MODULE 3 LESSON 1: Schools of Taxonomic Thought

Phylogenetics

conjecture

_____________ is the unraveling of evolutionary history.

• Sometimes it is considered a controversial area in biology.

• The controversy arises because, although some groups are well defined, phylogenetic relationships for most groups of organisms remain largely conjectural.

• Nonetheless, the situation has improved significantly over the last decade.
  
  

A ____________ refers to an opinion or conclusion that is based on incomplete information.

Even in plants like Cycas spp., cacti, and succulent euphorbias, superficial resemblance is misleading as an indication of relationship of groups. The reason is, resemblance does not always indicate evolutionary relationships, because although similarity may arise from relatedness, it can equally arise through the phenomenon of homoplasy.

In early phylogenetic analyses, such conjectures are of two main types, representing extremes.

• One would be a group that is well-defined and very easily recognized by the possession of one or a few very distinct features but that same feature(s) make it difficult to determine which other group(s) would be their close relative(s).

• The other extreme, represent groups that resemble each other rather closely but are actually only remotely related.

Homoplasy

_________________ is similarity resulting from convergent or parallel evolution of structures, by either chance or selection for similar functions.

For example, the wings of the bird and wings of a butterfly demonstrates homoplasy. They are similar in that they are both used in flight but are different in that these wings were not derived from a common ancestor.

homology

On the other hand, _______________ is similarity as the result of common ancestry. Only homology can provide information regarding phylogeny. The example below shows homology in the fore limbs of human, bats, birds, cats, dolphin or whale.

• Phylogeny

• systematics

• _____________ is the evolutionary history of a species or group of related species.

• The discipline of ___________ classifies organisms and determines their evolutionary relationships,

• Systematists use fossil, molecular, and genetic data to infer evolutionary relationships.

phylogeny

What is a _______________?

Branching diagram showing relationships between species (or higher taxa) based on their shared common ancestors

Phenetics

Schools of Taxonomic Thought: Phylogenetic Methods

____________ - applies numerical taxonomy to arranging groups into genera & higher ranks

Cladistics

Schools of Taxonomic Thought: Phylogenetic Methods

____________ - focuses on shared derived characters to group taxa

Evolutionary classification or evolutionary taxonomy (phyletics)

Schools of Taxonomic Thought: Phylogenetic Methods

________________________________ - incorporates genealogical relationship between groups with evolutionary distance

• Phenetics

• ____________- (from Greek phainein' - to show)

• relies on estimates of overall similarity

• Phenetics

• usually derived from morphology, but sometimes from behavior & other traits, and increasingly from molecular evidence

PHENETICS

• artificial

• Claim: "evolution is unknowable; the best that we can hope for are patterns

of resemblance ... “

• Others: the ______________ pattern revealed — as good an estimate of phylogeny as can be obtained

• Because phenetics may not recover the pattern of evolution resulted from evolutionary processes, its phenetic classifications are ____________

Cladistics

_____________ groups organisms by common descent

• clade

• A _________ is a group of species that includes an ancestral species and all its descendants

• It can be nested in larger clades, but not all groupings of organisms qualify as clades

Willi Hennig

• synapomorphies

• descent; modification

Cladistic methods (________________ 1966)

• Based on shared, derived characters = _______________

• Similarity is not enough – requires similarity reflecting ___________ with ____________

• Requires characters that can be assigned a particular character state

monophyletic

A valid clade is _____________, signifying that it consists of the ancestor species and all its descendants

paraphyletic

A ____________ group consists of an ancestral species and some, but not all, of the descendants.

polyphyletic

A _______________ grouping consists of various species with different ancestors.

1. ancestral

   • plesiomorphy

   • symplesiomorphy

2. derived

   • apomorphy

   • synapomorphy

Characters

1. ____________ - from primitive ancestor

   • ____________ - primitive/ancestral characters

   • _____________ - shared ancestral character

2. __________ - from recent ancestor

   • _____________ - advanced/derived character

   • ______________ - shared derived character

• Plesiomorphy

• Apomorphy

• Symplesiomorphy

• Synapomorphy

  

Terminology

• ________________ - Character state found in ancestor of group

• _________________ - Derived character state in descendants of group

• _________________ - Shared, ancestral character state

• __________________- Shared, derived character state (indicates homology)

Take this phylogenetic tree and fill in the blanks:

• Blue” and “square” are _________________

• “Small size” is an _________________ for A

• “Red” is a _________________ for A + B

• “Circle” is a _________________ for A + B + C …but a _________________ for A + B

1. simplicity/complexity

2. fossils/fossil records

3. outgroup

   • outgroup

How do you know the state of the character?

1. ____________/______________ of the character

2. through ___________/_____________

3. ___________ method ---

   • ___________- distantly related taxon

• ancestral

• derived

How do you know the state of the character?

simplicity/complexity of the character state---

• simpler structures - ___________

• more complex -- ____________

• ex. lungs of frogs vs. lungs of birds

• regression or reduction

  • derived

  • ancestral
    
    

  • derived; ancestral

How do you know the state of the character?

• simplicity/complexity of the character state---

  • however, simple structures may evolve from complex structures. (_________________)

    • eyelessness in cave fishes - ____________

    • presence of eyes in most fishes -- ______________
      
      

    • corolla tube (_________) ; free petals (_____________)

• ancestral

  • extant
    
    

  • scales (400 MYA) vs. feathers (195 MYA)
    
    

  • scales feathers

How do you know the state of the character?

• fossils -- character in the older fossils will be ____________ compared with the characters in the younger fossils

  • It is absent in the fossils but present in the _________ taxa
    
    

• ________ in fishes, reptiles, legs of birds ancestral compared with ____________ (of birds)

How do you know the state of the character?

• outgroup - taxon distantly related to any member of the lineage

• outgroup method - presence of characters (ancestral); if a charac

• homology

Basis of similarities among characters

• _____________ - resemblance in characters in different taxa due to a common origin

• homologous

Basis of similarities among characters

• similar ancestral characters in different taxa are always ______________

• homologous; common ancestor

Basis of similarities among characters

• Similar derived characters present in different taxa may be _____________ only if the character can be determined to be originating from a _____________________.

homology

Basis of similarities among characters

_________________

• arm of chimpanzee and arm of man

• hand and arm of man, flipper of seal, wing of bat and wing of bird-- structurally similar in bone though may perform different functions

• homologous

Basis of similarities among characters

• Any feature shared by two or more species that is inherited from a common ancestor is said to be __________________.

• divergent

Basis of similarities among characters

• Differences in homologous characters in 2 related taxa - ____________ evolution

divergent evolution

Basis of similarities among characters

• trend in evolution resulting in differences in evolutionary pathways followed by 2 descendant lineages from their ancestor

• analogy

Basis of similarities among characters

• ___________ - resemblance in structure/appearance in unrelated taxa due to similarity in function

• Analogous

Basis of similarities among characters

• _____________ structures - products of convergent evolution

convergent evolution

Basis of similarities among characters

• ______________ - a trend in evolution that produces resemblance in features of unrelated taxa due to exposure to similar environmental conditions

• selection pressures

Basis of similarities among characters

Why Analogous Structures Exist.

• Analogous structures evolve as a result of similar ______________________. These two animals are both burrowing mammals and are not closely related.

• placental mole and the southern marsupial mole from Australia

• Both have large claws for digging, thick skin in the nose area for pushing dirt around and an oval body which moves easily through tunnels

• homologous; analogous

Basis of similarities among characters

• While the bones found in the wings of birds and bats are ______________, the wing itself is _____________.

• The wing structure did not evolve from the same ancestor.

• homoplasy

Basis of similarities among characters

• ______________ - resemblance in structure of distantly related taxa because they are sameforming.

  • Similarity in characters is due to having followed similar developmental plans and not due to inheritance from a common ancestor

• homoplastic; parallel

Basis of similarities among characters

• The 2 unrelated taxa with the similarity in character inherited similar developmental plans (that resulted in the character) from a common but very distant ancestor

• _______________ characters - _____________ evolution

• Homoplasy

Basis of similarities among characters

• ____________ - similarity resulting from convergent or parallel evolution of structures, by either chance or selection for similar functions.
  
  

  • e.g., the wings of a bird and the wings of a butterfly demonstrate homoplasy. Similar since they are both used in flight but are different in that these wings were not derived from a common ancestor

• parallel evolution

Basis of similarities among characters

• _________________ - a trend in evolution that produces resemblance in features of unrelated taxa or distantly related taxa that have followed the same or similar developmental plans.

Evolutionary systematics

• a.k.a. classical evolutionary systematics/taxonomy, evolutionary taxonomy

• also uses estimates of derived similarity, but unlike cladistics,

• estimates of the amount of evolutionary change are included with the branching pattern in order to produce a classification.

Evolutionary systematics

• emphasizes distinctness

• grants higher taxonomic status taxa separated by 'gaps'

  • may be due to accelerated morphological innovation in a lineage, &/or by extinction of intermediate linking forms.