BIOE 20C Lecture Notes - Lecture 7: Polytomy, Adaptive Radiation, Polyphyly
12 Sep 2016
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Lecture 7 10/20/2015
Phylogenies
• Phylogeny=evolutionary history for group of organisms
• Typically depicted as a tree
o “Great big family tree”
Phylogenetic Trees
• 3 basic components
• Branches=populations through time
o Comes from Darwin’s ideas of evolution
• Nodes=forks where ancestor splits into two or more descendants
• Tips=extinct or extant species
o You don’t have to be alive to be a species
o extant: still alive, not extinct
• Can “spin” tree on any node and not change any of the information
that it shows
• Groups that occupy adjacent branches linked by a node=sister taxa
• Clade=ancestor and all its descendants (literally means “group”)
• Polytomy=more than two branches (groups) emerge from a node
o aka star phylogeny
o Rapid speciation caused by adaptive radiation
• Trees rooted-bottom node=most ancient
• Outgroup=taxon that diverged prior to most ancient node of a tree
o Outside of a clade
Phylogenetic Groups
• In any phylogeny, there are 3 potential groups
o 2 are bad (taxonomic baggage): want to get rid of them
o 1 is good
• Monophyletic group=true clade: ancestor and all its descendants
o Good group
• Paraphyletic group=group with common ancestor but only some of
its descendants (incomplete group)
o Bad
• Polyphyletic group=groups of species with different common
ancestors
o Worst
find more resources at oneclass.com
find more resources at oneclass.com
Adaptive Radiations
• Appear in phylogenies as polytomies (star phylogenies)
• Represents a period of rapid speciation
o ex. Hawaiian honeycreepers, Hawaiian silverswords
Three Potential Mechanisms
• Colonization events
• Morphological innovation
• Mass extinctions
Colonization Events
• Habitat unoccupied by competitors is colonized by a species
• Colonizing species quickly radiates to exploit new resources
• ex. Anolis in Hispaniola and Jamaica
Mass Extinctions
• Remove major competitors from the system
• Left with abundance of resources with no competitors
• Allows surviving species to exploit resources that were previously
unavailable
• Ex. explosion of placental mammals after dinosaur extinction
Morphological Innovation
• A new trait that appears allows new resources to be exploited
• Examples:
o Flowers
o Feathers
o Mouthpart modifications
Inputs Used to Create Phylogenies
• Fossil record
• Comparative molecular biology
o Molecular clock
▪ Allows use of coding and neutral DNA
find more resources at oneclass.com
find more resources at oneclass.com
