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Vertebrate Zoology Chapter 1 How do we learn from animals? • Experimentation * Physiological Science 1. How will a system respond to a disturbance? 2. Create the disturbance 3. Compare observations with expected results • Comparison * Evolutionary Science * Comparative anatomy * Molecular biology * Cell biology * Ecology Evolution Theories • Perpetual Change • Common Descent • Multiplication of Species • Gradualism • Natural Selection Perpetual Change Living organisms are not constant in form or function, nor are they perpetually cycling but always changing Proposed in antiquity Common Descent • All forms of life descended from a common ancestor through a branching of lineages (Phylogeny) • Supported by DNA & cell structure Phylogeny • The history of animal life depicted as a branching tree • Earliest animals are placed at the trunk • Each branch represents a new species which inherits many traits from the ancestor but also has a new (DERIVED) trait which appear for the 1st time Phylogenetic Tree Multiplication of Species • New species arise by the transformation of old ones Gradualism • Differences in anatomical traits within different species accumulate over long periods of time Charles Darwin (1809-1882) • Born in England • Attended medical school, HATED IT, and dropped out to become a priest • Boarded the H.M.S. Beagle for a 5 year UNPAID journey as a naturalist Journey of the H.M.S. Beagle Alfred Russel Wallace (1823-1913) Presented a paper with identical ideas as Darwin on July 1, 1858 at the Linnean Society meeting Was a botinist who came up with vitually the same concept of natural selection more or less independently through his studies on the Malay archipelago. Darwin panicked because he was not ready with his book yet! Where did Darwin and Wallace get the idea of evolution? Jean Baptiste Lamarck (1744-1829) • Lamarck claimed that evolution was driven by "use vs. disuse" • A used structure will become larger, stronger and more important. • A disused structure will atrophy and become VESTIGIAL. Theory of “Use vs Disuse” • The long necks of • Similarly, the big, giraffes were due “ripped” muscles to their stretching developed by the for food, and village blacksmith with giraffes passed all his hammering and their stretched slinging of heavy metal necks on to their objects would be offspring. expected to be passed on to his offspring. Theory of “Acquired Characteristics” • Lamarck claimed that traits acquired during an organism's lifetime could be inherited by that organism's offspring. Georges Cuvier (1769-1832) • Created Paleontology (The study of fossils) • He noted that deeper layers of sedimentary rock had diversity of organisms far different from present day life found in more recent layers • Proposed the idea of extinction based on fossils James Hutton (1726-1797) • A Scottish geologist who challenged Cuvier's view in 1795 with his idea of GRADUALISM • Proposed that large changes in the earth's surface could be caused by slow, constant processes such as erosion. Charles Lyell (1797-1875) • Earth processes had been going on constantly, and could explain the appearance of the earth. • This theory, uniformitarianism, was a strong basis for Darwin's later theory of natural selection. Thomas Malthus (1766-1834) • Suggested that much of humanity's suffering (disease, famine, homelessness and war) was the inevitable result of overpopulation: humans reproduced more quickly than their food supply could support them. • Malthus showed that populations, if allowed to grow unchecked, increase at a geometric rate. Darwin made some profound observations, from which he inferred some brilliant conclusions... • Observation #1. All species have huge potential fertility • Observation #2. Except for seasonal fluctuations, populations tend to maintain a stable size. • Observation #3. Environmental resources are limited. Inference #1 • The production of more individuals than the environment can support leads to a "struggle for existence," with only a fraction of offspring surviving in each generation. Observations • Observation #4: No two individuals in a population are exactly alike • Observation #5: Much of the observed variation in a population is heritable Inference #2 • Survival in this "struggle for existence is not random, but depends, in part, on the hereditary makeup of the survivors. • Those individuals who inherit characteristics that allow them to best exploit their environment are likely to leave more offspring than individuals who are less well suited to their environment. Inference #3 • Unequal reproduction between suited and unsuited organisms will eventually cause a gradual change in a population, with characteristics favorable to that particular environment accumulating over the generations. SO WHAT IS THIS THEORY OF NATURAL SELECTION? It can be broken down into four basic tenets, or ideas Theory of Natural Selection • 1. Organisms are capable of producing huge numbers of offspring. • 2. Those offspring are variable in appearance and function, and some of those variations are heritable. Theory of Natural Selection • 3. Environmental resources are limited, and those varied offspring must compete for their share. • 4. Survival and reproduction of the varied offspring is not random. Those individuals whose inherited characteristics make them better able to compete for resources will live longer and leave more offspring than those not as able to compete for those limited resources. What is speciation and who studies it? • Speciation is the creation of a new species • Scientists who study the processes and mechanisms that lead to such speciation events are EVOLUTIONARY BIOLOGISTS. Allopatric Speciation • A population becomes physically separated from the rest of the species by a geographical barrier that prevents interbreeding. • Because gene flow is disrupted by this physical barrier, new species will form. Sympatric Speciation • Two populations are geographically close to each other, but they are reproductively isolated from each other by different habitats, mating seasons, etc. Reproductive Barriers A reproductive barrier is any factor that prevents two species from producing fertile hybrids, thus contributing to reproductive isolation. • Habitat Isolation • Temporal Isolation • Behavioral Isolation • Mechanical Isolation • Gametic Isolation Species • A SPECIES is a group of similar organisms that can mate to produce fertile, viable offspring. • Different species are, by definition, REPRODUCTIVELY ISOLATED from one another. Adaptive Radiation • Adaptive Radiation - Evolutionary process in which the original species gives rise to many new species, each of which is adapted to a new habitat and a new way of life. E.g. Darwin's Finches Evidence for Evolution HOMOLOGY • In biology, a HOMOLOGY is a characteristic shared by two species (or other taxa) that is similar because of common ancestry. Types of homology • morphological homology – species placed in the same taxonomic category show anatomical similarities. • ontogenetic homology - species placed in the same taxonomic category show developmental (embryological) similarities. • molecular homology - species placed in the same taxonomic category show similarities in DNA and RNA. MORPHOLOGICAL HOMOLOGY • Structures derived from a common ancestral structure are called: HOMOLOGOUS STRUCTURES Ontogenetic Homology The human embryo has gills, a tail, webbing between the toes & fingers, & spends its entire time floating and developing in amniotic fluid has similar salt concentration as ocean water MORPHOLOGICAL HOMOLOGY • A structure that serves the same function in two taxa, but is NOT derived from a common ancestral structure is said to be an ANALOGOUS STRUCTURE Examples of Analogous structures: • wings of bat, bird, and butterfly • walking limbs of insects and vertebrates • cranium of vertebrates and exoskeleton head of insects Molecular Homology An ongoing process • Evolution can be considered a process of "remodeling" a population over the course of many generations, with the driving force being the natural selection factors that favor one form over another in specific environments. Vestigial Structures • Have marginal, if any use to the organims in which they occur. • EXAMPLES: • pelvic elements in pythonid snakes and cetaceans (whales) • appendix in humans • coccyx in great apes Whale Pelvis? Types of Evolution • Divergent Evolution - Method of evolution accounting for the presence of homologous structures. Multiple species of organisms descended from the same common ancestor at some point in the past. • Convergent Evolution - Method of evolution accounting for the presence of analogous structures. Organisms of different species often live in similar environments, thus explaining the presence of features with similar functions. Rate of Evolution • Gradual evolution occurs where the increment of change is small compared to that of time. • Punctuated evolution occurs where the increment of change is very large compared to that of time in discrete intervals, while most of the time there is virtually no change at all. Natural Selection in Action Industrial Melanism Natural Selection in Action Camouflage Natural Selection in Action Mimicry Coral vs. King Snakes: Red on yellow, kill a fellow, red on black won’t hurt Jack Natural Selection in Action Warning Coloration Natural Selection in Action Disruptive Coloration Natural Selection in Action Counter Shading Natural Selection in Action: Eye Spots Causes of Evolution 1. Mutations - random changes in genetic material at the level of the DNA nucleotides or entire chromosomes 2. Natural Selection - most important cause of evolution; measured in terms of an organism's fitness, which is its ability to produce surviving offspring a. Stabilizing Selection - average phenotypes have a selective advantage over the extreme phenotypes b. Directional Selection - phenotype at one extreme has a selective advantage over those at the other extreme c. Disruptive Selection - both extreme phenotypes are favored over the intermediate phenotypes Natural selection favors the average individuals within a population Natural selection favors on one of the extreme variations within a species Individuals with both extreme phenotypes are selected for Causes of Evolution 3. Mating Preferences - Organisms usually do not choose their mates at random, thus the selection process can cause evolution 4. Gene Flow - Transfer of genes between different populations of organisms. This situation leads to increased similarity between the two populations 5. Genetic Drift (Founder Effect & Bottleneck) - Situation that results in changes to a population's gene pool caused by random events, not natural selection. This situation can have drastic effects on small populations of individuals. Common on islands. Gene Flow Genetic Drift The change in gene frequency in a population resulting in different phenotypes Founder Effect Bottleneck Effect The study of phylogeny • Understanding a phylogeny is a lot like reading a family tree. • The root of the tree represents the ancestral lineage, and the tips of the branches represent the descendents of that ancestor. • As you move from the root to the tips, you are moving forward in time. Phylogenic Speciation • When a lineage splits (speciation), it is represented as branching on a phylogeny. • When a speciation event occurs, a single ancestral lineage gives rise to two or more daughter lineages. Shared Ancestry • Phylogenies trace patterns of shared ancestry between lineages. • Each lineage has a part of its history that is unique to it alone and parts that are shared with other lineages. Common Ancestors • Each lineage has ancestors that are unique to that lineage and ancestors that are shared with other lineages — called common ancestors. Clades – Cladistics (The study of clades) • A clade is a grouping that includes a common ancestor and all the descendents (living and extinct) of that ancestor. Nested Clades • Clades are nested within one another — they form a nested hierarchy. • A clade may include many thousands of species or just a few. Reading Phylogeny Evolution produces a pattern of relationships A B C D among lineages that is tree-like, not ladder-like. Reading Phylogeny Just because we tend to read phylogenies from left to right, there is no correlation with level of "advancement." Reading Phylogeny For any speciation event on a phylogeny, the choice of which lineage goes to the right and which goes to the left is arbitrary. The following phylogenies are equivalent: Misconceptions about humans It is important to remember that: 1. Humans did not evolve from chimpanzees. Humans and chimpanzees are evolutionary cousins and share a recent common ancestor that was neither chimpanzee nor human. 2. Humans are not "higher" or "more evolved" than other living lineages. Since our lineages split, humans and chimpanzees have each evolved traits unique to their own lineages. Character Types • A character is a recognizable feature of an organism. Characters may be morphological, behavioral, physiological, or molecular. • A shared character is one that two lineages have in common • A derived character is one that evolved in the lineage leading up to a clade and that sets members of that clade apart from other individuals. • Shared derived characters can be used to group organisms into clades. For example, amphibians, turtles, lizards, snakes, crocodiles, birds and mammals all have, or historically had, four limbs. Review So What Does This Mean?
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