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Species Classification - Evolution - Lecture Slides, Slides of Theory of Evolution

Species Classification, Evolution and Classification, Physical Attributes, Numerical Taxonomy, Phenetic Classification, Neighbour-Joining, Joining Clusters, Mosaic Evolution are the key important points of lecture slides of Evolution.

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2012/2013

Uploaded on 01/02/2013

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Lecture 10: Evolution & Classification
cont ’d
Species Classification:
•Phenetic: physical attributes, numerical
taxonomy
•Cladistic (Phylogenetic): evolutionary
relationships
•Evolutionary: synthesis of the two
Reflect Philosophical Differences
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Lecture 10: Evolution & Classification

cont’d

Species Classification:

  • Phenetic: physical attributes, numerical taxonomy
  • Cladistic (Phylogenetic): evolutionary relationships
  • Evolutionary: synthesis of the two

Reflect Philosophical Differences

Phenetic Classification

  • “Like with like”
  • Use many characters to define overall similarity
  • Linnaean
    • Before Darwin so not based on Evolution (but may reflect history)
  • Current: reaction to uncertainty of cladistics
  • Problem: uses all types of characters (analogies, ancestral & derived homologies)

  1. construct matrix with pairwise S values

  2. use clustering technique to produce a dendrogram

e.g. UPGMA (Unweighted Pair Group Method with Arithmetic Averaging) or Neighbour-joining

Unweighted/Equal weighting = all characters given equal consideration

unweighting is a type of weighting!

may introduce bias…..

Example

Taxon 1 2 3 4 5 6 7 8 9 10 A 0 1 1 0 0 0 1 1 1 0 B 0 0 0 1 1 1 0 1 1 1 C 0 0 1 0 0 1 0 0 0 1 D 1 1 0 0 0 1 1 1 1 0

Character Matrix

Taxon A B C D A -- 0.3 0.4 0. B -- 0.5 0. C -- 0. D --

S-value Matrix

Problems

  • Different methods or characters = different dendrograms
  • If used all characteristics would = natural classification (Impossible!)
  • dendrogram = phylogeny if differences between taxa proportional to time elapsed since common ancestor

Unfortunately…

  1. Mosaic Evolution: differences in rate of change of characters in a lineage
  2. Homoplasy: shared characters not in common ancestor (analogy)

Why retained?

A) Developmental Canalization

  • Character change requires change

in developmental program (rare)

B) General Adaptations

  • Useful in large number of ecological contexts

e.g. Rodentia - incisors conserved

  • legs evolved rapidly

Homoplasy

↑ # characters used, ↑ chance of homoplasy

A. Convergent Evolution

  • Similar phenotypic response to similar ecological conditions
  • Different developmental pathways

C. Evolutionary Reversal

  • degeneration of complex structure
  • looks primitive, actually derived
  • e.g. Winglessness in Fleas & Lice
    • 2 different winged ancestors

Dollo’s law : complex structures that are lost are unlikely to be regained

Exceptions: snake eyes, molars in some felids

Frogs with Teeth?

  • Reversals & Parallelism common because of potentialities (bias) of developmental systems
  • Frogs lost teeth in lower jaw in the Jurassic
  • Teeth can be expt’lly induced
  • Gastrotheca guentheri – re-evolved true teeth

Example of phenetics gone wrong

  • Limpet, Barnacle, Lobster:
  • But, lobster & barnacle more closely related…convergence

Barnacle Limpet Lobster

Cladistics

  • Greek: klados = branch
  • Join spp. into truly MONOPHYLETIC groups (avoid pitfalls of phyletic approach)
  • Hennig (1979) - key to monophyletic groups:

Unique Synapomorphies: shared, derived characters

  • Focus on CLADOGENESIS, ignores anagenesis

Ancestral traits

Criteria to determine primitiveness:

  • Presence in fossils
  • Commonness across taxa
  • Early appearance in phylogeny
  • Presence in outgroup

Cladograms

  1. select group of organisms

  2. determine characters & states

  3. for each character, classify ancestral & derived

  • comparison to outgroup
  • traits shared with outgroup = ancestral

  1. group by shared derived characters (synapomorphies)

  2. choose most parsimonious tree

(fewest evolutionary transitions)