3. Introduction to systematics
The geological time:
•Life first started 600 million years ago.
•By human standards, this is a long, long time
•Insects 1st appeared in Silurian period (400-440
million years ago)
–The human species is less than 2 million years old
–Birds and mammals appeared less than 200 million
years ago
–Dinosaurs appeared 230 million yrs ago
–Primitive land plants appeared 425 million years ago
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4. Introduction to systematics
The geological time
•When did the first arthropods 1st appear?
•Go back in time to 600 million years ago, i.e.,
the Cambrian period of the Paleozoic era
•Bacteria and marine algae were dominant
forms of plant life at that time
•Small invertebrates were abundant in warm,
shallow seas
•Land masses were largely devoid of life
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7. Introduction to systematics
The geological time …
•Is it not incredible to even think of
studying events that happened long ago?
•Biologists and paleontologists have tools to probe
today’s world to get clues of the distant past
•These clues merge into a rough outline of arthropods’
phylogenetic tree
•These help us to study similarities, differences and
relationships among surviving taxa.
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8. Introduction to systematics
Tools and techniques
•Foundations of phylogenetic research:
•Paleontology (study of prehistoric forms of life)
•Systematics (classification of organisms based on structural or
evolutionary relationships)
•Both approaches are based on two assumptions:
•All forms of life share similar DNA-based system of
inheritance
•Natural selection has remained unchanged throughput
evolutionary time
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9. 9
• Phylogenetics is the study of the
evolutionary history and
relationships among individuals,
groups of organisms
• e.g., populations, species, or
higher taxa,
• or other biological entities with
evolutionary histories (e.g.,
genes, biochemicals, or
developmental mechanisms).
10. Introduction to systematics
Tools and techniques …
Fossil record …
•Pre-eminent database for phylogenetic research
•Prehistoric arthropods were small and delicate
•Did not preserve as well as large animals (bones, teeth, shells)
•But they preserved better than invertebrates because:
•Exoskeleton maintained shape and did not decay rapidly
•Fossil arthropods are found in:
•Sedimentary rock strata and deposits of coal, shale, volcanic
ash throughout the world
•Good fossil beds containing arthropods are not common
•They are rather patchy
•Many species are represented by one species 10
11. Introduction to systematics
Tools and techniques …
Fossil record …
•Amber:
•Fossil insects can also be found in amber, Amber is a petrified
resin (sap) of prehistoric trees
•Entangled in the sticky resin, captive insects are preserved in
every detail as the viscous sap gradually hardens to glass-like
consistency
•Amber deposits containing insects are found in northern Europe
(shores of Baltic Sea), Burma, Siberia, Canada, Alaska, Mexico,
Dominican Republic)
•Ambers formed from early Cretaceous to recent times 11
12. Introduction to systematics
Tools and techniques …
Fossil record …
•Until recently scientists relied on their own interpretation
of fossils to reconstruct phylogenetic trees
•That was not reliable
•In the last 30 years, other techniques developed to take care of
fossils
•Chemistry
•Physics
•Computer science gave more precise and objective information about fossils
and their relationship to extant life forms
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13. Introduction to systematics
Tools and techniques …
Fossil record …
•1. Radiometric dating
•Approximate age of a fossil is vital where to fit in the
family tree of its relatives
•Traditionally, fossils have been dated by the rock strata
where they occur
•More accurate ages of these strata can be inferred by
measuring the concentration of radio active isotopes:
•Such as carbon-14
•Or by determining the ratio between a radio active element
(uranium-235, thorium-232, potassium-40) and its
spontaneous decay product 13
14. Introduction to systematics
Tools and techniques …
Fossil record …
•1. Radiometric dating …
•Only living plants and animals assimilate carbon-14
•So age of fossil can be determined by measuring the amount
of carbon-14 that has not decayed to nitrogen-14.
•Carbon dating measures only young fossils (<50 thousand
years old)
•Measurable amount of carbon-14 can be found on young fossils only
•Older strata of rock that bear trace amounts of radioactivity
may be dated by measuring the ratio between unstable
isotopes 14
15. Introduction to systematics
Tools and techniques …
Fossil record …
1. Radiometric dating …
•Unstable isotopes
•These isotopes have very long half-life
•Ranges from 713 million to 14 billion years
•Can measure samples that are 100,000 years old to before
the beginning of prehistoric life
Unstable isotope Decay product
Uranium-235 Lead-207
Thorium-232 Lead-208
Potassium-40 Argon-40
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16. Introduction to systematics
Tools and techniques …
Fossil record …
2. Numerical taxonomy
•Digital computer technology provides best approach to
evaluate similarities and differences among taxa
•Statistical techniques such as:
•Principal component analysis
•Cluster analysis
•Factor analysis
•Discriminant analysis
•Multidimensional scaling are used to sort out morphological,
behavioral and biochemical data
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17. Introduction to systematics
Tools and techniques …
Fossil record …
2. Numerical taxonomy …
•The statistical methods allow taxonomists to quantify
the degree of similarity
•Calculations may employ:
•Phenetic approach (primitive and advanced character states)
•Cladistic approach (only advanced character states)
•The resulting phylogenetic trees will be known as:
•Phenograms
•Cladograms
•Dendrograms . These are intended to show biological affinity
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18. Introduction to systematics
Tools and techniques …
Fossil record …
3. Biochemistry
•Enzymes and metabolic pathways can reveal inherent patterns
within an evolutionary lineage
•Nutrient processing
•Chemical defense
•Locomotion
•Intercellular and intracellular communication
•Homeostatic mechanisms
•If a novel biochemical mutation occurs, that may
mean selective advantage and adaptive radiation
from a certain common ancestor
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19. Introduction to systematics
Tools and techniques …
Fossil record …
4. Nucleotide sequencing
•Automated methods of sequencing nucleotides in
DNA (and ribosomal RNA) have opened a new window
to the past
•Evolutionary distance between two organisms can be
inferred from the number and frequency of changes in
the sequence of base-pairs in corresponding regions of
DNA (or RNA)
•Rate of mutation assumed constant, the time two
groups diverged from a common ancestor can be
estimated
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20. Introduction to systematics
Tools and techniques …
Fossil record …
4. Nucleotide sequencing …
•Recently, biologists have extracted and sequenced DNA
from fossils
•DNA fragments were isolated from termites and stingless bees
preserved in amber
•Fossil DNA was cloned (replicated) using polymerase chain reaction
(PCR)
•PCR is an enzymatic method that mass-produces identical
copies of DNA molecule
•Enough prehistoric DNA manufactures, then sequenced and
compared to similar fragments of living relatives
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