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The History of Organization Aristotle 384-322 BC Interested in biological classification. Patterns in nature. Carl Linnaeus 1707-1778 ACE Father of Biological Classification! Taxonomy: How do we sort life? • Taxonomy divides organisms into several categories that start out broadly and become more specific. Kingdom Phylum Class Order Family Genus Species Subspecies The Linnaean Hierarchical Classification System Taxonomy: Assigning Names • Rules – – – – – Latin 1st name capitalized 2nd name lower case Italicized Ex. Homo sapiens Scientific Name Kingdom Phylum Class Order Family Genus Species Subspecies Taxonomy: Relationships Kingdom Phylum Class Order Family Genus Species Subspecies Animalia Chordata Mammalia Primates Homididae Homo sapiens sapiens Animalia Chordata Osteichthyes Salmoniformes Salmonidae Onchorhynchus tshawytscha Plantae Pinophyta Pinopsida Pinales Cupressaceae Sequoia sempervirens Human King Salmon Coast Redwood • Genera are grouped into progressively larger categories Table 15.10 Classification Categories • The higher the category, the more inclusive • Organisms in the same domain have general characteristics in common • In most cases, classification categories can be subdivided into additional categories – – – – Superorder Order Suborder Infraorder Order Chiroptera (Ky-rop`ter-a) (Gr. cheir, hand, + pteron, wing) Suborder Megachiroptera (megabats) teropodidae Suborder Microchiroptera (microbats) Superfamily Emballonuroidea Emballonuridae (Sac-winged or Sheath-tailed bats) Superfamily Antrozoidae (Pallid bats) Molossidae (Free-tailed bats) SPECIES Evolution creates (and destroys) new species, but … What is a species? Its not as straightforward a question as most believe. These are members of different species - eastern (left) and western (right) meadowlark. What is a Species? And these are all members of a single species. What is a Species? The definition we’ll use is this: A species is a group of individuals capable of interbreeding to produce fertile offspring. This is the biological species concept. Like all attempts to define a species, it has many problems. One Problem in the Biological Species Concept For asexually-reproducing organisms, like these bacteria, what constitutes a species? How Many Species Are There? We don’t know. About 2 million species have been described. Estimates of existing species number range from 4 million to 100 million (with 10-15 million being a more commonly considered upper estimate). Species Come and Go Best estimates from the fossil record indicate that greater than 99% of species that have exited are now extinct. A typical “lifetime” for a species is about 1 million years. The Cretaceous/Tertiary Mass Extinction Gary Larson SYSTEMATICS AND PHYLOGENETIC BIOLOGY Systematists classify organisms by phylogeny • Reconstructing phylogeny is part of systematics – the study of biological diversity and classification Phylogeny • Phylogeny often represented as a phylogenetic tree – A diagram indicating lines of descent – Each branching point: • Is a divergence from a common ancestor • Represents an organism that gives rise to two new groups Evolutionary trends may reflect unequal speciation or survival of species on a branching evolutionary tree • Phylogenetic trees strive to represent evolutionary history – Phylogeny is the evolutionary history of a group of organisms, a description of the lines of descent of plants and animals as they lived from one era to the next. – The most complete line discovered is of the horse. Figure 15.8 Phylogenetic Trees • Classification lists the unique characters of each taxon and is intended to reflect phylogeny – Primitive characters: • Present in all members of a group, and • Present in the common ancestor – Derived characters: • Present in some members of a group, but • Absent in the common ancestor Cladistic Systematics • Traces evolutionary history of the group under study • Uses shared derived characters to: – Classify organisms, and – Arrange taxa into a cladogram • A cladogram is a special type of phylogenetic tree • A clade is an evolutionary branch that includes: – A common ancestor, together with – All its descendent species Cladistics Ideally, classification is based on establishing the evolutionary relationships between organisms. The evolutionary relationship between organisms is their phylogeny. Cladistics is the method of classification based on establishing phylogenies (i.e. getting at evolutionary relationships. Cladistics proceeds by comparing shared ancestral and shared derived characters between sets of organisms. Cladistics A phylogeny (cladogram) for vertebrates. each node indicates a common ancestor The greater the number of derived characters shared by a pair of organisms, the closer their degree of relationship. The closer the degree of relationship, the closer the most recent common ancestor. Constructing a Cladogram Parsimony (KISS) • Cladists are always guided by the principle of parsimony – The arrangement requiring the fewest assumptions is preferred – This would: • Leave the fewest number of shared derived characters unexplained • Minimize the number of assumed evolutionary changes • The reliability of a cladogram is dependent on the knowledge and skill of the investigator Alternate, Simplified Cladograms • Cladistic analysis is often a search for the simplest hypotheses about phylogeny – Phylogenetic tree according to cladistic analysis – Phylogenetic tree according to classical systematics Lizards Lizards Snakes Snakes Crocodiles Crocodiles Birds Birds Figure 15.13B, C Cladistic Versus Traditional View of Reptilian Phylogeny Results of Cladistic Analyses Sometimes Run Counter to Classical Classification Schemes Which pair is more closely related? A lizard/crocodile or bird/crocodile? Cladistic analysis indicates that the bird/crocodile pair is more closely related. • Taxonomists often debate the particular placement of organisms in categories as they strive to make their categories reflect evolutionary relationships. Because classification reflects evolutionary relationships, the same evidence for classification is used. • Fossil records • Homologous structures • Vestigial organs • Embryological development • Biochemical comparisons • Biogeography It’s Critical (and often difficult) To Distinguish Homology from Analogy Homologous structures, like the bat wing and gorilla arm, are similar because they are derived by modification of a shared ancestral structure. **Homology is the key to establishing phylogenies. Distinguishing Homology from Analogy Analogy is similarity due to convergent evolution. Analogy mistaken for homology confuses phylogenies. Another Set of Analogies Created by Convergent Evolution Ocotillo of the US southwest Allauidia of Madagascar • A phylogenetic tree based on molecular data Brown bear Polar bear Asiatic black bear American black bear Sun bear Sloth bear Spectacled Giant panda bear Lesser Raccoon panda Miocene Pleistocene Pliocene Oligocene Ursidae Procyonidae Common ancestral carnivorans Figure 15.12A Classification Systems • Until the middle of the twentieth century, biologists recognized only two kingdoms – Plantae (plants) and Animalia (animals) • Protista (protists) were added as third kingdom in the 1880s • Whittaker expanded to five kingdoms in 1969 by adding Fungi and Monera • Woese Kandler & Wheelis expanded the five kingdoms to six in 1977 by dividing Monera into Eubacteria and Archaebacteria • Woese, Kandler & Whellis separated the kingdoms into domains based on cell structure in 1990. • Currently, there is a push to separate the kindgom Protista into 3 new kingdoms for a total of eight! Summary of the History Linnaeus 1735 2 kingdoms Haeckel 1866[1] 3 kingdoms Chatton 1937[5] 2 empires Prokaryota (not treated) Copeland 1956[6] 4 kingdoms Monera Whittaker 1969[2] 5 kingdoms Woese et al. 1977[7] 6 kingdoms Woese et al. 1990[3] 3 domains Eubacteria Bacteria Archaebacteria Archaea Monera Protista Protista Protista Fungi Fungi Protista Vegetabilia Animalia Plantae Animalia Plantae Eukarya Plantae Plantae Animalia Animalia Plantae Animalia Domains: determined by cell type • The current system recognizes two basically distinctive groups of prokaryotes – The domain Bacteria – The domain Archaea • A third domain, the Eukarya, includes all kingdoms of eukaryotes BACTERIA ARCHAEA EUKARYA Earliest organisms Figure 15.14B Three-Domain System • The Bacteria and Archaea are so different they have been assigned to separate domains • Similar in that both are asexually reproducing unicellular prokaryotes • Distinguishable by: – Difference in rRNA base sequences – Plasma membrane chemistry – Cell wall chemistry Three-Domain System • Domain Eukarya • Unicellular and multicellular organisms • Cells with a membrane-bounded nucleus – Sexual reproduction common – Contains four kingdoms • • • • Kingdom Kingdom Kingdom Kingdom Protista Fungi Plantae Animalia 6 Kingdoms of Life Single Celled - prokaryotes • Archaea (“extremophiles”) • Eubacteria (“germs” & blue-green algae) Single Celled or Multicelled eukaryotes • Protista (one-celled eukaryotes) Multicellular - eukaryotes • Fungi • Plantae • Animalia Prokaryote - small cell with no nucleus Eukaryote - large cell will nucleus Figure 20.14 Extremophiles (Archea) Thermophiles Halophiles Cryophiles Methanogens Eubacteria Protista Fungi Plantae Animalia
