Phylogenies

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Chapter 14

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33 Terms

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Phylogeny

the evolutionary history of a group

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Phylogenetic tree

A diagrammatic reconstruction of that history showing relationships among species.

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Phylogenies

representations of evolutionary relationships among groups of organisms.

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Taxonomy

hierarchical way of categorizing species

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Binomial nomenclature

Gives every species a unique name consisting of two parts: the genus and the species. Ex. Homo sapiens

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Carl Linnaeus

The Swedish botanist who created the system of binomial nomenclature, classifying organisms into hierarchical categories.

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A phylogenetic tree may portray the evolutionary history of:

  • All life forms

  • Major groupings of taxa

  • Populations

  • Individuals

  • Small groups of closely related species

  • Genes and proteins

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Root

represents the ancestral lineage

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Nodes (branch points)

represent speciation events

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Sister taxa

Two taxa that are each other’s closest relatives (two branches off a single node)

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Sister clades

any two clades that are each other’s closest relatives

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Monophyletic group

A group of organisms that includes a common ancestor and all of its descendants, forming a complete branch on the tree of life.

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Paraphyletic group

A group that includes a common ancestor but not all of its descendants, resulting in an incomplete branch on the tree of life.

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Polyphyletic group

A group that does not include its common ancestor and contains members from different lineages.

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Parsimony

fewest character changes is our best hypothesis

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Synapomorphies

shared, derived characters used to establish evolutionary relationships.

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Ancestral characters

Found in common ancestor of two or more species/groups.

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Outgroup(s)

A reference group, should be closely related but without shared derived characters that unite the ingroup.

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Convergent evolution

Superficially similar traits may evolve independently in different lineages.

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Evolutionary reversal

A character reverts from a derived state back to an ancestral state

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Homoplasy

the similarity in traits or structures between different species or lineages that evolved independently, not from a shared ancestor.

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Morphological strengths

Allow inclusion of extinct species, determine ancestral states and date divergences

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Morphological weaknesses

Some taxa show few differences, difficult to compare distantly related species, variation is caused by the environment

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Developmental strengths

Clarifies deep relationships where significant divergence in form occurs in adults; we learn about mechanisms of diversification in form

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Developmental weaknesses

are “reused” for different functions

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Molecules strengths

Making for LOTS of characters, rates of change vary among loci in genome

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Molecules weaknesses

Only 4 traits states per character and homoplasies are common.

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Behavior strengths

Often as heritable as morphology (E,x. Fixed action patterns)

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Behavior weaknesses

Trait expression is often plastic, precise measurements of comparable behavior may be difficult

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Gonochoristic

Either male or female from birth to death.

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Protogynous hermaphrodites

Female first, larger individuals change to male

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Simultaneous hermaphrodites

Produce male and female gametes at the same time, mating partners may take turns fertilizing each other’s eggs.

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Molecular clock

The average rate at which a given gene or protein accumulates changes to gauge the time of divergence.