Delivered 1/30 and 2/1 Lecture V Phylogeny and Systematics Dr. Kopeny Lecture V How to Determine Evolutionary Relationships: Concepts in Phylogeny and Systematics Textbook Reading: pp 425-433, 435-437 in chapter 23: Reconstructing and using Phylogenies Nature 413, 277-281 (2001) Skeletons of terrestrial cetaceans and the relationship of whales to artiodactyls. J. G. M. Thewissen, E. M. Williams, L. J. Roe & S. T. Hussain. See webpage for link to pdf of this paper, and summary/persptive of this paper
Taxonomic classification is hierarchical and nested Taxonomy is the science of the classification (=naming) of organisms Linnean classification called binomial nomenclature, in reference to genus and specific epithet Taxon is a generic term for any taxonomic unit (level) Most inclusive taxon, not shown here, is Domain
Bass Frog Snake Bird Basal lineage Phylogeny history of descent of a group of organisms from their common ancestor Phylogenetic Tree or Cladogram. Depiction of a phylogeny. Carries information only on branching relationships; no information about passage of time or amount of phenotypic change. Each branching point (node) reflects a divergence (ie, speciation, cladogenesis) event that took place in the species that is the most recent common ancestor to the descendents of that cladogenesis event Lineage Organisms in an ancestor-descendent relationship Tunicate Bass Frog Snake Bird Vertebrata (fish, amphibians,reptiles, birds) Tetrapoda (frog, snake, bird) Amniota (snake, bird) The nested polygons here show taxonomic groupings, but with no regard for inclusion or exclusion of ancestors common to the groupings
Vertebrata Tetrapoda Amniota Tunicate Bass Frog Snake Bird The nested polygons here do show taxonomic groupings, but with regard for inclusion or exclusion of ancestors common to the groupings Determining monophyletic taxa is key to classifying organisms according to their evolutionary history: Monophyletic taxon is one in which a single ancestor gives rise to all species, and which includes all descendents of that single ancestor Paraphyletic taxon excludes one or more species descended from the most recent common ancestor of the taxon Polyphyletic taxon excludes the most recent common ancestor of all members of the taxon A taxon that includes only A and B would be paraphyletic A taxon that includes B, C and D would be polyphyletic A taxon that includes D, E and F would be monophyletic
SCHOOLS OF SYSTEMATICS TRADITIONAL EVOLUTIONARY TAXONOMY [Simpson and others] Establish taxa based on common ancestry (clades) and the extent of adaptive evolutionary change: evolutionary groups that represent adaptive zone constitute legitimate higher taxa -- a grade adaptive zone; characteristic reaction and mutual relationship between environment and organism, a way of life and not a place where life is led. paraphyletic taxa may be acceptable PHYLOGENETIC SYSTEMATICS (CLADISTICS) [Hennig] George Gaylord Simpson (1902-1984). Mammalian Paleontologist, regarded as one of the architects of the modern synthesis. Formulated the principles of evolutionary taxonomy Establish taxa based on clades; monophyletic taxa only Powerful methodological and analytic tool for determining relationships The tools of cladistics now represent the prevailing approach to determining relationships; the philosophy of strict monophyly wrt classification is still under debate -- bears on definition - concept- of species Willi Hennig (1913-1976). Hennig is best known for developing phylogenetic systematics, a coherent theory of the investigation and presentation of the relations that exist among species. http://www.cladistics.org/about/hennig.html
Systematists classify organisms and determine evolutionary relationships based on analysis of homologous characters (traits) Systematic investigation is based on analysis of homologous characters (traits); characters may be morphological, molecular, behavioral, physiological.. Homologous character; character that is shared by two or more taxa because those taxa inherited the character from a common ancestor Expect shared character to be quite similar, perhaps, but not identical among taxa, as a result of descent with modification Homology indicates common ancestry, which is information with which one can determine evolutionary history Divergent Evolution of Homologous Characters Homologous characters may evolve away from each other in structure
Analagous character; character occurring in two or more lineages because it evolved independently in each of those lineages, Analagies may arise through convergent evolution: lineages occupy similar ecological roles and similar selective forces Misinterpretation of analagous characters for homologus ones may lead to erroneous conclusions regarding phylogenetic relationships and unintended taxanomic groupings Aardvark, native to central, southern and eastern Africa Giant Anteater (at a termite mound), native to Latin America from Southern Mexico to Northern Argentina Pangolin, native to Africa and southern and southeastern Asia Convergent Evolution of Analogous Characters. Three distantly related mammals have structural similarities (analogous characters, homoplasious characters) due to convergent evolution. Each taxon independently evolved morphological traits for feeding on ants and termites. The supporting structures of bird and bat wings are homologous structures; derived from a common ancestor The supporting structures of insect wings are analogous to the structures of bird and bat wings; evolved independently.
Shoot develops from axillary bud Thorn develops from axillary bud Spine develops from midrib of leaf Spine of Japanese barberry is a modified leaf Thorn of downy hawthorn is a modified stem Analagous traits, or homoplasies, in two distantly related plant taxa Phylogenetic Systematics Dr. Willi Hennig (1913-1976) The history of diversification is recorded through descent with modification Modification exists in the form of evolutionary transformation of characters from one state to another state. Plesiomorphy: Ancestral character state Apomorphy: Derived character state Synapomorphy Derived character state that is exclusively shared by a subset of taxa under investigation. A synapomorphy is evidence that taxa bearing it are descended from the same common ancestor -- the ancestor in which the derived character arose. Cladistic or Phylogenetic Analysis: Procedural Outline SELECT ORGANISMS Identify the ingroup Select an appropriate outgroup BUILD TRANSFORMATION MATIX Select characters for analysis Assign character states Determine polarity of character states ANALYZE AND INTERPRET DATA Subject data to optimization algorithm (usually parsimony criteria) to produce an optimal tree, perhaps a concensus tree Seek congruence Product: Phylogenetic Hypothesis
Phylogenetic Systematics Dr. Willi Hennig (1913-1976) The history of diversification is recorded through descent with modification Modification exists in the form of evolutionary transformation of characters from one state to another state. Plesiomorphy: Ancestral character state Apomorphy: Derived character state Synapomorphy Derived character state that is exclusively shared by a subset of taxa under investigation. A synapomorphy is evidence that taxa bearing it are descended from the same common ancestor -- the ancestor in which the derived character arose. Cladistic or Phylogenetic Analysis: Procedural Outline SELECT ORGANISMS Identify the ingroup Select an appropriate outgroup BUILD TRANSFORMATION MATIX Select characters for analysis Assign character states Determine polarity of character states ANALYZE AND INTERPRET DATA Subject data to optimization algorithm (usually parsimony criteria) to produce an optimal tree, perhaps a concensus tree Seek congruence Product: Phylogenetic Hypothesis Reconstruct the phylogeny of three closely related bird species Species A Species B Species C Determine characters to use for analysis bill shape (derived character state: hooked; ancestral= not hooked) head feathers (derived = crest; ancestral = no crest) toe condition (derived = webbed; ancestral = no webbing)
Species A Species B Species C Hooked Bill Hooked Bill No Hooked Bill Crested Head No Crested Head Crested Head Webbed Toes Webbed Toes No Webbed Toes Character states variously arise in lineages. Character states variously accumulate in lineages, in descendents of the ancestor in which the character states arose A B C?
Outgroup Closely related species that we know diverged from ancestral lineage before our three species of interest diverged Ingroup Outgroup Species A Species B Species C Closely related species that diverged from ancestral lineage before our three species of H=hooked bill interest C=crest diverged (outgroup) Transformation Series Bill Shape Head Plumage Toe Condition Outgroup H- C- W- Species A H+ C+ W+ Species B H+ C- W+ Species C H- C+ W- W=webbed toes +=species has trait -=species lacks trait Assume character state seen in outgroup is ancestral character state.? (ingroup)
Choosing Among Competing Hypotheses: The Parsimony Principle The Parsimony Principle holds that, all other things being equal, the hypothesis requiring the fewest number of evolutionary transformations has the highest likelihood of being the correct hypothesis H- C- W- H+ C- W+ H+ C+ W+ H- C+ W- OG B A C C+ Outgroup Species A W+ Species B H+ Species C Closely related species that Transformation W+ H+ Series C+ H+ diverged from Bill Shape Head Plumage Toe C+ Condition ancestral Outgroup H- C-? W- lineage before (ingroup) our Species three A H+ C+ five evolutionary W+ transformations to This explain phylogenetic the distribution hypothesis of character species of Species B H+ C- requires four evolutionary W+ interest W- transformations to explain diverged Species C H- W- C- C+ the distribution of W- H- character C- (outgroup) H- states among taxa under Assume character state seen in investigation outgroup is ancestral. W+ This phylogenetic hypothesis requires states among taxa under investigation