Chapter 17 Speciation and Macroevolution PDF

Title Chapter 17 Speciation and Macroevolution 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  Outli...

Title Chapter 17 Speciation and Macroevolution 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  Outline 17.1 How New Species Evolve 17.2 Modes of Speciation 17.3 Principles of Macroevolution 2  Outcomes 17.1 How New Species Evolve 1) Compare and contrast the processes of microevolution and macroevolution 2) Use a phylogeny (phylogenetic tree) to explain the “anatomy“ of speciation. 3) Explain four ways that species are defined 4) Identify and compare features of prezygotic and postzygotic reproductive isolation. 3  17.1 How New Species Evolve/Separation of Species 1. Microevolution is any allele frequency change within the gene pool of a population. 2. Macroevolution is evolution on a large scale. Macroevolution involves the splitting of one species into two or more species, or speciation = origin of species. Final result of changes in gene pool allelic and genotype frequencies. READ 2 A. The Anatomy of Speciation (Theme Evolution) 1. Phylogeny is a tool evolutionary biologists use to investigate the history of evolution among organisms. 2. The following are some important terms used with a phylogenetic tree: a. Node: the point where two lineages intersect, and represent a shared common ancestor. b. Root: the origin of species’ shared common ancestry. c. Extinction: an extinct taxon is represented by a shortened branch on the phylogenetic tree. d. Monophyletic group (monophyly): also known as a clade. A group of species and their common ancestor. 3 Fig. 17A 4 B What is a Species?. 1. Taxonomists are scientists who classify living organisms into groups. 2. These classification groups can change over time, as new information unfolds. 3. The four species concepts are the # morphological species concept, # the evolutionary species concept, # the phylogenetic species concept and # the biological species concept 5  4. The morphological species concept is based on differences in appearance or morphology; it states that each species is defined by one or more distinct physical characteristics called diagnostic traits that distinguish one species from another. a. An advantage of this species concept is that it can be used to diagnose new species in the fossil record. b. Another advantage is that it applies to both sexually and asexually reproducing organisms. 6 The morphological species concept (cont) c. A disadvantage is some species do not have many measurable traits (bacteria and other microorganisms), and some trait differences are subtle and difficult to detect. d. Another disadvantage:sexual dimorphism. 7 5. The evolutionary species concept was proposed to explain speciation in the fossil record. a. Also relies on identification of certain morphological diagnostic traits to distinguish one species from another. b. In addition, it also requires that the members of a species share the same distinct, evolutionary pathway. 8 Fig. 17.2 9 6. The phylogenetic species concept states that an evolutionary family tree (phylogeny) is used to identify species based on a common ancestor. a. An advantage of defining species according to this concept is that it does not rely only on morphological traits to define a species. b. A branch of a phylogenetic tree that contains all of the descendants of a common ancestor is monophyletic. 10 7.The biological species concept says that the members of one species interbreed and have a shared gene pool, and each species is reproductively isolated from every other species. a. An advantage to this species concept is that it can designate species even when trait differences may be difficult to find. 11 b. A disadvantage is that this concept cannot be applied to: 1. asexually reproducing organisms 2. organisms only known by the fossil record, or 3. species that could possibly interbreed if they lived near one another. 12  B. Reproductive Isolating Mechanisms 1. For two species to be separate, gene flow must not occur between them. 2. A reproductive isolating mechanism is any structural, functional, or behavioral characteristic that prevents successful reproduction from occurring 13 3. Prezygotic (“before formation of a zygote”) isolating mechanisms are anatomical or behavioral differences between the members of two species that prevent mating or make it unlikely fertilization will take place if mating occurs Examples in textbook: read 14 a. Habitat isolation occur when two species occupy different habitats, even within the same geographic range, so that they are less likely to meet and to attempt to reproduce 15  b.Temporal isolation occurs when two species live in the same location, but each reproduces at a different time of year, and so they do not attempt to mate 16 Fig. 17.5 17 c. Behavioral isolation results from differences in mating behavior between two species. d. Mechanical isolation is the result of differences between two species in reproductive structures or other body parts, so that mating is prevented 18 e. Gamete isolation includes incompatibility of gametes of two different species so they cannot fuse to form a zygote; an egg may have receptors only for the sperm of its own species or a plant stigma prevents completion of pollination. 19 4.Postzygotic (“after formation of a zygote”) isolating mechanisms prevent development of a hybrid after formation of the zygote has taken place. Examples: Textbook a. Hybrid inviability (zygot mortality) is when hybrids (offspring of parents of two different species) = zygote/embryo do not develop properly. b. Hybrid sterility occurs when the hybrid offspring are sterile (e.g., mules). c. F2 Fitness : Hybrid is fertile, but F2 hybrid has reduced fitness. 20 Fig. 17.4 21  Outcomes 17.2 Modes of Speciation 1) Define two modes of speciation and give examples of each 2) Explain adaptive radiation with the aid of an example. 3) Discuss convergent and divergent evolution. Refer to relevant examples. 24  17.2 Modes of Speciation 1. Speciation is the splitting of one species into two or more species or the transformation of one species into a new species over time. 2. Researchers recognize two modes of speciation: geographic isolation and reproductive isolation. 22  A. Allopatric Speciation 1. Allopatric speciation occurs when new species result from populations being separated by a geographical barrier that prevents their members from reproducing with each other. 2. First proposed by Ernst Mayr of Harvard University. 3. While geographically isolated, variations accumulate until the populations are reproductively isolated. 23  4. Examples of Allopatric Speciation a. An ancestral population of Ensatina salamanders migrated from northern California to southern California. The Central Valley prevented gene flow between the eastern and western populations of these salamanders. Genetic differences increased resulting in two distinct forms of Ensatina salamanders 24 Fig. 17.8 25  b. The green iguana of South America is believed to be the common ancestor for the marine iguana on the Galápagos Islands (to the west) and the rhinoceros iguana on Hispaniola (to the north). A few of these iguanas may have swam to the islands and over time formed populations separate from each other and from the parent population of South America Read Paragraph 26 Fig. 17.9 Read in text book and discuss also video 27  5. Reinforcement of Reproductive Isolation a. A side effect to adaptive changes involving mating is reproductive isolation. b. As populations become reproductively isolated, postzygotic isolating mechanisms may arise before prezygotic isolating mechanisms 28  5. Reinforcement of Reproductive Isolation c. An example is a horse reproducing with a donkey, resulting in a sterile mule. d. Natural selection would favor any variation in populations that prevents the occurrence of hybrids when they do not have offspring. e. Reinforcement refers to the process of natural selection favoring variations that lead to reproductive isolation. (read) 29  B. Sympatric Speciation 1. Speciation without the presence of a geographical barrier is sympatric speciation. 2. Sympatric speciation would occur when members of a single population develop a genetic difference (e.g., chromosome number) that prevents them from reproducing with the parent type. 33 2. Polyploidy is when an organism has a chromosome number beyond the diploid (2n) number. a. Polyploidy is predominantly seen in plants and makes a significant contribution to the evolution of new plants. b. A polyploidy plant can reproduce with itself, but cannot reproduce with the 2n population. c.The two types of polyploidy are autoploidy and alloploidy. 34 3. Autoploidy occurs when a diploid plant produces diploid gametes due to nondisjunction during meiosis. a. A triploid (3n) plant is sterile because the chromosomes cannot pair during meiosis. (fruit without seeds) b. If two diploid gametes fuse, the plant is a tetraploid (4n) and the plant is fertile, so long as it reproduces with another of its own kind. (Larger fruit) Strawberries (8n) 35 4. Alloploidy requires two different but related species of plants to hybridize. a. When hybridization occurs, it is followed by chromosome doubling. b. However, the offspring that has parents with different numbered pairs of chromosomes will be sterile. 36 c.An example of alloploidy can be seen in the wheat plant used to produce bread. The parents of the present day bread wheat had 28 and 14 chromosomes. The hybrid with 21 chromosomes is sterile, but bread wheat with 42 chromosomes is fertile since the chromosomes can pair during meiosis 37  C. Adaptive Radiation 1. Adaptive radiation is a type of allopatric speciation that occurs when a single ancestral species rapidly gives rise to a variety of species, each adapted to a specific environment. 2. An ecological niche is where a species lives and how it interacts with other species. Ecological release? 30 3. The case of Darwin’s finches illustrates the adaptive radiation of 13 species from one founder mainland finch. Words to remember: Ancestral ˃ descendants ˃ ecological release ˃ open niches ˃ geographical isolation ˃ natural selection ˃ adaptation ˃ speciation 4.On the Hawaiian Islands, a wide variety of honeycreepers descended from one goldfinch-like ancestor 31 Fig. 17.11 32  1. Convergent evolution occurs when a similar biological trait evolves in two unrelated species as a result of exposure to similar environments. 2. Analogous traits are those that evolve convergent in two unrelated lineages because of a response to a similar lifestyle or habitat. 3. Homologous traits are those that are similar because they evolved from a common ancestor Divergent evolution: different selection pressures 1 Analogous traits 2 Analogous structures that resemble each other due to parallel adaptations to similar environments are results of convergent evolution. The wings of these flying animals are superficially similar but have different anatomical bases from unrelated lineages: bird, reptile, and mammal 3 Homologous traits 4  Outcomes 17.3 Principles of Macroevolution 1) Discriminate between the gradualistic and punctuated equilibrium models of evolution. 2) Explain how gene expression can influence speciation. 3) Support, by providing an example, that macroevolution is not goal orientated. 45  17.3 Principles of Macroevolution 1. Macroevolution is the evolution of new species and higher levels of classification. 2. Some evolutionists support a gradualistic model of macroevolution, meaning that speciation occurs after populations become isolated, with each group continuing slowly on its own evolutionary pathway. a. According to this model, ancestral species gradually gives rise to two separate species. b. This model suggests that it is difficult to indicate when speciation occurred because there would be so many transitional links. 5 Fig. 17.13 6 3. Other evolutionists support a punctuated equilibrium model to explain the pace of evolution. a. According to this model, periods of equilibrium (no change) are punctuated (or interrupted) by speciation. b. This model suggests that transitional links are less likely to become fossils and less likely to be found. 7 c. Speciation is more likely to involve only an isolated population at one locate, because a favorable genotype could spread more rapidly within such a population. 8 Fig. 17.13 9 4. These two models could both assist in interpretation of the fossil record. For example, some species may fit into one model, and other species.into the other model OR? Textbook: Read 10 A. Genetic Basis of Beak Shape in Darwin’s Finches (Nature of Science reading) LINK 1. The finches on the Galapagos Islands are an example of species originating from a common ancestor. 2. Each type of finch adapted to a particular way of life, and their beak size and shape is related to their diet. 3. DNA sequencing supports that Darwin’s finches are closely related to one another. 4. In 2006, two genes that are responsible for finch beak shape were discovered. a. The gene for bone morphogenic protein 4 (Bmp4) determines how deep or tall the beak will be. b. The gene for calmodulin (CaM) regulates how long a beak will grow. 11 12  B. Developmental Genes and Macroevolution 1. Genes can bring about radical changes in body shapes and organs. a.The Pax6 gene is involved in eye formation in all organisms. b. Homeotic (Hox) genes determine the location of repeated structures in all vertebrates. c. Tbx5 gene: limb development. 13 2. Gene expression influences organisms’ developmental processes. a. These genes can bring about huge changes in body shapes and organs. b. Despite millions of years of divergent evolution, all animals share the same control switches for development. Read: Textbook 14  3. Development of the Eye a.Eyes of species vary in size, compound or simple, etc. b. Despite these differences, there is one gene, Pax6, required for eye formation. c. The gene Pax6 was discovered by Walter Gehrig and colleagues in 1994. d. Interestingly, the mouse Pax6 gene can cause an eye to develop in the leg of a fruit fly 15 16  4. Development of Limbs a. The Tbx5 gene for the development of limbs in humans and wings in birds. b.Tbx5 triggers different genes in birds and humans, which may explain why the same protein is used in developing limbs in humans and wings in birds. 17 18 5. Development of Overall Shape a. Hox genes control the number and appearance of repeated structures along the main body axes of vertebrates (= segmented animals) b. Shifts when the Hox gene is expressed can explain why some vertebrates, like the snake, have hundreds of vertebrae, and others, like the chick only have seven. Read 19 20  7. Human Evolution a. Human DNA base sequencing is similar to that of chimpanzees, mice, and all vertebrates. b. Scientists predict that differential gene expression and/or new functions for “old” genes will explain how humans evolved. Read 22 C. Macroevolution Is Not Goal- Oriented 1. The evolution of the horse, Equus, seems to represents a gradual, directed straight-line evolution until its goal, the modern horse, has been achieved. a.The trends seen in the evolution of the horse are: increase in overall size, toe reduction, and change in tooth size and shape 23 2. However, based on fossils, it is easier to see that the horse lineage is not a straight-line evolution, but rather forming a thick bush of many equine species. 3. One may have deducted that since the only genus that remains is Equus and the other genera have become extinct, that evolution was directed towards producing Equus. However, each of the ancestral species was adapted to its environment 24 4. Adaptation occurs because the members of a population with an advantage are able to have more offspring than other members. 5. Natural selection is not goal-oriented, but rather opportunistic. 25 Fig. 17.17 26