updated notes BIOL 106
Minnesota State University, Mankato
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BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ 1 CHAPTER 18: Evolution "Nothing in biology makes sense except in the light of evolution." Theodosius Dobzhansky IMPORTANT NOTE on Darwin’s socalled “Theory of Evolution” Evolution itself is NOT the theory. Evolution was already accepted by many scientists before Darwin. How evolution occurred was not understood before Darwin. Darwin’s and Wallace’s contribution correctly stated: “the theory of evolution by natural selection” The mechanism for evolution, Natural Selection, is the theory. Definitions of evolution “Through time, species accumulate differences; as a result, descendants differ from their ancestors. In this way, new species arise from existing ones.” Darwin, quoted in text on p. 397. A heritable change in one or more characteristics of a population or species over many generation. Passed down through different generation (dictated by genetics), it’s not for an individual it has to be in a population or species. (evolved through populations =evolution) Definition of population A group of individuals of one species that live in the same geographic area at the same time. 20.1 Genetic Variation and Evolution PreDarwinian Concepts Leonardo da Vinci (14521519) Examined fossils and anatomy:people looked at fossils a really long time ago and they tried to figure out what organism they belonged to and they came up with a lot of questions. . . , George Louis LeClerc, Comte de Buffon (17491788) Founder of what became the Museum of Natural History, France: He reintroduced the ideas about the evolution of animal’s population, even when the environments are similar. it was also accepted that there were extinct species. BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ 2 Jean Baptiste de Lamarck (17441829): He published a book that detailed a mechanism for evolutionary change. He proposed that complex organisms are descended from less complex organism. Inheritance of Acquired Characteristics: Organisms can adopt changes during its life time. (i.e. Expansion of ear lobe, foot binding etc.). Therefore, these traits are being passed on to their offspring. modifications in an individual are caused by its environment, or the use or disuse of a structure during its lifetime, could be inherited by its offspring and thus bring about change in a species Georges Cuvier (17691832) Comparative anatomy – foundation for ideas that species were related, yet distinct, and could go EXTINCT, he looked at the anatomy of fossils and tried to figure if it was related to what had been seen before or not. Suggested that the earth was 6,000 years old and that only catastrophic events had changed its geological structure. Stretching to eat (configuring its neck) Give rise to an offspring with a configured neck 3 BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ Charles Darwin (18091882) He was only 22 when he accepted the position of naturalist abroad the HMS beagle, a British naval ship about to sail around the world. The voyage was supposed to take two years but it took five. Along the way, Darwin had the chance to collect and observe variety of life, many of which were different from those in his native England. His major mission was to expand the navy’s knowledge of natural resources (e.g., water and food) in foreign lands. By the time the trip was over, Darwin made observations that eventually led him to formulate the process by which life evolves over time in response to change in the environment. … Darwin was particularly affected by observations made on Galapagos Islands 13 principal islands and many small ones 950 km off the coast of Equator Darwin’s two important observations 1. Animals and plants on islands were similar to those of the South American mainland 2. Animals actually varied from island to island Sailors were able to identify which island tortoises they captured for food had come from He postulated that the beak of an ancestral Species had adapted over time to equip the finches to acquire different food sources Darwin called this mechanism natural selection. Prevalent thinkers and ideas in Darwin’s time Thomas Malthus (English clergyman and economist – 1798) discussed this principle in relation to human populations: proposed that death and famine are inevitable because human population tends to increase faster than the supply of food. Charles Lyell (Geologist – 1830) – superposition and fossils : Lyell’s ideas were influential on Darwin’s thinking: Lyell’s notion of the greater age of Earth gave more time for gradual change in species, and the process of change provided an analogy for gradual change in species. Charles Lyell suggested that changes in the Earth are directly caused by recurring events. For example, he suggested that geological process such as erosion existed in the past and happened at the same gradual rate as they do now. Artificial Selection: organisms could be altered in a heritable way by selection. The “struggle for existence.”: Because each generation has the same reproductive potential as previous generation there is a constant struggle for existence. GENES WITHIN POPULATIONS Darwin did not understand the mechanism by which characters or traits are passed from generation to generation although he did understand that variation among individuals within populations for certain traits was essential to his theory of natural selection. All of the alleles for each member of the population makes a gene pool each member of a population receives its BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ 4 gene from its parents, which, in turn, are members of the gene pool. Individuals that reproduce contribute to the gene pool of the next generation. Modern Synthesis; describes how evolutionary processes, such as natural selection, can affect a population’s genetic makeup, and, in turn, how this can result in the gradual evolution of populations and species. How successful traits were transferred was not understood in Darwin's time Gregor Mendel's work was "forgotten" until the early 20th century In the 1940s Darwin's theory and Mendel's principles were combined: the coherent understanding of the relationship between natural selection and genetics that took shape and is generally accepted today. Populations contain ample genetic variation to undergo selection Natural selection can only take place if there is variation, or differences, among individuals in a population. Importantly, these differences must have some genetic basis; otherwise, the selection will not lead to change in the next generation. This is critical because variation among individuals can be caused by nongenetic reasons such as an individual being taller because of better nutrition rather than different genes. Genetic diversity in a population comes from two main mechanisms: mutation and sexual reproduction. Natural Selection: 1. Individuals in a population vary in traits. 2. Traits can be heritable. Can be passed on to offspring 3. Species with certain traits can survive and reproduce at higher rates than those without those traits. • Individuals do not evolve! Only populations do! • Natural selection acts on individuals and leads to adaptive evolution What examples of natural selection can you think of? # Every time you go to the doctor you get an antibiotic giving to you in full dosage so as to kill the bacteria in your body completely. #The rich becomes richer and the poor becomes poorer BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ 5 How is artificial selection different than natural selection? Natural selection is when the traits that make an organism survive and reproduce better in their environment become more common. An example of natural selection would be light moths changing to darkcolored moths to adapt to their environment. Like the tree barks they live on turning black, they too would turn darkcolored for better survival and an advantage to hide from predators. Artificial selection is intentional breeding for certain traits. breeding a homozygous dominant trait healthy cow with a recessive healthy cow to get a healthy cow. Bad example but idea represented. BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ 6 Chapter 19 – Evolution of Populations Review/Learn terminology Gene – a unit of heredity that is transferred from a parent to offspring and is held to determine some characteristic of the offspring Chromosome – a threadlike structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes . How many sets of homologous chromosomes do many plants and most animals have? —23pair? No there is a wide range for different species Dogs=39 pairs (canis lupus) rats=46 pairs Mosquito=3 pairs Some type of Fish=52 pairs Black bear= 37 pairs Fruit fly=4 pair Jumper ant=1 pair Me and you=23 pairs Does the number of chromosomes differ according to species? all canis lupus (dog) have the same pair of chromosomes Horses and donkeys are different species and they produce a mule....they have different numbers of chromosomes and their offspring cannot breed with another donkey …so it’s not a viable specie What is the “origin” of the sets of chromosomes? – Locus (pl. loci) – specific site of a gene on a chromosom (location of genes) Allele – gene variations that arise by mutation and exist at the same relative locations on homologous chromosomes Dominant allele; trait which confers the same physical appearance whether an individual has two copies of the trait or one copy of the dominant trait and one copy of the recessive trait (capitalized) Recessive allele; an allele that produces its characteristic phenotype only when its paired allele is identical Homozygous dominant condition ; 2 dominant BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ 7 Homozygous recessive condition ; 2 recessive Heterozygous condition ; having two different alleles for a given gene on the homologous chromosome Genotype – underlying genetic makeup, consisting of both physically visible and nonexpressed alleles, of an organismgenotype (genetype) Phenotype – observable traits expressed by an organism (physicaltype) Gene pool – the sum of all the alleles in a population Frequency – allele frequency (or gene frequency) is the rate at which a specific allele appears within a population BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ 8 Changes in Allele Frequency; A change in this frequency over time would constitute evolution in the population. The allele frequency within a given population can change depending on environmental factors; therefore, certain alleles become more widespread than others during the process of natural selection. The HardyWeinberg Principle allows predictions of allele and genotype frequencies Godfrey Hardy, an English mathematician & Wilhelm Weinberg, a German physician came up with it independently in 1908. stated that a population’s allele and genotype frequencies are inherently stable—unless some kind of evolutionary force is acting upon the population, neither the allele nor the genotypic frequencies would change. Genetic equilibrium (HardyWeinberg equilibrium) occurs if FIVE assumptions/criteria/ conditions are met. There are no evolutionary forces acting upon it—generation after generation would have the same gene pool and genetic structure, and these equations would all hold true all of the time 1. No new mutations. no alteration of genes or new genes formed 2. No migration. no organisms are coming in or leaving 3. Random mating. – no preference of mating no artificial selection 4. Large population size. genes are less likely to be lost in a large population 5. No natural selection. – nothing like survival of the fittest Two equations p + q = 1: all the p alleles and all the q alleles make up all of the alleles for that locus that are found in the population p2 + 2pq + q2= 1: the frequency of pp individuals is simpl2; the frequency of pq individuals is 2pq; and the frequency of qq individuals is2q if the parent’s frequency is the same as the offspring’s then you have genetic equilibrium (no evolution) BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ 9 What does it mean when we say genetic equilibrium is not common in nature? We don’t see it in every species and evolution is occurring!!! HardyWeinberg predictions can be applied to data to find evidence of evolutionary processes 10 BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ Five Agents of Evolutionary Change If the frequencies of alleles or genotypes deviate from the value expected from the HardyWeinberg equation, then the population is evolving. When one or more of the five HardyWeinberg assumptions (criteria/conditions) are NOT met, small changes in genotype and/or allele frequencies occur from generation to generation in a population. Study hint: compare the following five agents of change to the five HW criteria to see how they’re related. What does it mean when we say genetic equilibrium is not common in nature? We don’t see it in every species and evolution is occurring (1) Mutation (the least important agent) changes alleles from A to a or vice versa. Species evolve because of the accumulation of mutations that occur over time. The appearance of new mutations is the most common way to introduce novel genotypic and phenotypic variance. Some mutations are unfavorable or harmful and are quickly eliminated from the population by natural selection. Others are beneficial and will spread through the population. Whether or not a mutation is beneficial or harmful is determined by whether it helps an organism survive to sexual maturity and reproduce. Some mutations do not do anything and can linger, unaffected by natural selection, in the genome. Some can have a dramatic effect on a gene and the resulting phenotype. (2) Gene Flow (migration )occurs when alleles move from one population to another While some populations are fairly stable, others experience more flux. Many plants, for example, send their pollen far and wide, by wind or by bird, to pollinate other populations of the same species some distance away. Even a population that may initially appear to be stable, such as a pride of lions, can experience its fair share of immigration and emigration as developing males leave their mothers to seek out a new pride with genetically unrelated females. This variable flow of individuals in and out of the group not only changes the gene structure of the population, but it can also introduce new genetic variation to populations in different geological locations and habitats. (3) Nonrandom mating shifts genotype frequencies because of patters about sexual selection. One reason is simple mate choice; for example, female peahens may prefer peacocks with bigger, brighter tails. Traits that lead to more mating for an individual become selected for by natural selection. Another cause of nonrandom mating is physical location. This is especially true in large populations spread over large geographic distances where not all individuals will have equal access to one another. Some might be miles apart through woods or over rough terrain, while others might live immediately nearby Assortative mating ;is an individual’s preference to mate with partners who are phenotypically similar to themselves. Assorting by similarity. Disassortative mating; mating of individuals having traits more dissimilar than likely in random mating.The mating of two individuals with dissimilar phenotypes . 11 BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ Inbreeding; breed from closely related people or animals, especially over many generations. The mating of closely related individuals, which can have the undesirable effect of bringing together deleterious recessive mutations that can cause abnormalities and susceptibility to disease. Inbreeding depression; the reduced biological fitness in a given population as a result of inbreeding, or breeding of related individuals. If a family of carriers begins to interbreed with each other, this will dramatically increase the likelihood of two carriers mating and eventually producing diseased offspring (4) Genetic Drift may alter allele frequencies in small populations (see p. 39 in this outline). (Allele frequency “drift “over time) simply the effect of chance. By chance, some individuals will have more offspring than others—not due to an advantage conferred by some geneticallyencoded trait, but just because one male happened to be in the right place at the right time (when the receptive female walked by) or because the other one happened to be in the wrong place at the wrong time (when a fox was hunting). Founder effect; An event that initiates an allele frequency change an isolated part of the population, which is not typical of the original population. Small subset of the original population. Bottleneck effect: Genetic drift can also be magnified by natural events, such as a natural disaster that kills—at random—a large portion of the population. Known as the bottleneck effect, it results in a large portion of the genome suddenly being wiped out In one fell swoop, the genetic structure of the survivors becomes the genetic structure of the entire population, which may be very different from the predisaster population . BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ 12 (5) Selection (by far, the most important agent!) Selection favors some genotypes over others some individuals possess more favorable phenotypes compared to others. The phenotypes in turn are controlled by the individual’s genotype. note: natural selection itself is not evolution, it is a key mechanism that causes evolution to happen (evolution occurs through natural selection) Quantifying Natural Selection [Fitness and Its Measurement] What do you describe as fitness? Fitness is the measure of reproductive success. An extremely fertile individual may have a higher fitness than a less fertile individual that appears more that appears more physically fit. *Fitness is the ability to compete for necessary resources *Do necessary task *Get food and shelter *reproduction BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ 13 Traits are associated (or tradeoff) and may influence fitness. Although an animal can adapt to its environment, it cannot maximize every trait. A tradeoff, then, is when an organism increases their proficiency in one area at the sake of another trait. Natural Selection’s Role in Maintaining Variation: Frequency dependent selection: is the term given to an evolutionary process where the fitness of a phenotype depends on its frequency relative to other phenotypes in a given population favors phenotypes that are either common (positive frequencydependent selection) or rare (negative frequencydependent selection) Negative frequencydependent selection: Negative frequencydependent selection serves to increase the population’s genetic variance by selecting for rare phenotypes Positive frequencydependent selection: positive frequencydependent selection usually decreases genetic variance by selecting for common phenotypes. In oscillating selection, the favored phenotype changes as the environment changes: Selection favors one phenotype at one time and another phenotype at another, changing as the environment changes. In some cases, Heterozygotes may exhibit greater fitness than homozygotes (heterozygote advantage). Only the expressed alleles are subject to natural selection. The heterozygote organism protects the recessive alleles that according to natural selection, should have been eliminated from the gene pool. But because the heterozygote remains in the genepool, it then becomes possible for the homozygote which might have greater fitness in changing environment. Therefore, natural selection favors the ratio of two or more phenotypes e.g. the orange, blue, and yellow above. (check if it’s a good example) if not stick with the example below. BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ 14 In regions where malaria is rampant, individuals with the heterozygous state have a distinct advantage, those with the sickle cell trait can resist malaria. The parasite that lives in and destroys the red blood cell that causes malaria can’t live in the red blood cell of a heterozygote of a sickle cell patient because the infection of malaria causes the red blood cell to become sickleshaped red blood cell lose potassium, and this causes the parasite to die. if they have homozygous recessive, they could die from sickle cell anemia. SO…. normal phenotype(AA)=dies due to malaria infection Carrier of sickle cell disease(As)=lives due to protection from both sickle cell and malaria. Sickle cell disease(ss)=dies due to sickle cell disease BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ 15 How Selection Acts on Traits affected by Multiple Genes Normal distribution (population in absence of selective pressure for comparison) Disruptive selection or diversifying: Sometimes two or more distinct phenotypes can each have their advantages and be selected for by natural selection, while the intermediate phenotypes are, on average, less fit. Known as diversifying selection. this is seen in many populations of animals that have multiple male forms. Large, dominant alpha males obtain mates by brute force, while small males can sneak in for furtive copulations with the females in an alpha male’s territory. In this case, both the alpha males and the “sneaking” males will be selected for, but mediumsized males, which can’t overtake the alpha males and are too big to sneak copulations, are selected against. Diversifying selection can also occur when environmental changes favor individuals on either end of the phenotypic spectrum. Imagine a population of mice living at the beach where there is lightcolored sand interspersed with patches of tall grass. In this scenario, lightcolored mice that blend in with the sand would be favored, as well as dark colored mice that can hide in the grass. Mediumcolored mice, on the other hand, would not blend in with either the grass or the sand, and would thus be more likely to be eaten by predators. The result of this type of selection is increased genetic variance as the population becomes more diverse. Disruptive selection, also called diversifying selection, describes changes in population genetics in which extreme values for a trait are favored over intermediate values. In this case, the variance of the trait increases and the population is divided into two distinct groups. Directional selection; When the environment changes, populations will often undergo directional selection. which selects for phenotypes at one end of the spectrum of existing variation. A classic example of this type of selection is the evolution of the peppered moth in eighteenth and nineteenthcentury England. Prior to the Industrial Revolution, the moths were BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ 16 predominately light in color, which allowed them to blend in with the lightcolored trees and lichens in their environment.But as soot began spewing from factories, the trees became darkened, and the light colored moths became easier for predatory birds to spot. Over time, the frequency of the melanic form of the moth increased because they had a higher survival rate in habitats affected by air pollution because their darker coloration blended with the sooty trees. Similarly, the hypothetical mouse population may evolve to take on a different coloration if something were to cause the forest floor where they live to change color. The result of this type of selection is a shift in the population’s genetic variance toward the new, fit phenotype. Stabilizing selection; If natural selection favors an average phenotype, selecting against extreme variation, the population will undergo stabilizing Selection. In a population of mice that live in the woods, for example, natural selection is likely to favor individuals that best blend in with the forest floor and are less likely to be spotted by predators. Assuming the ground is a fairly consistent shade of brown, those mice whose fur is most closely matched to that color will be most likely to survive and reproduce, passing on their genes for their brown coat. Mice that carry alleles that make them a bit lighter or a bit darker will stand out against the ground and be more likely to fall victim to predation. As a result of this selection, the population’s genetic variance will decrease. Robins typically lays four eggs, an example of stabilizing selection. Larger clutches may result in malnourished chicks, while smaller clutches may result in no viable offspring BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ 17 Ecotype: describes a genetically distinct geographic variety, population or race within a species, which is adapted to specific environmental conditions. Interactions among “Agents of Evolutionary Change” Mutation and genetic drift may reduce effects of natural selection Gene flow may promote or constrain evolutionary change BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ 32 THE EVIDENCE FOR EVOLUTION The Beaks of Darwin’s Finches: Evidence of Natural Selection Galapagos finches exhibit variation related to food gathering Darwin observed species of organisms on different islands that were clearly similar, yet had Distinct differences. For example, the ground finches inhabiting the Galapagos Islands comprised several species with a unique beak shape. The species on the islands had a graded series of beak sizes and shapes with very Small differences between the most similar. He observed that these finches closely resembled another finch species on the Mainland of South America. Darwin imagined that the island species might be species modified from one of the original Mainland species. Upon further study, he realized that the varied beaks of each finch helped the birds acquire a specific Type of food. For example, seedeating finches had stronger, thicker beaks for breaking seeds, and insect eating finches had Spearlike beaks for stabbing their prey. Peppered Moths and Industrial Melanism: (looking back at directional selection example) the moths were predominately light in color, which allowed them to blend in with the lightcolored trees and lichens in their environment. But as soot began spewing from factories, the trees became darkened, and the light colored moths became easier for predatory birds to spot. Over time, the frequency of the melanic form of the moth increased because they had a higher survival rate in habitats affected by air pollution because their darker coloration blended with the sooty tree. BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ 33 Artificial Selection: HumanInitiated Change: * all the different dogs are from one species canis lupus BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ 34 Fossil Evidence of Evolution Fossils provide solid evidence that organisms from the past are not the same as those found today, and fossils show a progression of evolution. Scientists determine the age of fossils and categorize them from all over the world to determine when the organisms lived relative to each other. The resulting fossil record tells the story of the past and shows the evolution of form over millions of years’ scientists have recovered highly detailed records showing the evolution of humans and horses. The whale flipper shares a similar morphology to appendages of birds and mammals. indicating that these species share a common ancestor. There are different ways fossils are formed…we can just have a bunch of tissues laid in the mud and pigments can still be gotten from it. BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ 35 Kinds of fossils: Impressions – organisms or parts of organisms are pressed into clay surfaces. I’m impressed!! Petrified wood – logs are buried in wet places; their cells are infiltrated by water containing dissolved minerals. Minerals gradually harden and replace the cells. Amber – insects or other bits and pieces are trapped within sticky pine sap, which is then fossilized. whole organism being captured. DNA can be gotten from the organisms to get their molecular information. BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ 36 Cast fossils – like making sculpture or machine parts in a foundary. Organisms are buried in clay, rot away, and leave a hollow mold. Water and minerals flow in, harden; the mold breaks away. You can also get the imprint of organism; we don’t have anything about their DNA or their molecular information odder than their outside structure. Footprints – indirect evidence of body sizes and rates of motion. The age of fossils can be estimated. 37 BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ Steno’s law of superposition: at the time when any given stratum was being formed, all the matter resting upon it was fluid, and, therefore, at the time when the lower stratum was being formed, none of the upper strata existed; the older the rocks the deeper they are or there’s more stuff onto them th 1600n 17 century Sharp teeth He figured out they were petrified Isotopic decay [Radioactive decay]: A common way to estimate the ages of fossil is by analyzing the decay of radioisotopes within the accompanying rock. Elements may be found in multiple form called isotopes that differ in the number of neutrons they contain. Radioisotope is an unstable isotope of an element that decays spontaneously. halflife of isotope. Elements are stable if they are balance in their electronic protons. If there is an unbalanced atom, it will slowly breakdown at a predictable rate of it halflife and because of that, you can take samples of minerals that are nearer or father of the fossil and figure out how long it’s been there. Fossils present a history of evolutionary change Transitional Forms: The evolution of horses is a prime example of evidence from fossils; extinct species of the genus Equus reveals that these ancient species resembled the modern horse (Equus ferus) but varied in size. The fossil record of horses supports the theory of descent with modification. Forelimb fossils are similar to one another, but show changes over time from the earliest horse ancestors to modernday horses, as species diverged from s common ancestor.in the fossil record we can observe over time a reduction in toe number, as the central toe became dominant, allowing horses to move more rapidly in new prairielike environments BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ 38 Anatomical Evidence for Evolution Homologous characters (homology) Another type of evidence for evolution is the presence of structures in organisms that share the same basic form. For example, the bones in the appendages of a human, dog, bird, and whale all share the same overall construction resulting from their origin in the appendages of a common ancestor. Over time, evolution led to changes in the shapes and sizes of these bones in different species, but they have maintained the same overall layout. Scientists call these synonymous parts homologous structures. Homology: functions may not be the same, but they are similar in structure Analogy: similarity of function and superficial resemblance of structures that have different originssimilar to something else and has different structures. BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ 39 Vestigial structures/characters; Some structures exist in organisms that have no apparent function at all, and appear to be residual parts from a past common ancestor. These unused structures without function are called vestigial structures. Other examples of vestigial structures are wings on flightless birds, leaves on some cacti, and hind leg bones in whales . 40 BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ Convergent Evolution; Another evidence of evolution is the convergence of form in which two different species from different linages have independently evolved similar characteristics because they occupy BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ 41 similar enviroments.. For example, species of unrelated animals, such as the arctic fox and ptarmigan, living in the arctic region have been selected for seasonal white phenotypes during winter to blend with the snow and ice (Figure 18.8ab). These similarities occur not because of common ancestry, but because of similar selection pressures—the benefits of not being seen by predators. Convergent evolution can lead us to believe that certain groups of organisms are more closelyrelated than they actually are. Using convergent characters to establish relationships among organisms is a form of “homoplasy.” Today we explored the convergent morphologies and relationships of animals that eat ants. THE ORIGIN OF SPECIES (covered in part in chapters 18/19) The Nature of Species and Different Species Concepts What is a species? # A species is a group of individual organisms that interbreed and produce fertile, BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ 42 viable offspring. According to this definition, one species is distinguished from another when, in nature, it is not possible for mattings between individuals from each species to produce fertile offspring. How do species remain distinct from one another?; Members of the same species share both external and internal characteristics, which develop from their DNA. The closer relationship two organisms share, the more DNA they have in common, just like people and their families. People’s DNA is likely to be more like their father or mother’s DNA than their cousin or grandparent’s DNA. Organisms of the same species have the highest level of DNA alignment and therefore share characteristics and behaviors that lead to successful reproduction. Species’ appearance can be misleading in suggesting an ability or inability to mate. For example, even though domestic dogs (Canis lupus familiaris) display phenotypic differences, such as size, build, and coat, most dogs can interbreed and produce viable puppies that can mature and sexually reproduce 1.Horses and donkeys are different species and they produce a mule.... they have different numbers of chromosomes and their offspring cannot breed with another donkey …so it’s not a viable specie 2. different locations Terms: Sympatric: Two population together but not the same or interbreeding Is it that they make the choice not to mate or if they try to mate it won’t work? Both could happen. It could be behavior or mechanical BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ 43 Allopatric: species live in different areas. Could interbred Allopatric speciation (allo = "other"; patric = "homeland") involves geographic separation of populations from a parent species and subsequent evolution . A geographically continuous population has a gene pool that is relatively homogeneous. Gene flow is relatively free because individuals can move and then mate with individuals in their new location. Thus, the frequency of an allele at one end of a distribution will be similar to the frequency of the allele at the other end. When populations become geographically discontinuous, that freeflow of alleles is prevented. When that separation lasts for a period of time, the two populations are able to evolve along different trajectories. Thus, their allele frequencies at numerous genetic loci gradually become more and more different as new alleles independently arise by mutation in each population. Typically, environmental conditions, such as climate, resources, predators, and competitors for the two populations will differ causing natural selection to favor divergent adaptations in each group. Isolation of populations leading to allopatric speciation can occur in a variety of ways: a river forming a new branch, erosion forming a new valley, a group of organisms traveling to a new location without the ability to return, or seeds floating over the ocean to an island. The nature of the geographic separation necessary to isolate populations depends entirely on the biology of the organism and its potential for dispersal. If two flying insect populations took up residence in separate nearby valleys, chances are, individuals from each population would fly back and forth continuing gene flow. However, if two rodent populations became divided by the formation of a new lake, continued gene flow would be unlikely; therefore, speciation would be more likely . BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ 44 Sympatric species inhabit the same area but remain distinct Populations of a species exhibit geographic variation (the populations usually are allopatric) If the groups are sufficiently “different “they may be considered subspecies or varieties Colder term “races” SPECIES CONCEPTS (1) Morphological Species Concept – our first and “longest running” concept. If populations differ in a number of physical characters they belong to different species. People would just look at population to see if they differ in physical characteristics. The morphological species concept groups species according to morphological similarities and ignores other differences such as DNA or inability to reproduce between individuals. The morphological species concept stems from the morphology, which is the study of the physical aspects of an organism and their arrangement. Problems with this species concept: if you start having integration of traits what becomes a species then? And in some cases members of the same species can look very similar (2) Biological Species Concept – Ernst Mayr (1940s) One or more populations whose members interbreed with each other to produce fertile offspring BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ 45 and do NOT interbreed with members of other populations. The biological species concept defines a species as members of populations that actually or potentially interbreed in nature, not according to similarity of appearance. Although appearance is helpful in identifying species, it does not define species Problems with this species concept: (3) Ecological species concept Species are defined by the ecological niches they fill. what does that mean?Unique sets of habitat resources that a species requires, as well as its influence on the environment and other species. if you have species that have different niche and they end up interbreeding with another species with a different niche and they have a hybrid it might not have fitness and would not be suited for any kind of environment. The hybrid will have lower fitness than its parent Useful in distinguishing bacterial or another species that do not reproduce sexually. (4) Phylogenetic species concept Species are defined by shared derived characters. A phylogeny is a family tree or the idea of what species came free. a species is a “tip” on a phylogeny, that is, the smallest set of organisms that share an ancestor and can be distinguished from other such sets. Under this definition, a ring species is a single species that encompasses a lot of phenotypic variation. A phylogenetic or cladistics species (PSC) is an evolutionarily divergent lineage—a lineage that has maintained its hereditary integrity with respect to other lineages through both time and space At some point in the evolution of such a group, members may diverge from one another: when such a divergence becomes sufficiently clear, the two populations are regarded as separate species. This category of species definition differs from evolutionary species in that the parent of the phylogenetic species goes extinct taxonomically when a new species evolves; the mother and daughter populations now forming two new species. subspecies as such are not recognized under this definition; either a population is a phylogenetic species or it is not taxonomically distinguishable. We will focus on the Biological Species Concept, which works well for most animals and many other organisms that reproduce sexually. The concept relies on reproductive isolation. 46 BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ REPRODUCTIVE ISOLATION (See Chapters 18/19); the ability to interbreed, of the two populations Prezygotic isolating mechanisms prevent the formation of zygotes; prezygotic barrier is a mechanism that blocks reproduction from taking place; this includes barriers that prevent fertilization when organisms attempt reproduction Birds that are noctoriol or they are not going to be interacting with one another Geographic isolation; Geographic isolation is a term that refers to a population of animals, plants, or other organisms that are separated from exchanging genetic material with other organisms of the same species. Typically, geographic isolation is the result of an accident or coincidence. Ecological isolation; has to do with niche where they are living what place occupy they don’t occupy the same environment in the way they could interact. ) Ecological isolation. Individuals mate in their preferred habitat, and therefore do not meet individuals of other species with different ecological preferences Behavioral isolation; Behavioral isolation occurs when the presence or absence of a specific behavior prevents reproduction from taking place. For example, male fireflies use specific light patterns to attract females. Various species of fireflies display their lights differently. If a male of one species tried to attract the female of another, she would not recognize the light pattern and would not mate with the male. Two birds singing offkey (become less attractive due to poor 47 BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ musical talent) Temporal isolation; Differences in breeding schedules. Temporal isolation means 'isolated in time', so this is a mechanism that prevents species from mating because they breed at different times. These differences can be time of day, season, or even different years. Individuals of different species do not mate because they are active at different times of day or in different seasons. American toad and the Fowler's toad. These are closely related species, but the American toad mates in the early part of summer, while the Fowler's toad mates later in the season. Mechanical isolation; The mechanisms of reproductive isolation or hybridization barriers are a collection of mechanisms, behaviors and physiological processes that prevent the members of two different species that cross or mate from producing offspring, or which ensure that any offspring that may be produced are sterile Prevention of gamete fusion; Other prezygotic barriers work when differences in their gamete cells (eggs and sperm) prevent fertilization from taking place; this is called a gametic barrier. Similarly, in some cases closely related organisms try to mate, but their reproductive structures simply do not fit together. For example, damselfly males of different species have differently shaped reproductive organs. If one species tries to mate with the female of another, their body parts simply do not fit together. Postzygotic isolating mechanisms allow zygotes to form but prevent or inhibit their normal development into reproducing adults. organisms don’t survive the embryonic stage and those that are born sterile Hybrid embryos don’t develop properly 48 BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ Hybrid adults don’t survive to reproduce in nature Hybrid adults are sterile or partially sterilefor example the mule, which is sterile, is produced from a cross a cross between a male donkey and a female horse Reproductive isolation often isn’t perfect! . . . especially where populations are “differentiating.” Formation of hybrid zones; After speciation, two species may recombine or even continue interacting indefinitely. Individual organisms will mate with any nearby individual who they are capable of breeding with. An area where two closely related species continue to interact and reproduce, forming hybrids, is called a hybrid zone; e. Over time, the hybrid zone may change depending on the fitness of the hybrids and the reproductive barriers (Figure 18.22). If the hybrids are less fit than the parents, reinforcement of speciation occurs, and the species continue to diverge until they can no longer mate and produce viable offspring. If reproductive barriers weaken, fusion occurs and the two species become one. Barriers remain the same if hybrids are fit and reproductive: stability may occur and hybridization continue Natural Selection can help keep populations of two sympatric species distinct Reinforcement; When two populations which have been kept apart, come back into contact, the reproductive isolation between them might be complete or incomplete. Gene flow may counter speciation The Role of Genetic Drift and Natural Selection in Speciation See p. 32 of this outline. The Geography of Speciation Allopatric speciation takes place when populations are geographically isolated 49 BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ Sympatric speciation occurs without geographic separation Allopolyploidy in plants (Handout will be provided);; One form of sympatric speciation can begin with a serious chromosomal error during cell division. In a normal cell division event chromosomes replicate, pair up, and then separate so that each new cell has the same number of chromosomes. However, sometimes the pairs separate and the end cell product has too many or too few individual chromosomes in a condition called aneuploidy Adaptive Radiation and Biological Diversity In some cases, a population of one species disperses throughout an area, and each finds a distinct niche or isolated habitat. Over time, the varied demands of their new lifestyles lead to multiple speciation events originating from a single species. This is called adaptive radiation because many adaptations evolve from a single point of origin; thus, causing the species to radiate into several new ones. Key innovation The Pace of Evolution Gradualism; species diverge gradually over time in small steps Punctuated equilibrium; a new species undergoes changes quickly from the parent species, and then remains largely unchanged for long periods of time afterward. because it begins with a punctuated or periodic change and then remains in balance afterward. While punctuated equilibrium suggests a faster tempo, it does not necessarily exclude gradualism. 50 BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ CHAPTER 20: SYSTEMATICS, PHYLOGENIES, AND COMPARATIVE BIOLOGY Some of the material in these notes does not appear in either textbook. Nomina si nescis, perit & cognitio rerum. “If you don’t know the names, one loses all knowledge of the entities.” – Linnaeus, C. 1737. Critica Botanica. Conrad Wishoff, Leiden. the evolutionary history and relationship of an organism or group of organisms is called its phylogeny. A phylogeny describes the relationships of an organism, such as from which organisms it is thought to have evolved, to which species it is most closely related, and so forth. Phylogenetic relationships provide information on shared ancestry but not necessarily on how organisms are similar or different. Phylogenetic Trees;; A phylogenetic tree is a diagram used to reflect evolutionary relationships among organisms or groups of organisms. Scientists consider phylogenetic trees to be a hypothesis of the evolutionary past since one cannot go back to confirm the proposed relationships. In other words, a “tree of life” can be constructed to illustrate when different organisms evolved and to show the relationships among different organisms The point where a split occurs, called a branch point, represents where a single lineage evolved into a distinct new one. A lineage that evolved early from the root and remains unbranched is called basal taxon. When two lineages stem from the same branch point, they are called sister taxa. A branch with more than two lineages is called a polytomy and serves to illustrate where scientists have not definitively determined all of the relationships. It is important to note that although sister taxa and polytomy do share an ancestor, it does not mean that the groups of organisms split or evolved from each other. Organisms in two taxa may have split apart at a specific branch point, but neither taxa gave rise to the other. Systematics Taxonomy (which literally means “arrangement law”) is the science of classifying organisms to construct internationally shared classification systems with each organism placed into more and more inclusive groupings. Think about how a grocery store is organized. One large space is divided into departments, such as produce, dairy, and meats. Then each department further divides into aisles, then each aisle into categories and brands, and then finally a single product. This organization from larger to smaller, more specific categories is called a hierarchical system 51 BIOL 106 – Fall 2016 – Lecture Outline Date ____________________________ Study/reconstruction of phylogeny; determining the family tree of all species Study of the process of evolution: using the family tree to determine how species evolved HISTORY of our CLASSIFICATION SYSTEM [Chapter 26 in 9th edition]?
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