PLANT EVOLUTION. Absence of evidence is not evidence of absence.

Transcription

1 LECTURE 13 : PLANT EVOLUTION Absence of evidence is not evidence of absence.

2 Early history of life Solar system~ 12 billion years ago (bya) Earth~ 4.5 bya Life~ 3.5 to 4.0 bya Prokaryotes~ 3.5 to 2.0 bya stromatolites Oxygen accumulation~ 2.7 bya photosynthetic cyanobacteria Eukaryotic life~ 2.1 bya Muticelluar eukaryotes~ 1.2 bya Animal diversity~ 543 mya Land colonization~ 500 mya

3 The Origin of Life Spontaneous generation vs. biogenesis (Pasteur) The 4-stage Origin of life Hypothesis: 1. Abiotic synthesis of organic monomers 2. Polymer formation 3. Origin of Self-replicating molecules 4. Molecule packaging ( protobionts )

4 Organic monomers/polymer synthesis Oparin (Rus.)/Haldane (G.B.) hypothesis (primitive earth): volcanic vapors (reducing atmosphere) with lightning & UV radiation enhances complex molecule formation (no O2) Miller/Urey experiment: water, hydrogen, methane, ammonia all 20 amino acids, nitrogen bases, & ATP formed Fox proteinoid formation (abiotic polypeptides) from organic monomers dripped on hot sand, clay or rock Oparin (coacervates) protobionts (aggregate macromolecules; abiotic) surrounded by a shell of H2O molecules coated by a protein membrane

5 Abiotic genetic replication First genetic material Abiotic production of ribonucleotides Ribozymes (RNA catalysts) RNA cooperation Formation of short polypeptides (replication enzyme?) RNA~ DNA template?

6 The Major Lineages of Life

7 EVOLUTION Descent with Modification: A Darwinian View of Life

8 What is Evolution? The kind we re talking about is sometimes called organic evolution to distinguish it from non-biological changes over time. Working definition: Evolution is the progressive change in organisms over time.

9 Evolution Evolution: the change over time of the genetic composition of populations Natural selection: populations of organisms can change over the generations if individuals having certain heritable traits leave more offspring than others (differential reproductive success) Evolutionary adaptations: a prevalence of inherited characteristics that enhance organisms survival and reproduction November 24, 1859

10 Darwin s Voyage of Discovery A reconstruction of the HMS Beagle sailing off Patagonia.

11 The Voyage of the Beagle

12 Darwin s Ideas Did Not Develop in a Vacuum Contributor s to Darwin s thinking included: 1. Charles Lyell uniformatarianism 2. Georges Cuvier species extinction. 3. Thomas Malthus struggle for existence 4. Jean Baptiste de Lamarck evolution by acquired characteristics. Alfred Russel Wallace Independently Drew the Same Conclusions as Darwin (1) (2) Papers from Wallace and Darwin were jointly presented (with little impact) to the Linnaean Society in (3) (4)

13 Darwin s Observations and Inferences Observation 1: Left unchecked, the number of organisms of each species will increase exponentially, generation to generation. Observation 2: In nature, populations tend to remain stable in size. Observation 3: Environmental resources are limited. Inference 1: Production of more individuals than can be supported by the environment leads to a struggle for existence among individuals, with only a fraction of offspring surviving in each generation.

14 Darwin s Observations and Inferences Observation 4: Individuals of a population vary extensively in their characteristics with no two individuals being exactly alike. Observation 5: Much of this variation between individuals is heritable.

15 Darwin s Observations and Inferences Inference 2: Survival in the struggle for existence is not random, but depends in part on the heritable characteristics of individuals. Individuals who inherit characteristics most fit for their environment are likely to leave more offspring than less fit individuals.

16 Darwin s Observations and Inferences Inference 3: The unequal ability of individuals to survive and reproduce leads to a gradual change in a population, with favorable characteristics accumulating over generations (natural selection). Taken together, these three inferences are a statement of Darwin s Theory of Evolution.

17 Evolutionary history Linnaeus: taxonomy Hutton: gradualism Lamarck: evolution Malthus: populations Cuvier: paleontology Lyell: uniformitarianism Darwin: evolution Mendel: inheritance Wallace: evolution

18 The Weak Link of Genetics and the Modern Synthesis A major problem in Darwin s theory was the lack of a mechanism to explain natural selection. How could favorable variations be transmitted to later generations? With the rediscovery of Mendel s work and its vast extension in the first half of the 20th century, the missing link in evolutionary theory was forged. Darwinian theory supported by genetics is known as the modern synthesis. Darwin in his early years.

19 TOPICS OF DISCUSSION Introduction Early history of life The Origin of Life Evolution A Darwinian View of Life Working definition Evolutionary history Darwin s Observations and Inferences Plant Evolution N

20 Discomfort With Evolution The upheaval surrounding evolution began with publication of On the Origin of Species and continues nearly 150 years later. An early disparaging view of evolutionary theory and its creator. 1925

21 Discomfort With Evolution Two of many arguments made against evolution are: - Evolution is only a theory. - No one s ever seen evolution. The first point is true, but misses the meaning of scientific theory, and the second point is easily countered.

22 Evidence for Evolution The Fossil Record

23 Evidence for Evolution - Comparative Morphology Why use the same skeletal plan for these very different appendages?

24 Evidence for Evolution - Comparative Embryology Why do embryos of different animals pass through a similar developmental stage? Recent discoveries of the conservation of molecular mechanisms of development are even more compelling.

25 Evidence of Evolution Conservation and Diversification at the Molecular Level Why should different organism possess related genes? Why does the degree of relationship of genes match their degree of relationship established by other methods?

26 Evidence for Evolution Evolution Observed Evolution of pesticide resistance in response to selection.

27 Evolutionary Time Scales Macroevolution: Long time scale events that create and eliminate species.

28 Evolutionary Time Scales Microevolution: Short time scale events (generation-to-generation) that change the genotypes and phenotypes of populations. We ll begin our more intensive look at evolution with microevolution.

29 Evolution evidence: Molecular Biology Similarities in DNA, proteins, genes, and gene products Common genetic code

30 Plant Evolution

31 Adaptations Cuticle Alternation of generations Specialized tissues Cuticle Waxy coating on surfaces resists drying out stomata exist to allow necessary gas exchange

32 Alternation of generations Plants live part of their life in a haploid stage and part in a diploid stage haploid portion is called the gametophyte generation because it produces the reproductive cells diploid portion called sporophyte generation because it produces spores

33 The gametophyte plant produces male and female sex organs (male and female gametangium) eggs are fertilized by sperm to form a zygote embryo development (seed) occurs within the female gametangium Specialized tissues Other than bryophytes all other plants have vascular tissues xylem - conducts water and minerals phloem - conducts food

34 Bryophytes Only nonvascular plants (mosses, liverworts) no ability to internally transport water and materials require moist environment live in colonies, has rhizoids to anchor it important in soil formation

35 Ferns Seedless, flowerless, vascular plants have xylem and phloem has alternation of generation, the common familiar leafy plant is the sporophyte generation has a rhizome and leaves

36 Ferns II Spore production occurs on places on the fronds, sporangia are formed in which meiosis occurs to form spores. Spores are often born in clusters called sori spores are released and if they germinate will grow into the gametophytes method of fertilization is primitive like bryophytes

37 Ferns Whisk ferns - extinct, no roots, no leaves but did have vascular system above and below ground! Horsetails - roots, rhizomes and vertical Horsetails - roots, rhizomes and vertical stems

38 Heterospory Homospory - one type of spore produced by bryophytes and many ferns Heterospory - some ferns have two types of spores produced microspores (male gametophytes) and macrospores (female gametophytes) the development of heterospory leads two the two most successful kinds of plants

39 Gymnosperms Vascular, seed bearing, flowerless plants means naked seed largest division is conifers - woody cone bearing gymnosperms leaves are called needles most have male and female parts on same plant. Reproductive parts in cone.

40 Gymnosperm reproduction Microspores and macrospores formed in separate cones Male cones smaller than female, on lower branches meiosis in male cone produces a male gametophyte, also called a pollen grain carried by air current to female gametophyte

41 Angiosperms Flowering, vascular plants most successful plants fertilization in flowering plants called double fertilization 2 sperm involved - 1 fertilizes the egg, the other fuses with 2 cells in female gametophyte to form endosperm

42 2 classes of Angiosperms Monocots - mostly herbaceous, long, narrow leaves, parallel veination, flower parts occur in threes, single cotyledon (embryonic leaf), endosperm present in seed vascular bundles scattered

43 2 classes of Angiosperms Dicotyledons - herbaceous or woody, leaves variable in shape, netted veination, flower parts occur in 4 and 5, 2 cotyledons, endosperm usually absent in mature seed vascular bundles arranged in a circle

44 Absence of evidence is not evidence of absence. Final words...