CH 23 Systematics, Phylogenies & Comparative Biology

Systematics

Study of evolutionary relationships among organisms.

• All organisms have

  • Composed of one or more cells 

  • Carry out metabolism 

  • Transfer energy with ATP 

  • Encode hereditary info. In DNA & RNA 

  • Respond to stimuli 

(not virus)

Phylogeny

hypothesis about patterns of relationship among species 

Ancestral Characteristic

similarity that is inherited from the most recent common ancestor of an entire group 

Derived Characteristic

similarity that arose more recently & is shared only by a subset of the species 

Cladistic Method

only derived characters are considered informative about evolutionary relationships 

• used for cladistic analysis

Character States

Recognizable forms of traits in organisms. ("tail" in vertebrates has two states, present in most & absent in humans, apes & some other groups such as frogs)

• Morphology, Physiology, Behavior, or DNA

(very binary, does it have it or not)

Cladistic Analysis

• Polarize characters (are they ancestral or derived)

• Outgroup comparison (related but not member of group studies, may exhibit ancestral character)

• When group states & one other traits is exhibited by outgroup, then state is ancestral & others are derived

Morphology

Study of organism structure and form.

Physiology

Study of organism functions and processes.

Outgroup

Species closely related but not part of study group. (is outed when b/c it does not share the derived characteristics of the rest)

Clade

species that share common ancestor as indicted by possession of shared derived characters 

• Clade is evolutionary unit & refers to common ancestor & all descendants 

Cladogram

Diagram showing hypothesized evolutionary relationships based on characters.

Synapomorphy

Derived character shared by members of a clade. (similar morphy)

Pleiomorphism

Ancestral states of characters in evolution. (more/previous morphism)

Symplesiomorphy

Shared ancestral traits among different species. (shared morphy)

Parsimony Principle (KISS)

Favoring cladograms with fewest evolutionary changes.

Molecular Clock Approach

• Rate of evolution of a molecule is constant through time 

• Divergence in DNA can be used to calculate the times at which branching events have occurred 

DNA Sequencing in Cladograms

• Systematists increasingly use DNA sequence data to construct phylogenies b/c of the large number of characters that can be obtained through sequencing 

• Character states are polarized by reference to sequence of an outgroup 

• Cladogram is constructed that minimizes amount of character evolution required 

Cons/Controversy of Phylogenetic Methods

• rapid evolution + parsimony principle may be misleading (doesn’t show time)

• Stretches of non-functional DNA have higher rates of evolution b/c of zero selection

• Only ATCG so probability two species will independently evolve same derived character state is high

  • b/c of convergent evolution cladistic method can be misleading (make them seem more related than they are)

  • could recognize even slightly diff. populations as distinct species

Statistical Approach

• Start with an assumption about rate at which characters evolve 

• Fit the data to these models to derive the phylogeny that best accords (that is max. Likely) w/ these assumptions 

Evolutionary Unit

Clade representing a common ancestor and descendants.

Phylogenetic Methods

• Cladistic Method (relations ships based on characters)

• DNA sequence on Cladograms

• Statistical Approach

• Molecular Clock

Taxonomy

Science of classifying organisms into groups.

Classification

How we place species & higher groups into the taxonomic hierarchy 

Scientific Name

is the same anywhere in the world; no two organisms have the same one 

• First word is the genus organism belongs to (capitalized) 

• Second is the species (not capitalized) 

  • Genus & species italicized 

Genus

First part of a scientific name, capitalized.

Species

Second part of a scientific name, lowercase.

Classification Order

Dear King Philip Came Over For Great Spaghetti

• Domain

• Kingdom

• Phylum

• Class

• Order

• Family

• Genus

• Species

Domain

Divides cellular life into three domains

(Archaea, Bacteria, Eukarya)

Kingdom

Groups similar organisms into 6

(Plantae, Animalia, fungi, Protista, eubacteria, archbacteria)

Phylum

Groups organisms based on major body plans.

Class

Further division within a phylum.

Order

Groups families sharing common characteristics.

Family

Groups related genera sharing traits.

Monophyletic Group

Includes most common ancestor and all its descendants. (clade)

Paraphyletic Group

Includes most common ancestor but not all descendants.

Polyphyletic Group

Does not include the most recent common ancestor.

Homologous Structures? AKA what?

Similar structures derived from a common ancestor. (Non- homoplastic)

• includes similiar behaivor (parental care)

Analogous Structures? AKA what?

Similar functions but different evolutionary origins. (homoplastic = similar, repair/function)

Homoplastic Convergence

Similar traits evolved independently in different lineages. (clades)

Comparative Biology

Most complex characters do not evolve in one step 

• Evolve through a sequence of evolutionary changes 

  • Ex. Modern-day birds are exquisite flying machines (wings, feathers, light bones, breastbone 

Competing Hypothesis

Phylogenetic methods distinguish between different evolutionary theories.

Phylogenetic Species Concept

species is a population or set of populations characterized by one or more shared derived characteristics (useful for situations that don’t fit other species concept)

What conclusions were drop after testing larval dispersal of snails?

Evolutionary increase in no dispersing larvae through time may be a result of both bias in evolutionary direction & increase in rate of diversification 

• Selection increased a trait, lack of evolutionary reversal is not surprising (one-way street)

How does phylogenetics help explain species diversification?

• can give insight on correspondence b/w phylogenetic position & timing of origins

  • Gives time and how species started diverging and where they went

Beetle diversification

• different beetles have a specific diet

• highest diverse species

Disease evolution

Study of evolutionary changes in pathogens over time.

Phylogenetic Analysis of HIV

• Descended from SIV

• Diff. strains exist and evolve so rapidly they are closer to SIV than each other

  • infected often contain a mix of strains so you can track were they got it from

• Humans have acquired HIV from different host species

Phylogenetic Analysis of SIV

• found in multiple primates

• humans are immune, suggests adaptation

Community v. Independent Transmission

• community indirect spread of infection in a population, or from traveling to a place affected by a pandemic (greater event of an event occurring)

• separate occurrences of a pathogen being passed from infected to individual (does not affect probability of reassurance)

Phylogenetic Analysis of Covid

• showed closely related virus lineages from bats

• fist emerged in a market in Wuhan China, were bats weren’t present, possible intermediate species host

Virus

Aren’t alive (lack cells, metabolism, ATP, hereditary) but respond to some stimuli and have DNA or RNA (not both)

• are able to mutate and evolve