Download 12-History of Lineages

Reconstructing the history of lineages
Class outline
• Systematics
• Phylogenetic systematics
• Phylogenetic trees and maps
Class outline
• Definitions
• Systematics
• Phylogenetic systematics/Cladistics
Systematics
• Study of evolutionary relationships
between organisms
– Classify biodiversity (Taxonomy)
– Unravel ancestor-descendant
relationships (Phylogenetics)
Phylogenetic systematics
How can we reconstruct the history of
evolution without seeing speciation events?
Identification of key characters that represent evolved
(derived) traits
Construct a tree (cladogram) based on the observed
similarities between species
Clade: Any monophyletic evolutionary branch in a
phylogeny using derived characters
Monophyletic taxon/clade - includes all descendant
species and their ancestor (natural taxa)
Vertebrate Lineage
Paraphyletic taxon– group that includes an ancestral
taxon and some, but not all of its descendent taxa
(artificial)
Vertebrate Lineage
Polyphyletic taxon– group of organisms that does not
include their most recent common ancestor (artificial)
need to pass through one or more ancestors before arriving at a
common ancestor for the group.
Vertebrate Lineage
Let’s test our knowledge!
Let’s test our knowledge!
Let’s test our knowledge!
Phylogenetic Systematics/Cladistics
• Based on Willi Hennig work (1950)
• Modern approach that investigates how evolution
occurred to generate the observed similarities
between species
• Objective – deduce ancestry
through observations of the
changes in characteristics
• Method – construction
of phylogenetic trees
Phylogenetic Systematics
How can the history of evolution be reconstructed
without seeing speciation events?
1) Identification of key characters (heritable parts or
attributes of an organism)
2) Transform characters into transformation series
3) Compare these characters to an outgroup
4) Construct a cladogram based on the observed
similarities between species
Outgroup: a related taxon used to infer primitive
and derived character states
Characters
• Heritable traits with
different states that can
be used to infer
evolutionary
relationships
• Morphological
– Physical measurements
– General form
• Molecular
Characters
• Heritable traits with
different states that can
be used to infer
evolutionary
relationships
• Morphological
• Molecular
– DNA sequencing
Phylogenetic systematics
Why bother to know if the trait is primitive or
ancestral?
• Structures and functions usually not created
de novo (but are modified)
Phylogenetic systematics
• Homology
– Character state shared by two or more taxa due
to inheritance from a common ancestor
• Homoplasy
– Character state shared by two or more taxa due
to convergent evolution (independent origin)
• Can only use homologous characters to
understand evolutionary relationships
Phylogenetic systematics
Praying mantis
Lacewing
• Only homologies should be used to understand
evolutionary relationships and create phylogenetic trees
Phylogenetic systematics
What kind of characters are used to
construct phylogenetic trees?
• Classes of Homologous traits
– Plesiomorphic (primitive)
– Apomorphic (derived)
apomorphic
plesiomorphic
Phylogenetic systematics
What kind of characters are used to
construct phylogenetic trees?
• Classes of Homologous traits
– Plesiomorphic (primitive)
– Apomorphic (derived)
– Symplesiomorphic (primitive-shared)
– More inclusive than focal clade
– Synapomorphic (derived-shared)
– Includes only focal clade
Let’s test our knowledge!
synapomorphic
synplesiomorphic
Hennig’s Rules for Phylogenetic Systematics
1. Assume homology, not homoplasy in absence of
evidence
2. Homologies found within a monophyetic group
that are shared with members of sister groups are
pleisiomorphic while those found only in the
ingroup are apomorphic
3. Only synapomorphies provide evidence of common
ancestral relationships (not symplesiomorphies or
homoplasies)
4. Can combine multiple transformation series
Phylogenetic Systematics
Constructing a cladogram
1) Identification of key characters (heritable parts or
attributes of an organism)
2) Transform characters into transformation series
3) Compare these characters to an outgroup
4) Construct a cladogram based on the observed
similarities between species
Outgroup: a related taxon used to infer primitive
and derived character states
Monophyletic
descendent
taxa
Ancestral
What about trait E’?
Trait E’ must be a homoplasy!
Molecular Systematics (molecular phylogenetics)
• Can include hundreds/thousands of characters in a
phylogenetic study
• Morphological characters still useful
• Partition characters’ rates of evolution
Molecular clocks
Can we know when speciation occurred?
• Some DNA and proteins evolve at known and
constant rates  used as a molecular clock to
date evolutionary steps
• Ongoing debate on the reliability of molecular
clocks
• How are molecular clocks calibrated?
Molecular clocks
How are molecular clocks calibrated?
• Comparing known
rates of molecular
change with
speciation in the
fossil record
Molecular clocks
Fossils
• Provides direct factual evidence of evolution
• Provide evidence of character evolution and
ancestral traits
• Document divergence times
• Document localities of past occurrence (distribution)
Fossil limitations
• Incomplete
• Biased preservation
• Only remains
• Trace fossils
• Destroyed/inaccessible
• Less known further
back in time
• Transported from original distribution
Why are fossils and phylogenies important to
biogeography?
• Evolutionary histories
Influences of vicariance and dispersal events
• Biogeographic history of a place
Changes in dispersal barriers
How these barriers influenced the biotas
Taxon vs. Area approaches
• Taxon biogeography
– Reconstructs the history of lineages across areas
at a single lineage at a time
• Area biogeography
– Reconstructs the relationships among the areas
and the biotas living on those areas
Taxon biogeography
• The goal is to reconstruct the biogeographic
history of just one taxon.
• However, it could be to compare several taxon
and see if there is any congruence across
them.
Area biogeography
• The goal is to reconstruct the biogeographic history
of a set of areas based on the relationships of taxa
distributed across those areas
Area biogeography
Modern Historical Biogeography
• Emphasis on rigorous logic and hypothesis
testing.
• Reliance on robust phylogenetic hypotheses.
• Use of taxon-area cladograms based on the
delineation of areas of endemism.