invasion hypothesis 1. Only low elevation lakes possess limnetic and benthic species pairs. Evidence for secondary invasion hypothesis 1. Only low elevation lakes possess limnetic and benthic species pairs. 2. Cores from lakes with limnetic and benthic species pairs show evidence of salt water influx (e.g, clams etc.). Evidence for secondary invasion hypothesis 1. Only low elevation lakes possess limnetic and benthic species pairs. 2. Cores from lakes with limnetic and benthic species pairs show evidence of salt water influx (e.g, clams etc.). 3. Higher elevation lakes have neither limnetic and benthic species pairs nor evidence of salt water influx. What types of genes are involved in speciation? Sensory drive in Victoria Cichlids Ole Seehausen Some generalities 1. The magnitude of prezygotic and postzygotic isolation both increase with the time. Some generalities 1. The magnitude of prezygotic and postzygotic isolation both increase with the divergence time. • in Drosophila, it takes about 1.5 to 3 million years for complete isolation to evolve. Some generalities 1. The magnitude of prezygotic and postzygotic isolation both increase with the time. • in Drosophila, it takes about 1.5 to 3 million years for complete isolation to evolve. • in marine bivalves, it may take 4 to 6 million years! Some generalities 1. The magnitude of prezygotic and postzygotic isolation both increase with the time. • in Drosophila, it takes about 1.5 to 3 million years for complete isolation to evolve. • in marine bivalves, it may take 4 to 6 million years! 2. Among recently separated groups, prezygotic isolation is generally stronger than postzygotic isolation. Some generalities 3. In the early stages of speciation, hybrid sterility or inviability
Load more

Recommended publications
  • Speciation in Heliconius Butterflies: Minimal Contact Followed 2 by Millions of Generations of Hybridisation 3 Simon H
    bioRxiv preprint doi: https://doi.org/10.1101/015800; this version posted March 2, 2015. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC 4.0 International license. 1 1 Speciation in Heliconius Butterflies: Minimal Contact Followed 2 by Millions of Generations of Hybridisation 3 Simon H. Martin*1, Anders Eriksson*1,2, Krzysztof M. Kozak1, Andrea Manica1 and 4 Chris D. Jiggins1 5 1 Department of Zoology, University of Cambridge, Downing Street, Cambridge, CB2 6 3EJ, United Kingdom 7 2 Integrative Systems Biology Laboratory, King Abdullah University of Science 8 and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia 9 * These authors contributed equally 10 Corresponding Author: S.H. Martin, [email protected] 11 Running Head: Change in the rate of gene flow during butterfly speciation bioRxiv preprint doi: https://doi.org/10.1101/015800; this version posted March 2, 2015. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC 4.0 International license. 2 12 Abstract 13 Documenting the full extent of gene flow during speciation poses a challenge, as 14 species ranges change over time and current rates of hybridisation might not reflect 15 historical trends. Theoretical work has emphasized the potential for speciation in the 16 face of ongoing hybridisation, and the genetic mechanisms that might facilitate this 17 process.
    [Show full text]
  • Allopatric Speciation with Little Niche Divergence Is Common Among
    Journal of Biogeography (J. Biogeogr.) (2016) 43, 591–602 ORIGINAL Allopatric speciation with little niche ARTICLE divergence is common among alpine Primulaceae Florian C. Boucher1*, Niklaus E. Zimmermann2,3 and Elena Conti1 1Institute of Systematic Botany, University of ABSTRACT Zurich,€ 8008 Zurich,€ Switzerland, 2Dynamic Aim Despite the accumulation of cases describing fast radiations of alpine Macroecology, Swiss Federal Research plants, we still have limited understanding of the drivers of speciation in alpine Institute WSL, 8903 Birmensdorf, Switzerland, 3Department of Environmental floras and of the precise the timing of their diversification. Here, we investi- Systems Science, Swiss Federal Institute of gated spatial and temporal patterns of speciation in three groups of alpine Technology ETH, CH-8092 Zurich,€ Primulaceae. Switzerland Location Mountains of the European Alpine System. Methods We built a new phylogeny of Primulaceae including all species in three focal groups: Androsace sect. Aretia, Primula sect. Auricula and Soldanella. Combining phylogenetic information with a detailed climatic data set, we investigated patterns of range and ecological overlap between sister-species using an approach that takes phylogenetic uncertainty into account. Finally, we investigated temporal trajectories of diversification in the three focal groups. Results We found that a large majority of sister-species pairs in the three groups are strictly allopatric and show little differences in substrate and cli- matic preferences, a result that was robust to phylogenetic uncertainty. While rates of diversification have remained constant in Soldanella, both Androsace sect. Aretia and Primula sect. Auricula showed decreased diversification rates in the Pleistocene compared to previous geological epochs. Main conclusions Allopatric speciation with little niche divergence appears to have been by far the most common mode of speciation across the three groups studied.
    [Show full text]
  • Can Secondary Contact Following Range Expansion Be Distinguished from Barriers to Gene flow?
    Can secondary contact following range expansion be distinguished from barriers to gene flow? Johanna Bertl1,2, Harald Ringbauer3,4 and Michael G.B. Blum5 1 Department of Molecular Medicine, Aarhus University, Aarhus, Denmark 2 Vienna Graduate School of Population Genetics, Vetmeduni Vienna, Vienna, Austria 3 Department of Human Genetics, University of Chicago, Chicago, IL, USA 4 Institute of Science and Technology Austria, Klosterneuburg, Austria 5 Laboratoire TIMC-IMAG, UMR 5525, Université Grenoble Alpes, CNRS, Grenoble, France ABSTRACT Secondary contact is the reestablishment of gene flow between sister populations that have diverged. For instance, at the end of the Quaternary glaciations in Europe, secondary contact occurred during the northward expansion of the populations which had found refugia in the southern peninsulas. With the advent of multi-locus markers, secondary contact can be investigated using various molecular signatures including gradients of allele frequency, admixture clines, and local increase of genetic differentiation. We use coalescent simulations to investigate if molecular data provide enough information to distinguish between secondary contact following range expansion and an alternative evolutionary scenario consisting of a barrier to gene flow in an isolation-by-distance model. We find that an excess of linkage disequilibrium and of genetic diversity at the suture zone is a unique signature of secondary contact. We also find that the directionality index c, which was proposed to study range expansion, is informative to distinguish between the two hypotheses. However, although evidence for secondary contact is usually conveyed by statistics related to admixture coefficients, we find that they can be confounded by isolation-by-distance. We recommend to account for the spatial repartition of fl Submitted 29 November 2016 individuals when investigating secondary contact in order to better re ect the Accepted 1 July 2018 complex spatio-temporal evolution of populations and species.
    [Show full text]
  • Microevolution: Species Concept Core Course: ZOOL3014 B.Sc. (Hons’): Vith Semester
    Microevolution: Species concept Core course: ZOOL3014 B.Sc. (Hons’): VIth Semester Prof. Pranveer Singh Clines A cline is a geographic gradient in the frequency of a gene, or in the average value of a character Clines can arise for different reasons: • Natural selection favors a slightly different form along the gradient • It can also arise if two forms are adapted to different environments separated in space and migration (gene flow) takes place between them Term coined by Julian Huxley in 1838 Geographic variation normally exists in the form of a continuous cline A sudden change in gene or character frequency is called a stepped cline An important type of stepped cline is a hybrid zone, an area of contact between two different forms of a species at which hybridization takes place Drivers and evolution of clines Two populations with individuals moving between the populations to demonstrate gene flow Development of clines 1. Primary differentiation / Primary contact / Primary intergradation Primary differentiation is demonstrated using the peppered moth as an example, with a change in an environmental variable such as sooty coverage of trees imposing a selective pressure on a previously uniformly coloured moth population This causes the frequency of melanic morphs to increase the more soot there is on vegetation 2. Secondary contact / Secondary intergradation / Secondary introgression Secondary contact between two previously isolated populations Two previously isolated populations establish contact and therefore gene flow, creating an
    [Show full text]
  • Coupling, Reinforcement, and Speciation Roger Butlin, Carole Smadja
    Coupling, Reinforcement, and Speciation Roger Butlin, Carole Smadja To cite this version: Roger Butlin, Carole Smadja. Coupling, Reinforcement, and Speciation. American Naturalist, Uni- versity of Chicago Press, 2018, 191 (2), pp.155-172. 10.1086/695136. hal-01945350 HAL Id: hal-01945350 https://hal.archives-ouvertes.fr/hal-01945350 Submitted on 5 Dec 2018 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Distributed under a Creative Commons Attribution| 4.0 International License vol. 191, no. 2 the american naturalist february 2018 Synthesis Coupling, Reinforcement, and Speciation Roger K. Butlin1,2,* and Carole M. Smadja1,3 1. Stellenbosch Institute for Advanced Study, Wallenberg Research Centre at Stellenbosch University, Stellenbosch 7600, South Africa; 2. Department of Animal and Plant Sciences, The University of Sheffield, Sheffield S10 2TN, United Kingdom; and Department of Marine Sciences, University of Gothenburg, Tjärnö SE-45296 Strömstad, Sweden; 3. Institut des Sciences de l’Evolution, Unité Mixte de Recherche 5554 (Centre National de la Recherche Scientifique–Institut de Recherche pour le Développement–École pratique des hautes études), Université de Montpellier, 34095 Montpellier, France Submitted March 15, 2017; Accepted August 28, 2017; Electronically published December 15, 2017 abstract: During the process of speciation, populations may di- Introduction verge for traits and at their underlying loci that contribute barriers Understanding how reproductive isolation evolves is key fl to gene ow.
    [Show full text]
  • Plant Speciation
    PLANT SPECIATION Niarsi Merry Hemelda, M.Si. MK Keanekaragaman Tumbuhan Departemen Biologi FMIPA -UI OUTLINE: Evolution Modes of plant speciation Features of plant evolution Speciation EVOLUTION SPECIES The cumulative The basic biological change in the heritable unit around which characteristics of a classifications are population over time. based. Speciation: an evolutionary process by which a new species comes into being. Evolution Microevolution Macroevolution • Microevolution is a change in generally refers to evolution gene frequency in a population in above the species level. short period of time. • Processes that can directly affect gene frequencies in a population: (mutation, migration, genetic drift, non random mating, natural selection) Patterns of evolution: A. Divergent Evolution: the two species gradually become increasingly different. B. Convergent Evolution: species of different ancestry begin to share analogous traits because of a shared environment or other selection pressure C. Parallel Evolution: two species evolve independently of each other, maintaining the same level of similarity. Parallel evolution usually occurs between unrelated species that do not occupy the same or similar niches in a given habitat. How a new species originate: • Species are created by a series of evolutionary processes. • Classically, speciation has been viewed as a three stage process: oIsolation of populations. oDivergence in traits of separated populations (e.g. mating system or habitat use). oReproductive isolation of populations that maintains
    [Show full text]
  • Speciation in Geographical Setting
    Speciation Speciation 2019 2019 The degree of reproductive isolation Substantial variation exists in among geographical sets of species - anagenesis populations within an actively 1859 1859 evolving species complex is often Achillea - yarrow tested by crossing experiments — as in the tidy tips of California 100K bp 100K bp back in time back in time back Rubus parviforus K = 4 mean population assignment 2 mya 2 mya ID CO WI_Door 5 mya BC_Hixton BC_MtRob WI_BruleS 5 mya BC_McLeod CA_Klamath MI_Windigo WA_Cascade WA_BridgeCr SD_BlackHills OR_Willamette MI_Drummond Speciation Speciation 2019 Reproductive isolation will ultimately stop all Although simple in concept, the recognition of species and thus the definition genetic connections among sets of populations of what are species have been controversial — more than likely due to the – cladogenesis or speciation continuum nature of the pattern resulting from the process of speciation 1859 Example: mechanical isolation via floral shape changes and pollinators between two parapatric species of California Salvia (sage) 100K bp back in time back 2 mya S. mellifera 5 mya Salvia apiana 1 Speciation Speciation Although simple in concept, the recognition of species and thus the definition Animal examples of speciation often show of what are species have been controversial — more than likely due to the clear reproductive barriers - hence zoologists continuum nature of the pattern resulting from the process of speciation preference (as opposed to botanists) for the Reproductive isolating Biological
    [Show full text]
  • L22-Speciation Announcements
    L22-Speciation Announcements 1st Drafts for papers due Oct 29th -DO NOT INCLUDE YOUR NAME TITLE OF PAPER by --first and last initials and ZS1234 last four-digits of student ID --include the recitation date and time as well. Announcements Supplemental materials on speciation posted to Carmen (will be in exam 3) PollEverywhere msg that “maximum responses reached”...don’t worry! THINK-PAIR-SHARE (90 sec) If 'things' look alike, what would qualify them as being of the same species? _________ speciation follows subdivision of a population due to physical barriers. A. parapatric B. peripatric C. sympatric D. allopatric Low relative genetic diversity is a consequence of the founder effect in peripatric speciation. A. True B. False THINK-PAIR-SHARE (90 sec) Why are there so many unusual species on the Galapagos Islands or in Madagascar? What kind of speciation might explain this phenomenon? Modes of speciation: Parapatric speciation A gradient or cline causes adjacent populations to experience different selective conditions -but the populations can still mate, generating hybrids Hybrids may lack traits that facilitate success in any part of the cline, causing them to be outcompeted by nonhybrids Modes of speciation: Parapatric speciation A gradient or cline causes adjacent populations to experience different selective conditions -but the populations can still mate, generating hybrids Bounded hybrid superiority suggests that hybrids occupying the HZ harbor unique traits exclusive of the progenitors that make them well-suited to environmental conditions
    [Show full text]
  • Speciation and Recessive Mutations for BMC Biology
    Essay: On the close relationship between speciation, inbreeding and recessive mutations. Etienne Joly, [email protected], Toulouse, September 2010 All the ideas developed in this essay are relatively simple, and most of them are related to many Foreword previously published works. So much work, however, This past year, 2009, was the Darwin year, celebrating has already been published on evolution and speciation the 200th anniversary of Charles Darwin's birth, and 150 that an autodidactic newcomer such as myself could years since the publication of his fabulous milestone not hope to read, let alone understand and remember all book, ‘The Origin of Species’ (to which I will the primary papers published previously on evolution subsequently refer to as ‘The Origin’). At the start of and speciation. If I have failed to acknowledge 2009, I was inhabited by a nagging ethical concern : how previous works developing ideas related to those put would humans deal with a situation where a group of forward here, the reader can be assured that this was individuals found themselves fertile among one another, not done maliciously but simply as a result of my but with limited fertility with the rest of the human race ? relative naivety on the subject. I do, however, hold the In other words, could speciation occur within the human firm conviction that, if some of the ideas developed in race ? This concern sprouted from the idea that this essay prove to be correct and relatively novel, it chromosomal rearrangements seemed to me like a very was only possible because of this naivety.
    [Show full text]
  • Allopatric Speciation
    Lecture 21 Speciation “These facts seemed to me to throw some light on the origin of species — that mystery of mysteries”. C. Darwin – The Origin What is speciation? • in Darwin’s words, speciation is the “multiplication of species”. What is speciation? • in Darwin’s words, speciation is the “multiplication of species”. • according to the BSC, speciation occurs when populations evolve reproductive isolating mechanisms. What is speciation? • in Darwin’s words, speciation is the “multiplication of species”. • according to the BSC, speciation occurs when populations evolve reproductive isolating mechanisms. • these barriers may act to prevent fertilization – this is prezygotic isolation. What is speciation? • in Darwin’s words, speciation is the “multiplication of species”. • according to the BSC, speciation occurs when populations evolve reproductive isolating mechanisms. • these barriers may act to prevent fertilization – this is prezygotic isolation. • may involve changes in location or timing of breeding, or courtship. What is speciation? • in Darwin’s words, speciation is the “multiplication of species”. • according to the BSC, speciation occurs when populations evolve reproductive isolating mechanisms. • these barriers may act to prevent fertilization – this is prezygotic isolation. • may involve changes in location or timing of breeding, or courtship. • barriers also occur if hybrids are inviable or sterile – this is postzygotic isolation. Modes of Speciation Modes of Speciation 1. Allopatric speciation 2. Peripatric speciation 3. Parapatric speciation 4. Sympatric speciation Modes of Speciation 1. Allopatric speciation 2. Peripatric speciation 3. Parapatric speciation 4. Sympatric speciation Modes of Speciation 1. Allopatric speciation Allopatric Speciation ‘‘The phenomenon of disjunction, or complete geographic isolation, is of considerable interest because it is almost universally believed to be a fundamental requirement for speciation.’’ Endler (1977) Modes of Speciation 1.
    [Show full text]
  • Introduction Speciation Is a Burning Issue in Evolutionary Biology, but It
    Introduction Speciation is a burning issue in evolutionary biology, but it is both fascinating and frustrating. Defining speciation depends on one’s species concept viz., typological, biological, evolutionary, recognition etc. In its simplest form, speciation is lineage splitting (ancestor-descendent sequence of populations); the resulting lineages are genetically isolated and ecologically distinct. Speciation is the process of evolutionary mechanism by which new biological species (or taxa) arise. There are two ways of new species (or taxa) origin from the pre-existing one:- i. by splitting of the parent species into two or more species (by the splitting of phylogenetic lineage) and ii. by transformation of the old species into a new one in due course of time. The Biologist O.F. Cook (1906) seems to have been the first to coin the term ‘speciation’ for the splitting of lineages (cladogenesis).The process of evolutionary mechanism by which new biological plant species (or taxa) arise, is known as plant speciation. General Mechanism of Speciation operating in nature: The mechanism of speciation is a two- staged process in which reproductive isolating mechanisms (RIM's) arise between groups of populations. Stage 1 • gene flow is interrupted between two populations. • absence of gene flow allows two populations to become genetically distinct as a result of their adaptation to different local conditions (genetic drift plays an important role here). • as populations differentiate, RIMs appear because different gene pools are not mutually coadapted. • reproductive isolation appears primarily in the form of postzygotic RIMs: hybrid failure. • these early RIMs are a byproduct of genetic differentiation, not directly promoted by natural selection.
    [Show full text]
  • Analysis of Host-Parasite Cospeciation: Effects of Spatial and Temporal Scale
    Louisiana State University LSU Digital Commons LSU Historical Dissertations and Theses Graduate School 1996 Analysis of Host-Parasite Cospeciation: Effects of Spatial and Temporal Scale. James W. Demastes Louisiana State University and Agricultural & Mechanical College Follow this and additional works at: https://digitalcommons.lsu.edu/gradschool_disstheses Recommended Citation Demastes, James W., "Analysis of Host-Parasite Cospeciation: Effects of Spatial and Temporal Scale." (1996). LSU Historical Dissertations and Theses. 6331. https://digitalcommons.lsu.edu/gradschool_disstheses/6331 This Dissertation is brought to you for free and open access by the Graduate School at LSU Digital Commons. It has been accepted for inclusion in LSU Historical Dissertations and Theses by an authorized administrator of LSU Digital Commons. For more information, please contact [email protected]. INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type o f computer printer. The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the upper left-hand comer and continuing from left to right in equal sections with small overlaps.
    [Show full text]