Chapter 26 harmful organisms. Life is easier when we organize things - PDF document

2/11/2017 Why Classify? Classification has been around ever since people paid attention to organisms. One primeval system was based on “harmful” and “non - Chapter 26 harmful” organisms. Life is easier when we organize things into groups. Phylogeny History of Taxonomy Systematics • Biodiversity: variety of organisms at all levels from populations to ecosystems. classifying organisms and determining their evolutionary relationships • Taxonomy : the science of classifying and naming living organisms according to their morphological/physical characteristics and includes evolutionary history Taxonomy (classification) • Taxa : categories into which the organisms are and classified. Phylogenenetics (evolutionary history) • Phylogeny : evolutionary history of a species or group of species according to their DNA Taxonomy: Linnaean System Linnaean System • Binomial Nomenclature Taxa: (2 word naming system) (categories) Domain Dear Genus : category containing similar species Kingdom King (noun, capitalized) Phylum Phillip Class Came Order Over Species : single descriptive word Family For (always lower case) Genus Great Species Spaghetti Ex: Red oak: Quercus rubra Willow oak: Quercus phellos (common name) (scientific name) most broad category  least inclusive 1

2/11/2017 Phylogenetic Tree Phylogenetics • Phylogenetics : analysis of the evolutionary relationships among taxa (categories) based on: • fossil record Phylogenetic Tree • morphological (structural) similarities - embryological similarities Branching diagram that shows evolutionary history of a group of - homologous features organisms • molecular evidence (DNA, amino acids) (connection between classification and phylogeny) how to read a tree video how to understand an evolutionary tree video Reading Phylogenetic Trees Reading Phylogenetic Trees • like reading a family tree • Node : when a lineage splits (speciation), it is • root of the tree represents the ancestral lineage represented as branching on a phylogeny • tips of the branches represent the descendents of that ancestor • When a speciation event occurs, a single ancestral • as you move from the root to the tips, you are moving lineage gives rise to two or more daughter lineages. forward in time. (node) Reading Phylogenetic Trees Reading Phylogenetic Trees • Phylogenies trace patterns of shared ancestry between • Similarly, each lineage has ancestors that are lineages. unique to that lineage and ancestors that are shared with other lineages — common ancestors • Each lineage has a part of its history that is unique to it alone and parts that are shared with other lineages. 2

2/11/2017 Reading Phylogenetic Trees • For any speciation event on a phylogeny, the choice of which lineage goes to the right and which goes to the left is arbitrary. • The following phylogenies are equivalent: • Can be rotated at any node � or any combination of nodes � without changing the structure of the tree. • Leftmost tree shown in each row is identical from a phylogenetic perspective to the trees shown to the right. • Colors indicate the nodes that were rotated in each case. Reading Phylogenetic Trees Reading Phylogenetic Trees Branch point 3 represents Evolution produces a pattern of relationships among common ancestor of taxa lineages that is tree-like, not ladder-like . A,B,and C The position of branch (node) 3 point 4 to the right of 3 4 indicates that taxa B and C 2 diverged after their shared lineage split for taxon A. 5 1 Just because we tend to read phylogenies from left to right, Sister taxa: share an there is no correlation with level of "advancement ." immediate common ancestor (relationships not clear) Basal taxon: diverges early Branch lengths can represent time or genetic change in history (outgroup) Extant species: presently living Reading Phylogenetic Trees Draw a phylogenetic tree based on the data below. • Misconceptions about humans Draw hatch marks on the tree to indicate the • Humans did not evolve from origin(s) of each of the 6 characters. chimpanzees. • Humans and chimpanzees are evolutionary cousins and share a recent common ancestor that was neither chimpanzee nor human. • Humans are not "higher" or "more evolved" than other living lineages. • Since our lineages split, humans and chimpanzees have each evolved traits unique to their own lineages. 3

2/11/2017 What We Can and Can’t Learn from Phylogenetic Trees • Phylogenetic trees show patterns of descent. • Phylogenetic trees do not indicate when species evolved or how much genetic changed occurred in a lineage. • It shouldn’t be assumed that a taxon evolved from the taxon next to it. backbone hinged jaw • Phylogeny provides important information about similar characteristics in closely related species. four limbs amnion milk dorsal fin Cladistics • Developed by Hennig (German) in 1966 • Shared ancestral characters/traits : - evolved from common ancestor of both groups (taxa) - feature that evolved only within the group Cladistics : system of taxonomy based on common ex: feathers in birds (evolved only in bird ancestry based on shared and derived lineage, not inherited from ancestors that birds share with reptiles) characteristics • Shared derived character/traits : - determines sequence that different groups - set of unique characteristics found in specific clade of organisms evolved (common in all members of group) - evolved in an ancestor of one group but not the other - focuses on nature of characters (traits) in different groups of organisms ex: hair in mammals Cladograms Cladograms Cladogram : phylogenetic diagram that shows evolutionary • Clade : evolutionary branch that includes common relationships ancestor and all descendents (living and extinct) of that ancestor. • Arranges organisms across • Ingroup : species we are studying the top according to • Outgroup : species/group of species diverged before evolutionary history other lineages (least related) Video (Bozeman) • Separates organisms by video 2 (Educreations) characteristics • Shows organisms most closely related to each other 4

2/11/2017 • Clades are nested within one another — they form a Not all groupings qualify as Clades nested hierarchy. • A clade may include many thousands of species or just a few. • Some examples of clades at different levels are marked on the phylogenies below. • Notice how clades are nested within larger clades. “single tribe” “beside the tribe” “many tribes” ancestral species and ancestral species and includes various taxa that all its descendants. some of its descendants. lack common ancestor true clade Constructing a Cladogram Constructing a Cladogram • Identify homologies  shared characteristics derived from one ancestor. Maximum parsimony: use simplest explanation for tree construction • The greater the number of homologous parts between two organisms, - DNA: fewest base changes the more closely related they are. • Similarities can be either: - morphology: fewest evolutionary events - Shared primitive characters : homologous characters shared by more than one taxon ex: backbone is shared by mammals and reptiles - Shared derived characters , characters unique for a particular clade. more derived characters = more evolutionarily unique • Analogous structures may look similar to one another, but are not derived from a common ancestor (in contrast to homologous structures) Phylogenetic bracketing predicts features of an • example of convergent evolution : independent development of ancestor from features of its descendants. similarity between species due to similar selection pressures Constructing a Cladogram Constructing a Cladogram practice video 4. Construct a character table and tabulate the data.  The more shared characters, the more closely related are the species. 1. Select your species for which you want to make a cladogram. These are called the ingroup. 5. Construct a cladogram based on the number of shared characters. For example: 2. They have shared primitive and derived characters. The outgroup here, the lancelet has a notochord, the shared primitive Select an outgroup  a species that is closely related to the species 3. character. The ingroup is five vertebrates under study, the outgroup has a shared primitive character that is common to all species. Minions practice video 5

2/11/2017 Difference Between Phylogenetic Tree and Cladogram Modern Classification Both show hypothesized evolutionary relationships Three Domains/Superkingdoms (1990’s) (phylogeny) between taxa. - Domain: taxonomic category above kingdom level PHYLOGENETIC TREE CLADOGRAM - Different branch lengths - Branches are of equal length. - Branch lengths are proportional to the amount - Show common ancestry, of inferred evolutionary but do not indicate the change over time amount of evolutionary "time" 6