BIOL214 Exam 2 - Phylogeny (Ch 4)

Evolution

accumulated inherited changes in a population over time

Population

group of individuals of the same spaces living in the same location

Microevolution

short term adaptations that result from changes in the environment

Macroevolution

the process of the development of new species from common ancestors

Phylogeny

• history of descent with branching

• like a genealogy that records family histories

Phylogenetic Tree

• depicts the process of speciation

• contains branches and nodes

Branching in a Phylogenetic Tree

• represent diverging populations

• branching order hypothesizes the evolutionary relationship within a group

Nodes in a Phylogenetic Tree

• represent the last common ancestor before branching off

• can be rotated without changing the evolutionary relationships of the groups

Tips in a Phylogenetic Tree

• present-day species

Sister Groups

• two taxons (groups) are considered to be each other’s closest relatives if they share a common ancestor not shared by any other group

• sister groups are two taxons that are considered each other’s closest relatives

• closeness is determined by seeing how recently the groups share a common ancestor

Monophyletic Group

• includes a common ancestor and all of its descendants

• only monophyletic groups reflect evolutionary relationships because they include the common ancestor and all of its descendants

Paraphyletic Group

• includes and common ancestor and some, not all of its descendants

Polyphyletic Group

• does not include the common ancestor

Classifications

• Kingdom

• Phylum

• Class

• Order

• Family

• Genus

• Species

Characters

• features that are compared when constructing a phylogenetic tree

• can be similar due to:

  • common descent

  • convergent evolution

• a character state is an observed condition of said character

Common Descent

• an ancestor that had the same character state

Convergent Evolution

• in which the character state evolved independently in two separate groups

Homology

• characters are similar because of common descent

Homoplasy (Analogy)

• similarities due to adaptations by different species

Synapomorphy

• shared derived characters

• shared by some, but not all, members of the group

Cladistics

• phylogenetic reconstruction on the basis of synapomorphies

Outgroup

• a group that falls on an earlier branch of the tree

• used for comparison to the group we are studying

The Principle of Parsimony

• the best-fit tree is the one with the fewest number of changes

  • minimizes the total number of independent origins of character states

Phylogenetic Trees with Genetics

• variation in DNA and RNA can be used as character states

• phylogeny can be determined by distance than synapomorphies

  • low distance indicates recency of common ancestry

Evolutionary Rates

• If the rate of evolution varies, few changes may have occurred within one lineage and many in the other

• unequal rates of evolution result in predicting incorrect phylogenetic relationships

• rate constancy assumption is less likely to be violated when using molecular data (versus morphological data)

Using Fossils to Create Phylogenies

• fossils allow us to calibrate phylogenies in terms of time

• provide a record of extinct species

• place evolutionary events in context with the Earth’s history

• phylogenies hypothesize impressive morphological and physiological shifts through time

Fossil Types

• Trace Fossil

• Molds and Casts

• Replacement

• Petrified or Permineralized

• Amber

• Original Material

• Molecular Fossils

Trace Fossil

• any indirect evidence left by an organism

• footprints, burrows, and fossilized feces

Molds and Casts

• an impression of an organism

• a cast is a mold filled with sediment

Replacement

• the original material of an organism is replaced with mineral crystals that can leave detailed replicas of hard or soft parts

Petrified or Permineralized

• empty pore spaces are filled in by minerals, such as in petrified wood

Amber

• preserved tree sap traps an entire organism

• sap hardens into amber and preserves the trapped organism

Original Material

• mummification or freezing preserves original organisms

Molecular Fossils

• DNA, proteins, and lipids

Burgess Shale

• sedimentary rock formation that preserved the deep seafloor of 505 million years ago

• fossil record of marine life is more complete because marine habitats are more likely to be places where sediments accumulate and become rock

Messel Shale

• about 50 million years ago, this shale formed in a lake in what is now Germany

• released toxic gases and suffocated local animals

• their carcasses settled into oxygen-poor muds on the lake floor

• retains impressions of fur and color patterning

Biogeography

• study of the distribution of species and ecosystems in geographic space and through

Archaeopteryx Example

• in 1861, German quarry workers discovered a fossil that is a famous example of a transitional form

• lived 150 million years ago

• skeleton shares many characteristics with dromaeosaurs

• fossils found preserve evidence of feathers

  • close relationship between birds and dinosaurs

Tiktaalik

• phylogenies hypothesize that all land vertebrates are descended from fish

• fossils discovered in 2004

• it had fins, scales, and gills

• it also had wrist bones, fingers, and an amphibian-like skull

• true neck, like tetrapods

What was Darwin’s brilliant insight?

• all living things on Earth are related and can be depicted in a “Tree of Life”

• evolution is a branching process

Phylogeny Definition

• the evolutionary history of a lineage or lineages (populations, genes, or species)

Phylogenetic Tree Definition

• a visual representation of a phylogeny

Reading a Phylogenetic Tree

• Nodes: represent common ancestors for all descendent lineages

• Clades: a common ancestor and all of its descendants (monophyletic groups)

• Taxa: can be rotated around the nodes

• Tip: the terminal end of an evolutionary tree, representing the species, molecules, or populations being compared

Evolutionary Reversal

• reversion back to an ancestral character state

  • can happen though mutations

Polytomy

• we cannot determine which members of these branches are most closely related

Neil Shubin and Colleagues…

• predicted where transitional fossils would be found

• Mid-Devonian rocks in Northern Canada

Mammalian Ear Bones are Homologous to…

• bones of the reptilian jaw

Feathers Evolved Before Flight

• exaptation (preadaptation)

• a trait can evolve because it served a particular function, but it may come to serve another

• feathers originally evolved for other function, such as species recognition

Exaptation (Preadaptation)

• a shift in the function of a trait during evolution

• natural selection co-opts a trait for a new function

• a trait can evolve because it served a particular function, but it may come to serve another

Heterochrony

• evolutionary change in form due to change in rate or timing of developmental events

• a change in growth rate of parts can produce a new final shape

Paedomorphosis

• a change of timing produces a sexually mature adult with juvenile features