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evolution > Phylogeny & Taxonomy > Flashcards

Phylogeny & Taxonomy Flashcards

w4

1
Q

taxonomy

A
  • science/study of classification
  • taxonomic ranks for cellular organisms inc domain, kingdom, phylum, class, order, family, genus, sp
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2
Q

phylogeny

A

evolutionary history of groups of organisms (such as clade, sp or individuals, which may be referred to as taxa)

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3
Q

phylogenetics

A
  • systematic study of organism relationships based on evolutionary similarities & diffs
  • modern taxonomy based on phylogeny
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4
Q

tree of life

A
  • metaphor, model & research tool used to explore evolution of life & describe relationships between organisms, both living & extinct
  • graphical / diagrammatic representation of biological entities connected through common ancestors
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5
Q

phylogenetic tree

A
  • hypothesis of genealogical relationships…
  • inferred from observed traits (“characters”)
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6
Q

basic assumptions of phylogenetic tree

A
  1. organisms are related by descent from common ancestor
  2. characteristics change over time as organisms evolve
  3. new clades created by binary splitting
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7
Q

clade encompassing a group of taxa

A
  • consists of last common ancestor (taxon) of those taxa…
  • and all taxa that descended from last common ancestor
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8
Q

importance of phylogenetics

A
  • establishing relationships of organisms
  • permitting more precise approach to studying “biodiversity” & to build classification of organisms
  • reconstructing evolutionary histories & processes
  • developing better evolutionary models & enabling predicting power
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9
Q

character

A

heritable feature of organism

e.g…
no. of appendages?
feathers present?
no. of teeth?

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10
Q

character states

A

values character can take

eg. 1, present
0, absent

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11
Q

2 important types of characters used for reconstructing phylogenies…

A
  1. molecular characters -> inc. seqs of DNA, RNA, genome, protein
  2. morphological characters -> inc. structures, behaviours, lifestyles
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12
Q

internal node

A

hypothetical ancestor of 2 given taxa

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13
Q

root node

A

hypothetical common ancestor of all taxa in tree

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14
Q

branches

A

accumulation of evolutionary change through time

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15
Q

tip

A

a taxon (sp, family, order etc.)

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16
Q

sister taxa

A

taxa closer to each other than any others on the tree

17
Q

outgroup

A

most distantly related taxon to all the others

(the others can be referred to as the ingroup)

18
Q

using phenetics school of thought…

given a group of taxa, can we be confident that the 2 taxa that are most similar overall are the most closely related?

A

no -> observed similarities can come from 2 sources…

  • similar characters could have been inherited from common ancestor (homology)
  • OR…
  • could have evolved independently (homoplasy)
19
Q

homology

A
  • similarity between structures in diff organisms…
  • that is attributable to their inheritance from common ancestor
20
Q

homoplasy

A
  • similar traits in diff organisms…
  • that do not share common ancestor but due to convergent evolution
21
Q

So the 2 taxa that share largest no. of homologies are the closest relatives, right?

A

no.

  • all homologies are not equal
  • some homologous characters were recently derived, others are ancient features of a lineage
  • only shared, derived features (synapomorphies) are informative about close relationships
22
Q

apomorphy

A
  • derived character state that has evolved within a taxa
  • can be used to separate one taxa from other
23
Q

synapomorphy

A

apomorphy shared by 2+ taxa and their most recent common ancestor

24
Q

plesiomorphy

A
  • primitive / ancestral character state…
  • that is homologous within particular group of organisms
  • but is not unique to members of that group
25
Q

symplesiomorphy

A

plesiomorphy shared by 2+ taxa of a group

26
Q

cladistics
aka
“phylogenetic systematics”

A
  • introduced by German entomologist Willi Hennig (1966) as method used in phylogenetic analysis…
  • although now sometimes used to refer to the whole field
27
Q

cladogram

A
  • outcome of cladistic analysis: dichotomous branching diagram that represents a hypothesis of phylogenetic relationships
  • taxa grouped into nested hierarchy defined by sharing common ancestor
28
Q

Hennig’s 2 key principles of cladistics

A
  1. only features that are informative about phylogenetic relationships are shared, derived homologies
    -> rules out both homoplasies & plesiomorphies/symplesiomorphies of taxa being studied
  2. proper classification of organisms requires grouping taxa into clades / monophyletic groups
29
Q

monophyletic group

A
  • group of taxa composed only of common ancestor & all its descendants
  • monophyletic group = a clade
  • monophyletic groups characterised by shared derived characteristics inherited from their common ancestor (synapomorphies)
30
Q

Paraphyletic group

A
  • group of taxa that include most recent common ancestor, but not all of its descendants
  • paraphyletic and polyphyletic groups cannot be called true clades (they don’t represent full phylogenetic story)
31
Q

polyphyletic group

A
  • group of taxa that does not inc common ancestor of all members of group
  • paraphyletic and polyphyletic groups cannot be called true clades (they don’t represent full phylogenetic story)
32
Q

Importance of Phylogenetics in Fossil Studies

A

Allow palaeontologists to use a more objective analytical method to:

  • establish evolutionary relationships among fossil taxa and between fossil and living taxa
  • precisely study “biodiversity” in the past and build a classification of fossil organisms
  • integrate fossil taxa with living taxa to reconstruct evolutionary histories and process
  • develop better models for macroevolution
33
Q

eg. of how palaeontologists use phylogenetics to solve scientific q’s

A

enigmatic worm = Facivermis yunnanicus Hou & Chen, 1989

  • greatly elongated & limbless portion of trunk
  • pear-shaped terminal swelling with 2/3 rings of hooks
  • reminds us of Luoishania longicruris
  • phylogenetic analyses (parsimony, Bayesian inference & max. likelihood) => ppl thinking they are more closely related to ‘velvet worms’…
  • indicates that Facivermis lost some features over time to fit tube-dwelling lifestyle = rare eg. of 2ndary loss of morphological characters so early in history
34
Q

cambrian lobopodiums

A
  • group of extinct organisms
  • close affinities to living anthropods
  • long bodies
35
Q

importance of fossils in phylogenetics

A
  • fossils provide direct evidence of evolutionary history
  • contain info about evolution we cannot obtain from living organisms (ancient time, extinct phenotypes)
  • unique morphological comboss can reveal crucial evolutionary links between extant taxa & fill gaps in our knowledge of trait acquisition along lineages
  • can be used to test phylogenetic hypothesis
  • useful in assessing direction of character evolution & could aid in detecting instances of convergence
  • can improve phylogenetic analyses of morphological characters
36
Q

evolutionary link to crocodiles & birds

A
  • are each others closest living relatives
  • phylogenetics shows birds evolved from theropod dinosaurs during Jurassic (around 165-150 mya)
  • birds’ classic small, lightweight, feathered, & winged body plan was pieced together gradually over 10s of millions of years of evolution rather than in 1 burst
37
Q

fossils help in molecular dating

A
  • molecular clock: rate of evolution at molecular level is ~ constant through time & among sp, so its possible to use molecular seqs to estimate time when 2+ life forms diverged
  • fossils provide min. age time constraints for divergences of groups
  • fossil calibrations are utmost source of info for resolving distances between molecular seqs into estimates of absolute times & absolute rates in molecular clock dating analysis
38
Q

fossils can help us test hypotheses.

give an eg.

A
  • Dannychaeta tucolus Chen et al. 2020
  • Annelids are diverse group of animals (inc. earthworms, ambush predators, & suspension feeders). Figuring out their early evolution has been tricky because genetic studies & fossils don’t always match up.
  • fossils from Cambrian period show annelids living near ocean floor, while genetic studies suggest they might have lived in different ways
  • scientists found new fossil (Dannychaeta tucolus) from Cambrian period -> type of bristle worm & preserved in thin tubes made of organic material
  • Dannychaeta has distinct head with spade-shaped parts & long side pieces
  • elongated abdomen with biramous parapodia with parapodial lamellae
  • ^ this combo of features is similar to modern Magelonidae worms
  • by studying Dannychaeta, scientists learned that it’s 1 of oldest types of bristle worms we know about…
  • & it helps us understand how annelids evolved over time
  • P.S. Dannychaeta in clade Palaeoannelida
39
Q

crown & stem group

A

Any clade can theoretically be ÷ into 2 components:

  1. crown group: contains living taxa of group & most recent common ancestor & all of its descendants (both extant & extinct)
  2. stem group: paraphyletic assemblage composed of fossils that are closer to crown group than to any other living organisms

-> crown + stem = total group

-> in tree analogy, total group is crown group & all branches back to (but not including) the split with closest branch to have living members

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