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Biology Content Standards 5. Evolution and Biodiversity Broad Concept: Genes allow for the storage and transmission of genetic information. They are a set of instructions encoded in the nucleotide sequence of each organism. Genes code for the specific sequences of amino acids that comprise the proteins that are characteristic of that organism. 5.1 Explain how evolution is demonstrated by evidence from the fossil record, comparative anatomy, genetics, molecular biology, and examples of natural selection. 5.2 Describe species as reproductively distinct groups of organisms. Recognize that species are further classified into a hierarchical taxonomic system (kingdom, phylum, class, order, family, genus, species) based on morphological, behavioral, and molecular similarities. Describe the role that geographic isolation can play in speciation. 5.3 Explain how evolution through natural selection can result in changes in biodiversity through the increase or decrease of genetic diversity from a population. What is Evolution ? • The processes that have transformed life on earth from its earliest forms to the vast diversity that characterizes it today. • A change in the genes! • Charles Darwin – “Father of Evolution” Evolution Evolution is the cause of something as insignificant as an increase in the frequency of the gene for dark wings in beetles from one generation to the next, to something as grand as the evolution of the dinosaur lineage. These two extremes represent classic examples of microevolution and macroevolution. Microevolution: small scale (w/in a population) Macroevolution: transcends the boundaries of a single species. 1 Old Theories of Evolution Jean Baptiste Lamarck Ideas that shaped Darwin • over time. (1744-1829) He was among the 1st scientists to recognize that living things changed over time. He also, long before Darwin, realized that organisms were somehow adapted to their environments. In explaining how adaptation occurred, however, he relied on 3 assumptions we now know to be incorrect … • Desire to change • Use and Disuse • Inheritance of Acquired Geology – Earth is very old and changes Characteristics Ideas that shaped Darwin • Charles Lyell – Principles of Geology • Farmers – Farmers altered and improved their crops and livestock through breeding programs. Artificial selection allowed only the individuals who suited the farmers’ needs to produce offspring. But, in nature there is no human intervention … Darwin wondered, “how could such a process therefore operate?” ” Charles Robert Darwin Malthus & Population Controls – Thomas Malthus was an economist. If the human population continues to increase, there will not be enough living space and food. The Malthusian Doctrine states, “The only conditions that will prevent the endless growth of human populations are famine, disease, and war.” ” Darwin realized that the Malthusian Doctrine applied more to animals and plants than humans, for most other species produce far more offspring than we do. What determines which individuals survive and reproduce? British ;aturalist 1809 -1882 From 1831 to 1836 Darwin served as a naturalist aboard the H.M.S. Beagle on a British science expedition around the world. 2 Charles Robert Darwin The H.M.S. Beagle was chartered for a 5-year mapping and collecting expedition to South America and the South Pacific. Darwin’s post as a naturalist required that he collect specimens and keep careful records of his observations. During the Beagle’s 5 year trip, Darwin often left the ship at one port and was picked up months later at another port. During his time on land, Darwin trekked 100’s of kilometers through unmapped regions. He collected many different types of fossils and observed 1000’s of species of organisms! Charles Robert Darwin Two main points: 1. Species were not created in their present form, but evolved from ancestral species... Common Descent 2. Proposed a mechanism for evolution: 1ATURAL SELECTIO1 Charles Robert Darwin On the Galapagos Islands,, Darwin Islands observed species that lived no where else in the world. These observations led Darwin to write a book. 1859 Galapagos tortoise On the Origin of Species by Means of 1atural Selection. Theory of Natural Selection 1. Variation 2. Overproduction of offspring Far more organisms are born than ever grow to adulthood! 3. Struggle for existence Organisms compete with each other (limited resources). 4. Differential survival and reproduction Organisms will evolve or change over very long periods of time. Generation after generation of this kind of selection causes organisms to become better and better adapted to their environment. 3 Adaptation Feature common in a population because it provides some improved function. Many forms: • Behavior: better evasion of predators. • Protein: functions better at body temperature • Anatomical feature: allows the organism to access a valuable new resource. Many of the things that impress us most in nature are thought to be adaptations! The creosote bush is a desert-dwelling plant that produces toxins. These toxins are an adaptation that prevent other plants from growing nearby, thus reducing competition for nutrients and water. Mimicry of leaves by insects is an adaptation for evading predators. This example is a katydid from Costa Rica. Echolocation in bats is an adaptation for catching insects. 4 Evidence of Evolution FOSSILS - trace of a long-dead organism Scientists who study fossils are called PALEO;TOLOGISTS. • The Earth is very old: more than 4 billion years old Sedimentary fossils usually develop from the hard body parts of an organism, such as the shell, bones, teeth, or, in the case of plants, the woody stem. • Earth’ ’s land is constantly moving and shifting. • Life on Earth has also changed over time. Fossils are often found in layers of sedimentary rock, which is formed when sediment, such as dust, sand, or mud, is deposited by wind or water. Nebraska's Ashfall Fossil Beds Over long periods of time, hard minerals replace the tissue of the organism, leaving rocklike structures. Relative Dating One of the few animals for which we have a fairly complete evolutionary record is the horse. All the main stages of horse evolution have been preserved in fossil form. Over 60 million years the horse evolved from a dogsized rainforest-dwelling creature, into an animal adapted to plains-dwelling and standing up to 2 meters high. In the process it traded-in its multi-toed feet, adapted for walking across the forest floor, for single-toed hooves, suited for running over open country. Technique used to determine the age of fossils relative to other fossils in different layers of rock. 5 Radioactive Dating – method of measuring rates of decay of radioactive materials to determine how long ago an event occurred or an organism lived. Fossils and DNA - The greater the differences between genes of related species the longer the time since those species shared a common ancestor. • Half-life – length of time required for ½ of the radioactive atoms in a sample to decay. (Ex) ½ life of C-14 is 5770 years. During that period, ½ the C-14 decays to ;-14. • C-14 is particularly useful because it can be used to date material that was once alive such as bones, or to date objects that contain once-living material. Because it has a relatively short ½ life, C14 is not really useful in dating samples that are more than 60,000 years old. Evidence of Evolution EMBRYOLOGY Living fossils are those relatively rare species that remain unchanged for long periods of time. One example is the horseshoe crab, Limulus, whose living members are almost identical to ancestors that lived hundreds of millions of years ago. They are exceptionally well adapted. Also, no new species entered into competition. Each of these species inherited the same genes for early embryonic development. ;ature takes the development plan and modifies it at different stages to produce different adults. The similarity of early embryonic development demonstrates that all the vertebrates share a common ancestor. 6 Evidence of Evolution Evidence of Evolution HOMOLOGOUS STRUCTURES A;ALOGOUS STRUCTURES Parts of different organisms with similar structure, but different functions – suggest common ancestry - Divergent Evolution. Parts of different organisms with similar function, but different structures. – Convergent Evolution. Evidence of Evolution Evidence of Evolution VESTIGIAL ORGA;S SIMILARITIES in MACROMOLECULES They are usually degenerated or underdeveloped. These organs are thought to have been functional in the ancestral species but have now become unnecessary and non-functional. Wings of flightless birds Protein Pelvic bones of whales D;A Hemoglobin Cytochrome c 7 Evolution of Populations Microevolution Population A localized group of individuals belonging to the same species. Some scientists view evolution as a process of change where minor genetic changes occur in populations through random mutations which can lead to a change in gene frequency. A population is the smallest unit of living organisms that can undergo evolution! changes in allele frequencies within a species. A group of populations whose individuals have the Refers to Gene Pool The total collection of genes in a population at any one time. Within a gene pool, every allele has a particular ratio or frequency. Species potential to interbreed and produce viable offspring. Five Mechanisms of Microevolution 1. Mutation 2. Migration (Gene Flow) 3. ;on-random mating The frequency of an allele is the number of occurrences of that allele in that population 4. Genetic Drift 5. ;atural selection 8 Mutation Migration (Gene Flow) The gain or loss of alleles from a population by the movement of individuals or gametes (pollen). Immigration or Emigration. Genes from crops rapidly can take over those in related wild plants. The end result could be major changes in the genetic make-up of wild plants, decreases in their population size, and the permanent loss of natural traits that could improve crop health. “The fact is that most genes for crop It is probable that melanism is a favorable evolutionary mutation with a selective advantage under certain conditions for its possessor, since it is more commonly found in regions of dense forest, where light levels are lower. NonNon-Random Mating Artificial Selection improvement have come from wild relatives of those same crops. Gene flow from crops to wild relatives is one of a host of environmental issues that humans must deal with.” Genetic Drift Change in the gene pool of a small population due to chance. The selective breeding of domesticated plants and animals by man. 9 Genetic Drift Bottleneck Effect Two examples: 1. Bottleneck effect Resulting from a disaster that drastically reduces population size. (Earthquakes & Volcanoes) 2. Founder effect Resulting from the colonization of a new location by a small number of individuals. ;atural Selection Founder Effect The pressures of natural selection can affect the distribution of phenotypes in a population in several ways … • Directional Selection • Stabilizing Selection • Disruptive Selection 10 Directional Selection A population may find itself in circumstances where individuals occupying one extreme in the range of phenotypes are favored over the others. Over long periods of time, in the constant presence of hungry peccaries, the population of cacti will gradually shift in the direction of the more heavily spined cactus varieties. Disruptive Selection Individuals at both extremes of a range of phenotypes are favored over those in the middle. Stabilizing Selection Individuals at both extremes of a range of phenotypes are being “weeded out”, resulting in the reproductive success of those near the mean. Stabilizing selection is common. In humans, for example, the incidence of infant mortality is higher for very heavy as well as for very light babies. Speciation How new species evolve from old ones. SPECIES group of organisms with similar characteristics that can interbreed with one another to produce fertile offspring. Individuals in the same species share a common gene pool. Canis familiaris 11 The Competitive Exclusion Principle (Gause’s Principle): ;O two species can occupy the same ;ICHE in the same location for a long period of time! ;ICHE Combination of an organism’s habitat and its role in that habitat. Speciation begins with … REPRODUCTIVE ISOLATIO;! Results from barriers to successful breeding between population groups in the same area. ;ew species arise when genetic differences accumulate to the point when the two groups can no longer successfully mate and reproduce (if and when they come back into contact). Allopatric Speciation = populations are physically separated Sympatric Speciation = populations are ;OT physically separated Allopatric Speciation Isolation might occur because of great distance or a physical barrier, such as a desert or river, as shown below. In order for a speciation even to be considered “allopatric,” ” gene flow between the soon-to-be species must be greatly reduced — but it doesn’’t have to be reduced completely to zero. Sympatric Speciation Gene flow has been reduced between flies that feed on different food varieties, even though they both live in the same geographic area. 12 200 years ago, the ancestors of Apple maggot flies laid their eggs only on hawthorns—but today, these flies lay eggs on hawthorns (which are native to America) and domestic apples (which were introduced to America by Apple maggot flies immigrants and bred). Females generally choose to lay their eggs on the type of fruit they grew up in, and males tend to look for mates on the type of fruit they grew up in. So hawthorn flies generally end up mating with other hawthorn flies and apple flies generally end up mating Apples with other apple flies. This means that gene flow between parts of the population that mate on different types of fruit is reduced. This host shift from hawthorns to apples may be the first step toward sympatric speciation — in fewer than 200 years, some genetic differences Hawthorns between these two groups of flies have evolved. Reproductive Barriers Behavioral Isolation Little or no sexual attraction between populations. • Pre-zygotic barriers • Post-zygotic barriers 12 different species of fiddler crabs on the same beach in Panama could be distinguished by the display of waving their large cheliped, elevating the body, and moving around in their burrow courtship display ritual! 13 Geographic Isolation Physical separation of members of a population • Islands of land in a sea of water • Islands of water in a sea of land • Islands of trees in a sea of grass • Mountains as barriers • Rivers and canyons as barriers Galapagos Finches • Darwin studied 13 similar but separate species of Galapagos finches. • Each finch species had a distinctive bill that is specialized for a particular food source. Despite the bill differences, the overwhelming similarities of the Galapagos finches implied that the finches shared a recent common ancestor, meaning they descended from a single species. • Darwin thought that perhaps all of the islands’ ’ finches had descended from a few birds or even a single female that had blown off course from South America. • Because the Galapagos are geologically young islands, @ 5 million years old, Darwin assumed that the offspring of the original finches had been adapting to different environments and food sources for a relatively short time . Darwin reasoned, therefore, that over many millions of years, many large differences could accumulate between species. Temporal Isolation Breeding occurs at different times for different species. Rana aurora - breeds January - March Rana boylii - breeds late March - May 14 Patterns of Evolution Macroevolution = large-scale evolutionary changes that take place over long periods of time. It refers to changes in populations of plants and animals so that new species develop from old ones. There are 6 important patterns: • • • • • • Mass Extinctions Adaptive Radiation Convergent Evolution Coevolution Punctuated Equilibrium Changes in Developmental Genes Adaptive Radiation Many related species evolve from a single ancestral species. The Galapagos finches diverged in response to the availability of different types of food in their different habitats. Mass Extinctions Huge numbers of species disappear! The Permian Extinction was the greatest mass extinction ever, but it’ ’s not the only big one. Five times in Earth’ ’s history—at the end of the Ordovician (440 million years ago), the Devonian (370 m.y.a.), the Permian (250 m.y.a.), the Triassic (210 m.y.a.), and the Cretaceous (65 m.y.a.) periods— mysterious events wiped out more than half the species alive. Some researchers think that humans have put so much stress on the environment that we’ ’re causing another mass extinction (see “The Sixth Extinction,” ” 1ational Geographic Magazine, February 1999). www.nationalgeographic.com Convergent Evolution Unrelated species become more similar as they adapt to the same kind of environment. EXAMPLE: Shark and porpoise have analogous structures. Sharks are fishes. Porpoises are mammals. They have analogous structures – similar fins. They have large, streamlined bodies. 15 Coevolution The mutual evolution of 2 different species interacting with one another. EXAMPLE: Plants and the animals that pollinate them. Gradualism This is the classical, traditional view stating that large changes (reproductive isolation and morphological differentiation) occur due to the gradual accumulation of many genetic changes. The classic example put forth in many natural history museums in the form of a nice display is that of the evolution of the modern horse. Punctuated Equilibrium This newer hypothesis was put forth in 1972 by Eldredge and Gould. They suggested that major changes occur relatively suddenly, and are "punctuated" by periods of relatively little change. Evidence for this theory is supplied by the fossil record. By studying the fossil record scientists have found what appears to be long periods of time with relatively little change in species followed by sudden periods of intense change http://evolution.berkeley.edu/evosite/evo101/VIIA1bPunctuated.shtml 16