evolution of life 2014

8/15/2019 Evolution of Life 2014

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Study Area 3Study Area 3

Prepared by RaajeswariRajendran


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This chapter describes how biologists trace phylogeny◦ The evolutionary history and relationships of a species or

group of related species.

◦ The phylogeny of a group of organisms can be described by

the pattern of branching depicting their evolutionaryrelationships – a branching diagram called a phylogenetic

tree or cladogram.

◦ The phylogenetic tree (the pattern of relationships) can also

be the basis for hypothesizing how organisms evolved (the process of evolution).


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To determine phylogeny scientists use a branch of science

!nown as systematics – a scientific discipline focused on

classifying organisms and determining their evolutionary

relationships.

"iologists use systematics◦ As an analytical approach to understanding the diversity and

relationships of organisms both present#day and e$tinct.

◦ %hylogenies are based on common ancestries inferred from

fossil morphological and molecular evidence.


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&urrentlysystematists use

◦ 'orphological biochemical

and molecularcomparisons toinferevolutionaryrelationships


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nvolves the study of body form and shape. nformation about phylogeny can be obtained through

*. +mbryology

,. Study of vestigial organs3. The fossil record


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f the early stages of development in vertebrates are compared

gill slits are observed to form in all embryos even though theydo not persist in adults other than in fishes.

The stri!ing similarity of the embryos of fishes frogs lizards

birds and mammals has led biologists to hypothesize that these

organisms had a single line of descent and are all classified asvertebrates.

This similarity indicates that all vertebrates share a

fundamental step in their developmental programs and it is the

modification of the later stages of development which

accounts for the great diversity of form within the vertebrates.

+.g. birds develop feathers and humans have a brain larger

than that of other primates.


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Striking similarity between the embryos of vertebrates, from

fishes to mammals


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-estigial organs are rudimentary organs with no apparent

function but are also clues to evolutionary relationships whencomparing organisms.

+.g. humans have a vestigial tail (coccy$) similar to the

prehensile tail of mon!eys an adult baleen whale lac!s teeth

but develops them as an embryo. The best e$planation of vestigial organs is that they were

functional and present in ancestral species and therefore are

indicators of phylogeny.


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"iologists draw on the fossil record

◦ /hich provides information about ancient organisms Sedimentary roc!s

◦ Are the richest source of fossils

◦ Are deposited into layers called strata

1 Rivers carry sediment to the

ocean. Sedimentary rock layerscontaining fossils form on the

ocean floor.

2 Over time, new strata are

deposited, containing fossils

from each time period.

3 As sea levels change and the seafloor

is pushed upward, sedimentary rocks are

exposed. Erosion reveals strata and fossils.

Younger stratum

with more recent

fossils

Older stratum

with older fossils


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The fossil record

◦ s based on the se0uence in which fossils have accumulated in such

strata.

1ossils reveal

◦ Ancestral characteristics that may have been lost over time.

◦ 1ossils can also be compared with living organisms and included in

phylogenetic trees although only the hard parts of organims such as bones teeth and wood are preserved and available for comparative

study.

◦ 1ossil records supply evidence of both the forms of life in the past and

their geological ages.

◦

2owever there is no way of !nowing whether a fossil is a directancestor of a more recent species or represents a related line of descent

(lineage) that became e$tinct. Also the fossil may not be complete.


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Though sedimentary fossils are the most common

◦ %aleontologists study a wide variety of fossils

(a) inosaur !ones !eing excavated

from sandstone

(g) "usks of a #$,%%%&year&old mammoth,

fro'en whole in Si!erian ice

(e) (oy standing in a )*%&million&year&old

dinosaur track in +olorado

(d) +asts of ammonites,

a!out $* million

years old

(f) -nsects

preserved

whole in

am!er

(b) etrified tree in Ari'ona, a!out

)/% million years old

(c) 0eaf fossil, a!out 1% million years old


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Three types of evolution have been noted

*. ivergent evolution

,. &onvergent evolution

3. %arallel evolution


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&omparative morphology focuses on the basic similarity of

organisms as evidence of how they diverged during evolutionand departed from a common ancestral form – divergentevolution.

+.g. the flightless emu and a sparrow are different in manyways but both have feathers indicating they are related as

birds. 4i!ewise the comparative study of bones reveals thatthe flipper of a whale has the same basic structure as the frontleg of a frog or crocodile and the wing of a bird or bat.

Structures that have the same basic plan but not necessarilythe same function are !nown as homologous structures thatindicate divergent evolution.

2omologous structures indicate common inheritance – acommon ancestor.


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2omologous structures between organisms

◦ Are anatomical resemblances that represent variations on a structural theme that was present in a common ancestor.

◦ 2omologous structures indicates that birds frogs crocodiles bats and whales are related as tetrapods mammalian forelimbs arehomologous structures that indicate humans cats whales and bats descended from a common ancestor.

Human Cat Whale Bat


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n convergent evolution organisms from different

unrelated or distantly related lineages come to resembleone another superficially.

Structures that have a similar function as a result ofconvergence are called analogous structures.

+.g. plants of the families &actaceae in the 5ew /orldand +uphorbiceae in the 6ld /orld loo! remar!ablysimilar with their succulent leafless stems both groupsof plants are adapted to arid environments and their

succulence is an analogous feature that serves as a storeof water.


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&onvergent evolution occurs when similar environmental pressures andnatural selection produce similar (analogous) adaptations in organisms

from different evolutionary lineages. +.g. a forest#dwelling Australian marsupial called the sugar glider is

superficially very similar to flying s0uirrels which are gliding eutheriansthat live in 5orth American forests – the ability to glide through the airevolved independently in these two distantly related groups of mammals.

Another e$ample shown below is the similarity between the marsupialmole and the mole which is eutherian.

Marsupial mole

Mole


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Prepared by RaajeswariRajendran

n Australia convergent evolution

◦ 2as resulted in a diversity of marsupials that resemble eutherians inother parts of the world

Marsupial mammals Eutherian mammals

Plantigale

Marsupial mole

Sugar

glider

Wombat

Tasmanian devil

Kangaroo

eer mouse

Mole

Wood!hu!"

#lying s$uirrel

Wolverine

Patagonian !avy


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n addition to fossil organisms

◦ %hylogenetic history can be inferred from certain morphological and

molecular similarities among living organisms n general organisms that share very similar morphologies or similar 5A

se0uences

◦ Are li!ely to be more closely related than organisms with vastlydifferent structures or se0uences

Systematists use computer programs and mathematical tools◦ /hen analyzing comparable 5A segments from different organisms

◦ /ith the development of techni0ues for se0uencing amino acids in proteins and nucleotides in 5A it is now possible to compareorganisms at the most basic level.


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There are several ways to study homologies in molecules

*. Study of amino acid se0uences

,. Study of nucleotide se0uences

3. Study of mitochondrial 5A se0uences

7. Study of ribosomal 85A

9. 5A#5A hybridization – a techni0ue where single strands of 5A fromtwo organisms are combined to form hybrid double helices. The melting

point of this hybrid 5A is directly related to how closely the nucleotidese0uences match and gives an overall measure of the genetic similarity of a

pair of organisms the lower the melting point the greater the difference between the two strands while the higher the melting point the closer the

similarity between the two strands.


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%hylogenetic systematics connects classification with evolutionary history

Ta$onomy

◦ s the ordered division of organisms into categories based on a set ofcharacteristics used to assess similarities and differences.

"inomial nomenclature

◦ s the two#part format of the scientific name of an organism

◦ /as developed by &arolus 4innaeus.

The binomial name of an organism or scientific epithet

◦ s latinized

◦ s the genus and species


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Systematists depict evolutionary relationships

◦ n branching phylogenetic trees.

Panthera pardus

4leopard5

Mephitismephitis

4striped skunk5

Lutra lutra4European

otter5

Canisfamiliaris

4domestic dog5

Canislupus

4wolf5

Panthera Mephitis Lutra Canis

2elidae 3ustelidae +anidae

+arnivora O r d e r

F a m

i l y

G e n u s

S

p e c i e s


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+ach branch point

◦ 8epresents the divergence of two species

0eopard omestic cat

+ommon ancestor


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:eeper; branch points

◦ 8epresent progressively greater amounts of divergence

0eopard omestic cat

+ommon ancestor

6olf


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%hylogenetic systematics informs the construction of phylogenetic trees based

on shared characteristics

A cladogram

◦ s a depiction of patterns of shared characteristics among ta$a

A clade within a cladogram

◦s defined as a group of species that includes an ancestral species and all itsdescendants

&ladistics

◦ s the study of resemblances among clades

&lades

◦ &an be nested within larger clades but not all groupings or organisms

0ualify as clades


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n cladistic analysis

◦ &lades are defined by their evolutionary novelties.

A shared primitive character

◦ s a homologous structure that predates the branching of a particular clade

from other members of that clade

◦ s shared beyond the ta$on we are trying to define

A shared derived character

◦ s an evolutionary novelty uni0ue to a particular clade


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Systematists use a method called outgroup comparison

◦ To differentiate between shared derived and shared primitivecharacteristics.

As a basis of comparison we need to designate an outgroup

◦ which is a species or group of species that is closely related to theingroup the various species we are studying

6utgroup comparison

◦ s based on the assumption that homologies present in both theoutgroup and ingroup must be primitive characters that predate thedivergence of both groups from a common ancestor


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The outgroup comparison

◦ +nables us to focus on


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#$%$ &ancele(ougroup)

&amprey

'ass

Frog

#urle

&eopard

erebral

column

(bacbone)

Four *aling

legs

+inged ,a*s

$mnion

+air

erebral

column

+inged ,a*s

Four *aling legs

$mnion

+air

(a) Characer able (b) Phylogeneic ree

C + $ - $ C # . - S

& a n c e l e

( o u g r o u p )

& a m p r e y

' a s s

F r o g

# u r l e

& e o p a r d

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An outgroup is a species or group of species that isclosely related to the ingroup the various species being

studied

The outgroup is a group that has diverged before the

ingroup

Systematists compare each ingroup species with the

outgroup to differentiate between shared derived and

shared ancestral characteristics


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Any chronology represented by the branching pattern of a phylogenetic

tree

◦ s relative rather than absolute in terms of representing the timing of

divergences


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The best hypotheses for phylogenetic trees

◦ Are those that fit the most data morphological molecular and fossil. 'uch of an organism=s evolutionary history is documented in its genome

&omparing nucleic acids or other molecules to infer relatedness

◦ s a valuable tool for tracing organisms= evolutionary history


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The tree of life

◦ s divided into three greatclades called domains"acteria Archaea and

+u!arya The early history of these

domains is not yet clear

(acteria Eukarya Archaea

0 Sym!iosis of

chloroplast

ancestor with

ancestor of green

plants

3 Sym!iosis ofmitochondrial

ancestor with

ancestor of

eukaryotes

2 ossi!le fusion

of !acterium

and archaean,

yielding

ancestor of

eukaryotic cells

1 0ast common

ancestor of all

living things

0

3

2

1

)

#

$

1

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( i l l i o n y e a r s a g o

Origin of life

evolution of life 2014

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