This week in lab - trip to Green Oaks! - dress appropriately (sturdy shoes, long pants, etc.) Arrive promptly at lab - need to leave quickly

Studying diversity of forest trees in 2 habitats

Last day… started talking about systematics: study of relationships between organisms & their classification & naming Defined 3 types of possible groups that can be created from the taxa that are arranged in a phylogeny

Most systematists today try to use only monophyletic groups in classification, but traditional classifications often include paraphyletic groups

Paraphyletic groups are most controversial - usually considered ‘bad’, but still frequently used - e.g. ‘reptiles’ or ‘Reptilia’ Share many characters, but mostly ancestral…

‘Reptiles’ excludes some descendants (birds, mammals?)

What does a ‘tree’ represent? Relationships between taxa Relative time since taxa split (sometimes absolute time or genetic distance) What does the horizontal axis represent?

Phylogeny often has branches at top What does ‘x’ axis represent? nothing….

Branches can be rotated without changing meaning, only branching pattern is important

Phylogenies constructed using similarities between species, because related species are expected to share most traits

If two taxa share many traits, we expect them to be closely related - alternative: same characters occur in unrelated spp.; character may have evolved multiple times Not impossible! Convergent evolution… Actually, Alluaudia

Try to use only homologous characters: characters whose similarity is due to inheritance from a common ancestor - recognized by detailed similarity in structure, organization, development, etc. (but not always easy!)

However, we assume it is more likely that shared characters indicate related species Principle of Parsimony suggests simplest explanation preferred Most parsimonious phylogeny has characters evolving fewest times possible (Mutations and evolutionary change assumed to be relatively rare) William of Ockham, of Occam’s Razor fame

e.g. mosses & tracheophytes share many characters - if not closely related, those characters would each have to evolve twice, many more evolutionary changes Instead, we assume they are closely related

Not all characters are equally useful for indicating relationships - e.g number of legs in mammals Try grouping cats, whales, deer, bats & rodents based on # of legs…

Can’t group mammals that have 4 legs together because ancestor had 4 legs… all mammal groups inherited this trait Shared ancestral traits are not useful

Instead, try to use shared derived traits: traits that have been modified from ancestral trait since the group started evolving (AKA synapomorphies) Modification of front legs into flippers, hind legs reduced to vestigial bones can be used as shared derived trait for whales

To determine ancestral trait, examine outgroups: taxa that are not part of the focal group but are closely related

Phylogenies built by finding which taxa share the largest number of derived traits Look at an example of constructing a phylogeny

An example… ‘bird-hipped’ dinosaurs

What sort of characters can be used in phylogenetic analysis? - almost anything that can be measured and has a genetic basis - some characters more useful than others because more or less stable, or easier to compare - may depend on breadth of study (for phylogeny of a phylum use slow-evolving characters, for phylogeny of a genus use fast-evolving characters)

Morphological characters - easy to measure, many traits available - usually only characters available for fossils, if used can combine modern & fossil taxa in analysis

Developmental characters Essentially morphological, but traits seen in embryo may disappear in adult

Behavioral characters Variable, may be hard to compare but can add much potential information e.g. duck courtship displays King Eiders

Different wasp families differ in their nest structures Vespidae Crabronidae

Molecular characters Probably most current studies use molecular characters - potential characters include: - enzyme frequencies use electrophoresis to determine variation

Amino acid sequence of proteins Each position in sequence is a character - having same amino acid is a shared trait Must align sequences first…

DNA hybridization - compares similarity of whole strands of DNA from 2 spp. by how tightly they bond together - heat DNA until 2 strands separate, when cooled they join together again in double helix

DNA from 2 different species will form hybrid DNA, but will separate again at lower temperatures

Which of these pairs do you think is most closely related? A) American Black Bear & Asiatic Black Bear B) Sloth Bear & Spectacled Bear C) Grizzly Bear & Polar Bear American Black Bear Asiatic Black Bear Sloth Bear Spectacled BearPolar Bear Grizzly Bear

Phylogeny must be based on overall DNA similarity (measured by dissociation temperature), not by number of shared characters