Need for systematics. Applications of systematics. Linnaeus plus Darwin. Approaches in systematics. Principles of cladistics

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1 Topics Need for systematics Applications of systematics Linnaeus plus Darwin Approaches in systematics Principles of cladistics Systematics pp Systematics - Study of diversity and evolutionary connections of organisms Eukaryotes ~ mill spp. - Only ~1.9 mill spp. described Quality of life - depends on tightly interwoven www of life Human dependence - Composition of atmosphere - Fresh and sea water - critical food sources - Pharmaceuticals - >40% - living systems (many from rain forests) - Many cultures directly depend on biodiversity of nature Biodiversity - currently challenged by human impact at a multitude of levels - unpredictable disasters Systematics p Systematics Taxonomy - Science of naming, describing and classifying organisms Taxonomy Systematics - Study of biodiversity with the objective of determining evolutionary relationships of organisms (phylogenetic analysis) 1

2 Systematics pp Why Systematics? A universally accepted name to every organism Grouping - Aid to memory Understand evolution Stronger interpretation of experimental results Systematics pp Carolus Linnaeus, 1758 Two main features of Linnaean Taxonomy - Binomial Nomenclature - Grouping into taxonomic categories Systematics p Binomial Nomenclature Generic name - Genus Specific epithet - Species Writing scientific names 2

3 Grouping into Taxonomic Categories Systematics p Plantae Terrestrial, multicellular, photosynthetic organisms KINGDOM Anthophyta PHYLUM Vascular plants with flowers, fruits, and seeds Monocotyledones CLASS Monocots: Flowering plants with one seed leaf (cotyledon) and flower parts in threes Domain Eukarya on top ORDER Commelinales Monocots with reduced flower parts, elongated leaves, and dry 1-seeded fruits FAMILY Poaceae Grasses with hollow stems; fruit is a grain; and abundant endosperm in seed GENUS Zea Tall annual grass with separate female and male flowers SPECIES Zea mays Only one species in genus corn Picture in 7 th Ed. Systematics p KINGDOM Animalia PHYLUM Chordata CLASS Mammalia Domain Eukarya on top ORDER Carnivora FAMILY Felidae GENUS Felis SPECIES Felis catus Systematics pp Clade-based PhyloCode rather than Linnaean hierarchical classification 3

4 Systematics p Systematists Reconstruct Phylogeny Systematics tries to reconstruct evolutionary relationships (phylogenies) Homologous structures - important in establishing such relationships Use homologous characters - structural, behavioral, physiological, developmental, molecular - not just morphological Convergent evolution and reversed structures - reveal homoplasy - not always easy to distinguish from homology Systematics p Systematics p Relationships among or within taxa Ideally, a taxon - evolutionary relationships Monophyletic taxon - Ancestor and all of its decendents - a natural grouping - clade Paraphyletic taxon - Common ancestor and some, but not all, of its descendents - reflects many/complex lines of evolutionary processes Polyphyletic taxon - Several evolutionary lines - does not necessarily include the most recent common ancestor to all compared types descendants from many ancestors To be avoided/further analyzed. Do not represent natural associations 4

5 Tree-like Diagrams (Phylogenetic Trees) Source: Biology of Plants. Raven, Evert and Eichhorn Systematics pp Shared Characters in Systematics Shared ancestral characters - traits in a common ancestor that persist in all descendants (plesiomorphic characters) Shared derived characters - first appeared in more recent common ancestor(s) and found in the descendants of that ancestor only (synapomorphic characters) A synapomorphic character in a more inclusive taxon becomes a plesiomorphic character in a narrower taxon Different approaches to construct phylogenetic trees Systematics p Phenetics Neumerical taxonomy - use phenotypic and other similarities - shared characteristics (derived + ancestral) use molecular similarities too test statistical significance of similarities Cladistics Phylogenetic systematics - analyses shared derived characteristics to determine evol. relationships use common ancestry and homologous characters Evolutionary Systematics (Classical/traditional Evol. Syst.) Use phenotypic similarity + shared ancestral and derived characters recognizes (allows) paraphyletic taxa 5

6 Cladistics - Phylogenetic Systematics Systematics pp Focuses on common ancestry/branching sequence, not evolutionary divergence/phenotypic similarity Constructs cladograms using common ancestor (based on shared derived characters determined through outgroups), parsimony analysis (grouping organisms based on minimum number of character changes during evolution - simplest explanation - best) and maximum likelihood Outgroup is missing shared derived character(s) of ingroup Outgroup Analysis Systematics pp Characters and their states states can be more than two Ch. 23 Understanding Diversity: Systematics pp

7 Systematics p Systematics p Evolutionary Systematics Vs. Cladistics More monophyletic groups Systematics p Minimum number of changes in characters - more accurate construction of the phylogeny Use of modern molecular techniques - Molecular Systematics - Character changes are changes on DNA - mutations Use of computational Power 7