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545.Lecture2.pptx

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Prasad Burange, PhD

This document discusses the history of different schools of thought regarding phylogenetic inference: Evolutionary taxonomy focused on detailed study of individual groups but lacked objective methodology. Phenetics grouped organisms based on overall similarity rather than ancestry. Cladistics analyzed shared derived characteristics to define monophyletic groups, using maximum parsimony to resolve conflicts. Statistical phylogenetics is now dominant, estimating phylogenies and quantifying uncertainty with statistical models.

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Lecture 2 - The History of Phylogenetic Inference Haeckels evolutionary trees are among the first attempts at phylogeny inference.
Darwins tree Schools of thought A. Evolutionary Taxonomy The basic view was that the best way to understand the evolution of a group is to spend a lifetime learning all one can about the biology of the group. Many were paleontologists and recognized paraphyletic groups (e.g., Reptilia).
Schools of thought A. Evolutionary Taxonomy Advantage Generated a generation of knowledgeable taxon specialists. Flaw Lack of objective methodology and resulting lack of reproducibility. In spite of a lack of explicit methodology, many of the phylogenies produced by evolutionary taxonomists have been corroborated over the years.
Schools of thought B. Phenetics (Numerical Taxonomy) There is no way to infer the pattern of common ancestry of a group in a scientific manner. Therefore, we should group (classify) organisms on the basis of overall similarity. Many modern clustering approaches (UPGMA) owe their origins to Numerical Taxonomy. The goal was to produce a phenogram, NOT a phylogeny, that visualized the hierarchical pattern of overall similarity.
Schools of thought C. Cladistics (Phylogenetic Systematics) It is, in fact, possible to infer common ancestry in a scientific manner. Attributes that are derived and shared by a set of taxa are prima facie evidence for exclusive common ancestry (Synapomorphies). Only derived characters (apomorphies) can be phylogenetically informative, so the first step is to determine which character states are derived and which are primitive. Therefore, our classifications must only recognize monophyletic groups.
Schools of thought C. Cladistics (Phylogenetic Systematics) Example: Trout Lungfish Cow Cow Lungfish Trout Phenogram Cladogram Synapomorphy of limbs unites tetrapods and sarcopterygian fish, which share an ancestor not shared by actinopterygian fish. The Hennigian approach is to identify synapomorphies to define clades.
Schools of thought C. Cladistics (Phylogenetic Systematics) If we look at many characters, there will be conflict. The only methodology that is permissible to cladists to resolve such conflicts is the method of maximum parsimony. The MP tree is that tree which maximizes synapomorphies, and therefore defines groups following Hennigs principles. Pattern cladists parsimony trees represent pattern of character variation rather than a phylogeny. The term cladists is a loaded one and Quinn (2017) has identified as many as 7 ways the term is used.
Schools of thought D. Statistical Phylogenetics Currently, the dominant paradigm in phylogenetics is that phylogenies are estimated with uncertainty and that one must quantify that uncertainty. Trout Lungfish Cow Cow Lungfish Trout .and to what degree? Which fits the data better? Answers to these questions require the use of statistical models.

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545.Lecture2.pptx

  • 1. Lecture 2 - The History of Phylogenetic Inference Haeckels evolutionary trees are among the first attempts at phylogeny inference.
  • 2. Darwins tree Schools of thought A. Evolutionary Taxonomy The basic view was that the best way to understand the evolution of a group is to spend a lifetime learning all one can about the biology of the group. Many were paleontologists and recognized paraphyletic groups (e.g., Reptilia).
  • 3. Schools of thought A. Evolutionary Taxonomy Advantage Generated a generation of knowledgeable taxon specialists. Flaw Lack of objective methodology and resulting lack of reproducibility. In spite of a lack of explicit methodology, many of the phylogenies produced by evolutionary taxonomists have been corroborated over the years.
  • 4. Schools of thought B. Phenetics (Numerical Taxonomy) There is no way to infer the pattern of common ancestry of a group in a scientific manner. Therefore, we should group (classify) organisms on the basis of overall similarity. Many modern clustering approaches (UPGMA) owe their origins to Numerical Taxonomy. The goal was to produce a phenogram, NOT a phylogeny, that visualized the hierarchical pattern of overall similarity.
  • 5. Schools of thought C. Cladistics (Phylogenetic Systematics) It is, in fact, possible to infer common ancestry in a scientific manner. Attributes that are derived and shared by a set of taxa are prima facie evidence for exclusive common ancestry (Synapomorphies). Only derived characters (apomorphies) can be phylogenetically informative, so the first step is to determine which character states are derived and which are primitive. Therefore, our classifications must only recognize monophyletic groups.
  • 6. Schools of thought C. Cladistics (Phylogenetic Systematics) Example: Trout Lungfish Cow Cow Lungfish Trout Phenogram Cladogram Synapomorphy of limbs unites tetrapods and sarcopterygian fish, which share an ancestor not shared by actinopterygian fish. The Hennigian approach is to identify synapomorphies to define clades.
  • 7. Schools of thought C. Cladistics (Phylogenetic Systematics) If we look at many characters, there will be conflict. The only methodology that is permissible to cladists to resolve such conflicts is the method of maximum parsimony. The MP tree is that tree which maximizes synapomorphies, and therefore defines groups following Hennigs principles. Pattern cladists parsimony trees represent pattern of character variation rather than a phylogeny. The term cladists is a loaded one and Quinn (2017) has identified as many as 7 ways the term is used.
  • 8. Schools of thought D. Statistical Phylogenetics Currently, the dominant paradigm in phylogenetics is that phylogenies are estimated with uncertainty and that one must quantify that uncertainty. Trout Lungfish Cow Cow Lungfish Trout .and to what degree? Which fits the data better? Answers to these questions require the use of statistical models.