Processes of Evolution

Transcription

1 15 Processes of Evolution

2 How do biologists use evolutionary theory to develop better flu vaccines?

3 Evolution Is Both Factual and the Basis of Broader Theory In science, a theory is a well-substantiated, unifying explanation for a set of verified, proven hypotheses Evolutionary theory is the understanding and application of the processes of evolutionary change to biological problems. Applications: Study and treatment of diseases Development of crops and industrial processes Understanding the diversification of life

4 Evolution Is Both Factual and the Basis of Broader Theory Even before Darwin, biologists had suggested that species had changed over time, but no one had proposed a convincing mechanism for evolution.

5 Evolution Is Both Factual and the Basis of Broader Theory Charles Darwin was interested in geology and natural history.

6 Evolution Is Both Factual and the Basis of Broader Theory In 1831, Darwin began a 5-year voyage around the world on a Navy survey vessel, the HMS Beagle.

7 The Voyage of the Beagle

8 Evolution Is Both Factual and the Basis of Broader Theory From the observations and insights made on the voyage and new ideas from geologists on the age of the Earth, Darwin developed an explanatory theory for evolutionary change: Species change over time Divergent species share a common ancestor (descent with modification) The mechanism that produces change is natural selection

9 Concept 15.2 Mutation, Selection, Gene Flow, Genetic Drift, and Nonrandom Mating Result in Evolution Many of Darwin s observations of variation and selection came from domesticated plants and animals. Darwin bred pigeons and recognized similarities between selection by breeders and selection in nature. In both cases, selection simply increases the frequency of the favored trait from one generation to the next.

10 Evolution Is Both Factual and the Basis of Broader Theory By 1900, the fact of evolution was established, but the genetic basis of evolution was not yet understood. Then the work of Gregor Mendel was rediscovered, and during the 20 th century, work continued on the genetic basis of evolution. A modern synthesis of genetics and evolution took place

11 Evolution Is Both Factual and the Basis of Broader Theory The structure of DNA was established by 1953 by Watson and Crick. In the 1970s, technology developed for sequencing long stretches of DNA and amino acid sequences in proteins. Evolutionary biologists now study gene structure and evolutionary change using molecular techniques.

12 Evolution of Staph

13 Natural selection does not create new traits, but edits or selects for traits already present in the population The local environment determines which traits will be selected for or selected against in any specific population

14 Evidence supporting evolution Fossil record transition species Anatomical and Molecular Homology anatomy embryology & development molecular (DNA & protein) Vestigial Biogeography Artificial selection human-caused evolution

15 Fossil record Layers of sedimentary rock contain fossils new layers cover older ones, creating a record over time fossils within layers show that a succession of organisms have populated Earth throughout a long period of time

16 Tiktaalik missing link from sea to land animals

17 What are Homologous structures? Similar structure Similar development Different functions Evidence of close evolutionary relationship recent common ancestor

18 Anatomical record Homologous structures similarities in characteristics resulting from common ancestry

19 colored leaves Homologous structures in plants! spines leaves succulent leaves needles tendrils

20 Analogous structures Separate evolution of structures similar functions similar external form different internal structure & development different origin no evolutionary relationship Don t be fooled by their looks! Solving a similar problem with a similar solution

21 Analogous Structures are evidence for Convergent evolution Flight evolved in 3 separate animal groups evolved similar solution to similar problems analogous structures Does this mean they have a recent common ancestor?

22 Convergent evolution Fish: aquatic vertebrates Dolphins: aquatic mammals similar adaptations to life in the sea not closely related Those fins & tails & sleek bodies are analogous structures!

23 Parallel Evolution filling similar ecological roles in similar environments, so similar adaptations were selected but are not closely related marsupial mammals placental mammals

24 Comparative embryology Similar embryological development in closely related species all vertebrate embryos have similar structures at different stages of development gill pouch in fish, frog, snake, birds, human, etc.

25 Which one is the salamander, human, fish, cow, pig, rabbit, turtle, and chicken?

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27 Nucleotide substitutions Molecular record Comparing DNA & protein structure universal genetic code! DNA & RNA compare common genes cytochrome C (respiration) hemoglobin (gas exchange) Why compare these genes? Closely related species have sequences that are more similar than distantly related species DNA & proteins are a molecular record of evolutionary relationships Horse/ donkey Sheep/ goat Rabbit/ rodent Llama/ cow Pig/ cow Dog/ cow Human/ cow Horse/cow Human/kangaroo Human/rodent Goat/cow Millions of years ago

28 Comparative hemoglobin structure Human Macaque Dog Bird Frog Lamprey Why does comparing amino acid sequence measure evolutionary relationships? Number of amino acid differences between hemoglobin (146 aa) of vertebrate species and that of humans

29 Vestigial organs Modern animals may have structures that serve little or no function remnants of structures that were functional in ancestral species deleterious mutations accumulate in genes for noncritical structures without reducing fitness snakes & whales remains of pelvis & leg bones of walking ancestors eyes on blind cave fish human tail bone This is not LaMarck s loss from disuse!

30 Vestigial organs Hind leg bones on whale fossils Why would whales have pelvis & leg bones if they were always sea creatures?

31 Biogeography Biogeography- the geographic distribution of species Earth s continents were formerly united in a single large continent called Pangaea, but have since separated by continental drift An understanding of continent movement and modern distribution of species allows us to predict when and where different groups evolved

32 Artificial selection Artificial breeding can use variations in populations to create vastly different breeds & varieties descendants of wild mustard descendants of the wolf

33 Speciation and the Origin of Life

34 How and why do new species originate? Species are created by a series of evolutionary processes populations become isolated geographically isolated reproductively isolated isolated populations evolve independently Isolation allopatric geographic separation sympatric still live in same area

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

36 Geographic isolation Ammospermophilus spp Species occur in different areas physical barrier allopatric speciation other country Harris s antelope squirrel inhabits the canyon s south rim (L). Just a few miles away on the north rim (R) lives the closely related white-tailed antelope squirrel

37 Ecological isolation Species occur in same region, but occupy different habitats so rarely encounter each other reproductively isolated 2 species of garter snake, Thamnophis, occur in same area, but one lives in water & other is terrestrial lions & tigers could hybridize, but they live in different habitats: lions in grasslands tigers in rainforest

38 Temporal isolation Species that breed during different times of day, different seasons, or different years cannot mix gametes reproductive isolation sympatric speciation same country Eastern spotted skunk (L) & western spotted skunk (R) overlap in range but eastern mates in late winter & western mates in late summer

39 Behavioral isolation sympatric speciation? Unique behavioral patterns & rituals isolate species identifies members of species attract mates of same species courtship rituals, mating calls reproductive isolation Blue footed boobies mate only after a courtship display unique to their species

40 Mechanical isolation sympatric speciation? Morphological differences can prevent successful mating reproductive isolation Even in closely related species of plants, the flowers often have distinct appearances that attract different pollinators. These 2 species of monkey flower differ greatly in shape & color, therefore cross-pollination does not happen. Plants

41 Mechanical isolation For many insects, male & female sex organs of closely related species do not fit together, preventing sperm transfer Animals lack of fit between sexual organs: hard to imagine for us but a big issue for insects with different shaped genitals! I can t even imagine! Damsel fly penises

42 Gametic isolation sympatric speciation? Sperm of one species may not be able to fertilize eggs of another species mechanisms biochemical barrier so sperm cannot penetrate egg o receptor recognition: lock & key between egg & sperm chemical incompatibility o sperm cannot survive in female reproductive tract Sea urchins release sperm & eggs into surrounding waters where they fuse & form zygotes. Gametes of different species red & purple are unable to fuse.

43 POST-reproduction barriers Prevent hybrid offspring from developing into a viable, fertile adult reduced hybrid viability reduced hybrid fertility hybrid breakdown Liger: Mom was tiger Tigon: Mom was lion

44 Reduced hybrid viability sympatric speciation? Genes of different parent species may interact & impair the hybrid s development Species of salamander genus, Ensatina, may interbreed, but most hybrids do not complete development & those that do are frail.

45 Reduced hybrid fertility 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 Mules are vigorous, but sterile Horses have 64 chromosomes (32 pairs) Mules have 63 chromosomes! Donkeys have 62 chromosomes (31 pairs)

46 Hybrid breakdown sympatric speciation? Hybrids may be fertile & viable in first generation, but when they mate offspring are feeble or sterile In strains of cultivated rice, hybrids are vigorous but plants in next generation are small & sterile. On path to separate species.

47 Gradualism Gradual divergence over long spans of time assume that big changes occur as the accumulation of many small ones

48 Punctuated Equilibrium Rate of speciation is not constant rapid bursts of change long periods of little or no change species undergo rapid change when they 1 st bud from parent population Time

49 ARCHEAN Millions of years ago PRECAMBRIAN PROTEROZOIC Cenozoic Mesozoic Paleozoic Colonization of land by animals Appearance of animals and land plants First multicellular organisms Bacteria Archaebacteria Protista Plantae Fungi Animalia 1500 Oldest definite fossils of eukaryotes Appearance of oxygen in atmosphere Oldest definite fossils of prokaryotes Molten-hot surface of earth becomes cooler Formation of earth The evolutionary tree of life can be documented with evidence. The Origin of Life on Earth is another story

50 What is Life? First we have to define LIFE organized as cells respond to stimuli regulate internal processes homeostasis use energy to grow metabolism develop change & mature within lifetime reproduce heredity o DNA / RNA adaptation & evolution

51 Conditions on early Earth Reducing atmosphere water vapor (H 2 O), CO 2, N 2, NO x, H 2, NH 3, CH 4, H 2 S lots of available H & its electron no free oxygen Energy source lightning, UV radiation, volcanic What s missing from that atmosphere? low O 2 = organic molecules do not breakdown as quickly

52 Origin of Organic Molecules: Organic Soup Model Abiotic synthesis 1920 Oparin & Haldane propose reducing atmosphere hypothesis 1953 Miller & Urey test hypothesis formed organic compounds o amino acids o adenine Water vapor Mixture of gases ("primitive atmosphere") Heated water ("ocean") Electrodes discharge sparks (lightning simulation) CH 4 NH 3 H 2 Condenser Water Condensed liquid with complex, organic molecules

53 Origin of Genetics RNA is likely first genetic material multi-functional codes information self-replicating molecule makes inheritance possible natural selection & evolution enzyme functions ribozymes replication regulatory molecule transport molecule trna & mrna Dawn of natural selection

54 Prokaryotes Prokaryotes dominated life on Earth from bya 3.5 billion year old fossil of bacteria modern bacteria chains of one-celled cyanobacteria

55 Stromatolites Lynn Margulis Fossilized mats of prokaryotes resemble modern microbial colonies

56 Oxygen atmosphere Oxygen begins to accumulate 2.7 bya reducing oxidizing atmosphere evidence in banded iron in rocks = rusting makes aerobic respiration possible photosynthetic bacteria (blue-green algae)

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

58 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

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

60 Theory of Endosymbiosis 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 Lynn Margulis