What does natural selection mean? Ch. 23 review What does natural selection mean? Offspring w/in a varied population, whose characteristics best adapt them to the environment are most likely to survive and reproduce more fit individuals produce more offspring than less fit individuals How and why? Over production of offspring Limited natural resources Heritable variations Differential or unequal reproductive success

Ch. 24 -- What is a species? …and, Speciation? Species - Population (or group of populations) whose members can interbreed and produce fertile offspring Identified species are named & classified = Taxonomy binomial scientific name: Homo sapiens Genus - species Macroevolution: origin of new species; increases diversity How does this happen? What is required?

Gene flow of alleles between populations of a particular species What would happen if gene flow was blocked? Variation continues, but within isolated populations leads to divergence 20 light 10 dark 20 light 20 dark

Barriers that lead to speciation Reproductive barriers can prevent interbreeding of closely related populations Prezygotic = prevents fertilization Postzygotic = prevents development Fig. 24.3

Barriers that lead to speciation Reproductive barriers can prevent interbreeding of closely related populations Prezygotic = prevents fertilization Postzygotic = prevents development Spilogale gracilis Spilogale putorius Temporal isolation: difference of time, (day/night, seasons, etc) e.g. western skunks in fall; eastern skunks in late winter e.g. purple sea urchins (late fall to early spring) vs. white sea urchins (late spring to early fall) Stronglyocentrotus purpuratus Lytichinus pictus

Habitat isolation Behavioral isolation Living in different places (habitats) w/in general geographic region e.g. herbivorous insects feeding on two different host plants Behavioral isolation Different unique mating rituals to attract mates of same species e.g. many birds have courtship rituals before mating can commence

Mechanical isolation Gametic isolation Incompatible female and male sex organs aka “square peg into a round hole” problem e.g. flower parts of one species differs from another; pollinator only passes to one Gametic isolation Fertilization success depends on molecular recognition of cell membranes (gametes) e.g. open (broadcast) spawning of aquatic species e.g. windblown pollen of plants

Postzygotic reproductive barriers in the absence of pre-zygotic isolation barriers… Hybrid zygotes = fertilization of two spp. Natural blocks to continued hybridization? Zygotic mortality Hybrid inviability: death in early devpmnt Hybrid sterility: mature individuals, but sterile female horse x male donkey = sterile mule Camel x llama = Cama Lion x tiger = Liger Horse x zebra = zebroid or zorse

Geographic Barriers Allopatric speciation (allos = other, patra = fatherland) Mountain range emerged Large lake subsides and splinters into many smaller bodies of water Baja peninsula and Isthmus of Panama separates marine life on each side Grand canyon separated by Col. River

Ch 25: History of life …as we understand it Conditions on early Earth made the origin of life possible Chemical and physical processes on early Earth may have produced very simple cells through a sequence of stages: Abiotic synthesis of small organic molecules Joining of these small molecules into macromolecules Packaging of molecules into protocells Membraneous packets of chemicals

Synthesis of Organic Compounds… Earth formed about 4.6 billion years ago, along with the rest of the solar system Bombardment of Earth by rocks and ice likely vaporized water and prevented seas from forming before 4.2 to 3.9 billion years ago Earth’s early atmosphere likely contained water vapor and chemicals released by volcanic eruptions (nitrogen, nitrogen oxides, carbon dioxide, methane, ammonia, hydrogen, hydrogen sulfide)

Are the key building blocks of life hard to come by? Amino acids have been found in meteorites RNA monomers have been produced “spontaneously” from simple molecules In water, lipids and other organic molecules can “spontaneously” form vesicles with a lipid bilayer Adding clay can increase the rate of vesicle formation Vesicles exhibit simple reproduction and metabolism and maintain an internal chemical environment Resultprotocells

The fossil record documents this history of life in geologic time Dimetrodon Stromatolites Fossilized stromatolite Coccosteus cuspidatus 4.5 cm 0.5 m 2.5 cm Present Rhomaleosaurus victor Tiktaalik Hallucigenia Dickinsonia costata Tappania 1 cm 1 m 100 mya 175 200 300 375 400 500 525 565 600 1,500 3,500 270 Stromatolites – mineralized organics or prokaryotic cells layered (strata) from aquatic environment Figure 25.4

How Rocks and Fossils Are Dated Sedimentary strata reveal the relative ages of fossils The absolute ages of fossils can be determined by radiometric dating A “parent” isotope decays to a “daughter” isotope at a constant rate Each isotope has a known half-life, the time required for half the parent isotope to decay Refer to: Keeping Time handout (see under Ch.25 ppt)

Limitations of Carbon dating Radiocarbon dating can be used to date fossils up to 75,000 years old For older fossils, other isotopes can be used to date sedimentary rock layers above and below the fossil

Geologic record is divided into the Archaean, the Proterozoic, and the Phanerozoic eons The Phanerozoic encompasses multicellular eukaryotic life and is divided into three eras: Paleozoic, Mesozoic, and Cenozoic The Cambrian explosion refers to the sudden appearance of a multitude of modern body designs (530 million years ago) first evidence of predator-prey interactions

Appearance of selected animal groups in the fossil record Sponges Cnidarians Echinoderms Chordates Brachiopods Annelids Molluscs Arthropods Ediacaran Cambrian PROTEROZOIC PALEOZOIC Time (millions of years ago) 635 605 575 545 515 485 And, the colonization of land… Fungi, plants, and animals began to colonize land about 500 million years ago Vascular tissue in plants transports materials internally and appeared by about 420 million years ago Plants and fungi today form mutually beneficial associations and likely colonized land together Arthropods and tetrapods are the most widespread and diverse land animals Tetrapods evolved from lobe-finned fishes around 365 million years ago Figure 25.10

The fossil record shows that most species that have ever lived are now extinct… Further reading: the last parts of Ch 25 that includes Mass extinctions

Ch 26: Phylogeny and Systematics What is meant by phylogeny? Evolutionary history of a species… Based on common ancestry Supported by shared characteristics and genetics Documented by fossils and genetics Eon > Era > Periods > Epochs

Systematics? = study of the organismal diversity of life How do we make sense of all this diversity? Organize it… using fossil, molecular, and genetic data to infer evolutionary relationships Taxonomy & classification * visually clear diagram, yet oversimplified

Phylogenies show evolutionary relationships --Diversity of Life Taxonomy is the ordered division and naming of organisms Domain Kingdom Phylum Class Order Family Genus Species Each group is nested within the level above Broad or less specific More specific

Closely related species belong to the same genus, similar genera are included in a family, etc… Species that share the same structures, behaviors, etc, can interbreed and produce fertile offspring.

Grouped by shared characters (Evolutionary relationships) Systematists depict evolutionary relationships in branching phylogenetic trees Grouped by shared characters (Evolutionary relationships) Embryology Reproduction strategies Symmetry (body plan) Morphology Feeding mode Interspecific interactions (e.g. symbiosis) Etc…

where lineages diverge A phylogenetic tree represents a hypothesis about evolutionary relationships Each branch point represents the divergence of two species Sister taxa are groups that share an immediate common ancestor Branch point: where lineages diverge ANCESTRAL LINEAGE This branch point represents the common ancestor of taxa A–G. This branch point forms a polytomy: an unresolved pattern of divergence. Sister taxa Basal taxon Taxon A Taxon B Taxon C Taxon D Taxon E Taxon F Taxon G

Cladistics groups organisms by common descent A clade is a group of species that includes an ancestral species and all its descendants Terminal taxon share the most recent common ancestor at the branch node Which node occurs earliest in time? Of the cladograms shown below, which one shows a different evolutionary history from the others? B and C are sharing the most recent common ancestor, whereas in the others, C shares its most recent common ancestor with D

Try to create a cladogram from the given character table? Figure 26.11 Try to create a cladogram from the given character table? TAXA Lancelet (outgroup) (outgroup) Lancelet Lamprey Lamprey Leopard Bass Frog Turtle Lancelet Lamprey Bass Frog Turtle Leopard Backbone Hinged Jaws Tetropod Amnion Hair Vertebral column (backbone) 1 1 1 1 1 Bass Vertebral column Hinged jaws 1 1 1 1 Frog Hinged jaws Four walking legs CHARACTERS 1 1 1 Turtle Four walking legs Amnion 1 1 Figure 26.11 Constructing a phylogenetic tree. Amnion Hair 1 Leopard Hair (a) Character table (b) Phylogenetic tree Phylum Chordata

How has taxonomy evolved? It depends on the types and amount of data Historical 5 Kingdom system… until about 1970

3 domains, many kingdoms