Chapter 25 - Phylogenies and History of Life

macroevolution

patterns of evolution over large time scales (mya)

microevolution

evolution that occurs quickly

* ex - antibiotic resistance

polytomy

indicates that insufficient data were available to resolve which taza is more closely related; DNA sequences are identical

* “many splits”

monophyletic group

an ancestral population and all of its descendants

synapomorphy

trait unique to a monophyletic group. (hair) 

homology

similarity among organisms of different species due to shared ancestry

* organisms may be similar for other reasons

outgroup

taxon that is not part of the group being studied

building phylogenic trees using characters presence/absence

1. identify taza of interest (ex - lizard, dog, human)
2. select useful traits or characteristics
3. define character states (1 = present, 0 = absent)
4. add an outgroup
5. use data to construct the tree

homoplasy

similarity among organisms of different species due to reasosn other than common ancestry, such as convergent evolution

polyphyletic group

share similarities, but not a common ancestor

* ex - dolphin and ichthyosaur

convergent evolution

independent evolution of similar traits in distantly related organisms due to adaptation to similar environments and lifestyles

what does the length of branches indicate on phylogenic trees?

a scale bar can indicate number of base substitutions per site, years, etc

precambrian era

the interval between the formation of Earth and the appearance of most animal groups

major events of the precambrian era

* formation of earth
* first oceans
* origin of life (without oxygen)
* presence of oxygen in atmosphere
* eukaryote fossils and photosynthetic eukaryotes
* sexual structures in eukaryotes

when did the earth form

4\.6 billion years ago

when did life originate

3\.5 billion years ago

cambrian era

began 541 million years ago (following the precambrian)

phanerozoic eon

interval between 541 mya and present

* paleozoic era
* mesozoic era
* cenozoic era

paleozoic era

major animal lineages appeared

* transition to land

mesozoic era

diversification of dinosaurs and gymnosperms

cenozoic era

diversifiation of birds, mammals, and angiosperms

* humans evolved

adaptive radiation

rapid evolutionary diversification within a lineage, producing numerous species with a wide range of adaptive forms

causes of adaptive radiaiton

* ecological opportunity
* morphological, physiological, or behavioral innovation

ecological opportunity

the availability of more resources or new types of resources

ex - hawaiian silverswords


1. immigration of a single species to hawaii (5 mya)
2. dispersal and colonization of different habitats (few competitors; empty ecological niches)
3. genetic divergence (selection, genetic drift, and mutation)

* ex of allopatric speciation by dispersal

how does a clade look if it underwent an adaptive radiation?

1. the species involved form a monophyletic group
2. speciation occurred relatively radpidly compared with other groups
3. the species diversified ecologically (occupy many niches)

morphological, physiological, or behavioral innovation

an adaptive breakthrough

ex - angiosperm vs gymnosperms

* angiosperms have flowers, which are more efficient movement of pollen
* gymnosperms have no flowers/ fruits and rely on wind to transfer pollen from the male to female flowers

cambrian explosion

produced all of the major animal phyla existing today

causes of the cambrian explosion

1. higher oxygen levels - larger bodies, more movement
2. evolutioon of predation - arms race between predators and prey
3. explotation of new niches - more movement
4. duplication and diversification of Hox genes

what will NOT trigger adaptive radiation?

an unusual event splitting a habitat, like a hurricane will NOT trigger adaptive radiation

* causes genetic drift

mass extinction

a large-scale, sudden (within 1 mil years) extinction event that is geographically and taxonomically widespread

background extinction

involves routine/typical ecological events (predation, competition, diseases) and gradual environmental change

* reflects action of natural selection

contributors to the end-permian extinction

* giant volcanic eruptions
* extreme global warming
* low oxygen in atmosphere and oceans
* acidic oceans and drop in sea levels