Lecture 2 & 3 Taxonomy

Question 1

what is nomenclature?

Answer 1

a system of rules for naming things

Question 2

what is taxonomy?

Answer 2

the practice of naming and classifying organisms

Question 3

what is systematics?

Answer 3

the theory and practice of classifying organisms baed on evolutionary history (phylogeny)

Question 4

what is the Linnean system?

Answer 4

• Carl von Linné
• use of unique binomen
• classify and group species using hierarchical categories based on relatedness and or similarity

Question 5

what is the binomial nomenclature?

Answer 5

genus + species

Question 6

what is phylogeny?

Answer 6

evolutionary history of a species or a group of related species

Question 7

what does a phylogenic tree show?

Answer 7

• evolutionary relationships between organisms between common ancestors + descendants
• patterns of descent, NOT phenotypic similarity
• DONT indicate when a species evolved or how much change occurred in a lineage
• dont assume that a taxon evolved from the taxon next to it

Question 8

what is a branch point/node?

Answer 8

divergence of 2 species, speciation event, represent common ancestors of those descendants

Question 9

what are sister taxa?

Answer 9

two descendants that split from the same node- share an immediate common ancestor

Question 10

what is a polytomy?

Answer 10

branch where more than 2 groups emerge
unresolved pattern of divergence
- can indicate: lack of knowledge/insufficient data to resolve
- can indicate: rapid speciation- daughter lineages are equally closely related to one another

Question 11

what is a basal taxon/group?

Answer 11

diverges early in history originates near common ancestor of group

Question 12

how are phylogenetic tree relationships interpreted?

Answer 12

order in which branches are split

Question 13

what is an in-group?

Answer 13

group whose relationships we are interested in untangling

Question 14

what is an out-group?

Answer 14

one or more taxa that are related to the ingroup, but that have diverged from it at an earlier time

Question 15

what is a character & state?

Answer 15

character: type of structure, behaviour, DNA sequence, etc
state: manifestation of that character

Question 16

what are homologies?

Answer 16

phenotypic and genetic similarities due to shared ancestry

• more likely with similar morphologies and DNA
• more likely with greater complexity of structure

Question 17

what are homologous characters?

Answer 17

• look the same + have the same evolutionary origin
• usually bone structure
• phylogenetic tree building/cladistics works best when all character states are homologous

Question 18

what are analogous character states?

Answer 18

• appear the same but actually evolved independently
• convergent evolution
• aka homoPLASIES

Question 19

what is convergent evolution?

Answer 19

• independent evolution of similar traits in different lineages
• often similar environments + environmental pressures + NS produce similar adaptations

Question 20

how is homology distinguished from analogy?

Answer 20

fossil evidence + degree of complexity (more complex more likely homologous)

Question 21

what is cladistics?

Answer 21

method of inferring phylogeny from homologous characters - groups organisms by common descent

Question 22

what is a valid/ideal clade?

Answer 22

monophyletic, ancestor species + ALL descendants, NO unrelated taxa

Question 23

what is the goal of phylogenetic classification?

Answer 23

• organize species into groups with common ancestry that reflect ancestor-descendant relationship – ONLY MONOPHYLETIC TAXA

Question 24

what is a paraphyletic grouping?

Answer 24

• ancestor + some but not all of descendants

- often result of removal of taxa that are HIGHLY DIVERGENT - often the group removed is monophyletic

Question 25

what is a polyphyletic grouping?

Answer 25

• various species with different ancestors
• causes: more than one common ancestor, lacking common ancestor that unites members in a group, incorrectly grouped due to artificial similarities

Question 26

what is the principle of parsimony/Occam’s Razor?

Answer 26

goal is to reconstruct a set of nested relationships that minimize # of times a character has to change states
- most probably phylogeny is one with the fewest evolutionary events

Question 27

what is apomorphy?

Answer 27

derived character

Question 28

what is plesiomorphy?

Answer 28

ancestral character

Question 29

what is snapomorphy?

Answer 29

shared derived character

Question 30

what is a symplesiomorphy?

Answer 30

shared ancestral character

Question 31

what is an autopmorphy?

Answer 31

a unive derived character restricted to a single taxon

Question 32

what is a phylogram?

Answer 32

tree where length of branch reflects # of changes that took place between taxa in that lineage

• difference between two taxa is the sum of branch lengths between common ancestor
• branch length: can be chronological time and branching points determined from fossil record or molecular clock calculations

Question 33

what is the strongest support for any phylogenetic HYPOTHESIS?

Answer 33

• agreement bw molecular data and anatomical evidence

Question 34

ultimately, what are cladograms/phylograms?

Answer 34

HYPOTHESES