Title: Chapter 20 Classification of Living Things
1Chapter 20 Classification of Living Things
2Taxonomy Science of Classification
- Branch of biology concerned with identifying,
describing and naming organisms. - Ideally, classification is based on our
understanding of how organisms are related to one
another through evolution - Not an artificial system
3Taxonomy - History
- Began with Greeks and Romans
- Aristotle - first taxonomic system
- Plants trees, shrubs, and herbs
- Animals air-dwellers, water-dwellers,
land-dwellers - System flawed because scientifically valid
characteristics were often not used in
determining the categories.
4Carolus Linnaeus (Sweedish botanist)father of
modern taxonomy (1707- 1778)
- Eliminated use of common names
- Used Latin as a basis for nomenclature
- Created "binomial nomenclature" identifying each
organism by a two-part name
5Linneaus, contd
- Used morphological (form structure)
characteristics as a basis for classification - Linnaeus considered each species to have a unique
structure that made it distinct
6Species name Scientific name
- e.g. Magnolia grandiflora underlined
- Magnolia grandiflora italicized
- genus - Magnolia
- specific epithet - grandiflora
- species - Magnolia grandiflora M. grandiflora
7- Created seven taxa for classification purposes
- Kingdom..most inclusive
- Phylum
- Class
- Order
Classification Family
Hierarchy - Genus
- Species.least inclusive
- Taxon a group of organisms that fills a
particular category of classification
8Hierarchy of taxa for Callinectes sapidus
Callinectes (Gk. Beautiful swimmer) sapidus (L.
savory)
- Domain Eukarya (Eucaryota)
- Kingdom Animalia
- Phylum Arthropoda
- Class Malacostraca
- Order Decapoda Atlantic Blue Crab
- Family Portunidae
- Genus Callinectes
- Species Callinectes sapidus
9Classification of organisms
- Additional levels of classification can be added
by adding super-, sub-, or infra- (e.g.,
sub-order) - Taxonomists lumpers or splitters
10Classification of organisms
- the higher the classification category, the more
inclusive it is - A character is any structural, chromosomal, or
molecular feature that distinguishes one group
from another. - members of a kingdom share general characters
members of a species share quite specific
characters
11- The Linnaean system of classification is still
in use today. - Linnaeus was devoutly religious, but his
taxonomic system was later to be used to
demonstrate the phylogenetic (evolutionary)
relationships among living organisms. - Linnaeus Latinized his own name from
- Carl von Linne
12Some points about species
- The biological definition of a species states a
group of organisms capable of interbreeding and
producing fertile offspring they share the same
gene pool. - Distinguishing species on the basis of
reproductive isolation can also be a problem. - Some species do not reproduce sexually.
- Some species hybridize where their geographic
ranges overlap. - Reproductive isolation can be difficult to
observe. - When a species has a wide geographic range,
variant types may tend to interbreed where they
overlap these populations are called subspecies,
and are designated by a three-part name.
13Genus name may include more than one species or
sub-species
Ursus americanus
Ursus maritimus
Ursus thibetanus
binomial and trinomial
Ursus arctos mittendorfii
Ursus arctos horribilis
14Classification - an ongoing process
- there are estimated to be between 3 and 30
million species living on earth - we have currently named one million species of
animals and a half million plant and
microorganismic species - some groups, such as birds, are nearly all known
some insect groups are mostly unknown
15Major kingdoms of life
- Work of R.H. Whittaker (1969)
- Five are generally recognized based on
- Cell type
- Organization
- Nutrition
16Five Kingdoms of Life (KEY)
- 1. Cell type
- A. Prokaryotic (P) - primitive, lack
membrane-bound internal organelles - B. Eukaryotic (E) - true nucleus, membrane-bound
organelles - 2. Cells
- Unicellular (U)
- Colonial (C)
- Multicellular (M)
- 3. Nutrition
- A. Autotrophic (A) - Source of carbon is simple,
such as carbon dioxide (CO2) - B. Heterotrophic (H) - Source of carbon is
complex, such as - carbohydrates, proteins, lipids, or
nucleic acids
17KINGDOM MAJOR EXAMPLES CELL TYPE CELLS NUTRITION
(1) Monera Bacteria P U H
Blue-green algae P U, C A
(2) Protista Protozoa E U H
Algae E U,C A
Seaweeds E M A
(3) Fungi Mushrooms E M H
Yeasts E U H
(4) Plantae Mosses, Liverworts, Ferns, Gymnosperms, Angiosperms E M A
(5) Animalia Sponges, Cnidaria, Worms, Arthropods, Molluscs, Echinoderms, Chordates E M H
18Kingdoms of Life
- Many modern taxonomic systems split bacteria
(Monera) into several different kingdoms. - Generally,
- protists are considered to have evolved from
monerans, and - the fungi, plants, and animals evolved from
protists via three separate lineages.
19A higher category, the domain, has been proposed
to be added to these 7 categories
- Three-Domain System
- sequencing of rRNA suggests all organisms evolved
along three distinct lineages domains - Bacteria
- Archaea
- Eukarya
-
20Three Domains
- 1. the bacteria diverged first archaea and
eukarya are more closely related than either is
to bacteria - 2. the archaea live in extreme
environments methanogens in anaerobic swamps,
halophiles in salt lakes, and thermoacidophiles
in hot acidic environments - the archaea cell wall is diverse but
not the same as the bacterial cell wall - 3. the eukarya contains unicellular to
multicellular organisms, always with a
membrane-bound nucleus
21eukarya
archaea
bacteria
22Phylogenetic (Evolutionary) Trees
- Systematics is the study of the diversity of
organisms using information from cellular to
population levels - (Cell, tissue, organ, organism, population)
- A goal of systematics is to determine phylogeny
- Phylogeny is the evolutionary history of a group
of organisms - Evolution is a core theme of biology.
- Evolution - the process by which life on earth
has changed over time. -
23Phylogenetic (Evolutionary) Trees
- a phylogenetic tree indicates common ancestors
and lines of descent or lineages - an ancestral (primitive) character is a trait
that is present in a common ancestor and all
species in its lines of descent - a derived character is present only in a
specific line of descent - Different lineages diverging from a common
ancestor have ancestral characteristicstraits
shared by the ancestor and the species in its
lines of descent.
24Simple phylogenetic tree
(skeletal differences)
(tree climbing)
25All give birth to live young
(placental mammal)
26highly branched
palmate
hollow horns male/female
solid horns (antlers) male only
even-toed hoofs
Classification and Phylogeny
27 Tracing Phylogeny
- Systematists use various methods used to discover
evolutionary relationships between species. - If you can determine common ancestors, then you
know how evolution occurred and you can classify
organisms correctly.
28Fossil Record
- because fossils can be dated, fossils can
establish the age of a species - most organisms decay and the chances of
becoming a fossil are low
29Homology morphological data
- Homology is a character similarity that is
due to having a common ancestor (anatomical and
embryological features) - homologous structures are related to each
other through common descent but may differ in
structure and function (e.g., the forelimbs of a
horse and the wings of a bat) - analogous structures have the same
function but are not derived from the same organ
in a common ancestor (e.g., the wings of an
insect and the wings of a bat) - convergent evolution is acquisition of
similar traits in distantly related lines of
descent as a result of adaptation to similar
environmental conditions - --both spurges and cacti are adapted to a
hot, dry environment and are both similar, but
details of flower structure indicate these two
groups are not closely related - parallel evolution produces similar
characters in related lineages without occurring
in a common ancestor
30Molecular Data
- Speciation (new species) occurs when
mutations bring about changes in base pair
sequences of DNA - Protein Comparisons
- earlier studies used immunological
reactions to antibodies, made by injecting a
rabbit with cells of one species, to determine
the relatedness of two species - we now use amino acid sequences to
determine the differences in proteins between two
species - cytochrome c is a protein found in all
aerobic organisms the amino acid differences in
cytochrome c between chickens and humans is 13
but between chickens and ducks is only 3 - since the number of universal proteins is
limited, most new studies use differences in RNA
and DNA.
31RNA and DNA Comparisons
- all cells have ribosomes for protein
synthesis comparing rRNA base pair sequences
provides a reliable indicator of similarity
between organisms - Chimpanzees and Humans
- DNA DNA hybridization shows chimpanzees
closer to humans than to other apes - yet humans are kept in a separate family
and chimpanzees are with the ape family due to
differences in adaptation to the environment - Mitochondria DNA (mtDNA) changes ten times
faster than nuclear DNA - mtDNA is often used for closely related
species
32PhenogramDNA data
- Length of branches
- indicates the relative
- number of nucleotide
- pair differences among
- species shown.
33Molecular Clocks
- When nucleic acid changes are not tied to
adaptation - the fairly constant changes provide
a "molecular clock to indicate relatedness and
evolutionary time - the fossil record can then be used to
calibrate the clock and confirm the hypothesis
drawn from molecular data
34Systematics today 3 main schools
- 1. Cladistic Systematics (Willi Hennig)
- cladistics analyzes primitive and derived
characters and constructs cladograms on the basis
of shared derived characters (homologies) - cladogram a diagram showing relationships
among species based on shared, derived characters - a clade is an evolutionary branch - that
includes a common ancestor and all its descendent
species (monophyletic taxon) - outgroup - taxon (taxa) that define the
primitive characters of the study group study
group taxa placed in a clade - Parsimony
- cladists are guided by principle of
parsimony the minimum number of assumptions is
most logical that is, the fewest number of
shared derived character are left unexplained
35Charcters of taxa being compared
Cladogram w/ 3 clades
monophyletic taxon
Common ancestor notochord in embryo
Notochord- shared ancestral character Others are
shared derived characters
36Systematics today
- 2. Phenetic Systematics
- phenetic systematists cluster species on
the basis of the number of shared similarities,
regardless of whether they might be convergent,
parallel, or depend on one another - results of their analysis are depicted in a
phenogram - phenograms vary for the same group of
organisms, depending on how the data are
collected and handled
37Systematics today
- 3. Traditional Systematics
- traditional systematics stresses common
ancestry and the degree of structural
(anatomical) difference among divergent groups in
order to construct phylogenetic trees - a monophyletic group does not include all
groups from all ancestors (as a clade does) - cladists would not use "reptiles" because
it does not include all organisms derived from
reptiles
38Traditional vs. cladistic systematics
Hair/ mammary glands
scaly skin
feathers
Traditional view
Cladistic view
Common ancestor-egg layer