Phylogeny and Systematics

Chapter 26:(Making “Trees of Life”)

Macroevolution•studies focus on change that occurs at or above the level of species▫The origin of taxonomic groups higher than species level

How does this occur?•Evolution of new traits (novelties)•mass extinctions•Open adaptive zones (divergent evolution)

•Currently, scientists use▫ Morphological, biochemical, and molecular comparisons to infer evolutionary relationships Obtained through fossil studies, DNA technology and current organisms

PhylogenyWhat is phylogeny?•The evolutionary history of a group

•Systematics attempts to reconstruct phylogeny, by analyzing evolutionary relatedness.▫ Use morphological and biochemical similarities

•Molecular systematics uses DNA, RNA and proteins to infer evolutionary relatedness.

•Different tools are used to reconstruct phylogenies called phylogentic trees.

Molecular systematics

Systematics•Uses evidence from fossil record and existing organisms to reconstruct phylogeny (Linneaus)

•Binomial nomenclature Genus species keeps identity of organism universal▫Other taxa used to classify

Domain, Kingdom, Phylum, Class, Order, Family, Genus, species

TaxonomyLinnaeus ordered

division of organisms into categories

based on a set of

characteristics used to assess similarities

and differences

Linking Classification and Phylogeny

•Systematists depict evolutionary relationshipsIn branching phylogenetic trees

Figure 25.9

Panthera pardus

(leopard)

Mephitis mephitis

(striped skunk)

Lutra lutra (European

otter)

Canis familiaris

(domestic dog)

Canislupus (wolf)

Panthera Mephitis Lutra Canis

Felidae Mustelidae Canidae

Carnivora

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•Each branch point▫Represents the divergence of two species

Leopard Domestic cat

Common ancestor

•“Deeper” branch points▫Represent progressively greater amounts of divergence

Leopard Domestic cat

Common ancestor

Wolf

Cladistics•Cladogram is a tree with two way branch points

•Each branch point represents divergence from common ancestor

•Each branch is called a clade

•Clades▫ Can be nested within larger clades, but not all groupings or organisms qualify as clades

•3 types of groupings ▫ Monophyletic ▫ Polyphyletic▫ Paraphyletic

Different Types of Clades•Monophyletic = single ancestor gave rise to all species in the taxon; ONLY valid clade

• Polyphyletic = includes numerous types of organisms that lack a common ancestor; not a valid clade

•Paraphyletic = a grouping that consists of an ancestral species and some, but not all, of the descendants; not a valid clade

Grouping 1

Monophyletic Paraphyletic

Grouping 2

Polyphyletic

Grouping 3

Clades

Let’s practice…

Making “Trees”: Morphological & molecular homologies

•similarities based on shared ancestries▫bone structure ▫DNA sequences

•beware of analogous structures convergent evolution

Not all Similarities Represent Common Ancestry

•Homologous structures indicate shared common ancestry▫Homologous structures are therefore evidence of divergent evolution

•Analogous structures are similar in function but not in evolutionary history▫Analogous structures are evidence of convergent evolution

•It is not always easy to sort homologous from analogous structures

•RECALL…•Convergent evolution occurs when similar environmental pressures and natural selection▫ Produce similar (analogous) adaptations in organisms from different evolutionary lineages

Eutherian (placental)

Marsupial

•1. Cladistics = ▫sorts homologous from analogous structures▫sorts primitive and shared derived characteristics

▫Makes cladograms

Making Evolutionary Life Trees: Illustrating

Phylogeny

The Universal Tree of Life • The tree of life is divided into three great clades called domains:▫ Bacteria, Archaea, and Eukarya

Figure 25.18

Bacteria Eukarya Archaea4 Symbiosis of

chloroplast ancestor with ancestor of green plants

3 Symbiosis of mitochondrial ancestor with ancestor of eukaryotes

2 Possible fusion of bacterium and archaean, yielding ancestor of eukaryotic cells

1 Last common ancestor of all living things

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Origin of life

•A shared primitive character▫a homologous structure that is shared by all groups we are trying to define

•A shared derived character▫A new evolutionary trait unique to a particular clade(s)

▫Making Cladograms Activity Time

A Cladogram

What is the shared primitive characteristic? Notochord

Phylograms• In a phylogram▫ The length of a branch in a cladogram reflects the number of genetic changes that have taken place in a particular DNA or RNA sequence in that lineage

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