Chapter 18 Classification

Chapter 18 Mystery Page 509… GRIN AND BEAR IT Hypothesis: Are polar bears and brown bears separate species?

Section 18.1 Finding Order in Diversity Objectives: What are the goals of binomal nomenclature and systematics? How did Linnaeus group species into larger taxa? Define: Binomial nomenclature Genus Systematics Taxon Family Order Class Phylum Kingdom

I. Assigning Scientific Names Groundhog woodchuck To understand diversity must describe and name each species Each scientific name must refer to one and only one species Everyone must use the same name for that species Common names are confusing (mean different things in different countries) Burro Donkey Gnus Wildbeast Bearded Antelope Puma Cougar Mountain lion panther

Assigned greek/latin names Describe species in great detail 18th century Assigned greek/latin names Describe species in great detail Names can be long still confusing Difficult to standardize b/c different scientists focused on different characteristics Differences can be used to ID species using dichotomous key

A. Binomial Nomenclature 1730s – swedish botanist – Carolus Linnaeus – developed 2-word naming system In binomial nomenclature, each species is assigned a 2-part scientific name. Written in italic First word begins w/ capital letter = genus to which org belongs Genus – group of similar species Second word is lowercased = unique to each species Species – group of individuals capable of interbreeding and producing fertile offspring Often description of important trait or habitat

B. Classifying Species into Larger Groups Scientists try to classify (organize) living and fossil species into larger groups that have biological meaning Systematics – science of naming and grouping organisms The goal of systematics is to organize living things into groups that have biological meaning Groups = taxa (singular = taxon)

Mystery Clue Page 512… Polar bears and brown bears interbreed and produce fertile hybrids in zoos, but they very rarely interbreed in nature. What do you think this means about the relationship between them?

II. The Linnaean Classification System Linnaeus developed classification system that organized species into taxa that formed a hierarchy (set of ordered ranks) Original system = 4 levels Over time, Linnaeus’s original classification system expanded to include seven hierarchial taxa: species, genus, family, order, class, phylum, and kingdom 2 smallest categories = genus & species Grouped species according to anatomical similarities and differences  placed into larger groups Example: Camelus bactrianus (Camel) * Camelus = genus name * bactrianus = species name * Camelus dromedarius (different species in same genus  Camel with 1 hump)

1. Family Group larger than genus Multiple genuses can be classified in the same family Example: Lama glama – South American llama Resembles Bactrian camels and dromedaries But more similar to other South American species than it is to European and Asian camels So different genus: Lama Several genera that share many similarities grouped into larger group (family) Example: Camelidae

2. Order Closely related families grouped into next larger rank = Order Example: Camels and llamas (family Camelidae)  grouped with several other animal families deer – family Cervidae cattle – family Bovidae = order Artiodactyla (hoofed animlas with even number of toes)

3. Class Similar orders grouped into next larger rank  class Example: order Artiodactyla placed in class Mammalia Includes all animals that are warmblooded, have body hair, and produce milk for their young

4. Phylum Classes are grouped into a phylum Includes orgs that are different but share impt characteristics Example: class Mammalia grouped w/ Birds (class Aves), reptiles (class Reptilia), amphibians (class Amphibia), and all classes of fish into phylum Chrodata All share impt body-plan features (nerve cord along back)

5. Kingdom Largest and most inclusive taxonomic category All multicellular animals are placed in kingdom Animalia

A. Problems with Traditional Classification Members of a species determine which orgs belong to that species by deciding w/ whom they mate and produce offspring Researchers define Linnaean ranks above the level of species b/c different groups have been defined in different ways at different times How to determine which similarities and differences are most important? Linnaeus chose characteristics carefully (century before Darwin) Modern systematists apply Darwin’s ideas to classification and try to look beyond simple similarities and differences and look to evolutionary relationships Today try to assign species to a larger group in ways that reflect how closely members of those groups are related to each other

Section 18.2 Modern Evolutionary Classification Objectives: What is the goal of evolutionary classification? What is a cladogram? How are DNA sequences used in classification? Define: Phylogeny Clade Monophyletic groups Cladogram Derived character

I. Evolutionary Classification Phylogeny – the evolutionary history of lineages The goal of phylogenic systematics, or evolutionary classification, is to group species into larger categories that reflect lines of evolutionary descent, rather than overall similarities and differences

A. Common Ancestors Phylogenic systematics places orgs into higher taxa whose members are more closely related to one another than they are to members of any other group The larger a taxon is, the farther back in time all of its members shared a common ancestor

B. Clades Clade – group of species that includes a single common ancestor and all descendants of that ancestor (living and extinct) Clade must by monophyletic group – includes single common ancestor and all of its descendants Some groups defined before advent of evolutionary classification = monophyletic Some groups = paraphyletic – the group includes common ancestor but excludes one or more groups of descendants

II. Cladograms Cladistic analysis – compares carefully selected traits to determine order in which groups of organisms branched off from common ancestor Cladogram – links groups of organisms together by showing how evolutionary lines (lineages) branched off from common ancestor

A. Building Cladograms Speciation event – one ancestral species splits into 2 new species = basis of each branch point (node) Node – represents last point at which the 2 new lineages shared a common ancestor Node splits a lineage into 2 separate lines of evolutionary ancestry Bottom (root) represents common ancestor shared by all orgs in cladogram Branching patterns indicate degrees of relatedness among orgs

B. Derived Characters Cladistic analysis focuses on certain kinds of characters (derived characters) when assigning orgs to clades Derived character – trait that arose in most recent common ancestor of a particular lineage and was passed along to its descendants Whether or not a character is derived depends on the level at which you’re grouping orgs Example: several traits shared by coyotes and lions (clade Carnivora) (clade Tetrapoda-4 legs) (clade Mammalia-hair)

C. Losing Traits 4 limbs = derived character of clade Tetrapoda Snakes (no limbs) but ancestors of snakes had 4 limbs Trait for limbs was lost Distantly related groups of orgs can sometimes lose the same character  systematists cautious about using absence of a trait as a character Whales do no have 4 limbs either, but snakes more closely related to other reptiles than they are to whales

D. Interpreting Cladograms Lowest node represents last common ancestor of all 4-limbed animals (clade Tetrapoda) Forks show order in which various groups branched off from tetrapod lineage over course of evolution Position of characters reflect order in which those characteristics arose in lineage Derived characters that occur “lower” on cladogram than the branch point for a clade are not derived for that particular clade

E. Clades and Traditional Taxonomic Groups True clad must be monophyletic – contains ancestral species and all of its descendants (can’t leave any out) Also cannot include any species not descendants of original ancestor Many traditional taxonomic groups do form valid clades class Mammalia corresponds to clade Mammalia  all vertebrates w/ hair and other impt chars Some traditional groups do not form valid clades Today’s reptiles all descended from common ancestor Birds also descended from same ancestor (not in class Reptilia) Reptilia w/o birds is not a clade Aves = bird clade Dinosaura & Reptilia clades = reptiles + birds Evolutionary biologists look for links b/w groups & how each is related to others Bird = also dinosaur, reptile, tetrapod, chordate

III. DNA in Classification Cladistic analysis based largely on physical chars: skeletons & teeth Goal of systematics = understrand evolutionary relationships of all life on earth Bacteria, plants, snails, apes No physical similarities, so how can they be related??

A. Genes as Derived Characters All orgs carry genetic info in DNA passed from earlier generations Orgs share number of genes and show impt homologies used to determine evolutionary relationship Example: eukaryotic cells have mitochondria & all mitochondria have their own genes All genes mutate over time  shared genes contain differences that can be treated as derived characters in cladistic analysis The more derived genetic characters 2 species share, the more recently they shared a common ancestor and the more closely they are related in evolutionary terms

B. New Techniques Suggest New Trees Use of DNA characters helped make evolutionary trees more accurate Example: African vulture vs. American vulture – look alike and traditionally classified as falcons American vulture – urinates on legs when overheated  similar behavior to stork; not African vulture Analysis of DNA: American vulture more similar to storks than African vultures Suggests: American vultures and storks = more recent common ancestor than American and African vultures Molecular analysis = powerful tool routinely used by taxonomists to supplement data from anatomy Example: Giant panda & red panda Share anatomical similarities w/ bears and raccoons Peculiar wrist bones that work like a human thumb DNA analysis = giant panda shares more recent common ancestor w/ bears than raccoons DNA places red pandas outside bear clade in different clade that includes raccoons, seals, weasels

Mystery Clue Page 522… DNA comparisons show that some populations of brown bears are more closely related to polar bears than they are to other brown bears. What do you think this means for the classification of polar bears?

Section 18.3 Building the Tree of Life Objectives: What are the six kingdoms of life as they are now identified? What does the tree of life show? Define: Domain Bacteria Archea Eukarya

I. Changing Ideas About Kingdoms Linnaeus time – only differences among living things were fundamental chars that separated animals from plants Animals = orgs that moved from place to place and used food for energy Plants = green orgs that generally did not move and got energy from sun Problem: Linnaeus’s 2 kingdoms did not reflect full diversity of life so classification system changed dramatically and still changing

A. Five Kingdoms Single celled microorganisms significantly different from plants and animals At first  all placed in one kingdom (Protista) Then  yeasts, molds, mushrooms (Fungi) Later  bacteria (no nuclei, mitochondria, chloroplasts = prokaryotes (Monera) Single-celled eukaryotic orgs remained in Protista 5 Kingdoms: Monera, Protista, Fungi, Plantae, Animalia

B. Six Kingdoms 1990s – researchers learned a great deal about genetics and biochemistry of bacteria Orgs in Monera = 2 genetically and biochemically different groups (Eubacteria & Archaebacteria) The six-kingdom system of classification includes the kingdoms Eubacteria, Archaebacteria, Protista, Fungi, Plantae, and Animalia

C. Three Domains Genomic analysis revealed that 2 main prokaryotic groups are ever more different from each other and from eukaryotes than previously thought  new taxonomic category (domain) Domain – larger, more inclusive category than kingdom 3 domains – Bacteria (kingdom Eubacteria), Archaea (kingdom Archaebacteria), Eukarya (kingdoms Fungi, Planta, Animalia, “Protista”) “Protista” – paraphyletic group – not a true clade no way to put all unicellular eukaryotes into clade that contains single common ancestor, all of its descendants, and only those descendants

II. The Tree of All Life Goal – present all life on single evolutionary tree Relationships studied  grouping changes & names of groups change Cladograms = visual presentations of hypotheses about relationships (not hard and fast facts) The tree of life shoes current hypotheses regarding evolutionary relationships among the taxa within the three domains of life

A. Domain Bacteria Unicellular Prokaryotic Cells have thick, rigid walls that surround cell membrane Cell walls contain peptidoglycan Some photosynthesize and others don’t Some need oxygen to survive and others are killed by oxygen Corresponds to kingdom Eubacteria

B. Domain Archaea Unicellular Prokaryotic Live in some of most extreme environments (volcanic hot springs, brine pools, black organic mud) Many can survive only in absence of oxygen Cell walls lack peptidoglycan Cell membranes contain unusual lipids that are not found in any other orgs Corresponds to kingdom Archaebacteria

C. Domain Eukarya Consists of all orgs that have nucleus 4 major groups: “Protista,” Fungi, Plantae, Animalia

The “Protists”: Unicellular Eukaryotes Paraphyletic group Current cladistic analysis divides into at least 5 clades Each group of “eukaryotes formerly known as protists” is separate & each shares closest common ancestor with other groups rather than with each other. Most unicellular 1 group – brown algae = multicellular Some photosynthetic & others heterotrophic Some display characters that most closely resemble those of plants, fungi, or animals

2. Fungi Heterotrophs Cell walls containing chitin Feed on dead or decaying organic material Secrete digestive enzymes into food  breaks down into smaller molecules  absorb small molecules into bodies Some multicellular (mushrooms) Some unicellular (yeasts)

3. Plantae Autotrophs Cell walls contain cellulose Conduct photosynthesis using chlorophyll Sister group to red algae (protists) Includes green algae, mosses, ferns, cone-bearing plants & flowering plants

4. Animalia Multicellular Heterotrophic No cell walls Most can move about (some for only part of life cycle) Incredible diversity Many species of animals exist in nearly every part of planet

Solve the Chapter Mystery Page 533… List the evidence that supports classifying polar bears and brown bears into two different species. Then list the evidence that indicates that polar bears and brown bears belong to the same species What evidence indicates that different populations of brown bears belong to different clades? Do you think that the classic definition of species – “a group of similar organisms that can breed and produce fertile offspring” – is still adequate? Why or why not?