Phylogenies

Anatomy of a Phylogeny

• Root: Starting point of the tree. It represents the common ancestor of all the organisms shown.

• Terminal Nodes (Tips):

  • Represent present-day living species or contemporary taxa.

  • Located at the tips of branches, typically on the far right of the phylogeny.

• Time Axis:

  • The far right represents present-day time.

  • Moving from right to left moves deeper into past evolutionary history.

• Branches:

  • Lineages connecting internal nodes to terminal nodes.

  • Reflect independent evolutionary changes that occurred in lineages after diverging from a shared ancestor.

• Internal Nodes:

  • Branch points where two lineages join in the past.

  • Represent common ancestors shared by descendant lineages.

• Root:

  • The deepest internal node of the tree.

  • Represents the single common ancestor shared by all taxa included in the phylogeny.

• Topology:

  • The overall shape and branching pattern of the tree.

  • Hypothesizes the specific evolutionary relationships among the taxa.

Hypothesis about Evolutionary Relationships

• Diversification Rates:

  • Phylogenies tell us about the species and lineages we know about

  • Doesn’t take into consideration extinct species

• Evolution:

  • All species around today all have the same amount of evolutionary time

  • Outcompeting does not mean more evolved

  • Species must go extinct to be considered done evolving

How do you get hyperdiversification lineages?

• Subquestion 1: How do you get speciation?

  • 1. Reduce gene flow between two lineages, e.g.

    • Geographic separation (e.g different islands, Darwin's finches)

    • Local physical separation

    • Temporal separation (e.g Flowering late vs early in the season)

  
  

  • 2. Evolutionary divergence between lineages E.g

    • Divergent natural selection —> Environmental pressures or ecological niches favour distinct traits

    • Genetic Drift —> Random fluctuations in allele frequencies, particularly in small or isolated populations, contribute to non-adaptive evolutionary differences

  
  

  • 3. Reproductive isolation. E.g

    • Species are physically or genetically are not able to mate and produce offspring

    • Species are no longer able to recognize each other as mates

    • Species no longer encounter each other

• Subquestion 2: What could increase diversification rates?

  • Anything that would promote speciation would increase diversification

    • Reduced gene flow —> areas with a lot of geographic separation

    • High mutation rates

    • Lots of environmental heterogeneity

    • Strong sexual selection

    • Increased ecological opportunity