Mikael Mara CLASSIFICATION

Species A species is a population of organisms that share similar characteristics and can breed with one another, producing fertile offspring. Biologists have already identified and named about 1.5 million species. They estimate that anywhere between 2 and 100 million additional species have yet to be discovered! Through the discipline of taxonomy, scientists classify organisms and assign each one a universally accepted name.

Why Classify? By using a scientific name, biologists can be certain that everyone is discussing the same organism. The organisms are classified, or organized, in a manner that has biological significance. Organisms placed into a particular group are more similar to each other than they are to organisms in other groups. Two birds have more similarities than a bird and a mammal.

Assigning Scientific Names Scientists recognized that using common names was a problem since the same animal could have multiple common names, such as a mountain lion which is also called a cougar, a puma, or a panther depending on where you live. They decided to use a single word for each species, and since 18 th century scientists understood Greek and Latin, they chose to use those two languages in naming organisms—a practice that is still followed today: Felis concolor ->

Binomial Nomenclature Carolus Linnaeus developed a two-word naming system called binomial nomenclature. Binomial = two words Nomenclature = naming system Each species, even today, is assigned a two-part scientific name which is: 1.written in italics. 2.the first word is Capitalized 3.the second is lowercased

Binomial Nomenclature The grizzly bear is called Ursus arctos using binomial nomenclature. The first part of the name is called the genus. A genus is a group of closely related species. The genus Ursus, for example, contains five other kinds of bears, including the polar bear—Ursus maritimus. The second part of the name, arctos or maritimus, is the organism’s unique species. A species’ name is often a Latinized description of some important trait of the animal. The Latin word maritimus, referring to the sea, comes from the fact that polar bears often live on pack ice that floats in the sea.

Linnaeus’ System of Classification Linnaeus’ classification system is hierarchal—meaning it consists of levels. It includes seven levels, or taxa (plural of taxon) from largest to smallest: Kingdom Phylum Class Order Family Genus Species

Linnaeus’ System of Classification Species: the smallest and most exclusive group; organisms here can breed to produce fertile offspring. Genus: group of closely related species. Family: genera (plural of genus) that share many characteristics. Order: broad category composed of similar families. Class: composed of similar orders. Phylum: composed of many different classes. Kingdom: the largest and most inclusive of Linnaeus’ taxonomic categories.

Linnaeus’ System of Classification Grizzly bearBlack bearGiant panda Red fox Abert squirrel Coral snake Sea star KINGDOM Animalia PHYLUM Chordata CLASS Mammalia ORDER Carnivora FAMILY Ursidae GENUS Ursus SPECIES Ursus arctos

Modern Evolutionary Classification Linnaeus’ system used the physical traits of animals to characterize organisms into different taxa, however that is not always the best way of classifying animals, since many animals which look similar are not related, and many who look dissimilar are related. Phylogeny is a line of evolutionary descent, and it is the way which biologists now group organisms. The strategy of grouping organisms together based on their evolutionary history is called evolutionary classification.

Modern Evolutionary Classification Species within a genus are more closely related to each other than to species in another genus, even if they do look physically different. This is because all members of a genus share a recent common ancestor. The higher the level of the taxon, the further back in time is the common ancestor of all the organisms in the taxon. Due to natural selection, different organisms living in similar environments develop similar body structures—convergent evolution. Barnacles and limpets used to be grouped together due to their physical characteristics, however through the use of phylogeny, scientists now say that barnacles are more closely related to crabs than they are to limpets. Barnacles and clams actually share a more recent ancestor, making them both crustaceans, whereas clams and limpets share a more distant ancestor. Instead, limpets are mollusks.

Modern Evolutionary Classification

Classification Using Cladograms To refine the process of evolutionary classification, scientists now use cladistic analysis, which categorizes organisms using evolutionary innovations—new characteristics that arise as lineages evolve over time. Characteristics that appear in recent parts of a lineage but not in its older members are called derived characters. These derived characters are used to construct a cladogram, a diagram that shows the evolutionary relationships among a group of organisms. Cladogram is derived from the Greek “κλάδος” which means “branch.”

Kλάδος and Cladograms Just like a family tree shows the relationships among different lineages within a family, a cladogram represents a type of evolutionary tree, showing evolutionary relationships among a group of organisms.

Similarities in DNA and RNA Because DNA and RNA are so similar across all forms of life, these molecules provide an excellent way of comparing organisms at their most basic level— their genes. Similarities in DNA can be used to help determine classification and evolutionary relationships. Scientists can now compare the DNA of different organisms to trace the history of genes over millions of years and group organisms together. Ex: Both humans and yeast have a gene which codes for myosin, a protein found in our muscles. The same protein helps internal cell parts in yeast to move. This indicates a common ancestor between humans and yeast!

Similarities in DNA and RNA In addition, the more similar the DNA of two species, the more recently they shared a common ancestor, and the more closely related they are in evolutionary terms. Even though the African vulture (left) and the American vulture (center) have been traditionally grouped together, DNA analysis has showed that the American vulture is more related to the stork (right)!

Draw Two Cladograms! In the traditional cladogram, the two vultures were grouped together under the family of “falcons;” however, both the American vulture and the stork have a curious tendency to urinate on their own legs in order to cool off. On a piece of paper draw two cladograms. The first cladogram is the traditional one which depicts the two vultures being grouped together, whereas the second cladogram should show the American vulture and stork grouped together. Make sure you include important details such as the behavior of the American vulture and stork!

Molecular Clocks DNA comparisons can also allow us to estimate the length of time that has passed since two species have been evolving independently. This is called a molecular clock. A molecular clock relies on continued mutations to estimate the time that the two species have diverged from a single one. Some mutations cause major phenotypic changes in animals— natural selection then chooses the more beneficial mutation to allow the organism to survive.

Molecular Clocks Other mutations have no effect on phenotype!! These “neutral” mutations accumulate in the DNA of different species at about the same rate. A comparison of these neutral mutations between two species can reveal how dissimilar the genes are. The degree of dissimilarity is an indication of how long ago the two species shared a common ancestor.

Kingdoms and Domains Linnaeus had grouped living organisms into two different kingdoms: Animalia and Plantae; animals could move and used food for energy, and plants were green and used the energy of the sun. Upon the discovery of microorganisms such as protists and bacteria, scientists created a third kingdom—Protista. Soon afterwards mushrooms, yeasts and molds were placed in their own kingdom— Fungi. After that scientists noticed that bacteria lacked many features of other cells, and were placed in their won kingdom— Monera. The process produced five kingdoms: Monera, Protista, Fungi, Plantae and Animalia.

Kingdoms and Domains In recent years, scientists have discovered further differences between the organisms in the kingdom of Monera—some of these microorganisms are as different as plants and animals! Monera has thus been broken into two kingdoms called: Eubacteria Archaebacteria There are now a total of 6 kingdoms!

Kingdoms and Domains Due to DNA analyses, an even more inclusive group than kingdom has been created—domain. The three domains are: Bacteria Corresponds to kingdom Eubacteria Archaea Corresponds to kingdom Archaebacteria Eukarya Corresponds to kingdoms Protista, Fungi, Plantae and Animalia

Domain Bacteria Members of the domain Bacteria: Unicellular Prokaryotic Thick, rigid cell walls Cell walls made of peptidoglycan Big diversity among them Soil organisms – deadly parasites Some photosynthesize, others do not Some aerobic, some anaerobic

Domain Archaea Members of the domain Archaea: Unicellular Prokaryotic Live in extreme environments Many are anaerobic Cell walls lack peptidoglycan Cell membranes contain unusual lipids not found in other organisms

Domain Eukarya Members of the domain Eukarya: All organisms contain a nucleus Protista, Fungi, Plantae, Animalia Kingdoms Protista: Eukaryotes that cannot be classified as animals, plants, or fungi. Members display the greatest variety. Most are unicellular, some multicellular Fungi: Heterotrophs Feed on dead or decaying organic matter Secrete digestive enzymes into their food before ingesting Most multicellular, some unicellular

Domain Eukarya Members of the domain Eukarya: All organisms contain a nucleus Protista, Fungi, Plantae, Animalia Kingdoms Plantae: Multicellular Photosynthetic (Autotrophs) Non-motile (they cannot move) Cell walls that contain cellulose Animalia: Multicellular Heterotrophic Cells lack cell walls Motile (they can move about) Extreme diversity within this kingdom: birds, mammals, reptiles, amphibians, etc.

Kingdoms Eubacteria Archaebacteria Protista Plantae Fungi Animalia DOMAIN EUKARYA DOMAIN ARCHAEA DOMAIN BACTERIA