2In this tutorial, you will learn: The traditional classification scheme of Linnaeus.Two theories of taxonomy:Traditional evolutionary taxonomyCladisticsHow to read a cladogramCredits:Figures and images by N. Wheat unless otherwise noted.Image of Linnaeus from WikipediaFunded by Title V-STEM grant P031S
3IntroductionThe practice of categorizing organisms according to similar features goes back to Aristotle.The goal of Taxonomy today is to produce a formal system for naming and classifying species to illustrate their evolutionary relationships.
4Classification vs. Systematization In classification, the taxonomist asks whether the species being classified contains the defining feature of a certain taxonomic grouping.Focus is on features.
5Classification vs. Systematization In systematization, the taxonomist asks whether the characteristics of a species support the hypothesis that it descends from the most recent common ancestor of the taxonomic group.Focus is on evolutionary origin of those features.
6Linnaeus and Classification In the 18th century, Carolus Linnaeus designed the hierarchical classification system still in use today.KingdomPhylumClassOrderFamilyGenusSpecies
7Taxa Taxa (singular = taxon) are the major groups of organisms. Each rank can be subdivided into additional levels of taxa.Superclass, suborder, etc.
8Binomial Nomenclature Binomial nomenclature is the system Linnaeus developed for naming species.The two-part scientific name includes the genus and speciesNames are latinized and italicized, only the genus is capatilized.Sitta carolinensis
9PhylogenyThe goal of systematics is to determine the phylogeny – the evolutionary history – of a species or group of related species.
10PhylogenyPhylogenies are inferred by identifying organismal features, characters, that vary among species.These characters can be:MorphologicalChromosomalMolecularBehavioral or ecological
11HomologyHomologous characters are shared characters that result from common ancestry.
12HomoplasyHomoplasies are shared characters that are not a result of common ancestry, but of independent evolution of similar characters (they are not homologous).Can result from convergent evolution.
13Convergent EvolutionConvergent evolution occurs when natural selection, working under similar environmental pressures, produces similar (analogous) adaptations in organisms from different evolutionary lineages.
14PhylogenyWhen trying to determine evolutionary relationships (inferring a phylogeny), we only want to consider homologous characters.Homoplasies can create errors.
15Shared Primitive and Shared Derived Characteristics Focusing on homologous structures, we need to determine when that character arose.Newer characters tell us more!Primitive (older) vs. derived (newer) characters
16Shared Primitive and Shared Derived Characteristics A shared primitive character is a homologous structure that is older than the branching of a particular clade from other members of that clade.It is shared by more than just the taxon we are trying to define.Example – mammals all have a backbone, but so do other vertebrates.
17Shared Primitive and Shared Derived Characteristics A shared derived character is a new evolutionary feature, unique to a particular group.Example - all mammals have hair, and no other animals have hair.These are the features that are most useful for determining evolutionary relationships!
18Ancestral Character States The ancestral character state is the form of the character that was present in the common ancestor of the group.Variations of the character that arose later are called derived character states.
19PolarityPolarity (which version of the trait is ancestral) is determined by using outgroup comparison.An outgroup is closely related, but not part of the group being examined (the ingroup).
20PolarityAn ancestral character is one that is found in both the study group and the outgroup.Derived character groups are those found in the study groups but not the outgroups.
21CladesClades are groups that share derived characters and form a subset within a larger group.A clade is a unit of common evolutionary descent.
22SynapomorphyA synapomorphy is a derived character that is shared by all the members of the clade.Using synapomorphies to define clades will result in a nested hierarchy of clades.
23SymplesiomorphyAncestral character states for a taxon are called plesiomorphic.Symplesiomorphies are shared ancestral characters.Symplesiomorphies do not provide useful information for forming a nested series of clades.
24CladogramThe nested hierarchy of clades can be shown as a cladogram that is based on synapomorphies.
25MonophyleticA valid clade is monophyletic, it consists of the ancestor species and all its descendants.
26ParaphyleticA paraphyletic clade consists of an ancestral species and some, but not all, of the descendants.
27PolyphyleticA polyphyletic clade includes many species that lack a common ancestor.
28CladisticsCladistics, also called phylogenetic systematics, is a taxonomic theory that is based on cladograms.All taxa must be monophyletic!
29Evolutionary Taxonomy Traditional Evolutionary taxonomy is based on common descent and the amount of evolutionary change to rank higher taxa.Sometimes this type of classification includes paraphyletic groupings.
30CladisticsSince all groupings must be monophyletic in cladistics, the paraphyletic arrangement of ape families doesn’t work.Humans, chimpanzees, gorillas, and orangutans are now all included together in one monophyletic family - Hominidae.
31Sister GroupsA sister group is a pair of taxa that are most closely related to each other.Humans are most closely related to chimpanzees, so humans & chimpanzees form a sister group.Gorillas form a sister group to the clade containing humans and chimpanzees.
32Cladistics vs. Evolutionary Taxonomy The important difference between these two theories of taxonomy is that traditional evolutionary taxonomy sometimes accepts paraphyletic clades, while cladistics does not.Both accept monophyletic clades.Both reject polyphyletic clades.
33Question 1Who developed the classification system including the binomial scientific name in use today?DarwinMendelLinnaeusAristotle
39Which example of binomial nomenclature is formatted correctly? Question 3Which example of binomial nomenclature is formatted correctly?Homo sapienshomo sapiensHomo SapiensIt doesn’t matter, they are all correct
45When defining a clade, what type of characters should we use? Question 5When defining a clade, what type of characters should we use?HomoplasiesShared primitive characters = symplesiomorphiesShared derived characters = synapomorphiesAll of the above
51A monophyletic clade is one that contains Question 7A monophyletic clade is one that containsAn ancestor and all of its descendants.An ancestor and some of its descendants.Several species that lack a common ancestor.One species.
54A polyphyletic clade is one that contains Question 8A polyphyletic clade is one that containsAn ancestor and all of its descendants.An ancestor and some of its descendants.Several species that lack a common ancestor.One species.
57A paraphyletic clade is one that contains Question 9A paraphyletic clade is one that containsAn ancestor and all of its descendants.An ancestor and some of its descendants.Several species that lack a common ancestor.One species.
63Question 11Which of the following statements about the difference between cladistics and traditional evolutionary taxonomy is false?Both accept monophyletic cladesBoth accept paraphyletic cladesCladistics rejects paraphyletic clades, while evolutionary taxonomy sometimes accepts them.Both reject polyphyletic clades.