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Transcript
Fields of Study in Animal Diversity

Phylogeny


Systematics


Determining evolutionary relationships of
organisms (the study of phylogeny).
Taxonomy


The evolutionary history of a species or group of
related species.
Assigning organisms to different categories
based on their evolutionary relationships.
Nomenclature

The science of naming organisms
The Kingdoms


How are relationships – evolutionary relationships – determined?

Structure

Breeding behavior

Geographical distribution

Chromosome comparison

Biochemistry
These provide clues to how organism evolved
Structure

Many shared physical traits implies species are closely related

Came from a common ancestor:
Examples

Lynx and bobcats have similar structure (skeletal) = more
similarities than to any other groups

Dandelions and sunflowers = similar flower and fruit
structures
Conclusion


So what happens if you come across an unknown animal that can retract its
claws similar to:

Lions

Tigers

Bobcats

Lynxes?
What family should it belong to?
Breeding Behavior

What if two species live in the same area, and are similar in structure?

What else could you do analyze to determine if one species, or two different?

Look at breeding patterns
Example
•
•
2 species of frog:
–
Hyla versicolor
–
Hyla chrysoscelis
During mating season, the males make different sounds to attract females,
only mate with females of their own species
Geographical distribution
•
Location of species on Earth helps biologists determine relationships with
other species
•
Similarities between species separated by large distances show common
ancestry
Example

Many species of finches on the Galapagos Islands off the coast of South
America
Example

How did the birds get there?

Some members of species of finches from South America reached the
Galapagos Islands

These finches spread into different habitats and evolved into diverse
species…but kept genetic similarities
Chromosome Comparison

Number and structure of chromosomes
Example

The following all look different, grow in separate climates, however they all
have nearly identical chromosomal structure!!

Cauliflower

Cabbage

Kale

Broccoli
Example

Humans, gorillas and chimpanzees have chromosomes with similar appearances
Chromosomal Comparisons
Chromosomes of Unrelated Species
Bacteria
Other Species
Conclusion

Chromosomal similarities suggest a common ancestry
Biochemistry

Biochemical – DNA – evidence shows closely related species have similar DNA
sequences

Similar proteins

Each specie’s DNA has a unique sequence and order:

DNA
is located on a small section of
the chromosome
Example
≠
║
║
Conclusion
•
The more similarities two species have between the sequence/order of their
DNA molecule, the more closely related
Unexpected Family Tree

Currently, systematists use

Structural, biochemical, fossil, and molecular comparisons to infer evolutionary
relationships
You
Your Cousin!
Morphological and Molecular Homologies

In general, organisms that share very similar structures, breeding patterns or
similar DNA sequences

Are likely to be more closely related than organisms with vastly different
structures or sequences.

Not always true! Analogy vs. Homology
Homology

Homologous Structures – structures in different species that are similar
because of common ancestry.
Analogy

Analogous Structures – similarity in structures due to adaptations from similar
evolutionary pressures (convergent evolution) and not a common ancestor.

Convergent evolution occurs when similar environmental pressures and
natural selection

Produce similar (analogous) adaptations in organisms from different evolutionary
lineages
Australian Mole –
marsupial mammal
North American Mole –
placental mammal
Sorting Homology from Analogy
•
A potential misconception in constructing a phylogeny
–
Is similarity due to convergent evolution, called analogy, rather than shared
ancestry
Ex: Humans, gorillas, and ravens have the ability to problem-solve, and are highly
intelligent. Humans and gorillas share ancestry: homology. Ravens are in a
separate phylum (birds), so developed their intelligence separately from humans.
Linking Classification and Phylogeny

Systematists depict evolutionary
relationships

In branching phylogenetic trees

Each branch point

Represents the divergence of two species

“Deeper” branch points

Represent progressively greater amounts of divergence
“KLADOS” = Greek word meaning “BRANCH” or
“SPROUT”

Cladogram - a shows pattern of shared, inherited characteristics; a “graphic
organizer” based on measurable traits and not evolutionary relationships.
Cladogram for Transportation

Wheels are the most
ancestral (oldest).

Wings are the most
derived (newest).
Construct a Cladogram for Us!
Gorilla

Four limbs

Fur

No tail
Tiger

Four limbs

Fur

Tail
Lizard

Four limbs

Tail
Fish

Tail
Chimpanzee

Four limbs

Fur

No tail
Clade With 4 Limbs
Clade With Fur
Clade With No Tail
Characteristics (Traits) for
Constructing this Cladogram

Tail is the most ancestral

Four limbs is the oldest derived trait

Fur is a later derived trait

Loss of tail is the most derived trait
One Possible Cladogram
Four Limbs
Where’s the Tail?

How do we know the gorilla and chimpanzee
have lost their tail?

Sometimes cladists must compare
embryological development and internal
anatomy to determine relatedness.

May not be exactly the same structures.
Coccyx- Primate Vestigial Tails
Gorilla Pelvic Girdle
Human Pelvic Girdle
Vestigial Structure - historical remnants of a structure
that has little or no use in a modern organism but had
a function in ancestors.
A Vertebrate Cladogram
Lancelet
Vertebrae
Birds
Mammals
Reptile
Feathers
Amphibian
Fur
Fish
Endothermic
Lancelet
Amniotic Egg
Four Limbs
Vertebrae

What is the shared primitive character for
this clade?
Ans:
Birds
Reptile
Mammals
Feathers
Amphibian
Fur
Fish
Endothermic
Lancelet
Amniotic Egg
Four Limbs
Vertebrae


What is the shared derived
character for amphibians,
reptiles, birds & mammals?
Ans: Four Limbs
For reptiles, birds &
mammals?
Ans: Amniotic Egg
Phylogenetic Trees and Timing
A cladogram is not a phylogenetic tree; may need more
information (fossils, molecular systemics, etc.).
 Any chronology represented by the branching pattern of
a phylogenetic tree
 Is relative rather than absolute in terms of
representing the timing of divergences.

Phylograms

In a phylogram:
The
length of a
branch reflects the
number of genetic
changes that have
taken place in a
particular DNA or
RNA sequence in
that lineage.
A phylogram of homologous
hedgehog genes.
Outgroup
Ultrametric Trees

In an ultrametric tree:
The
branching
pattern is the
same as in a
phylogram, but
all the branches
that can be
traced from the
common
ancestor to the
present are of
equal length.
Outgroup
A Rule about Phylogenetic Trees

William of Ockham – 14th Cent. English
philosopher, stated that, when all qualities of
hypotheses are equal, the simplest
explanation for a phenomenon is usually
correct; Occam’s Razor: "entities must not
be multiplied beyond necessity" (entia non
sunt multiplicanda praeter necessitatem).

Parsimony – stingy, economical, fewest
complications.