Chapter 26

Tree of Life

Where Are We Going?

TaxonomyScientific discipline of classifying and naming

organismsPhylogeny

Interpreting diagrams of evolutionary historyApplication

What evolutionary history says about biological diversity

Binomial Nomenclature

Common names for casual usage, but not accurateWhat animals come to mind you when hear the

word ‘fish’?Different words depending on language

Biologist use Latin scientific namesCarolus Linnaeus

2 part system: genus and specific epithetHomo sapiens or Panthera pardus

Hierarchical (Linnaean) ClassificationLinnaeus grouped named

animals into categoriesgenus Panthera: leopard

(P. pardus), lion (P. leo), tiger (P.tigris), & jaguar (P. onca)

Based on morphological similarities

Used by taxonomistsTaxon is any level of the

hierarchyReview: How can you

remember the hierarchical order of taxons?

Doesn’t always reflect evolutionary history

Phylogenetic TreesDiagrams hypotheses of

evolutionary history of organismsDegree of relatedness to

ancestorsUsed by systematists

Can reclassify if mistake found

Only implies pattern of descent, not time or age

Branch means common ancestor, not taxon from taxon

Reading Phylogenetic Trees

Which of the trees below depicts a different evolutionary history from the other two?

Series of branch points Root is last common ancestor of tree Sister taxa share an immediate ancestor

Homology vs AnalogyHomologies are similarities due to shared

ancestryUsed to construct phylogenies

Analogies are similarity due to convergent evolutionWhat is convergent evolution?

‘Moles’: marsupial vs eutherian; similar livesWings: bats vs. insects vs. birds; relation to cats

More points of resemblance make more likely ancestor was shared

Applies to morphological and molecularsimilarities

Constructing Phylogenetic Trees

Must first separate homologous from analogousSystematists then infer phylogeny using cladistics

Using common ancestry to classify organismsCreate clades or groups containing an ancestral

species and all descendants

Clades vs. Taxons

Similar to taxons because both are nested groupsEquivalent only if it is monophyletic, containing

ancestor and ALL descendantsParaphyletic contains ancestor and SOME

descendantsPolyphyletic contain taxa with different ancestors

Shared … Characteristics

Ancestral originates in an ancestor of the taxonBackbones are an example for mammals, why?

Derived is a novelty unique to a cladeHair is an example for mammals, why?

Ancestral can qualify as derived at deeper branchesWhat branch point allows backbones to be shared

derived characteristics?

Constructing PhylogeniesUse the 1st appearance of each shared derived characteristic

Determine the outgroup and ingroup

Determined from morphology, paleontology, embryonic development, or genes

Compare members of the ingroup to each other and to the outgroup

The Genome’s Role in PhylogenyNucleic acids and other molecules are also used

to determine and test hypotheses about evolutionary relationships

Important for organisms that are unlikely to have morphological similarities or organisms without fossil recordsFungi, plants, and animalsProkaryotes and other microorganisms

Determine relationships at all levels of the Tree of Life

Rates of gene evolution variesrRNA is slow = good for relationships that diverged

100’s of millions of years agomtDNA is rapid = good for recent evolution

Evolving GenomesOrthologous genes

Homologous genes in different species through speciation

Can diverge only after speciation

E.g cytochrome C (ETC protein)

Paralogous genes From gene duplication

= multiple copies in the same genome

Can diverge within a species

E.g 1000’s of olfactory receptors

Humans and mice 99% orthologous; and yeast 50%

The Changing Tree of LifeInitially 2 Kingdoms

Plants: bacteria (cell wall), chloroplast organims, fungi (sessile)

Animals: protozoans (movement and eat)5 Kingdoms

Monera: prokaryotesProtista: unicellular organismsPlantae, Fungi, and Animalia: eukaryotes

Recently 3 DomainsMolecular evidence that prokaryotes as different from

each other as eukaryotesBacteria: most prokaryotes, close to chloroplasts and

mitochondriaArchaea: diverse prokaryotes living in extreme

environmentsEukarya: cells with true nuclei

Domain Systems1 example of Life’s connectionsMost of living organisms are single-celledRed lines are multicellularMonera gone because it contains 2 domainsProtista disappearing due to diversity and similarity to other eukarya

Alternate Form of Life ConnectionHorizontal gene transfer: exchange of info between genomesMitochondrial ancestor of bacteria and eukaryaChloroplasts of bacteria and green plantsCan explain inconsistency of treesOnly diagrammable as a ring