BIOEE 1780 Lecture Notes - Lecture 9: Phylogenetics, Biogeography, Allopatric Speciation
28 Apr 2018
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Lecture 9 – Phylogenetics III
Biogeography: the study of the distribution of species across space (geography) and time
Dispersal: the movement of populations from one geographic region to another with very limited return
exchange (or none at all)
Vicariance: the formation of geographic barriers to dispersal and gene flow, resulting in the separation
of once continuously distributed populations
Factors Involved in Macroevolutionary Change
1. Intrinsic Factors
a. Example: the physiology of clades
2. Extrinsic Factors
a. Example: environment, climate, atmospheric conditions
Independent Contrasts: a series of comparisons are made between nodes and tips in the phylogeny
• Minimizes errors when making phylogenetic trees
Phylogenies are hypotheses.
• There may be competing hypotheses, where multiple phylogenies differ in the order of their nodes.
• It becomes difficult to compare all of these trees, so we use search algorithms (computational
methods of selecting the best tree.
• Methods for choosing the best phylogenetic tree
o Selecting the tree with the smallest number of character state changes
• Parsimony
• Provides the simplest explanation
• Most common approach for morphological characters
o Selecting the tree that is most probable, given what we know about character evolution
• Based on probability methods
• Typically used for DNA mutations
A phylogenetic tree is not a depiction of similarity between taxa.
• Some lineages may evolve very rapidly, decreasing the number of similarities with closely related
organisms.
Phylogenies can be used to trace the origins of epidemics.
Adaptation: a trait, modified by selection, that increases the ability of an individual to survive or
reproduce compared to individuals without the trait
Bat Adaptation Case Study - Using a Comparative Method
• Why do some bats have larger testes than others?
• Hypothesis: testis size is an adaptation due to competition in large group sizes
• Experimental Design: Look for evidence of correlated evolution on the tree between bat testes size
and their group sizes.
o Measure the change between testes size and group size as the species evolves.
o These phylogenetic contrasts tell us whether these traits are evolving together, which would be
evidence for adaptation.
