All life is interconnected by descent

Phylogeny and the Tree of Life Classification & Evolution ofCaminalcules All life is interconnected by descent
Humans Rattlesnake Pine tree Amoeba Bacterium How to determine the pattern of descent? Systematics - field of biology dealing with diversity and evolutionary history of life
Includes Taxonomy:DINC Description Identification Nomenclature Classification Goal: Determine Evolutionary History (Phylogeny) of Life Description = assign features Character = a feature (e.g., petal color) Character states = two or more forms of a character (e.g., red, white). Identification = associate an unknown with a known How? One way:
Taxonomic Key, e.g., Tree . Species A Leaves simple . Species B Leaves pinnate ....... Species C Herb Flowers red . Species D Flowers white ... Species E Nomenclature Naming, according to a formal system. Binomial: Species are two names (Linnaeus): E.g., Homo sapiens Homo = genus name sapiens = specific epithet Homo sapiens = species name Nomenclature Hierarchical Ranks: Domain Kingdom Phylum Class Order Family Genus Species Classification Placing objects, e.g., life, into some type of order.
Taxon = a taxonomic group (plural = taxa). How to classify life Phenetic classification
Based on overall similarity Those organisms most similar are classified more closely together. Problem with phenetic classification:
Can be arbitrary,e.g., classify these: Phylogenetic classification
Based on known (inferred) evolutionary history. Advantage: Classification reflects pattern of evolution Classification not ambiguous = representation of the history of life Ingroup group studiedOutgroup group not part of ingroup, used to root tree Branch point (node) Taxon A Taxon B Sister taxa Taxon C ANCESTRAL
Fig. 26-5 Branch point (node) Taxon A Taxon B Sister taxa Taxon C ANCESTRAL LINEAGE Taxon D Taxon E Taxon F Common ancestor of taxa AF Polytomy Apomorphy (derived trait)
= a new, derived feature E.g., for this evolutionary transformation scales > feathers (ancestral feature) (derived feature) Presence of feathers is an apomorphyfor birds. Taxa are grouped by apomorphies
Apomorphies are the result of evolution. Taxa sharing apomorphies underwent same evolutionary history should be grouped together. Principle of Parsimony
That cladogram (tree) having the fewest number of steps (evolutionary changes) is the one accepted. Okhams razor: the simplest explanation, with fewest number of ad hoc hypotheses, is accepted. Other methods of phylogeny reconstruction:
Maximum Likelihood or Bayesian analysis Uses probabilities Advantage: can use evolutionary models. Sequentially group taxa byshared derived character states (apomorphies)
Lancelet (outgroup) (outgroup) Lancelet Salamander Lamprey Leopard Lamprey Tuna Turtle Vertebral column (backbone) Tuna 1 1 1 1 1 Vertebral column Hinged jaws 1 1 1 1 Salamander Hinged jaws CHARACTERS Four walking legs 1 1 1 Turtle Four walking legs Amniotic (shelled) egg 1 1 Amniotic egg Leopard Hair 1 Hair (a) Character table (b) Phylogenetic tree Fig DNA sequence data most important type of data
1 Deletion 2 Insertion Fig. 26-8a DNA sequence data - alignment
3 Fig. 26-8b 4 Each nucleotide position = Character Character states = specific nucleotide Homology Similarity resulting from common ancestry.
E.g., the forelimb bones of a bird, bat, and cat. Homoplasy (analogy) Similarity not due to common ancestry
Reversal loss of new (apomorphic) feature, resembles ancestral (old) feature. Convergence (parallelism) gain of new, similar features independently. Convergent evolution: spines of cacti & euphorbs
Cactus Euphorb Convergent evolution: spines of cacti & euphorbs
euphorb spines cactus spines * * Leg-less lizards Snake
Both examples of reversal within Tetrapods:loss of a derived feature forelimbs. legged lizards leg-less lizards snakes * * Example of convergence relative to one another! Independently evolved. *= loss of legs gain of legs (Tetrapods) Convergent evolution: wings of some animals evolved independently Convergent evolution: Australian mole and N. Am. mole
Fig. 26-7 Convergent evolution: Australian mole and N. Am. mole Orthology genes homologous
Gene Duplication can occur! Ancestral gene Ancestral species Speciation with divergence of gene Orthology genes homologous Orthologous genes Species A Species B (a) Orthologous genes Species A Gene duplication and divergence Paralogy genes not homologous Paralogous genes Species A after many generations (b) Paralogous genes Fig Common ancestry Monophyletic Group a group consisting of: a common ancestor +
all descendents of that common ancestor C B FE D A Cladograms can be flipped at nodes, show same relationships One can date divergence times with molecular clock and fossils
Fig One can date divergence times with molecular clock and fossils Drosophila Lancelet Zebrafish Frog Chicken Human Mouse PALEOZOIC MESOZOIC CENOZOIC 542 251 65.5 Present Millions of years ago Relationship = recency of common ancestryi.e., taxa sharing a common ancestormore recent in time are more closely related than those sharing common ancestors more distant in time. Example: Are fish more closely related to sharks or to humans? Example: Are crocodyles more closely related to lizards or to birds? Paraphyletic group Consist of common ancestor but not all descendents
Paraphyletic groups are unnatural, distort evolutionary history, and should not be recognized. Reptilia here paraphyletic Re-defined Reptilia monophyletic Did humans evolve from apes?
Importance of a name: Did humans evolve from apes? Pongidae Great Apes Hominidae Pongidae Great Apes Pongidae or Hominidae Pongidae or Hominidae Pongidae or Hominidae We are human, but we are also apes.
We share unique human features. We also share features with other apes(and with other animals, plants, fungi, bacteria, etc.). Humans didnt evolve from apes, humans are apes. Importance of systematics & evolution:
1) Foundation of biology - study of biodiversity 2) Basis for classification of life 3) Gives insight into biological processes: speciation processes adaptation to environment 4) Can be aesthetically/intellectually pleasing! E.g., schistosomiasis Schistosomiasis:knowledge of species diversity and evolutionary history of primary host can aid in controlling parasite (Schistosoma, a fluke) Phylogeny of Oncomelania snails All of life is interconnected by descent. There are no higher or lower species.