Biology: Life on Earth Lecture for Chapter 18 Systematics: Seeking Teresa Audesirk • Gerald Audesirk • Bruce E. Byers Biology: Life on Earth Eighth Edition Lecture for Chapter 18 Systematics: Seeking Order Amidst Diversity Copyright © 2008 Pearson Prentice Hall, Inc.

Chapter 18 Opener Biologists studying the evolutionary history of type 1 human immunodeficiency virus (HIV-1) discovered that the virus, which causes AIDS, probably originated in chimpanzees.

Chapter 18 Outline 18.1 How Are Organisms Named and Classified? p. 358 18.2 What Are the Domains of Life? p. 360 18.3 Why Do Classifications Change? p. 364 18.4 How Many Species Exist? p. 366

Section 18.1 Outline 18.1 How Are Organisms Named and Classified? Classification Originated as a Hierarchy of Categories Systematists Identify Features That Reveal Evolutionary Relationships Anatomy Plays a Key Role in Systematics Molecular Similarities Are Also Useful for Reconstructing Phylogeny

Systematics Systematics is the branch of biology concerned with Reconstructing phylogeny (evolutionary history) Naming organisms and placing them into hierarchical categories based upon their evolutionary relationships

Major Categories of Classification The eight major categories of classification, in order of decreasing inclusiveness are Domain Kingdom Phylum Class Order Family Genus Species

Table 18-1 Classification of Selected Organisms, Reflecting Their Degree of Relatedness

Scientific Names The scientific name of an organism is formed from the genus and species The genus Sialia (bluebirds) includes three species: Sialia sialis (the eastern bluebird) Sialia mexicana (the western bluebird) Sialia currucoides (the mountain bluebird)

FIGURE 18-1 Three species of bluebird Despite their obvious similarity, these three species of bluebird—from left to right, the eastern bluebird (Sialia sialis), the western bluebird (Sialia mexicana), and the mountain bluebird (Sialia currucoides)—remain distinct because they do not interbreed.

Scientific Names Each two-part scientific name is unique and recognized worldwide

Scientific Names Scientific names are always underlined or italicized The first letter of the genus name is always capitalized The first letter of the species name is always lower case The species name is always paired with its genus name

The Origin of Classification Aristotle (384-322 B.C.) Was among first to develop a standardized language for naming organisms Classified about 500 organisms into 11 hierarchical categories based on various characteristics

The Origin of Classification Carolus Linnaeus (1707-1778) Laid the groundwork for the modern classification system Placed organisms into hierarchical categories based on their resemblance to other organisms Introduced the scientific name composed of genus and species

The Origin of Classification Charles Darwin (1809-1882) Published On the Origin of Species, which demonstrated that all life is related by common ancestry

Evolutionary Relationships Biologists realized that taxonomic categories should reflect evolutionary relatedness The more categories two organisms share, the closer their evolutionary relationship

Evolutionary Relationships All organisms share certain similarities Similarities result from common ancestry or convergent evolution

Present-Day Classification Systematists determine evolutionary relationships based on similarities due to common ancestry Similarities may be anatomical or molecular

Anatomical Similarities Systematists examine similarities in external body structure

FIGURE 18-1 Three species of bluebird Despite their obvious similarity, these three species of bluebird—from left to right, the eastern bluebird (Sialia sialis), the western bluebird (Sialia mexicana), and the mountain bluebird (Sialia currucoides)—remain distinct because they do not interbreed.

Anatomical Similarities Systematists examine similarities in internal body structures, such as skeletons and muscles

FIGURE 14-7 Homologous structures Despite wide differences in function, the forelimbs of all these animals contain the same set of bones, inherited through evolution from a common ancestor. The different colors of the bones highlight the correspondences among the various species.

Anatomical Similarities Systematists examine microscopic similarities to discern finer details Number and shape of the “teeth” on the tongue-like radula of a snail Shape and position of the bristles on a marine worm External structure of pollen grains of a flowering plant

FIGURE 18-2 Microscopic structures may be used to classify organisms (a) The "teeth" on a snail's tongue-like radula (a structure used in feeding), (b) the bristles on a marine worm, and (c) the shape and surface features of pollen grains are characteristics that are potentially useful in classification. Such finely detailed structures can reveal similarities between species that are not apparent in larger and more obvious structures.

FIGURE 18-2a Microscopic structures may be used to classify organisms (a) The "teeth" on a snail's tongue-like radula (a structure used in feeding),

FIGURE 18-2b Microscopic structures may be used to classify organisms (b) the bristles on a marine worm...

FIGURE 18-2c Microscopic structures may be used to classify organisms ...and (c) the shape and surface features of pollen grains are characteristics that are potentially useful in classification. Such finely detailed structures can reveal similarities between species that are not apparent in larger and more obvious structures.

Molecular Similarities Systematists examine genetic similarities between: DNA nucleotide sequences Chromosome structure It has been estimated that 99% of the chimpanzee genome is identical to that of humans

FIGURE 18-3 Human and chimp chromosomes are similar Chromosomes from different species can be compared by means of banding patterns that are revealed by staining. The comparison illustrated here, between human chromosomes (left member of each pair; H) and chimpanzee chromosomes (C), reveals that the two species are genetically very similar. In fact, the entire genomes of both species have been sequenced and are 96% identical. The numbering system shown is that used for human chromosomes; note that human chromosome 2 corresponds to a combination of two chimp chromosomes.

Section 18.2 Outline 18.2 What Are the Domains of Life? The Five-Kingdom System Improved Classification A Three-Domain System More Accurately Reflects Life’s History Kingdom-Level Classification Remains Unsettled

The Two-Kingdom System Before 1969, all forms of life were classified into two kingdoms Animalia Plantae (included plants, bacteria, fungi and photosynthetic eukaryotes)

The Five-Kingdom System Proposed by Robert H. Whittaker (1969) Kingdoms include Monera (all prokaryotes) Plantae Fungi Animalia Protista (eukaryotes that are not plants, fungi, or animals)

The Three-Domain System Introduced by Carl Woese (1990) Discovered that kingdom Monera included two very distinct groups (Bacteria and Archaea) based on nucleotide sequences of ribosomal RNA

FIGURE 18-4 Two domains of prokaryotic organisms Although similar in appearance, (a) Vibrio cholerae and (b) Methanococcus jannaschi are less closely related than a mushroom and an elephant. Vibrio is in the domain Bacteria, and Methanococcus is in Archaea.

The Three-Domain System Domains include Bacteria (prokaryotic) Archaea (prokaryotic) Eukarya (eukaryotic)

FIGURE 18-5 The tree of life The three domains of life represent the three main "trunks" on the tree of life.

Kingdom-Level Classification Systematists have yet to reach a consensus about the precise definitions of new prokaryotic and eukaryotic kingdoms Figure 18-6, p. 364, shows the evolutionary relationships among some members of the domain Eukarya…

FIGURE 18-6 A closer look at the eukaryotic tree of life Some of the major evolutionary lineages within the domain Eukarya are shown. The term "protist" refers to the many eukaryotes that are not plants, animals, or fungi.

Section 18.3 Outline 18.3 Why Do Classifications Change? Species Designations Change When New Information Is Discovered The Biological Species Definition Can Be Difficult or Impossible to Apply

New Information Is Discovered Systematists regularly propose changes in species-level classification

New Information Is Discovered African elephant species has been divided into two species, the savannah elephant and the forest elephant Discovered that the two groups have little gene flow between them

New Information Is Discovered Red wolves may not be a distinct species DNA evidence suggests that red wolves are hybrids between gray wolves and coyotes

Species Definitions Change The biological species concept defines species as “groups of interbreeding natural populations, which are reproductively isolated from other such groups” Cannot be applied to asexually reproducing organisms

Species Definitions Change Alternative species definitions have been proposed, one of which is the phylogenetic species concept

Phylogenetic Species Concept The phylogenetic species concept defines a species as “the smallest diagnosable group that contains all the descendants of a single common ancestor” Can be applied to sexually and asexually reproducing organisms May eventually replace the biological species concept

Section 18.4 Outline 18.4 How Many Species Exist?

How Many Species Exist? Biodiversity is the total number of species in an ecosystem

How Many Species Exist? Number of named species is currently about 1.5 million (biased toward large organisms in temperate regions) 5% prokaryotes and protists 22% plants and fungi 73% animals

How Many Species Exist? Estimated that 7 million to 10 million species may exist

How Many Species Exist? Between 7,000 and 10,000 new species are identified annually, mostly in the tropics Tropical rain forests are believed to be home to two-thirds of the world’s existing species, most of which have yet to be named

How Many Species Exist? Because tropical rain forests are being destroyed so rapidly, species may become extinct before we ever knew they existed

FIGURE 18-7 The black-faced lion tamarin Researchers estimate that no more than 260 individuals remain in the wild; captive breeding may be the black-faced lion tamarin's only hope for survival.