Adaptive Radiation and Phylogeny Past Paper PDF 2025

Unit 1: Evolution and Biodiversity What is Evolution? Phylogenetic Trees Evolution of Populations...

Unit 1: Evolution and Biodiversity What is Evolution? Phylogenetic Trees Evolution of Populations Origin of Species History of Life Biodiversity: Bacteria, Archaea, Protists, Fungi & Plants The Tree of Life/ The Phylogeny of Life Spring 2025 Adaptive Radiation & Phylogeny Ch. 25 & Ch 26 Synopsis for today Review sexual selection Review species hybridization zones Understand the history of life on Earth Understand phylogeny Ch.25: Big-picture patterns of the history of life [Concepts 25.3, 25.4 & 25.6] Ch. 26: You should focus on understanding how to read and interpret phylogenies.  Recap: Sexual Selection (nonrandom mating) Species A Species B 2 sympatric cichlid species from Lake Victoria (Currently experiencing loss of species, possibly due to water pollution and thus murkiness) Hypothesis: Females mate only with males of the same species, based on coloration 4  Sexual Selection (nonrandom mating) Lamp of orange light = Lamp of natural light = random mating Non-random mating Species A Species A Species B Species B Results: Supported the hypothesis that females identify and mate with their own species based on color. 5  Hybrid Zones Exist Between Separate Species Toad example: Ranges 4000-km long hybrid zone, but just 10 km wide Zone is along altitudinal gradient but toads can easily cross zone Species separation maintained because hybrid offspring have developmental defects & low survival Formation of a Hybrid Zone & Possible Outcomes Gene flow Population Barrier to gene flow Formation of a Hybrid Zone & Possible Outcomes Isolated population diverges. Gene flow Population Barrier to gene flow Formation of a Hybrid Zone & Possible Outcomes Isolated population Hybrid diverges. zone Gene flow Population Barrier to gene flow Hybrid individual Formation of a Hybrid Zone & Possible Outcomes Isolated Possible outcomes: population Hybrid diverges. zone Reinforcement – Hybrids eventually stop forming Fusion – Species Gene flow eventually fuse Population Barrier to gene flow Stability – Hybrids Hybrid continue to be individual produced  How Fast Does Speciation Occur? Darwin thought Gradualism was the reason: species arise because of a gradual accumulation of different traits. 11 Why Aren’t There More Intermediate Fossils? ? Taphonomy New species may have arisen allopatrically (different place) Rates of speciation aren’t always slow!  Punctuated Equilibrium Model Stephen J. Gould – theorized that species remain relatively constant over long periods of geologic time, then diverge in a rapid spurt, & change little thereafter. Geologic time Change in form 13 Scale of Geologic Time Think of the history of Earth as displayed on a clock. If you used a scale of one hour: - Animals 1st appeared 9 min ago - Humans 1st appeared < 0.2 sec ago 14 Important Events 3.5 Billion Years Ago: Oldest known fossils; prokaryotes 450 Million Years Ago: Colonization of land by plants and arthropods; first reptiles and amphibians 250 Million Years Ago: Age of reptiles; dinosaurs; first mammals 66 Million Years Ago: Explosive evolution of flowering plants, birds mammals You do NOT need to memorize these dates, but you should understand the relative ages of these major events. For example, reptiles predated mammals 15  Continental Drift Important role in evolution North America and Europe drift apart 2 cm each year Continental Drift Pangaea Formed 250+ mya Started breaking apart 180 mya Mass Extinctions 18  Mass Extinctions Permian extinction (252 million years ago) - 96% of marine animal species went extinct - Terrestrial animals also went extinct Cretaceous extinction (66 million years ago) - Dinosaurs (other than birds) went extinct - Many terrestrial plants and other animals went extinct - > 50% of marine species went extinct Causes of extinctions unclear: - Permian: enormous volcanic eruptions - Cretaceous: perhaps asteroid 19 Is a Sixth Mass Extinction Under Way? 20  After Mass Extinctions: Adaptive Radiation Mass extinctions are often followed by explosive increase in diversity Surviving organisms have new environmental opportunities An adaptive radiation (rapid speciation) of mammals after dinosaur extinctions Cretaceous extinction: 66 mya 21  What Else Can Lead to Adaptive Radiation? New environment – Example: Colonization of Hawaiian island chain by tarweed ancestor 5 mya 22 Over geologic time, evolution and speciation have generated a great diversity of living organisms 23 Biologists have identified and named close to 2 million species Approximately 10,000 new species are described every year! It is estimated that there are anywhere from 5-30 million species on Earth yet to be discovered. How do we keep track of all those species? Systematics: Study of the diversity of life 24  Taxonomy Name & Classification of Species Each species is placed into a hierarchical classification 25 Phylogeny Evolutionary history of a group of organisms Traced using fossil record and morphological and molecular homologies Can reveal common ancestry Evolutionary trends do not mean that evolution is goal directed 26 Do these Trees Convey the Same Information? 27 Primitive characteristics: traits present in ancestral group Derived characteristics: new traits unique to each lineage 28 If humans evolved from apes, then why are there still apes? Evolution did not (and does not) happen like this The pattern of evolution is tree-like! The pattern of evolution is tree-like! common ancestor The pattern of evolution is tree-like! X X X X common ancestor The pattern of evolution is tree-like! common ancestor Is a Mushroom More Closely Related to You or to a Flower? A B More recent common ancestor  Which evolutionary lineage is the oldest? past present Drosophila A Lancelet Zebrafish B Frog Chicken C Human Mouse D D All equally evolved!  Calibrated Branch Lengths can Represent Years Drosophila Lancelet Zebrafish Frog Chicken Human Mouse PALEOZOIC MESOZOIC CENOZOIC 542 251 65.5 Present Millions of years ago Use fossil dating to calibrate the nodes  Monophyletic, Paraphyletic & Polyphyletic Clade: Group of organisms containing the ancestral species and its descendants. Taxon is equivalent to Not all of the Usually results in the clade descendants are reclassifying the organisms. included Why? Because the most recent common ancestor is not included for all species. 38 Paraphyletic vs polyphyletic groups Streamlined shape in whales and Streamlined shape in penguins, dolphins: seals, and sharks: A. homologous A. homologous B. analagous B. analagous Streamlined shape in whales and Streamlined shape in penguins, dolphins: seals, and sharks: A. homologous A. homologous B. analagous B. analagous SUMMARY  Next: Diversity of Life -- Prokaryotes Bacteria on point of pin 43