Download Chapter 19 Systematics and Phylogeny

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Chapter 19
Systematics
and Phylogeny
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Systematics
• Systematics is a field of biology that is very analytical
and relies on combination of data from the fossil
record and comparative anatomy and development,
with an emphasis today on molecular data, to
determine evolutionary relationships.
• Taxonomy is the branch of biology concerned with
identifying, naming, and classifying organisms. It is a
part of systematics.
• Linnean Taxonomy
– Ideally, classification is based on our understanding of
how organisms are related to one another through
evolution.
– A natural system of classification, as opposed to an
artificial system, reflects the evolutionary history of
organisms.
– St. Augustine in the fourth century classified animals as
useful, harmful, or superfluous—to humans.  e.g. of
previous classification
• The Binomial System
– Carolus Linnaeus (1707-1778) developed the binomial
system to name species.
– Linnaeus grouped organisms according to their
similarities, mainly structural similarities.
– The binomial system of nomenclature names organisms
using a two-part Latin name.
•First part is the genus; closely related species are
assigned to the same genus.
•Second part is the specific epithet; it usually provides
something descriptive about an organism.
•A scientific name consists of both genus and specific
epithet (e.g., Lilium buibiferum and Lilium canadense).
•Both names are italicized or underlined; the first letter
of the genus name is capitalized.
•The genus, or generic, name can be used alone to
designate all species in the genus (for example, the
genus Quercus includes all oak species).
•The genus can be abbreviated when used with a
specific epithet if the full name was given before.
• Scientific names are derived in a number of ways. Some are
descriptive in nature, for example, Acer rubrum for the red
maple.
• Other may include geographic descriptions such as Alligator
mississippiensis for the American alligator.
• Scientific names can also include eponyms (named after
someone), such as the owl mite Strigophilus garylarsonii
(named after the cartoonist).
• The generic name for the bacterium Escherichia coli is based
on the name of the scientist, Theodor Escherich, who first
described it. The specific epithet coli reminds us that E. coli
lives in the colon.
• Many scientific names are derived from mythical characters,
such as Iris versicolor, named for Iris, the goddess of the
rainbow.
• Magnolia sirindhorniae Noot. & Chalermglin, 2000
Noot is the last name of
Nootiboom and
Chalermglin is the last
name of Dr. Piya
Chalermglin who coined
the scientific name in the
year 2000.
Professor Emeritus Paiboon Naiyanetr
Phricotelphusa sirindhorn Naiyanetr, 1989
Professor Dr. Tossaporn Wongratana
Setipinna paxtoni Wongratana, 1987
Thryssa whiteheadi Wongratana, 1983
Professor Dr. Somsak Panha
กิ งกือมั งกรสี ชมพู Desmoxytes purpurosea
Enghoff, Sutcharit & Panha, 2007
Why do organisms need scientific names?
• A common name will vary from country to country
because different countries use different languages.
• Even people who speak the same language sometimes
use different common names to describe the same
organism. For example, bowfin, grindle, choupique,
and cypress trout describe the same common fish,
Amia calva.
• Between countries, the same common name is
sometimes given to different organisms. A “robin” in
England is very different from a “robin” in the United
States, for example.
Why do scientists use Latin?
• Latin is a universal language that not too long ago was
well known by most scholars, many of whom were
physicians or clerics.
• The job of naming all species is far from finished.
– There are estimated to be between 3 and 30 million
species living on earth, but only about 1.7 million species
have been described.
– Currently, one million species of animals and a half
million plant and microorganismic species have been
named.
– Some groups, such as birds, are nearly all known; some
insect groups are mostly unknown.
– Biologists estimate that to date they have identified less
than 10% of bacteria, about 5% of fungi species, only
about 2% of nematode (roundworm) species, and less
than 20% of insect species.
– Thousands of new species are discovered each year.
• Linnean Classification Categories
– A taxon is a group of organisms that fills a particular
category of classification; Rosa and Felis are taxa at the
genus level.
– Aristotle classified life into 14 groups (e.g., mammals,
birds, etc.), and subdivided them by size.
– Ray grouped animals and plants according to how he
thought they were related.
– Linnaeus grouped plants by flower parts; his categories
were published in Systema Naturae in 1735.
– Today, taxonomists use seven categories of classification:
species, genus, family, order, class, phylum, and kingdom.
•A higher category, the domain, has recently been
added to these seven categories.
•The higher the category, the more inclusive it is.
•Members of a kingdom share general characters;
members of a species share quite specific characters. (A
character is any structural, chromosomal, or molecular
feature that distinguishes one group from another.)
•Since one taxonomic group exists inside another group,
these categories are also termed nested.
•Additional levels of classification can be added by
adding super-, sub-, or infra- (e.g., suborder); thus,
there are more than 30 categories of classification.
Fig. 19.3
Phylogenetic Trees
• Classification reflects phylogeny; one goal of
systematics is to create phylogenetic trees.
• Phylogeny is the evolutionary history of a group of
organisms.
• A phylogenetic tree indicates common ancestors and
lines of descent or lineages.
• Each branch in a tree is a divergence that give rise to
two or more new groups. For example, this portion of
an evolutionary tree says that monkeys and apes share
a common primate ancestor:
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Fig. 19.4
Biologists are moving away from
Linnaean categories
– Many systematists are moving away from the hierarchical
Linnaean categories because the categories are limiting and do
not fit well with recent findings.
– A new approach to identifying organisms is based on recently
developed molecular methods.
– Hebert holds that each organism has a DNA bar code. Biologists
can use bar codes to identify the species of an organism in any
stage of life, even as an egg or seed.
– Hebert has used a segment of mitochondrial DNA consisting of
only 648 base pairs.
– Hebert’s bar code does not work with all groups. Some groups,
such as bacteria, will require different bar code markers.
Determining the Major Branches
in the Tree of Life
• From the time of Aristotle to the mid-19th century,
biologists divided organisms into two kingdoms:
Plantae and Animalia.
• In 1866, a German biologist, Ernst Haeckel, proposed
that a third kingdom, Protista, be established to
accommodate bacteria and other microorganisms, such
as Euglena.
• Today, many biologists place algae (including
multicellular forms), protozoa, water molds, and slime
molds in kingdom Protista.
• In 1969, R. H. Whittaker proposed a five-kingdom
classification (Monera, Protista, Fungi, Plantae, and Animalia)
based mainly on cell structure and the way that organisms
derive nutrition from their environment.
• Kingdom Monera contained all the prokaryotes. These
unicellular organisms were collectively called the bacteria. The
other four kingdoms contain types of eukaryotes.
• Whittaker suggested that the fungi (which include the
mushrooms, molds, and yeasts) be removed from the plant
kingdom and classified in their own kingdom, Fungi.
• Kingdom Prokaryotae was established to accommodate the
bacteria.
The Three-Domain System
• In the late 1970s, Carl Woese and his collegues were studying
relationships among the prokaryotes using rRNA sequences.
• Woese found that the rRNA sequence of prokaryotes that lived
at high temperatures or produced methane was quite different
from that of all the other types of prokaryotes and from the
eukaryotes. Therefore, he proposed that there are two groups
of prokaryotes: the bacteria and archaea.
• In this course, we classify organisms into six kingdoms:
Bacteria, Archaea, Protista, Fungi, Plantae, and Animalia.
• The two designated domains are domain Bacteria and domain
Archaea. The eukaryotes are in the domain Eukarya.
Fig. 19.11
The viruses
are a special
case and are
not classified
in any of the
three
domains.
Domain Bacteria
• The bacteria are prokaryotic unicellular organisms
that reproduce asexually.
• Cyanobacteria are large photosynthetic prokaryotes.
• Most bacteria are heterotrophic.
• Bacteria are important in ecosystems because they
break down organic remains, thereby keeping
chemical cycling going.
• Some bacteria are parasitic and cause disease.
Domain Archaea
• Like bacteria, archaea are prokaryotic unicellular
organisms that reproduce asexually.
• The archaea are distinguishable from bacteria by a
difference in their rRNA base sequences and also by
their unique plasma membrane and cell wall
chemistry.
–
–
The chemical nature of the archaeal cell wall is diverse
and never the same as that of the bacterial cell.
The branched nature of diverse lipids in the archaeal
plasma membrane, for example, could possibly help
them live in extreme conditions.
• 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.
Domain Eukarya
•
•
•
Eukaryotes are unicellular to multicellular organisms, always
with a membrane-bound nucleus.
Sexual reproduction is common; various types of life cycles
are seen.
Protists
–
–
–
–
Protists are a diverse group of organisms that are hard to classify
and define.
They are eukaryotes and mainly unicellular, but some are
filaments, colonies, or multicellular sheets. Even so, protists do
not have true tissues.
Nutrition is diverse and some are heterotrophic by ingestion or
absorption and some are photosynthetic.
Green algae, paramecia, and slime molds are representative
protists.
• Fungi
– Fungi are eukaryotes that form spores, lack flagella, and
have cell walls containing chitin.
– They are multicellular with a few exceptions.
– Fungi are heterotrophic by absorption.
– Mushrooms, molds, and yeasts are representative fungi.
• Plants
– Plants are photosynthetic organisms that have become
adapted to a land environment.
– They share a common ancestor, which is an aquatic
photosynthetic protist.
– Land plants possess true tissues and have the organ system
level of organization.
• Animals
– Animals are motile eukaryotic multicellular organisms that
evolved from a heterotrophic protist.
– Like land plants, animals have true tissues and the organ
system level of organization.
– Animals ingest their food.
Table 19.2
Table 19.3