Lecture 2 - Phylogenies and Speciation Flashcards
3 Steps to Develop New Trait
- Priming (makes it possible)
- Actualization of the trait (makes it manifest)
- Refinement (makes it effective)
Priming
Step 1: Mutation becomes possible
- Earlier mutations develop a genetic background on which the desired function is accessible
- Primed generations are more likely to develop the mutation
ex: mutation that results in upregulation of Kreb’s cycle so that citrate may be used more effectively
Actualization
Step 2: Trait manifests
- Mutation occurs that allows trait to actually occur
- Small but significant competitive advantage
Refinement
Step 3: Makes mutation effective
- Population with the trait begins to thrive
- Small mutation makes the trait more efective
Evolution of the Eye
Evolution of a complex trait
- known to have evolved independently 50-100 times
Stages of Evolution of the Eye
- Priming:
- development of light detecting pigments in common ancestor
- other proteins that were already present for other functions were co-opted to function in the eye - Actualization
- now ready to evolve into a basic eye over and over - Refinement
- refined in each lineage to develop complexities such as color, lens, focusing
Evolutionary Constraints (5)
- evolution can’t produce any trait we want
1. Environment is constantly changing
2. Dependent on a mutation randomly arising
3. Evolution is limited to physical constraints
4. Adaptations are Compromises
5. Evolutions is limited by historical constraints
Environment is Constantly Changing (Evolutionary constraint)
- Environment influences what traits would be favored if evolving
Dependent on a Mutation Arising (Evolutionary constraint)
- Dependent on a mutation randomly arising (if an allele for a given trait does not exist , the trait cannot evolve even if it would be favorable)
Limit of Physical Constraints (Evolutionary Constraint)
- Evolution is limited to physical constraints
ex: limit to how light but strong birds wing bones can be
Adaptations are often compromises (Evolutionary constraints)
examples
- horses: thinner legs are lighter and faster but more prone to breaking
- snakes that are resistant to newt toxin are also slower…
Historical Constraints (Evolutionary Constraints)
Examples
- Modifications of PREVIOUSLY existing structures
- Build up what existed before in small steps
- Not going to start over from scratch
Examples
- Appendix is vestigial organ - don’t need to ruminate grass anymore
- hernias arise because we are built to be quadrupeds and it strains our spine to walk upright
- Hiccups are a reflex to make our now non-existent gills begin working when we are low in oxygen - gills are no longer there but still have the reflex
Laryngeal Nerve Example
Ex: Historical Constraint
- Path: brain, down the neck, loops through arteries in chest, then up neck to larynx
- Indirect –> not logical
- the way it existed originally was in fish with no necks
- As evolution occurred and animals developed neck, the nerve kept the same path
- resulted in a loop
Phylogeny
The evolutionary history of relationships among organisms or their genes
Phylogenic Tree
and features
Diagram used to portray phylogenies
- Based on similarities and differences in physical or genetic characteristics
- Lineages joined together in tree have descended from common ancestor
Node (Phylogenic Tree)
- split that represents point at which lineages diverged
Root (Phylogenic Tree)
- The common ancestor of all organisms in a tree
Taxon
- A group of species designated/named
- ex: humans, primates, vertebtrates
Clade
- Taxon that consists of all the evolutionary descendents of a common tree
- Are subsets fo larger clades
Taxon vs Clade
- Taxon is ANY group of species we designate or name
- A clade is a taxon that consists of all evolutionary descendents of a root
- Track clade back to the branch point, everything from that point on is included in the clade
- Clade is a taxon, but a taxon is not always a clade
Reptiles = Taxon but not clade
Clade would also include birds
Mammals = Clade
Tree of Life
- Phylogenic tree that represents the complete evolutionary history of life
- Describes relationships of all life on earth in an evolutionary context
Three main “branches” in tree of life
- Bacteria
- Eukarya
- Archaea
Homologous Traits
Any feature shared by two or more species that have been inherited from a common ancestor
ex: whale fin, human arm, lizard leg, bird wing
Ancestral Trait
A current trait that was present in the ancestor of its current group
Derived Trait
A trait found in a descendant that differs from the ancestral trait
Synapomorphies
- Shared derived traits
- Shared through a clade
- A newly derived homology
Ancestral vs Derived Traits
Depends on point of reference
Ex: Feathers
Ancestral
- Considered ancestral for any group of modern birds
- Homologous but not a synamopomorphy
- In phylogeny of all living vertebrates, feathers are considered derived
- synamopomorphy
Continuity of Evolution
- All species are constantly evolving
- Doesn’t make sense to say some are more highly evolved
Convergent Traits/Evolution
- Independently evolved traits subjected to similar selection pressures may become superficially similar
- Similar traits in unrelated organisms
Homoplasies
Similar traits generated by convergent evolution