The Living World Fifth Edition George B. Johnson Jonathan B. Losos Chapter 18 Exploring Biological Diversity Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

18.1 The Invention of the Linnaean System To talk about and to study organisms it is necessary to give them names  biologists use a kind of multilevel grouping of individuals called classification  the earliest classification scheme grouped animals and plants into basic units called genera (singular, genus) early biologists added a series of non-standardized descriptions to the genus name this created a string of subjective names called a polynomial

18.1 The Invention of the Linnaean System A much simpler system than the polynomial for the naming of organisms was developed by Carolus Linnaeus  Linnaeus assigned organisms a two-part name called a binomial  he also grouped similar organisms into higher-level categories based on similar characteristics this would have important, though unintended, applications to evolutionary connections

Figure 18.1 How Linnaeus named two species of oaks

18.2 Species Names Taxon (plural, taxa) is a group of organisms at a particular level in a classification system  the branch of biology that identifies and names such groups is called taxonomy  no two kinds of organisms can have the same name and all names are given in Latin

18.2 Species Names The scientific name for an organism is comprised of the two-part binomial  the first part is the genus, which is always capitalized  the second part is the specific epithet and is not capitalized  the two words together are written in italics or underlined

18.3 Higher Categories the binomial has been expanded into a Linnaean system of classification  genera with similar properties are grouped together into a family  families that share similar characteristics are put into the same order  orders with common properties are placed into the same class  classes with similar characteristics are placed into the same phylum  phyla are assigned to one of several gigantic groups called kingdoms  kingdoms are sometimes assigned to an additional level of classification, called domains

Figure 18.3 The hierarchical system used to classify an organism

18.4 What Is a Species? Since the time of Linnaeus, about 1.5 million species have been named  the actual number of species is much greater  the biological species concept is widely applied to animals but not as frequently to plants it does not apply to some kingdoms at all  molecular data are causing a reevaluation of traditional classification systems

18.5 How to Build a Family Tree Phylogeny is the evolutionary history of an organism and its relationship to other species Systematics is the study of and reconstruction of phylogenetic trees  it also includes the naming and classifying of organisms

18.5 How to Build a Family Tree Cladistics is the systematic approach that infers phylogeny according to similarities derived from a common ancestor  derived characters are characters that are present in a group of organisms that arose from a common ancestor that lacked the character a clade is a group of organisms, related by descent, that share a derived character  by examining the distribution of derived traits among related organisms, it is possible to construct a cladogram, a branching diagram that represents the phylogeny

Figure 18.5 A cladogram of vertebrate animals

18.5 How to Build a Family Tree Cladograms convey comparative information about relative relationships  organisms that are closer together on a cladogram simply share a more recent common ancestor than those that are farther apart  each cladogram must have an outgroup, a rather different organism to serve as a basis for comparisons among the other organisms being evaluated, called the ingroup

18.5 How to Build a Family Tree Cladistics is a relatively new but popular approach to studying evolution because it is objective and portrays the order in which a series of evolutionary events have occurred

18.5 How to Build a Family Tree An alternative approach to constructing phylogenies is traditional taxonomy  both ancestral and derived characters are used to build trees this wealth of additional information is often weighted by its biological significance but this is a more subjective process than cladisitics

Figure 18.6 Two ways to classify terrestrial vertebrates

18.6 The Kingdoms of Life Most biologists use a six-kingdom system first proposed by Carl Woese  four kingdoms consist of eukaryotes Animalia, Plantae, Fungi, and Protista  two kingdoms consist of prokaryotes Archaea and Bacteria Recognizing that there are further differences among the prokaryotes, the domain level above kingdom was created  Domain Archaea contains the Kingdom Archaea  Domain Bacteria contains the Kingdom Bacteria  Domain Eukarya contains the eukaryotic kingdoms

Figure 18.8 Different approaches to classifying living organisms

18.7 Domain Bacteria The bacteria are the most abundant organisms on earth  there are many different types of bacteria and the evolutionary links between them are not well understood most taxonomists recognize 12 to 15 major groups of bacteria although archaea are also prokaryotic like bacteria, the archaea are more closely related to eukaryotes

18.8 Domain Archaea The Archaea branched off from a line of prokaryotic ancestors that lead to the evolution of eukaryotes  modern Archaea live in some of the most extreme environments on earth and, although a diverse group, share some of the same key characteristics their cell walls lack the peptidoglycan that is characteristic of bacterial cell walls they possess unique lipids and rRNA sequences some genes in the archaea have introns

Figure 18.9 A tree of life

18.8 Domain Archaea Archaea are grouped into three general categories  methanogens obtain their energy by using hydrogen gas (H 2 ) to reduce CO 2 to methane gase (CH 4 )  extremophiles are able to grow under extreme conditions, such as extreme heat, salt, pH or pressure  nonextreme archaea grow in the same environments that bacteria do

18.9 Domain Eukarya Eukaryotes have a complex cellular organization but are fairly uniform in metabolism, when compared to prokaryotes  there are three largely multicellular kingdoms (fungi, plants, and animals)  the remaining eukaryotic kingdom, Protista, is a diverse array of mostly unicellular forms that basically don’t fit into the other kingdoms

18.9 Domain Eukarya Endosymbiosis may explain the origin of eukaryotes from prokaryotes Figure Endosymbiosis

Inquiry & Analysis Three great innovations in the jaw and tail occur during the history of the bony fishes, producing the superorders represented by strurgeons, then gars, then teleost fishes. In what period did each innovation occur? Graph of The Rate New Forms of Fish Have Appeared