BIO153 Lecture 5 notes

The study of how closely organisms are related through classification is pivotal in understanding biodiversity.

Organisms can be assessed on their relationships based on various traits:
- Morphological Traits: This includes body shape, tissue structure, and organelle presence.
- E.g., Comparison of vertebrate limb structures.
- Biochemical Traits: Refers to metabolic pathways and other biochemical signatures.
- Genetic Traits: Looks at gene presence and absence as well as gene sequence variations.

Organisms with shared complex traits (like bone structure) are likely from a common ancestor.
It is less likely for complicated traits to evolve independently in unrelated organisms, and end up looking near-identical by chance; instead, these traits are often indicative of evolutionary relationships and adaptive strategies that have been favored in similar environments.
Example: Skull morphology is heavily used in classifying various species due to its complexity.
Although similar morphology does not always mean relatedness.
Convergent Evolution: This is the phenomenon where unrelated organisms independently evolve similar traits due to adaptations to similar environments.
- E.g., Australian mole (marsupial) vs. North American mole (placental).
- evolved under selective pressure for their ground-burrowing lifestyle, leading to analogous characteristics.

Homology: Refers to traits inherited from a common ancestor.
- Example: All mammals have the trait of feeding milk, suggesting a shared ancestry.
Analogy: Traits that appear similar but evolved independently in different lineages.
- Example: Mole-like traits in Australian and placental moles.

Shared Ancestral Character: Traits held by a common ancestor and passed to all descendants.
- E.g., Milk feeding in mammals.
Shared Derived Character: Unique traits developed in a lineage after divergence.
E.g., The pouch in marsupials.

Shared ancestral/derived characters are relative terminologies, it changes depending on who you set as the common ancestor.
“Bag for infants” is a shared derived character unique to marsupials, if you use the common ancestor of all mammals as a reference.
“Bag for infants” is a shared ancestral character, if you use the common ancestor of all marsupials as the reference.
The milk-feeding trait of mammals becomes a shared derived trait in reference to all vertebrates, same logic applies to other traits.

Different lineages of marine mammals, for example: Dolphins and whales, seals, and manatees
These traits are shared derived characters in relation to entire mammals.
These traits are analogous to each other since they were acquired independently in their lineages.

Very complicated traits are unlikely to emerge in multiple independent lineages by convergent evolution
“forelegs” of humans and birds share clear similarities, this would be quite low chance for them to have evolved independently and match structures to this extent.
Forelegs of bats and birds are also shared-ancesteral homologs, however, they’re wing structures differ as birds have reduced digits (Metacarpals/Phalanges) with feathers attached to their forelimbs
Whilst in contrast bats have elongated digits, forming their wings through a stretched membrane that extends between the fingers, like an umbrella.
The ancestral ‘foreleg’ structure evolved differently bats and birds due to their adaptation to distinct environmental pressures and giving rise to a flying mechanism.
The wings of birds, bats, and dragonflies are all analogous
Birds and bats share homologous forelimbs whilst a dragonfly does not.

Recognizing whether traits are homologous or analogous helps deduce evolutionary relationships.
Similarities and differences in structures provide evidence of evolutionary relatedness.

Genes serve as indicators of evolutionary relationships. Types include:
- Orthologous Genes: Genes in different species that have evolved from a common ancestor.
  - Example: Human and Chimpanzee share a common ancestral gene.
- Paralogous Genes: Genes that have duplicated within a species and evolved separately.

Genes evolve at differing rates, influencing their utility in studying evolutionary history:
- Slow-evolving Genes: Retain similarities over long periods and are useful for deep evolutionary comparisons.
- Fast-evolving Genes: Accumulate mutations quickly and are better suited for recent evolutionary events.

Understanding both morphological and genetic traits aids in piecing together the tree of life.
Traits provide crucial insights into the relationships and evolutionary pathways of organisms across time.