EvoReview & Speciation (1) PDF

Speciation (part 1) Biologists recognize several evolutionary mechanisms: LO 2.1: Review the definitions of evolution and adaptation and differentiate the major evolutionary Natural Selection processes....

Speciation (part 1) Biologists recognize several evolutionary mechanisms: LO 2.1: Review the definitions of evolution and adaptation and differentiate the major evolutionary Natural Selection processes. Gene Flow Evolution = change in allele frequencies in a population over generations Adaptation = heritable trait that helps Movement of alleles an individual survive and reproduce in between populations Genetic Drift Mutation its current environment Environment favors certain Random change in alleles, which then Creation of new allele frequency increase in frequency alleles LO 2.2: Define speciation. LO2.3: Explain the various concepts biologists use to define a species and discuss advantages and disadvantages of each. Speciation = the splitting There is no single definition by which biologists define a species. Instead, we use various species concepts. of an ancestral lineage into Species Concept Criteria for distinguishing Advantages Disadvantages two or more descendants populations as species Biological Reproductive isolation (populations Easy to apply with sexually Not applicable to asexual of different species cannot breed or reproductive populations reproducers or fossil species produce fertile offspring) Morphological Morphological distinction Widely applicable Subjective; may misclassify (differences in physical structure) Phylogenetic Species are the smallest tips on a Widely applicable Lack of good phylogenetic phylogenetic tree data Speciation (part 2) LO 2.5: Explain how reproductive isolation can result in speciation. LO 2.4: Describe prezygotic and postzygotic reproductive isolating mechanisms. Recognize the different types of reproductive isolating mechanisms. Speciation occurs when populations become reproductively isolated. The various mechanisms of reproductive isolation are divided into two categories: prezygotic and postzygotic. Once populations become reproductively isolated, they no longer exchange Prezygotic isolation prevents the formation of a zygote, either genes. The separated populations become more distinct as each accumulates by preventing mating or preventing fertilization. new mutations and continues to evolve via natural selection and drift. Temporal isolation Species breed at different times of LO 2.6: Explain the difference between allopatric and sympatric day or year speciation and give examples of each. Habitat isolation Species prefer different habitats, so In allopatric speciation, the initial are unlikely to interact reproductive isolation occurs because Behavioral isolation Species have different courtship of geographic separation or physical barrier. For example, a river or rituals mountain range may separate two Mechanical isolation Species’ reproductive organs are populations and prevent them from incompatible interacting. Geographic barrier Gametic isolation Species’ gametes are incompatible In sympatric speciation, In postzygotic isolation a zygote is produced, but either fails reproductive isolation occurs without to develop or is sterile. geographic separation. Chromosomal changes that prevent Hybrid inviability Hybrid embryos do not survive populations from successfully mating (such as autopolyploidy) are an Hybrid sterility Hybrid offspring are not fertile example.  LO 2.1: Review the definitions of evolution and adaptation, and differentiate the major evolutionary processes (natural selection, genetic drift, gene flow, mutation). Evolution All life on Earth shares a common ancestry. Processes of evolution have produced the many millions of species that exist today. Evolution is defined as the change in allele frequencies in a population over time. -Recall that a population is a group of individuals of the same species, and alleles are variants of genes © University of California Museum of Paleontology, Understanding Evolution  LO 2.1: Review the definitions of evolution and adaptation, and differentiate the major evolutionary processes (natural selection, genetic drift, gene flow, mutation). Adaptation & Natural Selection Adaptations are heritable traits that help individuals survive and reproduce in their current environment. One mechanism of evolution, known as natural selection, increases the frequency of these advantageous traits in the population over time. Figure 18.8 The white winter coat of the (a) arctic fox and the (b) ptarmigan’s plumage are adaptations to their environments. (credit a: modification of work by Keith Morehouse). LO 2.1: Review the definitions of evolution and adaptation, and differentiate the major evolutionary processes (natural selection, genetic drift, gene flow, mutation). Adaptation & Natural Selection Natural Selection Individuals who are best adapted to their environment have greater biological fitness. (i.e. Individuals with favored traits reproduce more). As they reproduce, they pass down the heritable advantageous traits to the next generation. This differential reproductive success © University of California Museum of Paleontology, results in the entire population becoming better adapted to its Understanding Evolution environment.  LO 2.1: Review the definitions of evolution and adaptation, and differentiate the major evolutionary processes (natural selection, genetic drift, gene flow, mutation). Types of Natural Selection Different types of natural selection can impact the distribution of phenotypes within a population. Stabilizing selection: favors survival of individuals with intermediate phenotypes. Directional selection: favors individuals at one extreme of a phenotypic range. Disruptive selection: two or more extreme phenotypes are favored.  LO 2.1: Review the definitions of evolution and adaptation, and differentiate the major evolutionary processes (natural selection, genetic drift, gene flow, mutation). Other mechanisms of evolution Natural selection is the only mechanism of evolution that increases adaptation in populations, but there are other mechanisms of evolution that result in allele frequency change over time. These include… Genetic drift Mutation Gene flow © University of California Museum of Paleontology, Understanding Evolution  LO 2.1: Review the definitions of evolution and adaptation, and differentiate the major evolutionary processes (natural selection, genetic drift, gene flow, mutation). Genetic Drift Changes in allele frequency due to random chance events Stronger affect on smaller populations Tends to “fix” an allele in a population  LO 2.1: Review the definitions of evolution and adaptation, and differentiate the major evolutionary processes (natural selection, genetic drift, gene flow, mutation). Genetic Drift Examples of genetic drift include bottlenecks and founder effects. Both processes reduce genetic diversity in populations. New population Original population A bottleneck occurs when the population is dramatically reduced. Founder effect occurs when a subset of individuals establish a new population  LO 2.1: Review the definitions of evolution and adaptation, and differentiate the major evolutionary processes (natural selection, genetic drift, gene flow, mutation). Gene Flow Involves the movement of genes into or out of a population Individuals that enter a population may have new alleles increasing the genetic diversity of the population  LO 2.1: Review the definitions of evolution and adaptation, and differentiate the major evolutionary processes (natural selection, genetic drift, gene flow, mutation). Mutation Creation of new alleles → original source of all genetic variation Natural selection acting on mutation can create evolutionary changes  LO 2.2: Define speciation. Speciation The same evolutionary processes that produce changes in populations also contribute to speciation, the formation of two species from an ancestral species. Before we explore how speciation works, we need to discuss how biologists define the word species.  LO 2.3: Explain the various concepts biologists use to define a species and discuss advantages and disadvantages of each. Species Concepts There is no single definition by which biologists define a species. Instead, we use various species concepts, each of which has limitations. The biological species concept defines a species as those whose organisms can actually or potentially interbreed and produce viable, fertile offspring. (i.e. those that are reproductively isolated) These are both Eastern tiger swallowtail butterflies (Papilio glaucus). This species has different color morphs, but all individuals can successfully mate with each other. LO 2.3: Explain LO 2.3: the various Explain the concepts biologists various concepts use touse biologists define a species to define and and a species discuss advantages discuss and advantages disadvantages and disadvantagesofofeach. each. Species Concepts Sometimes closely related species can interbreed but produce sterile offspring. For example, a horse and donkey can mate to produce sterile mules. Since the offspring are not fertile, horses and donkeys are considered different species under the biological species concept. https://commons.wikimedia.org/w/index Adrian Pingstone, Public domain, via Wikimedia.php?curid=2940444 Commons Heather Moreton from Louisville, KY, USA, CC BY 2.0 , via Wikimedia Commons Horse (Equus caballus) Donkey (Equus asinus) Mule (a sterile hybrid) LO 2.3: Explain LO 2.3: the various Explain the concepts biologists various concepts use touse biologists define a species to define and and a species discuss advantages discuss and advantages disadvantages and disadvantagesofofeach. each. Species Concepts The biological species concept is widely used and easy to apply for sexually reproducing populations. Disadvantages: not applicable to asexual species or fossil species NIAID, Public domain, via Wikimedia Commons The biological species concept cannot apply to asexual reproducers, like these bacteria. LO 2.3: Explain LO 2.3: the various Explain the concepts biologists various concepts use touse biologists define a species to define and and a species discuss advantages discuss and advantages disadvantages and disadvantagesofofeach. each. Species Concepts The morphological species concept defines species as those whose members have similar morphology (similar in physical structure…body shape, color, size, etc). It is widely applicable and can be used for fossil and extant species. Disadvantages: similarities are subjective; members of the same species may look different; members of different species may look similar Gray treefrog Cope’s gray treefrog These two frogs may look similar but are actually different species. They do not interbreed and have distinct chromosome numbers. This illustrates the difficulty in applying the morphological species concept. LO 2.3: Explain LO 2.3: the various Explain the concepts biologists various concepts use touse biologists define a species to define and and a species discuss advantages discuss and advantages disadvantages and disadvantagesofofeach. each. Species Concepts The phylogenetic species concept defines a species as the smallest tip on a phylogenetic tree, or the smallest set of organisms that share a single common ancestor and certain shared traits. It focuses on evolutionary history and genetic similarity. Disadvantages: lack of phylogenetic data; how much difference is enough to be considered separate species? M ralser, CC BY-SA 4.0 , via Wikimedia Commons LO 2.3: Explain LO 2.3: the various Explain the concepts biologists various concepts use touse biologists define a species to define and and a species discuss advantages discuss and advantages disadvantages and disadvantagesofofeach. each. Species can be sometimes be difficult to define Species boundaries can often be blurry, particularly for closely related populations. Hooded and carrion crows have different morphologies, occupy different geographic ranges, and tend to mate within their own groups. However, where their ranges overlap, they can occasionally hybridize and produce fertile offspring. Should they be © University of California Museum of Paleontology, Understanding considered the same species? Evolution  LO 2.4: Describe prezygotic and postzygotic reproductive isolating mechanisms. Recognize the different types of reproductive isolating mechanisms. Reproductive Isolating Mechanisms The biological species concept defines a species as those whose members interbreed and produce viable, fertile offspring. In other words, a species is a group of organisms who are reproductively isolated. They can breed within their own group, but not outside of it. These Masai giraffes are one of four giraffe species, all of which are reproductively isolated from each other  LO 2.4: Describe prezygotic and postzygotic reproductive isolating mechanisms. Recognize the different types of reproductive isolating mechanisms. Reproductive Isolating Mechanisms Reproductive isolation can occur via a variety of mechanisms. These are broadly classified into two groups: Prezygotic isolating mechanisms Postzygotic isolating mechanisms Recall that during sexual reproduction, the process of fertilization produces a single- celled zygote. For animals, this is the first cell of the new organism.  LO 2.4: Describe prezygotic and postzygotic reproductive isolating mechanisms. Recognize the different types of reproductive isolating mechanisms. Prezygotic Isolating Mechanisms Prezygotic mechanisms are those that prevent the formation of a zygote Ex. temporal, habitat, and behavioral isolation prevent breeding from occurring Wikimedia Commons Temporal Isolation Behavioral isolation Species may breed at different Species may have different times of day or year. These two courtship behaviors. These two species of frogs have different Habitat Isolation songbird species have different breeding seasons. Species may prefer different mating calls. habitats, so are unlikely to interact.  LO 2.4: Describe prezygotic and postzygotic reproductive isolating mechanisms. Recognize the different types of reproductive isolating mechanisms. Prezygotic Isolating Mechanisms (cont.) Prezygotic mechanisms are those that prevent the formation of a zygote Ex. Mechanical isolation and gametic isolation prevent fertilization even if mating is attempted Mechanical Isolation Gametic isolation Species may have incompatible genitalia. Sperm and eggs of different species may The male reproductive organs of be chemical incompatible. damselflies only “match” the female reproductive tracts of their own species.  LO 2.4: Describe prezygotic and postzygotic reproductive isolating mechanisms. Recognize the different types of reproductive isolating mechanisms. Postzygotic Isolating Mechanisms In postzygotic isolation, a zygote is formed but may not develop properly. Or the organisms produced may be sterile. This is often due to a mismatch of chromosomes between species. Hybrid inviability The embryo fails to develop properly Wikimedia Commons Hybrid sterility The hybrid offspring survives to adulthood but is not fertile (cannot reproduce), as with a mule  LO 2.5: Explain how reproductive isolation can result in speciation. Speciation New species form when populations of an original species become reproductively isolated from each other. The process of speciation can be described as reproductive isolation (or genetic isolation) followed by genetic divergence. Reproductive isolation New species Original species © University of California Museum of Paleontology, Understanding Evolution  LO 2.5: Explain how reproductive isolation LO 2.5:can Explain resulthow in speciation. reproductive isolation can result in speciation. The separated populations Speciation develop new mutations and continue to evolve via natural selection and genetic drift, becoming increasingly different Reproductive isolation prevents from each other gene flow between the separated populations Reproductive isolation New species If the two populations are no longer able to successfully Original species These two interbreed, they are now populations are considered separate species no longer exchanging genes © University of California Museum of Paleontology, Understanding Evolution  LO 2.6: Explain the difference between allopatric and sympatric speciation and give examples of each. Allopatric Speciation Biologists recognize different patterns of speciation. In allopatric speciation, the initial cause of reproductive isolation is a geographic barrier (allo = “other”; patric = “homeland”). Populations are physically separated from each other. There are two categories: dispersal and vicariance In dispersal, some In vicariance, a ------- individuals disperse and physical barrier forms colonize a new habitat to separate that is geographical populations, such as a isolated from the original new river branch LO 2.6: Explain the difference LO 2.6: Explain between the allopatric difference and between sympatric allopatric speciation and sympatric and give speciation examplesandof give each. examples of each. Allopatric Speciation ------- Once populations are geographically separated, other reproductive isolation ------- mechanisms may evolve as the populations diverge. The two populations may become so different that they will no longer interbreed successfully, even if the barrier is removed LO 2.6: Explain the difference LO 2.6: Explain between the allopatric difference and between sympatric allopatric speciation and sympatric and give speciation examplesandof give each. examples of each. Allopatric Speciation - Examples https://www.bio.miami.edu/dana/107/107F23_17.html About 3 million years ago, the isthmus of Panama formed and separated the Pacific Ocean from the Caribbean. Woods Hole Oceanographic Institute Snapping shrimp on either side of the isthmus speciated. Sister species on either side are more closely related to each other than to those on the same side. (Ex. A. formosus more closely related to A. panamensis than A. nuttingi) LO 2.6: Explain the difference LO 2.6: Explain between the allopatric difference and between sympatric allopatric speciation and sympatric and give speciation examplesandof give each. examples of each. Allopatric Speciation - Examples Populations of Ensatina salamanders in California are geographically separated by the Central Valley. Those that inhabit the western and eastern mountain ranges have evolved different morphologies via natural selection…. -Western populations have red coloration to mimic toxic newts -Eastern populations have a marbled coloration that helps them camouflage on the forest floor At the southern end of their ranges, these populations look very different and rarely interbreed. BMC Evolutionary Biology 11, 194, with permission from BMC Evolutionary Biology. Reproduced from Pereira, R.J., Monahan, W.B., Wake, D.B., 2011. LO 2.6: Explain the difference LO 2.6: Explain between the allopatric difference and between sympatric allopatric speciation and sympatric and give speciation examplesandof give each. examples of each. Sympatric Speciation In sympatric speciation, populations become reproductively isolated without any physical separation. (sym = “same”; patric = “homeland”). For example, evidence shows that cichlid fish in certain lakes have diverged into different species within a relatively short time frame. The fish occupy the same lake (no geographic barriers) but have evolved into different species as they’ve adapted different feeding strategies. LO 2.6: Explain the difference LO 2.6: Explain between the allopatric difference and between sympatric allopatric speciation and sympatric and give speciation examplesandof give each. examples of each. Sympatric Speciation - Autopolyploidy One way in which sympatric speciation can occur is via chromosomal changes, such as polyploidy (having more than 2 sets of chromosomes). While polyploidy can occur in animals, it appears much more common in plants. In autopolyploidy, a diploid plant produces diploid gametes due to an error in meiosis (instead of its normal haploid gametes) If the diploid gametes undergo fertilization, they can produce a tetraploid offspring. LO 2.6: Explain the difference LO 2.6: Explain between the allopatric difference and between sympatric allopatric speciation and sympatric and give speciation examplesandof give each. examples of each. Sympatric Speciation – Autopolyploidy (continued) If the tetraploid plants survive and reproduce, they will make diploid gametes. If mating occurs between the new tetraploid and the original diploid plants, triploid zygotes will be produced. Triploid offspring are typically either non-viable or sterile. Therefore, the new tetraploid population is reproductively isolated from the original diploid population (via postzygotic isolation). LO 2.6: Explain the difference LO 2.6: Explain between the allopatric difference and between sympatric allopatric speciation and sympatric and give speciation examplesandof give each. examples of each. Sympatric Speciation – Allopolyploidy Allopolyploidy is another example. This also involves chromosomal changes but begins when gametes from two different species combine to form a hybrid.