Unit 3: Macroevolution

Phylogenies

Taxonomy & Classification

• Three domains: Bacteria, Eukarya, and Archaea

• Taxonomy order

  • Domain

  • Kingdom ← largest most inclusive level

  • Phylum

  • Class

  • Order

  • Family

  • Genus

  • Species ← most specific level

• Specie’s scientific name is Latin - genus & species

• Taxonomy: classification of organisms based on shared characteristics

• Monera: 2 domains, Archaea & Bacteria

  • Moneran: informal name of members of this group, as is prokaryote to denote a member of either domain

Phylogenetic Trees

• Phylogeny: the study of the evolutionary relationships among a group of organisms

• Phylogenetic tree (aka cladogram): a construct that represents a branching structure to illustrate the true evolutionary relationship of a group of organisms, based on

  • Morphology and fossil record

  • Embryology

  • DNA, RNA, and protein similarities

• Branch point (node): where an ancestral lineage splits into two descendant lineages

  • May occur because the group was divided by geographic isolation (different selection pressures and different mutations)

• Any organism not shown across the top of the tree is an extinct species

Traditional Classification and Phylogenies

• Classification began by using only physical traits, which was often reflective of the phylogeny of organisms

• The use of embryological and biochemical evidence supported changes in phylogenies and resulted in changing their classification

• Ex: birds are now classified as true reptiles

Taxa and Clades

• Taxon: any group of species designated by name (categories like kingdoms, classes, etc.)

• Every node gives rise to two lineages

  • Polytomy: If more than 2 lineages branch from 1 node; this is temporary (future evidence will solve this)

• Sister taxa: organisms sharing an immediate common ancestor

• Branches can be rotated as long as the common ancestor remains the same

• Clade: any taxon that consists of all the evolutionary descendants of a common ancestor

  • True clade (monophyletic group): contains a common ancestor and all of its descendants

  • Paraphyletic group: doesn’t contain all descendants from a common ancestor

  • Polyphyletic group: doesn’t have a unique common ancestor for all the descendants

Anagenesis v. Cladogensis

• Anagenesis (phyletic change): the accumulation of changes in a species that leads to speciation over time

  • Evolution of a whole population

  • Ancestral population can be considered extinct (evolutionary lineage)

  • Entire population is different from the ancestral population

  • Creation of a new species and og is extinct

• Cladogenesis: the budding of one or more new species from a species that continues to exist

  • Results in biodiversity

  • Much more common in the history of life on Earth

Recreating Phylogenies

• The fossil record served as the first evidence that evolution occurs and helps illustrate that species change over time

  • Deeper = Older

• Relative dating: location where fossils are found is indicative of its age which can be used to recreate phylogenies

• Radioactive carbon-14 dating is used to determine the age of the fossil

Homologous Features

• Homologous features: any feature shared by two or more species and inherited from a common ancestor

• Can be heritable traits like anatomical structures, DNA sequences, or similar proteins

• Traits change during evolutionary time

  • Ancestral trait: original shared trait

  • Derived trait: trait found in the newly evolved organism being examined

Analogous Structures

• Analogous structures are similar in function and sometimes structure but are not inherited from a common ancestor

• Cannot be used in establishing phylogenies

• From similar selective pressures or from habitat

• Can also exist due to evolutionary reversals

  • Ex: Fish gave rise to tetrapods → Cetaceans (whales and dolphins) are tetrapods that returned to the ocean

Molecular Clocks