Lecture 5 – The Tree of LifePhylogenies and the History of Life- Life has existed on Earth for ~3.8 billion years- What patterns can be discerned in the tree of life as species appeared and disappeared over the course of history?- Why do these patterns exist?Darwin’s Tree of LifeSpecies- Usually, two or more distinct species derive from one ancestral group- A species is a distinct type of organism, formally defined as an evolutionarily independent population or group of populationsSpecies: How to define- Biological Concepto Based on reproductive isolation and lack of gene flowo Prezygotic – cannot breedo Postzygotic – offspring do not survive or are sterile- Morphospecies Concepto Differences in morphological featureso Distinct features are most likely to arise if populations are independent and isolated from gene flowo Problem: Cryptic Species - a group of.species.which satisfy the biological definition of species—that is, they are reproductively isolated from each other—but whose morphology.is very similar (in some cases virtually identical)- Phylogenetic Concepto Based on evolutionary historyo All species related to a common ancestoro All life forms a tree from one trunko Monophyletic group/clade/lineage A group contains only descendants of a common ancestor These groups identified by synapomorphiesSynapomorphy- Trait found in certain organisms that exists in no others- It is a homologous trait inherited from a common ancestor- Clades Derived Similarity- Single origin in relatively recent common ancestor – impliesclose relationship- Homologous structureso Ex. Numerous structures in mammals Hair Milk 3 middle ear bones Single pair of lower jaw bones Diaphragm Precise occlusion of teethPhylogenies- Representations of relationships between organismso Understand underlying unity of lifeo Provide insights into evolutionary innovations- Based on types of similarities between specieso Primitive similarityo Convergent similarity Ex. Bird and Bat wingso o Derived similarity Types of Similarity- Problem – How can we distinguish derived similarity (which is informative) from convergent and primitive similarity (which are not)?- Two clueso Types of groupingso Timing of common ancestryMonophyletic Groups Taxonomic TreeMammalian Synapomorphy- Fur and lactation make mammals a monophyletic group- Placenta distinguishes placental mammals from marsupials two different monophyletic groups)DNA as an Evolutionary Trait- Similarity of DNA sequence determines how closely related organisms are. The assumptions are that the DNA came from a common ancestor and changes to the DNA sequence are quite rare. So any shared difference must be because organsisms share more recent historyAstragalus- The shape of this bone relates to running speed and mode of locomotion- Might be a great morphogenic trait!Artiodactyls: Even-toed ungulates Evolutionary Origins of WhalesShort Interspersed Elements (SINE)- Short DNA sequences- Non-coding- Usually “junk DNA”o Some in gene sequenceso Some may be transcribed- Entered genome via reverse transcriptase- About 11% of human genome- Good evolutionary genetic markerWhale Cladogram- To which group of artiodactyls are whales most closely related?- Whales are too highly derived for morphological data to be useful- Molecular data – SINE transposable elements construct character matrix for 20 different genetic loci- State 0 = SINE elements absent- State 1 = SINE elements presentSINE sequences (Artiodactyls)Number of CommonSINEsBegins with most commonality- Cow and Deer
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