Evolution 2 Evolution Speciation • The evolution of life is directly connected to the evolution of earth. • Evidence: – Fossils –Geology – Biogeography • Similarities in rock types • Glaciation • Fossil distributions Plate tectonics Plate tectonics Alfred Wegener (1880-1930) His theory was based on several 1915 – he suggested that 300 observations: mya all of the continents 1. The fit of the continents. formed a supercontinent that 2. Similarity of rock types across he called “Pangea”. Atlantic. 3. Glacial “tracks”. 4. Fossil distributions. Plate Tectonics Plate Tectonics Continental Margins 1 Plate Tectonics Plate Continental Margins Tectonics Near perfect fit when continents are joined by continental margins. South America Africa Plate Tectonics Plate Tectonics Glacial striations reveal ancient continental connections. Matching rock assemblages across the Atlantic Ocean. Plate Tectonics Plate Tectonics Glacial striations reveal ancient continental connections. Glacial Striations 2 Plate Tectonics Plate Tectonics Glacial Striations Glacial Striations Plate Tectonics Plate tectonics New evidence supporting Overlapping Fossil Wegener: assemblages 1. Sea floor spreading 2. Magnetic sea floor patterns 3. Sea floor age patterns Plate Tectonics Plate Tectonics Evidence of sea floor spreading The planet experience periodic reversals in the poles. Rock reflect direction of magnetism when they are created. Sea floor reveals a mirror image of rock magnetism. 3 Plate Tectonics Plate Tectonics Evidence of sea floor spreading Sea floor spreading The planet experience Age of seafloor N . A periodic reversals in the increases at m Europe a e n ri poles. equal rates i ca h India relative to C Rock reflect direction of oceanic rifts. Africa magnetism when they The oldest sea are created. floor is near the Sea floor reveals a continents. Australia mirror image of rock S. America magnetism. Evolution Evidence of Evolution Focus on how life changed after it began Evidence Fossils – buried remains and impressions of • Fossils – evidence of ancient life organisms that lived in the past • Biogeography – continental movement – stratified layers of sedimentary rock are a • Comparative Morphology – homologous historical record of life structures – the fossil record provides a uniformly good • Patterns of Development – similarities documentation of the life of the past • Comparative Biochemistry – cellular, – relative and absolute dating methods molecular • Current Observations – speciation, selection Evidence of Evolution Biogeography – involves continental movement – Theory of Continental Drift – Plate Tectonics – Distributions of fossils and descendants Dromaeosaurus Archaeopteryx 4 2 1 3 PTEROSAUR Homologous Evidence of Evolution 4 Bones 1 CHICKEN 2 Radius 3 Comparative Morphology – evidence of PENGUIN 2 descent with modification 3 1 Stem 2 3 – juvenile hoatzin and Archaeopteryx Reptile 4 1 5 PORPOISE – forelimbs 2 4 3 5 1 – vestigial structures 2 BAT – transitional forms 3 4 5 1 2 HUMAN 3 Figure 17.9 from 4 page 266 of your text 5 Homologous Structures Radius Vestigial Structures whale hind limbs Vestigial Structures – Indicate Relatedness Whale Evolution 5 Whale Evolution – Transitional Species Transition – Fish to Tetrapod Ambulocetus lived both on land and in water. It is believed that this is a linking species between modern whales and terrestrial whale ancestors. Latimeria menadoensis coelacanth Transition – Fish to Tetrapod Evidence of Evolution Patterns of Development – during some stages of development, organisms exhibit ancestral features in whole or incomplete form. – whale hind limb buds in the embryo – vertebrate embryo similarities Vertebrate Whale Embryo Hind Limb Bud Embryo Similarities Fish Salamander Chick Human 6 Cytochrome c Evidence of Evolution Comparisons Top row=yeast Comparative Biochemistry – at the Figure 17.14 from =identical sequences Middle row=wheat page 270 of your cellular and molecular level living things text =identical for 2 Bottom row=primate are remarkably similar to each other – plant and animal cells have mostly same organelles – cytochrome c similarities – nucleic acid hybridization Evidence of Evolution Artificial Selection Current Observations – speciation, selection Dogs – artificial selection (breeding) – natural selection – experiments – speciation Natural Selection Experimental Evidence Female guppies prefer to mate with brightly colored males. John Endler transplanted predators in a stream without predators and strong selection quickly Increasing Number of Predators of Number Increasing produced males with a duller coloration. 7 Species and Populations Biological Species Concept • The biological species concept defines a species as groups of actually, or potentially, interbreeding natural populations of organisms that are “Species are groups of interbreeding reproductively isolated from other such natural populations that are groups. reproductively isolated from other such groups.” •A population is defined as a unit of a species comprising those organisms that Ernst Mayr are actually interbreeding. Morphology & Species Variable Morphology • Morphological traits may not be useful in Grown in water Grown distinguishing species on land – Members of same species may appear different because of environmental conditions – Morphology can vary with age and sex – Different species can appear identical Arrangements of Populations Within Reproductive Isolation a Species • Allopatric populations: when the geographic • Cornerstone of the biological species ranges of 2 populations do not overlap we say concept. the populations are allopatric (geographic isolation). • Speciation is the attainment of • Parapatric populations: populations abut reproductive isolation. • Sympatric populations: populations overlap in • Reproductive isolation arises as a space by-product of genetic change. 8 Mechanisms of Reproductive Reproductive Isolating Isolation Mechanisms A. Pre–zygotic 1. Spatial isolation • Prezygotic isolation 2. Ecological isolation – Mating or zygote formation is prevented 3. Temporal isolation 4. Behavioral isolation 5. Mechanical isolation • Postzygotic isolation 6. Gametic isolation – Takes effect after hybrid zygotes form B. Post–zygotic – Zygotes may die early, be weak, or be sterile 1. Hybrid inviability 2. Hybrid sterility 3. Hybrid breakdown Hybrid Ecological Sterility: Isolation A Postzygotic Barrier Tiglon – a hybrid Liger – a hybrid Male Tiger X Female Lion 9 Speciation in Progress Ensatina eschscholtzii Ring Species in Gulls Can hybridize except for 2 species at endpoint of ring 4 Fates of a Lineage A Lineage 1. Populations can appear the same phenotypically over time. We call this stasis. Examples: crocodilians, beetles, horseshoe crabs. Lineage – a group of organisms related by 2. The populations may change over time, either due to natural selection or because of chance effects (e.g., descent from a common ancestor - A genetic drift or founder effects), but these changes are all temporal view. anagenetic effects. They don’t lead to any separation of one lineage from another. Examples: peppered moths over the last 100 years, horses. 3. When changes do lead to separation of a lineage from other lineages, we call these changes cladogenetic because new clades arise that are genetically separated from other lineages. When gene flow stops between two populations or two lineages, the lineages are reproductively isolated from one another. Example: mammals. 4. There is a fourth possible outcome for changes within populations – extinction. Example: dinosaurs. Stasis Stasis Leaf Beetles 30 Million Years Old from amber Recent crocodilians 10 4 Fates of a Lineage 1. Populations can appear the same phenotypically over Stasis time. We call this stasis. Examples: crocodilians, beetles, horseshoe crabs. Horseshoe 2. The populations may change over time, either due to Crabs natural selection or because of chance effects (e.g., genetic drift or founder effects), but these changes are all anagenetic effects. They don’t lead to any separation of one lineage from another. Examples: peppered moths over the last 100 years, horses. 3. When changes do lead to separation of a lineage from other lineages, we call these changes cladogenetic because new clades arise that are genetically separated from other lineages. When gene flow stops between two populations or two lineages, the lineages are reproductively isolated from one another. Example: mammals. 4. There is a fourth possible outcome for changes within populations – extinction. Example: dinosaurs. Anagenesis 4 Fates of a Lineage 1. Populations can appear the same phenotypically over time. We call this stasis. Examples: crocodilians, Form C beetles, horseshoe crabs. 2. The populations may change over time, either due to natural selection or because of chance effects (e.g., genetic drift or founder effects), but these changes are all anagenetic effects. They don’t lead to any separation of one lineage from another. Examples: peppered moths over the last 100 years, horses. Form B 3. When changes do lead to separation of a lineage from other lineages, we call these changes cladogenetic Time because new clades arise that are genetically separated from other lineages. When gene flow stops between two populations or two lineages, the lineages are reproductively isolated from one another. Example: mammals. 4. There is a fourth possible outcome for changes within Form A populations – extinction. Example: dinosaurs. Anagenesis Cladogenesis Cladogenesis 11 Patterns of Change