1. 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.

2. 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.

3. 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

4. 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

5. 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

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

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

8. 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)

9. 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.

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

11. 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

12. The Origin of Classification
Aristotle ( 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

13. The Origin of Classification
Carolus Linnaeus ( )
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

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

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

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

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

18. Anatomical Similarities
Systematists examine similarities in external body structure

19. 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.

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

21. 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.

22. 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

23. 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.

24. 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),

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

26. 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.

27. 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

28. 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.

29. 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

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

31. 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)

32. 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

33. 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.

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

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

36. 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…

37. 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.

38. 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

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

40. 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

41. 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

42. 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

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

44. 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

45. Section 18.4 Outline
18.4 How Many Species Exist?

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

47. 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

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

49. 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

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

51. 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.