The Tree of Life Chapter 17

17.1 Taxonomy The science of naming and classifying organisms 2000 years ago – Aristotle Grouped plants and animals Based on structural similarities Greeks and Romans included categories Genus = Latin for group

Taxonomy Mid – 1700’s Naming organisms Polynomials Descriptive phrases European honeybee Apis pubescens, thorace subgriseo, abdomine fusco, pedibus posticis glabis, untrinque margine ciliatus

Simpler System Carl Linnaeus Swedish biologist Developed binomial nomenclature Two-part naming system Ex: European honeybee Apis mellifera

Scientific Names Unique two-part name for a species Genus - First name Taxonomic category of similar organisms Organisms have common important characteristics

Scientific Names Species = Second name One specific kind of living thing Identifies the particular type of organism Most specific and basic naming unit

Rules for Scientific Names Genus Always first Capitalized 1st letter Species Always second NOT capitalized Both Italicized or underlined Base on Latin language Apis mellifera

Scientific Names Conform to rules established No two the same Gives biologist common way of communicating Common names have problems Ex: Robin Different bird in US and England!

Classifying Organisms Carl Linnaeus Classification system Ranked system of groups Large groups subdivided into smaller groups Increasingly similar 7 groups total Now we have one more group = Eight group levels

Classifying Organisms Groups Domain Kingdom Phylum Class Order Family Genus Species Definition Group of similar kingdoms Group of similar phyla Group of similar classes Group of similar orders Group of similar families Group of similar genera Group of similar species

Classifying Organisms Groups Domain Kingdom Phylum Class Order Family Genus Species Danish Kings Play Chess On Fine Green Silk Biggest Smallest Diverse Similar

Identifying Organisms Field Guides Use: Image Description General info Range Common name Scientific name

Identifying Organisms Dichotomous Keys Use: Pairs of descriptions OR a question that can be answered in ONLY 2 ways Read both descriptions or question Choose one Follow directions for next step End up with a scientific name Ex: 1a.   This organism has an exoskeleton    - go to number 2 1b.   This organism has an endoskeleton or no skeleton    - go to number 3

Identifying Organisms Species Unique Differences in appearance and structure Ex: Paramecium syngens Once thought to be a single species Look similar, but other differences

Species Biological species Defined by 1942 – Ernst Mayr: A group of organisms that can reproduce only among themselves and are usually contained in a geographic region

Hybrids Hybrids Offspring produced by different species interbreeding Reproductive barriers not complete Some are fertile! Ex: Dogs and wolves Dogs = Canis familiaris Wolves = Canis lupus

Biological Species Concept Reproduction: Most of kingdom Animalia = limited Strong barriers “Species only” fails in: Organisms that reproduce asexually Ex: prokaryotes Transfer genes outside of reproduction Still working on how to classify them

17.2 Classification of Species Put into groups based on similarities and differences More similar = closely related Suspect common ancestor

Classification of Species Similarity of structure can be misleading Not all characteristics inherited by offspring Ex: Wings Both birds and insects have . . .

Phylogeny Evolutionary history for a group of species

Looking at Structures Convergent evolution Analogous characters Converge = Come together When similarities develop in organisms not closely related b/c Live in similar habitats thus have similar adaptations Analogous characters Arise through convergent evolution

Characters in Groups Ancestral character Feature in common ancestor of both groups Ex: Backbone Birds and mammals

Characters in Groups Derived character Found in only some members of a group More shared = more closely related Ex: Feathers Birds but Not mammals

Cladistics Classification based on common ancestry Clade - group of species that shares a common ancestor

Cladogram Cladogram Branching diagram Shows hypothesized evolutionary relationships Tips represent groups of descendent taxa Nodes represent common ancestors

Cladistics Outgroup – shares no derived characters with other groups being studied

Cladogram Shared derived character Shared ancestral characters Evidence that groups are closely related Ex: mammary glands Shared ancestral characters Not evidence groups are closely related Ex: Limbs Classification 12 min

Cladograms Strengths Weakness Objectivity Either character exists or doesn’t Weakness Each character treated the same Character impact or importance ignored

Phylogenetic Tree Taxonomist assign importance to characters Branching tree-like diagram Shows evolutionary relationships inferred

Molecular Evidence Uses DNA to show relationships Often considered the “last word” by scientists Usually agrees with classification that was based on physical appearances Reclassification sometimes necessary

17.3 Molecular Clocks Models that use mutation rates to estimate evolutionary time Hypothesized that changes in DNA “add up” Rate of mutations = “ticking” of time More mutations = less closely related

Mitochondrial DNA mtDNA Found only in mitochondria Only inherited from mother Sperm loses mitochondria after fertilization Mutation rate ~10x faster than nuclear DNA Often used as molecular clock Help classify closely related organisms

Ribosomal RNA rRNA Useful when comparing different species that may be very distantly related Lots of time has passed Lower mutation rate Was used to reclassify Archaea and Bacteria into different domains

17.4 Domains and Kingdoms Domain Recent classification group Largest, broadest group Recent classification group 1977, Carl Woese American Prokaryotes differ fundamentally in rRNA

Domain Bacteria Contains kingdom Bacteria Unicellular prokaryotes Contains autotrophs and heterotrophs Classified by: Shape Need for oxygen Whether the cause disease

Domain Archaea Contain kingdom Archaea Unicellular prokaryotes Some autotrophic, some heterotrophic

Domain Archaea Cell walls do NOT contain peptidoglycan Live in “extreme” environments Salt lakes Antarctic waters Deep sea vents Hot geysers

Domains Archaea and Bacteria No true “species” Genes are shared outside of typical reproduction Still trying to decide how to classify Used to be classified together in one kingdom: Monera

Domain Eukarya Includes kingdoms: Eukaryotic cells Protista Plantae Fungi Animalia Eukaryotic cells Unicellular or multicellular

Review of Kingdoms Bacteria Archae Protista Fungi Plantae Animalia

Kingdom Bacteria Cell wall made of peptidoglycan Web-like carbohydrate strands and peptide bridges

Kingdom Archaea Cell wall Cell membrane No peptidoglycan Different lipids than bacteria or eukaryotes

Kingdom Protista Many unicellular Some have cell walls Heterotrophs or autotrophs Many move Most reproduce asexually

Kingdom Fungi Most multicellular Cell walls contain chitin Except yeasts Cell walls contain chitin Tough carbohydrate Heterotrophic

Kingdom Plantae Multicellular Cell walls Eukaryotic Autotrophic Cellulose (complex carb) Eukaryotic Autotrophic

Kingdom Animalia Multicellular Heterotrophs Eukaryotic Mostly diploid cells No cell wall Organized cells Motility