Evolution Evidence and Speciation

Evidence for Evolution Fossils Preserved remains of living things Paleontology is the study of the fossil record Most organisms do not leave a fossil after death Explains the “missing links” Sedimentation Fossils As the organism decomposes the spaces will be filled with the minerals from the silt

How old is that fossil? Relative Dating Absolute Dating Age of fossils based according to their location in strata Absolute Dating Age of fossils determined by analyzing the content of radioactive isotopes found in the fossil. Half-life: The length of time required for half of the radioactive elements to change into another stable element. Unaffected by temperature, light, pressure, etc. All radioactive isotopes have a dependable half life. Ex: C14 decays into N14

Relative Dating

How radioactive “naturally occurring” elements get inside an organism: Absolute Dating How radioactive “naturally occurring” elements get inside an organism: A.K.A – Radiometric dating

Evidence for Evolution 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

Evidence for Evolution Ontogenetic Homology The human embryo has gills, a post-anal tail, webbing between the toes & fingers, & spends its entire time floating and developing in amniotic fluid has similar salt concentration as ocean water

Figure 22.15 Pharyngeal pouches Post-anal tail Chick embryo Human embryo

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

Some similar mammals that have adapted to similar environments Have evolved independently from different ancestors Sugar glider AUSTRALIA NORTH AMERICA Flying squirrel

Evidence for Evolution Molecular Homology

Evidence for Evolution                                                                                                                                                                            

Evidence for Evolution

Evidence for Evolution Vestigial Structures Have marginal, if any use to the organisms in which they occur. EXAMPLES: femurs in pythonid snakes and pelvis in cetaceans (whales) appendix in humans coccyx in great apes

Vestigial organs These are remnants of structures that were functional in ancestral species Why would whales have pelvis & leg bones if they were always sea creatures? Remains of ancestral structures = mutations can occur without affecting survival & reproduction Evolutionary relationship snakes & whales — remains of pelvis & leg bones of walking ancestors eyes on blind cave fish human tail bone

Evolution evidence at the cellular level Domains: Archaea, Bacteria and Eukarya Elements conserved through all: DNA, RNA and many metabolic pathways. Eukaryotes – core features: Cytoskeleton Nucleus Membrane-bound organelles Linear chromosomes Endomembrane system

There’s something you need to know… The Origin of Species Mom, Dad… There’s something you need to know… I’m a MAMMAL! 2010-2011

Reproductively compatible So…what is a species? Population whose members can interbreed & produce viable, fertile offspring Reproductively compatible Distinct species: songs & behaviors are different enough to prevent interbreeding Humans re so diverse but considered one species, whereas these Meadowlarks look so similar but are considered different species. Meadowlarks Similar body & colorations, but are distinct biological species because their songs & other behaviors are different enough to prevent interbreeding Eastern Meadowlark Western Meadowlark 24

Correlation of speciation to food sources Seed eaters Flower eaters Insect eaters Rapid speciation: new species filling niches, because they inherited successful adaptations. Adaptive radiation

How do new species originate? When two populations become reproductively isolated from each other. Speciation Modes: allopatric geographic separation “other country” sympatric still live in same area “same country”

Allopatric Speciation Physical/geographical separation of two populations Allele frequencies diverge After a length of time the two population are so different that they are considered different species If the barrier is removed interbreeding will still not occur due to pre/post zygotic isolation

Sympatric Speciation Formation of a new species without geographic isolation. Causes: Pre-zygotic barriers exist to mating Polyploidy (only organism with an even number of chromosomes are fertile…speciation occurs quickly) Hybridization: two different forms of a species mate in common ground (hybrid zone) and produce offspring with greater genetic diversity than the parents….eventually the hybrid diverges from both sets of parents

Sympatric Speciation Gene flow has been reduced between flies that feed on different food varieties, even though they both live in the same geographic area.

Pre-zygotic Isolation Sperm never gets a chance to meet egg Geographic isolation: barriers prevent mating Ecological isolation: different habitats in same region Temporal isolation: different populations are fertile at different times Behavior Isolation: they don’t recognize each other or the mating rituals Mechanical isolation: morphological differences Gamete Isolation: Sperm and egg do not recognize each other Sea urchins release sperm & eggs into surrounding waters where they fuse & form zygotes. Gametes of different species— red & purple —are unable to fuse.

PRE-Zygotic barriers Obstacle to mating or to fertilization if mating occurs geographic isolation ecological isolation temporal isolation behavioral isolation mechanical isolation gametic isolation

Post Zygotic Isolation Hybrid Inviability – the embryo cannot develop inside the mothers womb Hybrid Sterility – Adult individuals can be produced BUT they are not fertile Hybrid Breakdown – each successive generation has less fertility than the parental generation Species of salamander genus, Ensatina, may interbreed, but most hybrids do not complete development & those that do are frail. Even if hybrids are vigorous they may be sterile; chromosomes of parents may differ in number or structure & meiosis in hybrids may fail to produce normal gametes Horse(64) x donkey(62) = mule (63 chromosomes) In strains of cultivated rice, hybrids are vigorous but plants in next generation are small & sterile. On path to separate species.

Patterns of Evolution Divergent Evolution (adaptive radiation) Convergent Evolution Two or more species that share a common environment but not a common ancestor evolve to be similar Is it a shark or a dolphin??

Coevolution Two or more species reciprocally affect each other’s evolution predator-prey disease & host competitive species mutualism pollinators & flowers

Evolutionary Time Scale Microevolution – changing of allele frequencies in a population over time. Macroevolution – patterns of change over geologic time. Determines phylogeny Gradualism – species are always slowly evolving Punctuated equilibrium – periods of massive evolution followed by periods with little to no evolution

Rate of Evolution Gradual evolution Punctuated evolution

Mass Extinctions At least 5 mass extinctions have occurred throughout history. Possible causes: dramatic climate changes occurring after meteorite collisions and/or continents drift into new and different configurations.

What must Earth have been like before living things took over? Origin of the Earth What must Earth have been like before living things took over?

The Primitive Earth Atmosphere: All chemicals/compounds necessary are thought to have originated on earth Inorganic precursors: Water vapor Nitrogen Carbon dioxide Small amounts of hydrogen and carbon monoxide These were the monomers for forming more complex molecules. Experiments have shown that it is possible to form organic from inorganic.

Origin of Organic Molecules Water vapor Condensed liquid with complex, organic molecules Condenser Mixture of gases ("primitive atmosphere") Heated water ("ocean") Electrodes discharge sparks (lightning simulation) Water Abiotic synthesis 1920 - Oparin first molecules formed by strong energy sources 1953 - Miller & Urey test hypothesis formed organic compounds amino acids adenine CH4 H2 NH3 Attempted to prove that chemical evolution could occur The experiment Used water, methane, ammonia, hydrogen sealed inside a glass container Water was heated to produce steam and sparks were generated from electrodes Water was then cooled and allowed to condense\ Experiment went on in this cycle for 1 week Results 15% of carbon was now present in the form of organic materials 13 out of 20 amino acids were present High concentrations of the base Adenine were also detected

Key Events in Origin of Life Origin of Cells (Protobionts) lipid bubbles  separate inside from outside  metabolism & reproduction Origin of Genetics RNA is likely first genetic material multiple functions: encodes information (self-replicating), enzyme, regulatory molecule, transport molecule (tRNA, mRNA) makes inheritance possible makes natural selection & evolution possible Origin of Eukaryotes endosymbiosis Life is defined partly by two properties: accurate replication and metabolism. Neither property can exist without the other. Self–replicating molecules and a metabolism–like source of the building blocks must have appeared together. How did that happen? The necessary conditions for life may have been met by protobionts, aggregates of abiotically produced molecules surrounded by a membrane or membrane–like structure. Protobionts exhibit some of the properties associated with life, including simple reproduction and metabolism, as well as the maintenance of an internal chemical environment different from that of their surroundings. Laboratory experiments demonstrate that protobionts could have formed spontaneously from abiotically produced organic compounds. For example, small membrane–bounded droplets called liposomes can form when lipids or other organic molecules are added to water.

Timeline Key events in evolutionary history of life on Earth 3.5–4.0 bya: life originated 2.7 bya: free O2 = photosynthetic bacteria 2 bya: first eukaryotes

Prokaryotic ancestor of eukaryotic cells First Eukaryotes ~2 bya Development of internal membranes create internal micro-environments advantage: specialization = increase efficiency natural selection! nuclear envelope endoplasmic reticulum (ER) plasma membrane infolding of the plasma membrane nucleus DNA cell wall plasma membrane Prokaryotic cell Prokaryotic ancestor of eukaryotic cells Eukaryotic cell

internal membrane system 1st Endosymbiosis Evolution of eukaryotes origin of mitochondria engulfed aerobic bacteria, but did not digest them mutually beneficial relationship natural selection! internal membrane system aerobic bacterium mitochondrion Endosymbiosis Ancestral eukaryotic cell Eukaryotic cell with mitochondrion

photosynthetic bacterium chloroplast & mitochondrion 2nd Endosymbiosis Eukaryotic cell with mitochondrion Evolution of eukaryotes origin of chloroplasts engulfed photosynthetic bacteria, but did not digest them mutually beneficial relationship natural selection! photosynthetic bacterium chloroplast mitochondrion Endosymbiosis Eukaryotic cell with chloroplast & mitochondrion

Theory of Endosymbiosis Lynn Margulis Evidence structural mitochondria & chloroplasts resemble bacterial structure genetic mitochondria & chloroplasts have their own circular DNA, like bacteria functional mitochondria & chloroplasts move freely within the cell mitochondria & chloroplasts reproduce independently from the cell

Cambrian explosion Diversification of Animals within 10–20 million years most of the major phyla of animals appear in fossil record 543 mya