The Classification of Life And the Six Kingdoms Why is classification important? • Classifying and categorizing nature is an ancient pursuit – it lies at the core at what it means to be human. • Our survival depended on being able to identify danger and food. • As humans became a more global species, we realized we needed a common system to keep track of the diversity of life. • Categorizing species in a consistent, systematic way allows us to understand the diversity of life on Earth. Biological Classification • Classification: arranging things into orderly groups or categories based on their similarities. • Humans make sense of the complicated world by placing them into categories. • In biology, the classification of organisms is referred to as taxonomy: identifying, naming, and classifying organisms. Why bother with taxonomy? • Taxonomy allows us to: • Accurately and uniformly name organisms. Names are specific to one species and descriptive. • Prevents misnomers: inaccurate or deceptive names. • Uses a common language for all names so that we are sure we are talking about the same organism. • Names (mostly) based on Latin words and Latin grammatical rules. Biodiversity • Biodiversity is the diversity of life (in a given place). • We talk about biodiversity from a global to very small scales. • So far, we’ve identified a bit more than 2 million different species (IUCN 2021). • New species are being discovered all the time. There could be anywhere from 5 million to up to a trillion different species! We truly have no idea. • On a finer scale, 1 g of healthy soil can have tens of thousands of different species of bacteria, viruses, fungi, and other small organisms. Binomial Nomenclature (Using Two Names) Genus species • Often referred to as the scientific name of a species. • Words used in names are mostly in Latin, a little in Greek. • Names are always italicized in print. Underlined when writing them out. • Genus is capitalized, species is not. Rules for Naming Organisms There are strict rules and conventions for naming species. • All species names must be approved by the International Naming Congresses: • International Code of Zoological Nomenclature (ICZN) - for animals • International Code of Nomenclature for algae, fungi, and plants (ICNafp) • These rules prevents duplicated names and conflicts among biologists (which can get nasty). Groups for Classification = Taxon (Taxa) • A taxon (taxa for plural) is a category into which related organisms are placed based on some similarity. • A taxon can be a large group (like the domain Bacteria, containing all known bacteria) or a single species. • There is a specific hierarchy of taxa from the broadest groups to the most specific. • As with anything in science, as we discover new evidence and learn more about life, taxa can (and constantly do) change. Hierarchy of Taxa Domain (broadest taxa) Kingdom Phylum Class Order Family Genus Species (most specific taxa) Cladogram • Diagram showing how organisms are related. • Based on shared, derived characteristics. • A representation of phylogeny– evolutionary relationships between taxa. Each branch represents a specific taxa. Phylogeny • Phylogeny: evolutionary relationships among organisms. • As organisms evolve, they gain new characteristics, but also retain ancestral characteristics. Such ancestral characteristics help us to piece together phylogenies. • Cladograms are used to illustrate phylogenetic relationships. Because we classify organisms based on said relationships, cladograms also reflect taxonomy. The Three Domains ● Archaea and Bacteria are prokaryotes – unicellular, lack nucleus and most organelles, smaller, simpler. • Each have one kingdom. • Eukarya are eukaryotes -more complex, have a nucleus and membrane-bound organelles, many are multicellular. • Four kingdoms. Kingdoms of Domain Archaea One Kingdom – Archaebacteria • Can be autotrophs or heterotrophs. • Capable of living in harsh environments = “extremophiles” • Found in: • Sewage treatment plants, wetlands, animal digestive systems - methanogens • Thermal or volcanic vents: thermophiles • Very salty water: halophiles Kingdoms of Domain Bacteria One Kingdom - Eubacteria • Can be autotrophs or heterotrophs. • Bacteria are the dominant taxa on the planet: they are everywhere and just about every living thing requires bacteria to survive. • There is oxygen in the atmosphere because: bacteria. • You get important vitamins/minerals from your food because: bacteria. • You don’t get infections of the skin and digestive system because: bacteria. • Involved in many symbiotic relationships: living inside or with other organisms. Bacteria Examples • Lactobacillus sp.– a “probiotic” – good for gut health. • Commonly found in fermented foods (yogurt, kimchi, sauerkraut, etc…). Domain Eukarya Usually divided into four kingdoms: • Plantae: multicellular plants. • Animalia: multicellular animals. • Fungi: mushrooms, molds, yeast. • Protista: mostly single- celled eukaryotes and other eukaryotes we’re not sure about – algae, amoebas, slime molds, etc. Kingdom Protista • The “we don’t know where these eukaryotes belong yet because we haven’t studied them enough” group. • The “junk drawer” of Eukaryota • A wide variety of organisms that live very different lives are placed in this group. • Most in this kingdom are unicellular, but some are multicellular. • Some are autotrophs, while others are heterotrophs. • Nearly all are aquatic organisms. ● Protista Examples Algae, amoebas Kingdom Fungi • Most, like mushrooms and molds are multicellular. Yeast is unicellular. • Heterotrophs: chemically digest food outside of their bodies, then absorbs the digested contents. • Important role as decomposers in various ecosystems. • Cell walls, but made of chitin instead of cellulose (like plants). Kingdom Plantae • All plants are multicellular. • Typically autotrophic – photosynthesis! • Absorbs sunlight to make glucose from water and CO2. • Cell walls made of cellulose. Kingdom Animalia • All animals are multicellular. • Heterotrophs: consume food and digest it inside of their bodies. • Feed on plants and/or other animals. Basis for Modern Taxonomy We place organisms into taxa based on phylogeny (evolutionary relationships. We study phylogeny by looking at: • Homologous structures- same structure, but may have different functions) • Similar embryo development – embryology. • Molecular similarity in genes or proteins – similar organisms are similar on a molecular level. • Looking at genes and proteins is now the primary way we study phylogeny,but it is beyond the scope of this course! What is Evolution? Evolution: a change over time. • In biology, evolution refers to changes in heritable characteristics in living populations over multiple generations. • Heritable characteristics: traits that are passed from one generation to the next. • Living populations: group of a species living in a given area. • Multiple generations: from grandmother to mother to daughter to granddaughter… and so on How are traits heritable? • The combination of genes that lead to our physical traits is called our genotype. • Genes are passed from generation to generation. • The collection of physical traits that we have is our phenotype. • Traits are NOT passed from generation to generation. Evolution acts on genes. When our genotype changes, it affects our phenotype. Genes change, not traits! Evolution acts on genes because genes are passed from one generation to the next (not traits!). One reason why we differentiate between genotype and phenotype is that the environment also affects the traits we have (our phenotype). • Adult human height depends on quality of diet in childhood. • Our temperature tolerance changes with seasons or exposure. • Lifting weights gives us larger, more powerful muscles. • The influence of environment on traits is called phenotypic plasticity. Evolution Acts on Populations • When we talk about the evolution of a species, we are talking about a population of that organism in a particular environment. • Population: all individuals of a species living in a particular place. • Each population has its own gene pool: the collection of different genes available within that population. Different Populations Change Differently • The distinction that evolution acts on populations of a species, not the entire species, is important. Why? • This is because different populations living in different places can evolve in very different ways, even though they are the same species. • If two different and separated populations evolve differently for long enough, they will become different species! Fitness and “Survival of the Fittest” • In life, all organisms try to accomplish two goals: • Survive long enough to reproduce. • Produce offspring that survive. • An organism’s fitness is its ability to achieve reproductive success. • Individuals with higher fitness in a population will pass on their genes more than individuals with lower fitness. • Any given trait can increase or decrease an organism’s fitness. Adaptations = Higher Fitness • Individuals with traits that increase fitness will have a greater chance of reproducing and passing on their genes (and therefore, those traits). • Traits that increase fitness in a given environment are called adaptations. • Over time, we expect adaptations to become more common in the population. • More specifically, we expect the genes that lead to adaptive phenotypes to become more common. Polar Bear - Adaptations Traits that increase fitness: • Large, wide paws helps swimming and prevents sinking in snow. • Small ears reduce heat loss. • Thick white fur for camouflage and warmth. • Thick layers of fat to prevent heat loss. Natural Selection and Adaptations • Natural selection is the process by which populations of organisms change and adapt to their environment. • This process is very slow, because evolutionary change occurs across generations, not within an organism’s lifetime. • Given enough time, natural selection leads to entire new traits and new species = that’s evolution, baby. How Natural Selection Works • Within a population: • Some individuals have low fitness = less likely to pass on their genes. • Some individuals have high fitness = more likely to pass on their genes. • Over time, this difference between individuals leads to: • Those with adaptive traits are more successful than others. Genes for adaptive traits become more common in the population. • Nature “selects” those genes that increase fitness to become more common. Artificial selection • When it suits our interests, humans will also try to make certain traits more common in populations. • This is known as selective breeding or artificial selection. • Breed individuals that have the traits you want. Selective Pressures It’s important to realize that there is almost never just one factor causing a “pressure” to change – biology is complicated. • Multiple factors affect reproductive success = multiple factors are driving natural selection, not just one! Types of Natural Selection • Typically, natural selection works on small, minor differences in traits. • Within a population, all traits exist on a spectrum. Some part of that spectrum leads to higher fitness than other parts. • Example: height, colour, length, etc. • If the environment changes and a new part of the spectrum leads to higher fitness, the spectrum shifts in that direction. • We’ll look at three common types of natural Directional Selection One extreme of the spectrum of a trait increases fitness. • Ex: giraffes and neck height. Those with the longest necks can reach the leaves of tall trees. • If longer necks increase the fitness of a giraffe, longer necks will become more common in a population of giraffes over time. Stabilizing Selection The middle part of the spectrum of a trait increases fitness. • Ex: crab spiders us camouflage to ambush pollinating insects. If the spider is too dark or too light, the insects can spot the spider. • Over time, the colour that allows the spider to camouflage best will become more common. Disruptive Selection • Either extreme of a spectrum of a trait increases fitness. • Ex: a species of snake ranges from small to large. Smaller snakes are better at catching small prey, while large snakes are better at catching large prey. Medium sized snakes aren’t good at either. • Both smaller and larger snakes will become more common. Disruptive selection can lead to new species! Sexual Selection • Remember that what traits become more common are those that lead to reproductive success. • Sometimes, what increases those odds the most is simply a trait that a mate prefers. Selection based on mating preferences is called sexual selection. • It often leads to weird traits/behaviors. Constraints on Selection • How organisms can evolve has its limits: • There’s only so much genetic variability to work with. • The current environment is always in a state of change. • An adaptation good for today may not be good tomorrow. • Many selection pressures acting simultaneously. • Genetic drift changes populations in random ways. • Laws of physics. Sources of Variation in Genes • Natural selection works best when there are a variety of different traits to choose from in a population. • There needs to be a variety of genes in the population. • Mutations cause new genes to appear in a population. • Mutations: changes in DNA sequence. These occur randomly, or because of damage. Mutations Mutations can create new genes. • They can result from copying errors or from damage. • A mutation can increase fitness (good), decrease fitness (bad), or have no effect on fitness (neutral). • The vast majority of mutations decrease fitness. • Some mutations are neutral. • Very few mutations increase fitness. • This is one of the reasons why evolution takes a long time: most mutations leave organisms worse off. Genetic Diversity in a Population • A healthy population of an organism will have a high genetic diversity (more genes to choose from). • If the environment changes, some of the population is more likely to survive and recover. • When genetic diversity is low, a population can become vulnerable to small changes to the environment. • Low genetic diversity also increases the prevalence of genetic disorders. • Aka inbreeding. Importance of Biodiversity • Biodiversity is important for similar reasons, but on the scale of the entire ecosystem rather than just one population of one species. • High biodiversity protects the ecosystem from changes in climate or big disturbances like natural disasters. • If something in the ecosystem changes suddenly, it is much more likely to be able to recover if there is high biodiversity. Genetic Drift Genetic drift: the effect of chance events on populations. • Chance events happen (like natural disasters or pandemics) that can wipe out a portion of the population. • Fitness is irrelevant if your forest catches fire or there’s an earthquake! Genetic Drift – Bottlenecks • When a population suffers a loss in genetic diversity due to a chance event, we call this genetic drift. • Sometimes we call this event a bottleneck. • The population has lost some random sample of the traits available to it. • There are now fewer traits left over on which natural selection can act.
