Biodiversity and Evolution PDF

BIOL S103F ESSENTIAL BIOLOGY BIODIVERSITY AND EVOLUTION Week 10 2 A Sea Voyage Helped Darwin Frame his Theory of Evolution 3  Charles Darwin  On the Origin of Species by Means of Natural Selection  Commonly referred to as The Origin of Species HMS Beagle  A survey ship preparing for a long exped...

BIOL S103F ESSENTIAL BIOLOGY BIODIVERSITY AND EVOLUTION Week 10 2 A Sea Voyage Helped Darwin Frame his Theory of Evolution 3  Charles Darwin  On the Origin of Species by Means of Natural Selection  Commonly referred to as The Origin of Species HMS Beagle  A survey ship preparing for a long expedition to chart poorly known stretches of the South American coast  Collected thousands of HMS Beagle in port specimens of fossils and Darwin in 1840 Great Asia living plants and animals Britain Europe North America on shore ATLANTIC OCEAN Africa  Kept detailed journals PACIFIC South Equator Pinta Galápagos OCEAN Islands of his observations America Marchena Genovesa Andes  Santiago Equator Cape of Daphne Islands PACIFIC Good Hope Fernan- Pinzón Santa OCEAN dinaIsabelaSanta Fe Cape Horn San Cruz Cristobal Tierra del Fuego 0 40 km Florenza Española 0 40 miles PACIFIC OCEAN Australia Tasmania New Zealand Darwin’s Observations 4    Darwin was particularly intrigued by the geographic distribution of organisms on the Galápagos Islands, including  Marine iguanas  Giant tortoises Darwin hypothesized that as the descendants of a remote ancestor spread into various habitats over millions and millions of years, they accumulated diverse modifications (adaptations), that fit them to specific ways of life in their environment Darwin’s theory of evolution  Living species are descendants of ancestral species that were different from present-day ones  Natural selection is the mechanism for evolutionary change Fossils of Transitional Forms Support Darwin’s Theory of Evolution Key Pakicetus Rodhocetus 5    Dorudon In The Origin of Species, Darwin predicted the existence of fossils of transitional forms Living cetaceans linking very different groups of organisms  If whales is evolved from land-dwelling mammals, then fossils should show a series of changes in a lineage of mammals adapted to a fully aquatic habitat Many fossils link early extinct species with species living today  A series of fossils traces the gradual modification of jaws and teeth in the evolution of mammals from a reptilian ancestor  A series of fossils documents the evolution of whales from a group of land mammals Thousands of fossil discoveries have since shed light on the evolutionary origins of many groups of plants and animals  Transition of fish to amphibian  Origin of birds from a lineage of dinosaurs  Evolution of mammals from a reptilian ancestor Pelvis Femur Tibia Foot Homologies Provide Strong Evidence for Evolution 6    Evolution  Descent with modification  Characteristics present in an ancestral organism are altered over time by natural selection as its descendants face different environmental conditions  Remodeling process  Related species can have characteristics that have an underlying similarity yet function differently Homology  Similarity resulting from common ancestry Humerus Radius Ulna Carpals Homologous structures Metacarpals Phalanges Bat Human Whale Cat  Anatomical similarities in different organisms  Darwin cited the anatomical similarities among vertebrate forelimbs as evidence of common ancestry  The same skeletal elements make up the forelimbs of humans, cats, whales, & bats, but the functions of these forelimbs differ Homologies Indicate Patterns of Descent that can be Shown on an Evolutionary Tree 7  Each branch point represents the common ancestor of the lineages beginning there and to the right of it Lungfishes Amphibians 1 Amnion Amniotes Tetrapod limbs Mammals 2 Lizards and snakes 3 4 Crocodiles 5 Feathers Ostriches 6 Hawks and other birds Birds A hatch mark represents a homologous character shared by all the groups to the right of the mark Tetrapods Evolutionary tree  Patterns of descent  Branching sequence determined by homologous structures  Anatomical structure  Molecular structure Darwin Proposed Natural Selection as the Mechanism of Evolution 8   4 Observations 1. Members of a population of the same species vary in their traits 2. Traits can be inherited / passed from parents to offspring 3. Populations are capable of producing more offspring than the environment can support 4. Due to lack of food or other resources, many of these offspring do not survive 2 Inferences 1. Individuals whose inherited traits give them a higher chance of surviving and reproducing in their environment tend to leave more offspring than other individuals 2. This unequal ability of individuals to survive and reproduce / differential survival and reproduction, will lead to the accumulation of favourable traits in the population over many generations Scientists Can Observe Natural Selection in Action 9 Pesticide application Chromosome with allele conferring resistance to pesticide Survivors Additional applications of the same pesticide will be less effective, and the frequency of resistant insects in the population will grow 10 Natural Selection CANNOT Fashion Perfect Organisms 11    Natural selection is more of an editing process than a creative mechanism Natural selection is contingent on time and place, favoring those heritable traits in a varying population that fit the current, local environment The evolution of organisms is constrained  Natural selection CANNOT fashion perfect organisms 1. Selection can act only on existing variations  New, advantageous alleles do not arise on demand 2. Evolution is limited by historical constraints  Evolution co-opts existing structures and adapts them to new situations 3. Adaptations are often compromises  The same structure often performs many functions 4. Chance, natural selection, and the environment interact  Environments often change unpredictably Mutation & Sexual Reproduction Produce the Genetic Variation that Makes Evolution Possible 12     Organisms typically show individual variation In The Origin of Species, Darwin could not explain  Cause of variation among individuals  How variations were passed from parents to offspring Just a few years after the publication of The Origin of Species, Gregor Mendel wrote a groundbreaking paper on inheritance in pea plants Mutation - ultimate source of genetic variation (raw material for evolution)    Changes in the nucleotide sequence of DNA  ultimate source of new alleles A change as small as a single nucleotide in a protein-coding gene can have a significant effect on phenotype, e.g. sickle-cell disease On rare occasions, a mutated allele may improve the adaptation of an individual to its environment and enhance its reproductive success  More likely when the environment is changing such that mutations that were once disadvantageous are favorable under new conditions Evolution Occurs within Populations 13    Evolution impact of natural selection is only apparent in the changes in a population of organisms over time Population  A group of individuals of the same species, that live in the same area, & interbreed  Different populations of the same species may be geographically isolated from each other to such an extent that an exchange of genetic material never occurs, or occurs only rarely  e.g. isolated populations in different lakes Gene pool   Consists of all copies of every type of allele, at every locus, in all members of the population Microevolution  Change in the relative frequencies of alleles in a population over a number of generations  Evolution occurring on its smallest scale The Hardy-Weinberg Equation 14  The shuffling of alleles that accompanies sexual reproduction does not alter the genetic makeup of the population  No matter how many times alleles are segregated into different gametes, & united in different combinations by fertilization, the frequency of each allele in the gene pool will remain constant unless other factors are operating Assumptions in Hardy-Weinberg Equilibrium 15 1. A very large population 2. No gene flow between populations 3. No mutations 4. Random mating 5. No natural selection   Rarely are all 5 conditions met in real populations  allele & genotype frequencies often do change The Hardy-Weinberg equation can be used to test whether evolution is occurring in a population Natural Selection, Genetic Drift, & Gene Flow can Cause Microevolution 16   If the 5 conditions for the Hardy-Weinberg equilibrium are not met in a population  the allele frequencies may change However,  Mutations are rare & random, & have little effect on the gene pool  Nonrandom mating may change genotype frequencies but usually has little impact on allele frequencies 3 main causes of evolutionary change 1. Natural selection 2. Genetic drift 3. Gene flow 3 Main Causes of Evolutionary Change 17 1. 2. 3. Natural selection  If individuals differ in their survival & reproductive success  natural selection will alter allele frequencies Genetic drift  Chance events cause allele frequencies to fluctuate unpredictably from one generation to the next  The smaller the population, the more impact genetic drift is likely to have Gene flow  A population may gain / lose alleles when fertile individuals move into / out of a population, or when gametes (e.g. plant pollen) are transferred between populations  Tends to reduce differences between populations Genetic Drift 18  Bottleneck effect leads to a loss of genetic diversity when a population is greatly reduced  Catastrophes may kill large numbers of individuals, leaving a small surviving population that is unlikely to have the same genetic makeup as the original population  May continue for many generations until the population is again large enough for fluctuations due to chance to have less of an impact  Human activities (e.g. overhunting & habitat destruction) may create severe bottlenecks for other species Genetic Drift 19  Founder effect is produced when a few individuals colonize an island or other new habitat  The smaller the group, the less likely the genetic makeup of the colonists will represent the gene pool of the original larger population  Relatively high frequency of certain inherited disorders among some human populations established by small numbers of colonists Biologists Currently Recognize a 3-Domain System 20   2 domains of prokaryotes  Bacteria  Archaea 1 domain of eukaryotes  Eukarya  Fungi  Plantae  Animalia Plant Diversity 21 Invertebrate Diversity 22 Vertebrate Diversity 23