I. Angiosperms and introduction to phylogenetics Flashcards
What are gymnosperms and angiosperms?
Gymnosperms: non-flowering plants (gymno = naked; sperm = seed) e.g. conifers, pine trees, only c. 1000 species
Angiosperms: flowering plants (angio = case), 454 families, c.13,500 genera, between 150k-400k species!
What are the two major angiosperm ‘phylogenetic groups’ or ‘clades’, and their key characteristics?
Eudicots = 70% of angiosperms, dominate the tropics, defined by pollen with 3 grooves, parts of 5 are dominant, highly diverse vegetation, often compound leaves, bilaterally similar.
Monocots = palms, grasses, non-woody and different forms of wood, simple leaves, parts of 3’s
Outline the history of angiosperm evolution.
Earliest unequivocally angiosperm fossils from ~140 Ma (early/mid-Cretaceous) in form of fossils (others 127 Ma).
Fossil evidence varied in terms of flower parts, fruits, pollen and leaves but mostly date to around 120 Ma.
Reaching dominance ~65 Ma (Tertiary) along with bilateral flowers (one plane of symmetry). Not until after K-Pg extinction event.
Confusion over why evolution and rise to dominance was so slow/late.
What are the main problems of identifying a date of origin?
Soft so didn’t fossilise well, so can’t date or sequence DNA.
Most fossil evidence from Mid-Cretaceous.
Drawings of fossils -> really hard to agree upon family
What are the two different theories used to explain the late-evolution of plants post end-cretaceous dinosaur extinction event?
1) CO-EVOLUTION (more speculative)
Dinosaurs required low-energy foods so plants only needed to produce small seeds and fruits. Mammals that rose in numbers after dinos died out require large energy foods, so plants become more complex for survival e.g. thorns, toxic, chemicals, communication networks. Success from the coevolution with insects and vertebrates e.g. to enable dispersal of fruits, seeds and gametes.
2) DARK AND DISTURBED HYPOTHESIS
The traits of angiosperms that determines their success i.e. hydraulics, responses to shade, disturbance and moisture, photosynthetic abilities.
Why is our estimation of the number of angiosperms so poor?
Endemic species difficult to find, especially in tropics - so large, many ecosystems, manual data collection! Investment issue.
Incomplete science of taxonomy; contestation. Philosophical issues.
NEW SPECIES OF 90M TALL TREE DISCOVERED IN BRAZIL ONLY LAST YEAR. Could be heaviest living organism.
Outline early history of plants in general (not angiosperms).
Earliest plants in the Precambrian ~540 Ma.
First vascular land plants in the Plaeozoic to early Devonian 420 Ma
Major expansion of seed plants in Palaeozoic to Permian 290-248 Ma, where distinct biomes developed. By early Jurassic, floras containing components reminiscent of modern-day flora.
Why are phylogenetics important in biogeography?
Can be used to test important hypotheses e.g. when and what traits evolved. Helps improve understaniding of how many times a certain plant family has evolved - tracking of important traits.
What is meant by ‘phylogenetics’?
The representation of the history of evolution with a bifurcating tree.
How does the new modern approach to evolutionary taxonomy compare to older ones?
Pre-Darwin attempts to ‘map out life’, as well as Darwin himself, but he realised the necessity of extinction in order for new forms of life to emerge.
Early mid-20th century used synthesised taxonomy but based only on expert opinions, a single hypothesis.
Modern approach is more numerical -> quantitative representation of tree-data relationships.
Reading phylogenetic trees: (1) how many terminals? (2) depiction?
- At least 3 terminals needed
- Two main different ways to draw them i.e. vertical square vs. circular. How it is presented is irrelevant to its meaning.
Reading phylogenetic trees: (3) key terminology?
Root: bottom of tree Branch: joining lines Node: where bifurcation occurs Terminal: names at end (terminal taxa) Monophyletic group/clade: a group that contains a common ancestor and all of its descendants i.e. can be cut off once from tree
Reading phylogenetic trees: (4) role of DNA; (5) criteria?
- Data are DNA sequences from gene sequencing. Those that share a position for a particular chemical can help to show a common/similar group. (agreement not guaranteed though!)
- DNA sequencing and phylogenetic modelling uses ‘optimality critera’ i.e. parsimony (old, simplest tree) vs model-based (tree fits model of DNA, Bayesian stats).
How can phylogenetic trees inform biogeography?
Biogeographic regionalisation can incorporate them i.e. distinction being based on different clades.
Wallace vs Huxley:
What is the significance of dated phylogenies?
To test biogeographic hypotheses i.e. evaluation of scenarios e.g. tectonics vs. dispersal
If the distributions of S America and S Africa are to be explained by tectonics, you would expect species to split at the time at which the Gondwanan plate broke up, which was 60Ma, but the average of species dijunction is much later at 10 Ma.
