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!

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


Why bother to know if the trait is primitive or ancestral?

• Structures and functions usually not created de novo (but are modified)


• 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


• Only homologies should be used to understand evolutionary relationships and create phylogenetic trees

Praying mantis

Lacewing


What kind of characters are used to construct phylogenetic trees?

• Classes of Homologous traits

– Plesiomorphic (primitive)

– Apomorphic (derived)

apomorphic

plesiomorphic


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

Ancestral

Monophyletic

descendent

taxa

Trait E’ must be a homoplasy!

What about trait E’?

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.

12-history of lineages

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