Topic 2: Comparative Method o Taxonomy, classification, systematics o Importance of phylogenies o A closer look at systematics o Some key concepts o Parts of a cladogram o Groups and characters o Homology and homoplasy What are taxonomy, classification, and systematics? o The naming of organisms and their categorization o The arrangement of organisms into groups based on trait similarity (justifying the groups) o The clustering of groups and organisms based on a unifying set of principles (evolutionary, or otherwise) How would you taxonomize, classify, and systematize this cutlery? Taxonomy naming of taxa Elk Wrasse Crested Gecko Japalura Monitor Dog Boa Goby Fly Solefugid www.visualdicationary.com
Classification categorization based on similarity Systematics clustering of taxa based on unifying principles Mammals Fishes Arthropods Squamates What are taxonomy, classification, and systematics? o Taxonomy and classification are used to things o Systematics is used to things Why is systematics important? Nothing in biology makes sense except in the light of evolution. - Dobzhansky, 973 The task of systematics is the creation of a general reference system and the investigation of the relations that extend from it to all other possible and necessary systems in biology. - Hennig, 950 (966)
What aspects of biology are informed by systematics? Why is systematics important? o Provides a framework for comparing species o Accounts for non- of species o Species pairs spent different amount of time evolving o o
Why is systematics important? o Informs about direction of evolution, how species can be compared The Evolution of Fur 2 Species 3 Species Key Concepts of Systematics o The guiding principle of science, stating that the simplest explanation that fits the evidence is most likely the correct explanation Some have it, some don t Fur evolved after scales, scales are, fur is derived A Closer Look at Systematics Key Concepts of Systematics o Systematics The clustering of groups or organisms based on a unifying set of principles (evolutionary, or otherwise) o If the system is based on evolution, then it is o These underlying principles are typically and o An evolutionary branching event, where new taxa arise from a common ancestor o Evolutionary change in a lineage through time (along a branch) Anagenesis Cladogenesis
Anatomy of a Cladogram Ingroup Clade: Amphibia Operational Taxonomic Unit (OTU) Outgroup Terminal Branch Node Internal Branch Sister group Topology Dichotomous Polytomy Root Modified from Pough et al., 2002. Fig. -3
Types of Groups o A group containing an ancestor and all of its descendents. o A group containing some, but not all, of its descendents. o A group containing taxa that lack a common ancestor. o An ancestral feature, common to taxa in the ingroup and outgroup o A shared derived feature, common to clusters of taxa of the ingroup o A unique derived feature, diagnostic of a taxon (OTU) in the ingroup o A character can comprise any quality or quantity that can be compared between the taxa under study o o Morphometrics o o Ecology o o o Allozymes o Karyotype o Protein structure o Etc. Plesiomorphy Synapomorphy Autapomorphy Sauropsids ( Reptilia & Aves) Amniotic egg Single centrale bone in ankle Of Diapsida: 2 temporal foramina in skull Diapsida (Archosauria & Lepidosauria) Single centrale bone in ankle 2 temporal foramina in skull Of Aves: Feathers Aves (Birds) 2 temporal foramina in skull Feathers o Sonography Modified from Liem et al 200, Focus -2, Table A o Alternate forms of a character in the taxa being studied e.g. Pupil shape These represent the variation that is analyzed by systematic methods Round Slitted Slit & pin-hole Taxon Frog 0 0 0 0 0 0 0 0 Turtles 0 0 0 0 0 0 Lepidosaurs 0 0 0 0 Crocodylians 0 0 0 0 Birds 0 0 0 Monotremes 2 0 0 0 0 0 Marsupials 0 0 0 0 0 0 Eutherians 0 0 0 0 0 0 K.P. Bergmann
Digits on Limbs Amniotic Egg Diapsid Skull Single Centrale Fenestra in jaw Hair Trunk in Shell Transverse Cloaca Feathers Liem et al. 200, Focus -2, Fig A Frog Turtle Lepidosaur Crocodilian Bird Monotreme Marsupial Eutherian is when homologous structures occur within an individual Examples: Vertebrae Feathers Hair Scales Teeth Front & Hind limbs is when sexually dimorphic homologous structures occur in males and females Examples: Testes & ovaries Glans penis & glans clitoridis Scrotum & labiae majorae o The fundamental similarity of a character between taxa within a group Structures compared between taxa must be of the same evolutionary origin (comparing apples to apples) o The similarity of a character or structure between taxa due to convergence o Homoplasy can obscure relationships between taxa by leading to erroneous: o Statements of homology o Coding of character states o Phylogeny reconstruction o Homology comparing apples to apples o Homoplasy is thought to occur due to: o in different groups o on the direction of evolution Endothermy: Aves Mammalia Allows sustained activity and independence of metabolism from environmental temperatures Modified from Linzey, 200 Photos PJB 2
Homology and Homoplasy Endothermy in Aves and Mammalia has evolved twice independently Frog Turtle Lepidosaur Crocodilian Bird Monotreme Marsupial Eutherian Photos PJB Liem et al. 200, Focus -2, Fig A o Homoplasy is thought to occur due to: Similar selective pressures in different groups Constraint on the direction of evolution Aves Chiroptera Pterosauria Homology or Homoplasy? Modified from Linzey, 200; Liem et al. 200, Fig -9C