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Biol 335: Phylogeny
Basic concepts of phylogeny
| Question | Answer |
|---|---|
| Character | heritable trait possessed by an organism, used to construct trees |
| State | alternative condition of a character |
| Polarity | direction of change in a character |
| Determining polarity | based on state in closely related groups (outgroup), or based on fossils (paleontological) |
| primitive vs. dervived | plesiomorphic vs. apomorphic (Hennig) or plesiotypic vs. apotypic |
| Can a character state be ancestral or descendant? | No, state can't have offspring |
| Types of derived character states/apomorphies | autapomorphies or synapomorphies |
| Autapomorphy | evolved only once in single terminal taxon |
| Synapomorphy | shared by 2 or more taxa and evolved once (homology) |
| Homology | similarity due to common ancestry |
| Homoplasy/Convergent evolution | state shared (synapomorphy) and evolved more than once |
| Monophyletic group | a clade which consists of all descendants of a common ancestor |
| Paraphyletic group | group contains some, but not all descendants of an ancestor |
| Polyphyletic group | group with more than one origin (mistaking homoplasy for homology) |
| Clade | a monophyletic group |
| Grade | paraphyletic or polyphyletic (e.g. fish (jaws but no legs), reptiles (Amnion but no fur or flight), flying vertebrates (convergent wings = polyphletic)) |
| Crown group | clade that includes all descendants of LCA and all extant species |
| Stem group | set of extinct taxa not in crown group but most closely related to that crown group |
| Total group | = crown + stem |
| Sister groups | the 2 groups which share a more recent common ancestor than either does with any other group (can only be monophyletic groups) |
| Basal taxon | taxon or clade which branched off earliest from the given clade |
| Study group | = ingroup, group of interest whose phylogenetic history we are trying to resolve |
| Outgroup | set of groups most closely related to the ingroup |
| Cladogram | shows summary of relationships |
| Additive tree | summary of relationships + amount of evolutionary change (length of branches is important) |
| Ultrametric tree | summary of relationships + timing of events |
| Soft polytomy | partially resolved tree which requires additional information to resolve the node |
| Gradualism | 'daughter' species different from each other and from parents if species always changing in small steps, leading to accumulation of traits and new species |
| Puncuated equilibrium | long periods of stasis interspersed (puncuated) by short time of rapid change |
| Punctuated equilibrium occurs when: | colonization of a new niche, strong selection, small founder population, genetic drift |
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