Evolution and Plant Diversity

EVOLUTION AND DIVERSITY OF LIFE OBJECTIVES 1. Explain the different evolutionary concepts associated in the evolution of life on Earth. 2. Enumerate the different phyla in the animal and plant kingdom 3. Discuss how humans evolved over time...

EVOLUTION AND DIVERSITY OF LIFE OBJECTIVES 1. Explain the different evolutionary concepts associated in the evolution of life on Earth. 2. Enumerate the different phyla in the animal and plant kingdom 3. Discuss how humans evolved over time 2 EVOLUTION A new era of biology began in 1859 when Charles Darwin published The Origin of Species which focused biologists’ attention on the great diversity of organisms. Darwin noted that current species are descendants of ancestral species. Evolution can be defined by Darwin’s phrase: descent with modification. Evolution can be viewed as both a pattern and a process. 3 THEORY OF USE AND DISUSE Lamarck hypothesized that species evolve through use and disuse of body parts and the inheritance of acquired characteristics. During his travels on the Beagle, Darwin collected specimens of South American plants and animals. He observed adaptations of plants and animals that inhabited many diverse environments. 4 SPECIATION OF GALAPAGOS FLINCHES Darwin’s interest in geographic distribution of species was kindled by a stop at the Galápagos Islands near the equator west of South America. Darwin perceived adaptation to the environment and the origin of new species as closely related processes. Recent biologists have concluded that speciation is indeed what happened to the Galápagos finches. 5 SPECIATION OF GALAPAGOS FLINCHES 6 ORIGIN OF SPECIES Darwin developed two main ideas: Descent with modification explains life’s unity and diversity. Natural selection is a cause of adaptive evolution. 7 ARTIFICIAL SELECTION Darwin noted that humans have modified other species by selecting and breeding individuals with desired traits, a process called artificial selection. Darwin then described four observations of nature and from these drew two inferences. 1. Members of a population often vary greatly in their traits 2. Traits are inherited from parents to offspring 3. All species are capable of producing more offspring than the environment can support 4. Overproduction leads to competition for food or other resources The individuals best adapted to their environment will survive and reproduce 8 SURVIVAL OF THE FITTEST Survival of the Fittest: Individuals with certain heritable adaptive characteristics survive and reproduce at a higher rate than other individuals. Natural selection increases the adaptation of organisms to their environment over time. Speciation: If an environment changes over time, natural selection may result in adaptation to these new conditions and may give rise to new species. 9 HOMOLOGY Homology is similarity resulting from common ancestry. Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor. 10 HOMOLOGY Homology is similarity resulting from common ancestry. Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor. 11 HOMOLOGY Vestigial structures are remnants of features that served important functions in the organism’s ancestors. Examples of homologies at the molecular level are genes shared among organisms inherited from a common ancestor. 12 EVOLUTIONARY TREE The Darwinian concept of an evolutionary tree of life can explain homologies. Evolutionary trees are hypotheses about the relationships among different groups. Evolutionary trees can be made using different types of data, for example, anatomical and DNA sequence data. 13 CONVERGENT EVOLUTION Convergent evolution is the evolution of similar, or analogous, features in distantly related groups. Analogous traits arise when groups independently adapt to similar environments in similar ways. 14 MICROEVOLUTION VS. MACROEVOLUTION Speciation, the origin of new species, is at the focal point of Darwin’s evolutionary theory. Evolutionary theory must explain how new species originate and how populations evolve. Microevolution consists of adaptations that evolve within a population, confined to one gene pool. Macroevolution refers to evolutionary change above the species level. 15 BIOLOGICAL SPECIES CONCEPT Biologists compare morphology, physiology, biochemistry, and DNA sequences when grouping organisms. The biological species concept states that a species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; they do not breed successfully with other populations. 16 REPRODUCTIVE ISOLATION Reproductive isolation is the existence of biological factors (barriers) that impede two different species from producing viable, fertile offspring. Hybrids are the offspring of crosses between different species. Reproductive isolation can be classified by whether factors act before or after fertilization. 17 PREZYGOTIC BARRIERS Prezygotic barriers block fertilization from occurring by: Impeding different species from attempting to mate. Preventing the successful completion of mating. Hindering fertilization if mating is successful. Prezygotic barriers maintain reproductive isolation and include: Temporal, Habitat, Behavioral, Mechanical, and Gamete Isolation. 18 PREZYGOTIC BARRIERS Habitat isolation: Two species encounter each other rarely, or not at all, because they occupy different habitats, even though not isolated by physical barriers. Temporal Isolation: Species that breed at different times of the day, different seasons, or different years cannot mix their gametes. 19 PREZYGOTIC BARRIERS Behavioral isolation: Courtship rituals and other behaviors unique to a species are effective barriers. Mechanical isolation: Morphological differences can prevent successful mating. Gametic isolation: Sperm of one species may not be able to fertilize eggs of another species. 20 POSTZYGOTIC BARRIERS Postzygotic barriers prevent the hybrid zygote from developing into a viable, fertile adult: Reduced hybrid viability -- weak offspring Reduced hybrid fertility -- sterile offspring Hybrid breakdown. 21 OTHER DEFINITION OF SPECIES The morphological species concept defines a species by structural features. The ecological species concept views a species in terms of its ecological niche. The phylogenetic species concept: defines a species as the smallest group of individuals on a phylogenetic tree. 22 MECHANISM OF SPECIATION Speciation can occur in two ways: Allopatric speciation: geographic barrier separates populations. Sympatric speciation: no geographic barrier 23 HISTORY OF LIFE ON EARTH Past organisms were very different from those now alive. The fossil record shows macroevolutionary changes over large time scales including: The emergence of terrestrial vertebrates The origin of photosynthesis Long-term impacts of mass extinctions. 24 ORIGIN OF LIFE Chemical and physical processes on early Earth may have produced very simple cells through a sequence of stages: 1. Abiotic synthesis of small organic molecules. 2. Joining of these small molecules into macromolecules. 3. Packaging of molecules into “protobionts.” 4. Origin of self-replicating molecules. 25 ORIGIN OF LIFE Earth formed about 4.6 billion years ago, along with the rest of the solar system. A. I. Oparin and J. B. S. Haldane hypothesized that the early atmosphere was a reducing environment. Stanley Miller and Harold Urey conducted lab experiments that showed that the abiotic synthesis of organic molecules in a reducing atmosphere is possible. 26 PROTOBIONTS Small organic molecules polymerize when they are concentrated on hot sand, clay, or rock. Replication and metabolism are key properties of life. Protobionts are aggregates of abiotically produced molecules surrounded by a membrane or membrane-like structure. Protobionts exhibit simple reproduction and metabolism and maintain an internal chemical environment. 27 RIBOZYMES The first genetic material was probably RNA, not DNA. RNA molecules called ribozymes have been found to catalyze many different reactions For example, ribozymes can make complementary copies of short stretches of their own sequence or other short pieces of RNA. 28 RADIOMETRIC DATING 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. 29 GEOLOGIC RECORD The geologic record is divided into the Archaean, the Proterozoic, and the Phanerozoic eons. The Phanerozoic encompasses multicellular eukaryotic life. The Phanerozoic is divided into three eras: the Paleozoic, Mesozoic, and Cenozoic. Major boundaries between geological divisions correspond to extinction events in the fossil record. 30 STROMATOLITES The oldest known fossils are stromatolites, rock-like structures composed of many layers of bacteria and sediment. Stromatolites date back 3.5 billion years ago Prokaryotes were Earth’s sole inhabitants from 3.5 to about 2.1 billion years ago. 31 ENDOSYMBIONT THEORY The oldest fossils of eukaryotic cells date back 2.1 billion years. The hypothesis of endosymbiosis proposes that mitochondria and plastids (chloroplasts and related organelles) were formerly small prokaryotes living within larger host cells An endosymbiont is a cell that lives within a host cell. 32 CAMBRIAN EXPLOSION The “snowball Earth” hypothesis suggests that periods of extreme glaciation confined life to the equatorial region or deep-sea vents from 750 to 580 million years ago. The Cambrian explosion refers to the sudden appearance of fossils resembling modern phyla in the Cambrian period (535 to 525 million years ago). The Cambrian explosion provides the first evidence of predator-prey interactions. Fossils in China provide evidence of modern animal phyla tens of millions of years before the Cambrian explosion. 33 COLONIZATION OF LAND Fungi, plants, and animals began to colonize land about 500 million years ago. Plants and fungi likely colonized land together by 420 million years ago. Arthropods and tetrapods are the most widespread and diverse land animals. Tetrapods evolved from lobe-finned fishes around 365 million years ago. 34 CONTINENTAL DRIFT THEORY At three points in time, the land masses of Earth have formed a supercontinent: 1.1 billion, 600 million, and 250 million years ago. Earth’s continents move slowly over the underlying hot mantle through the process of continental drift. Formation of the supercontinent Pangaea about 250 million years ago had many effects 35 MASS EXTINCTION At times, the rate of extinction has increased dramatically and caused a mass extinction. In each of the five mass extinction events, more than 50% of Earth’s species became extinct. 36 MASS EXTINCTION The Permian extinction defines the boundary between the Paleozoic and Mesozoic eras. This mass extinction caused the extinction of about 96% of marine animal species and might have been caused by volcanism, which lead to global warming, and a decrease in oceanic oxygen. The Cretaceous mass extinction 65.5 million years ago separates the Mesozoic from the Cenozoic. Organisms that went extinct include about half of all marine species and many terrestrial plants and animals, including most dinosaurs. 37 MASSIVE METEORITE IMPACT EVIDENCE The presence of iridium in sedimentary rocks suggests a meteorite impact about 65 million years ago. The Chicxulub crater off the coast of Mexico is evidence of a meteorite that dates to the same time. 38 DIVERSITY OF LIFE TAXONOMY Phylogeny is the evolutionary history of a species or group of related species. The discipline of systematics classifies organisms and determines their evolutionary relationships. Systematists use fossil, molecular, and genetic data to infer evolutionary relationships. Taxonomy is the ordered division and naming of organisms. 40 BINOMIAL NOMENCLATURE In the 18th century, Carolus Linnaeus published a system of taxonomy based on resemblances. The two-part scientific name: Genus species. The first letter of the genus is capitalized, and the entire species name is italicized Both parts together name the species. This is the species specific epithet. 41 HIERARCHICAL CLASSIFICATION Linnaeus introduced a system for grouping species in increasingly broad categories. The taxonomic groups from broad to narrow are domain, kingdom, phylum, class, order, family, genus, and species. A taxonomic unit at any level of hierarchy is called a taxon. 42 PLANT DIVERSITY Ancestral species gave rise to land plants which can be informally grouped based on the presence or absence of vascular tissue. Nonvascular plants are commonly called bryophytes. Most plants have vascular tissue; these constitute the vascular plants: seedless vascular and seed plants. 43 PLANT DIVERSITY Seedless vascular plants can be divided into clades: Lycophytes (club mosses and their relatives) Pterophytes (ferns and their relatives). Seedless vascular plants are paraphyletic, and are of the same level of biological organization, or grade. 44 PLANT DIVERSITY A seed is an embryo and nutrients surrounded by a protective coat. Seed plants form a clade and can be divided into further clades: Gymnosperms, the “naked seed” plants including the conifers / cone = sex organ Angiosperms, the flowering plants including monocots and dicots / flower = sex organ 45 NON-VASCULAR PLANTS Most bryophytes are small. They not only lack vascular tissues; they also lack true leaves, seeds, and flowers. Instead of roots, they have hair-like rhizoids to anchor them to the ground and to absorb water and minerals Bryophytes occupy niches in moist habitats, but, as they lack vascular tissue, they are not very efficient at absorbing water. Nonvascular plants were the first plants to evolve. 46 LIVERWORTS (HEPATICOPHYTA) Liverworts are tiny nonvascular plants that have leaf-like, lobed, or ribbon-like photosynthetic tissues rather than leaves. Their rhizoids are very fine, they lack stems, and they are generally less than 10 centimeters (4 inches) tall. They often grow in colonies that carpet the ground Some species of liverworts have the characteristic flattened leaf-like body (thallus) from which the group name is derived and are small 47 LIVERWORTS The dominant life stage of a liverwort is the gametophyte, which is the green leafy part of the body. From the gametophytes, they produce the male and female reproductive structures, archegonium and antheridium, respectively. Require water for reproduction because the sperm needs to swim to the female structure for sexual reproduction to take place. Gemmae are small pieces of haploid tissue that can grow into new gametophytes (asexual reproduction) 48 MOSSES (BRYOPHYTA) Mosses are larger nonvascular plants that have coarser, multicellular rhizoids that are more like roots. They also have tiny, photosynthetic structures similar to leaves that encircle a central stem-like structure. Mosses grow in dense clumps, which help them retain moisture. Since mosses are part of the bryophyte group, they don’t have true roots to absorb water; instead, they can do it directly from the surface of the gametophyte via osmosis. 49 MOSSES The visible green fluffy plant that we call moss is the gametophyte, which is their dominant stage. Once mosses are ready to reproduce, the egg and sperm combine to form a sporophyte that grows from the top of the gametophyte or on lateral areas of the stem in prostrate species, and produces spores, which germinate into male and female gametophytes. Mosses are important ecologically for several reasons. They act like sponges that can absorb and retain rainwater. 50 HORNWORTS (ANTHOCEROPHYTA) Hornworts are minute nonvascular plants, similar in size to liverworts. They also have very fine rhizoids and lack stems. Their sporophytes are long and pointed, like tiny horns. They rise several centimeters above the gametophytes of the plant. Hornworts have stomata in their sporophytes, a feature that is absent in liverworts and most mosses The gametophyte, which is the dominant stage in hornworts, grows in a loose circular arrangement from where the green photosynthetic horn-like sporophytes grow. 51 HORNWORTS (ANTHOCEROPHYTA) The dominant life stage of a hornwort is the gametophyte. From the gametophytes, they produce the male and female reproductive structures, archegonium and antheridium, respectively. Hornworts, just like mosses and liverworts, require water for reproduction because the sperm needs to swim to the female structure for sexual reproduction to take place. Once the sperm reaches the egg and fertilization takes place, a zygote (diploid, 2n) forms which then develops into the sporophyte which remains attached to the gametophyte 52 SEEDLESS VASCULAR PLANTS The vascular plants, or tracheophytes, are the dominant and most conspicuous group of land plants. In seedless vascular plants, the diploid sporophyte is the dominant phase of the lifecycle. The gametophyte is now an inconspicuous, but still independent, organism. Seedless vascular plants still depend on water during fertilization, as the sperm must swim on a layer of moisture to reach the egg. 53 SEEDLESS VASCULAR PLANTS The first type of leaf is the microphyll, or “little leaf”. A microphyll is small and has a simple vascular system. Microphylls are present in the club mosses and probably preceded the development of megaphylls, or “big leaves,” which are larger leaves with a pattern of branching veins. Pine cones, mature fronds of ferns, and flowers are all sporophylls—leaves that were modified structurally to bear sporangia. Strobili are cone-like structures that contain sporangia. 54 LYCOPHYTES (LYCOPODIOPSIDA) Their leaves originated from the emergences of the stem surface, and therefore are more similar to moss leaves. Lycophyte sporangia are associated with leaves and often form strobilus which is a condensation of sporangia-bearing leaves Lycophytes used to be the dominant plants of Carboniferous tropical swamp forests and their remains became coal. 55 FERNS (PTERIDOPHYTA) They have a sporic life cycle with sporophyte predominance whereas their gametophytes are often reduced to prothallium, small hornwort-like plant. Pteridophyta have true roots. Pteridophyta sporophytes always start their life from an embryo located on the gametophyte. While Pteridophyta have true xylem and phloem, they do not have developed secondary thickening. 56 HORSETAILS (EQUISETOPSIDA) The leaves of these plants are reduced into scales, and the stems are segmented and also photosynthetic; there is also an underground rhizome. Only one genus Equisetum The stem has multiple canals, this is somehow similar to stems of grasses. The sporangia are associated with hexangular stalked sporangiophores Gametophytes are typically minute and dioecious, but the plants themselves are homosporous 57 WHISK FERNS (PSILOTOPSIDA) They are herbaceous plants that grow as epiphytes. Whisk ferns are homosporous Contains only 2 genera: Psilotum and Tmesipteris Psilotopsida have protostele like the some lycophytes, and long-lived underground gametophytes Both Psilotum and Tmesipteris lack roots Psilotum also lacks leaves 58 TONGUE FERNS (OPHIOGLOSSOPSIDA) Ophioglossopsida have an underground rhizome (sometimes with traces of secondary thickening) with aboveground bisected leaves: one half of each leaf is the leaf blade while the other half becomes the sporophyll. The gametophytes also grow underground. 59 GIANT FERNS (MARATTIOPSIDA) These are similar to true ferns and have compound leaves that are coiled when young. They are also the biggest ferns, as one leaf can be six meters in length. They have short stems, and leaves with stipules. Spores are located at the bottom surface of leaves. Gametophytes are relatively large (1–2 cm), photosynthetic, and typically live for a long time. 60 TRUE FERNS (PTERIDOPSIDA) Their leaves are called fronds because of apical growth. True ferns are megaphyllous: their leaves originated from flattened branches. True ferns have unique sporangia: leptosporangia. Leptosporangia originate from a single cell in a leaf, they have long, thin stalks, and the wall of one cell layer Leptosporangia are also grouped in clusters called sori which are often covered with umbrella- or pocket-like indusia. 61 SEED PLANTS A seed consists of an embryo and nutrients surrounded by a protective coat The gametophytes of seed plants develop within the walls of spores that are retained within tissues of the parent sporophyte In addition to seeds, the following are common to all seed plants: Reduced gametophytes Heterospory Ovules Pollen 62 SEED PLANTS The ancestors of seed plants were likely homosporous, while seed plants are heterosporous. Megasporangia produce megaspores that give rise to female gametophytes. Microsporangia produce microspores that give rise to male gametophytes. 63 SEED PLANTS An ovule consists of a megasporangium, megaspore, and one or more protective integuments. A fertilized ovule becomes a seed. Gymnosperm megaspores have one integument. Angiosperm megaspores usually have two integuments. 64 SEED PLANTS Microspores develop into pollen grains, which contain the male gametophytes. Pollination is the transfer of pollen from the male to the female part containing the ovules. Pollen eliminates the need for a film of water and can be dispersed great distances by air or animals. If a pollen grain germinates, it gives rise to a pollen tube that discharges two sperm into the female gametophyte within the ovule. 65 GYMNOSPERMS The gymnosperms have “naked” seeds not enclosed by ovaries and exposed on modified leaves - cones. There are four phyla: Cycadophyta (cycads) Gingkophyta (one living species: Ginkgo biloba) Gnetophyta (three genera: Gnetum, Ephedra, Welwitschia) Coniferophyta (conifers, such as pine, fir, and redwood). 66 GYMNOSPERMS Three key features of the gymnosperm life cycle are: Dominance of the sporophyte generation. The transfer of sperm to ovules by pollen. Development of seeds from fertilized ovules. 67 GINKGOPHYTA This phylum consists of a single living species, Ginkgo biloba. It has a high tolerance to air pollution and is a popular ornamental tree. 68 CONIFEROPHYTA This phylum is by far the largest of the gymnosperm phyla. Most conifers are evergreens and can carry out photosynthesis year round. 69 ANGIOSPERMS Angiosperms are seed plants with reproductive structures called flowers and fruits. They are the most widespread and diverse of all plants. All angiosperms are classified in a single phylum: Anthophyta. The name comes from the Greek anthos, flower. 70 ANGIOSPERMS The two main groups of angiosperms are: monocots - one cotyledon eudicots (“true” dicots) - two cotyledons. More than one-quarter of angiosperm species are monocots. More than two-thirds of angiosperm species are eudicots. 71 REFERENCES Lisa A. Urry, Michael L, Cain, Peter V. Minorsky, Steven A, Wasserman, Jane B. Reece (2017), Campbell Biology Eleventh Edition, Pearson, New York. ISBN 10:0-134-09341-0 Formacion, M. J., Gacutan, M. V. C., & Katalbas, M. S. S. (2011). Fundamentals of Biology (1st ed.). Rex Book Store. 72