Chapter 19 Systematics and Phylogency. Systematics reconstructs evoluntary history and classifies or groups organisms according to evolutionary findings

Chapter 19

Systematics and

Phylogency

• Systematics reconstructs evoluntary history and classifies or groups organisms according to evolutionary findings

• An organized approach using data from fossil record, comparative anatomy, and molecular data to determine evolutionary relationships

• Taxonomy is the branch of biology that identifies, names, and classifies organisms

• A natural system of classification is based on the understanding of how organisms are related to each other through evolution

• Greek philosopher, Aristotle, identified organisms and put them in groups

• In Middle Ages, names were changed to Latin descriptions

• John Ray in seventeenth century shortened many of the descriptions

Fig. 19.2

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

a: Courtesy Uppsala University Library, Sweden; b: © Arthur Gurmankin/Visuals Unlimited; c: © Dick Poe/Visuals Unlimiteda.

b. Lilium canadense c. Lilium bulbiferum

• Mid-eighteenth century, Carlolus Linnaeus developed binomial nomenclature

• Each species has a two-part name

• First word is genus, a classification category that contains related species

• Second word is the specific epithet that sometimes tells us something descriptive about the organism

• Scientific name is in italics (or underlined if handwritten)

• Genus is capitalized and specific epithet is not

• Genus name can be used alone if referring to a group of organisms

• Genus can be abbreviated to a single letter if used with specific epithet and if full name has been given before

• Homo sapiens is the scientific name for modern humans

• Common names often vary from place to place

• Sometimes the same common name may indicate different organisms in different places

• Latin was the universal language at the time of Linnaeus and scholarly work appeared in the Latin

• Scientists throughout the world use the same scientific binomial name

• The Linnaean Society rules on the appropriateness of the binomial name for each species

• Today about a million species of animals and a half million species of plants and microorganisms have been named

• All birds have been named, but numerous insects remain to be named

Fig. 19.3


DOMAINS

Eukarya

KINGDOMS

Plantae

PHYLA

Anthophyta

Eudicotyledones

CLASSES

Vitales

ORDERS

Parthenocissus

SPECIES

Parthenocissus quinquefoliaVirginia creeper (five-leaf ivy)

Vitaceae

FAMILIES

GENERA

P. quinquefolia

• A taxon is a group of organisms that fills a particular category of classification

• Linnaeus published his work on classification in Systema Naturae in 1735

• Today, taxonomists used these major categories of classification: species, genus, family, order, class, phylum, kingdom, and domain

• The higher the category, the more inclusive it is

• Categories are nested because one group exists inside another group

• Ex. Domain contains many kingdoms and one kingdom contains many phyla etc.

• Traits shared by organisms in a classification category are called characters

• Aim of systemics is to determine phylogeny

• A depiction of evolutionary history is a phylogentic tree

• The tree has many branch points and they show that it is possible to trace the ancestry of a group of organisms back farther and farther in past

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reindeer monkeys apes

common ancestor(placental mammal)

• Because classification is hierarchical, classification categories can be used to construct a phylogenetic tree

• A species is more closely related to other species in the same genus and is related to, but less so, to genera in the same family

Fig. 19.4Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

AepycerosMelampus(impala)

Aepyceros Oryx Cervus Rangifer

CervidaeBovidae

Artiodactyla

Gen

us

Sp

ecie

sF

amily

Ord

er

Oryxgazella(oryx)

Cervuselaphus

(red deer)

Rangifertarandus(reindeer)

• Cladistics is based on the work of Willi Hennig

• A way to trace evolutionary history of a group by using shared traits, derived from a common ancestor, to determine which species are most closely related

• These traits are used to construct phylogenetic trees called cladograms

• Cladogram is the evolutionary history of a group based on the available data

• Begins with a table that summarizes the derived traits of the species being compared

• At least one (or more) species is considered an outgroup

• Ingroup are the species being studied

• Any trait found in both the ingroup and outgroup is a shared ancestral trait that has been present in a common ancestor

• An outgroup shows which traits are shared derived traits called synapomorphies

• Any trait not found in outgroup is a shared derived trait

• We can use fossil record to discover which traits are shared traits, but fossil record is rarely complete

• All synapomorphies indicate evolutionary relationships among members of ingroup that are used to construct the cladogram

• A cladogram contains several clades

• Each clade includes a common ancestor and all its descendants that share one or more synapomorphies

• Difference in synapomorphies distinguish clades

Fig. 19.5Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

chim

pan

zee

do

g

fin

ch

cro

cod

ile

liza

rd

fro

g

tun

a

lan

cele

t (o

utg

rou

p)

Species

Tra

its

mammary glands

gizzard

epidermal scales

amniotic egg

four limbs

vertebrae

hair

ingroup

notochord inembryo

• Cladogram is objective because it lists the data used

• Usually uses many traits

• A cladogram is a hypothesis that can be tested and either corroborated or refuted with new data

Fig. 19.6


vertebrae

four limbs

feathers

gizzard

hair, mammary glands

long canine teeth

enlarged brain

chimpanzee

tuna

frog

lizard

crocodile

finch

terrier

lancelet (outgroup)

common ancestor

epidermalscales

Amnioticegg

commonancestor

• Cladists use the principle of parsimony, which states that the minimum number of assumptions is the most logical

• Cladograms are constructed to leave the fewest number of shared derived characters unexplained or that minimizes the number of evolutionary changes

• Parsimony problems arise when DNA sequencing is used to make cladograms

• Mutations, especially in noncoding DNA, can be high so base changes are not reliable data to distinguish clades

• Because of this, some systematists use statistical tools not parsimony to build phylogenetic trees

• This branch of systematics is called statistical phylogenetics

• Clades are often nested inside other clades

• From the cladogram we looked at, birds are closely related to crocodiles and should be classified with them as well as with lizards

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• Birds, dinosaurs, lizards, snakes, and crocodilians can trace ancestry to amniotes called diapsids

• They have the skull openings of a diapsid

orbitdorsal temporalopening

lateral temporalopening


• Cladistics only allow monophyletic groupings

• A monophyletic group includes a common ancestor and all the descendants of that ancestor

• A paraphyletic group contains a common ancestor and does not include all the descendants

• A polyphyletic group contains some of the descendants of more than one common ancestor and not all the common ancestors

• Because Linnean classification system allows groupings other than monophyletic, biologists are presently trying to determine how it could be changed to reflect our current understanding of phylogeny

• Homology is structural similarity that stems from having a common ancestor

• Homologous structures are similar to each other because of common descent

• Convergent evolution has occurred when distantly related species have a structure that looks the same only because of adaptation to the same type of environment

• Analogy is similarity due to convergence

• Analogous structures have the same function in different groups, but do not have a common ancestry

• Evidence exists that dinosaurs cared for their young in a manner similar to crocodilians and birds

• Behavioral and morphological data indicates that dinosaurs, crocodilians, and birds are related through evolution

• Cytochrome c is a protein that is found in all aerobic organisms, and its sequence has been determined for a number of different organisms

• The amino acid differences indicate how closely related organisms are

• Study of RNA differences between prokaryotes and eukaryotes resulted in the acceptance of the three-domain system of classification

• DNA differences can substantiate data, help trace the course of macroevolution, and fill gap in fossil record

Fig. 19.10

• Molecular clocks use DNA sequence data to suggest how long primates have been separate


human

PRESENT

white-handedgibbon

rhesusmonkey

greenmonkey

capuchinmonkey

102030405060Million years ago (MYA)

Increased difference in DNA

commonchimpanzee

• From Aristotle to twentieth century, biologists used two kingdoms: kingdom Plantae and kingdom Animalia

• In 1880s, Ernst Haeckel proposed a third kingdom called Protista

• In 1969, R.H, Whittaker expanded the classification system to five kingdoms: Monera, Protista, Fungi, Plantae, and Animalia

• In late 1970s, Carl Woese using RNA data proposed two groups of prokaryotes the bacteria and the archaea

• They are so different that they are raised to a higher category called a domain

• Now we use a three domain system

• Domain Bacteria is a large diverse group found nearly everywhere on Earth

• Domain Archaea that look like bacteria, but are different in their rRNA base sequences and unique plasma membranes and cell wall chemistry

• Domain Eukarya are unicellular to multicellular organisms whose cells have a membrane-bound nucleus and various organelles

Fig. 19.11


common ancestor

ARCHAEABACTERIA

EUKARYA

animalsfungi

plants

cyanobacteria

protists protists

heterotrophicbacteria

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Chapter 19 Systematics and Phylogency. Systematics reconstructs evoluntary history and classifies or groups organisms according to evolutionary findings