The Evolutionary History of Biodiversity Phylogeny and the Tree of Life
Feb 23, 2016
The Evolutionary History of Biodiversity
Phylogeny and the Tree of Life
Phylogenies show evolutionary relationships
Phylogeny› the evolutionary history of a species or
group of related species› the cornerstone of a branch of biology
called systematic taxonomy› classifies organisms and their evolutionary
relationships using fossils morphology Genes molecular evidence
Phylogenies show evolutionary relationships
Taxonomy the ordered division of organisms into categories based on similarities and differences.
Binomial nomenclature two part naming system consisting of the genus /species. Developed by Carolus Linnaeus
Swedish biologist considered the father of modern taxonomy.
The binomial nomenclature Linnaeus used was developed in the late 16th and early 17th century by the Swiss botanists (brothers) Gaspard and Johann Bauhin, for some of the 6000 plants they described in their works, but it was Linnaeus who used it consistently and systematically.
Carl von Linné (Carolus Linnaeus)1707 – 1778
Hierarchical Classification
Hierarchical Classification Organisms are
classified into a hierarchies that group closely related organisms and progressively include more and more organisms. Each categorization at any level is called a taxon.
Phylogenetic trees The aim is to figure out
the evolutionary relationships among species.
Branching diagrams called phylogenetic trees hypothesize evolutionary relationships thought to exist among groups of organisms.
It does not show the ACTUAL evolutionary history of organisms.
Why a hypothesis?
Phylogenetic trees In a phylogenetic
tree the tips of the branches specify particular species and the branching points represent common ancestors.
Phylogenetic trees Phylogenetic trees
are constructed by studying features of organisms formally called characters.
Characters may be morphological or molecular.
Morphology Comparing physical structural
characteristics
Similarities due to shared ancestry
Homologous Structures
Convergent EvolutionThese animals have evolved similar adaptations for obtaining food because they occupy similar niches.
Analogous Structures
Convergent EvolutionSimilar solutions to similar problems
Analogous Structures
Molecular Systematics
Using DNA The more alike the DNA
sequences of two organisms, the more closely related they are evolutionarily.
Early phylogenetic tree of amniotes based on cytochrome c gene by Fitch and Margoliash (1967).
Note numbers on branches.
These represent estimated numbers of mutational changes in gene.
Cladograms Cladograms are diagrams that display patterns
of shared characteristics. If shared characteristics are due to common
ancestry (are homologous) the cladogram forms the basis of a phylogenetic tree.
Within a tree a clade is defined as a group that includes an ancestral species and all of its descendants.
Cladistics is the science of how species may be grouped into clades.
Ancestral vs. Derived Characters Ancestral
› Character present in the common ancestor of both groups
Derived› Character that evolved in one group but not the other
What derived character is shared by all the animals on the cladogram on the next slide?
Cladograms and Phylogenetic Trees
A cladogram and a phylogenetic tree are similar, but not identical.
Traditional evolutionary taxonomy is subjective and therefore more prone to bias. A phylogenetic tree’s branches put more emphasis on certain characters rather than others.
Cladistics treats each character equally. It is
more objective by ignoring how some characters have a higher impact on evolution. It is thought that evolutionary success is dependent on high-impact events.
Rate of Evolution An organism’s evolutionary history is
documented in its genome The rate of evolution of DNA sequences varies
from one part of the genome to another Comparing the different sequences helps us to
investigate relationships between groups of organisms that diverged long ago
DNA that codes for ribosomal RNA and
mitochondrial DNA are both used› rRNA changes relatively slowly –used with taxa that
diverged hundreds of millions of years ago› Mitochondrial DNA evolves rapidly – used to explore
more recent events
The Molecular Clock Hypothesis
Used to measure the absolute time of evolutionary change.
Amount of genetic difference between sequences is a function of time since separation.
Assumes that the rate of molecular change is constant (enough) to predict times of divergence
Taxonomy in Flux When the authors of
your text book were in high school they were taught two kingdoms: plants and animals.
When your teacher was in high school she was taught five kingdoms: Monera, Protista, Plantae, Fungi and Animalia
Taxonomy in Flux Now biologists have
adopted a three-domain system › Discovery that there
are two distinct lineages of prokaryotes
Characteristic Bacteria
Archaea
Eukarya
Nuclear envelope No No YesMembrane-enclosed organelles
No No Yes
Introns No Yes YesHistone proteins associated with DNA
No Yes Yes
Circular chromosome
Yes Yes No