L2: MODERN CONCEPTS IN UNDERSTANDING EVOLUTIONARY RELATIONSHIPS

What does the Primordial Soup Theory propose about the origin of life?

It suggests that life arose in a warm, shallow sea rich in organic molecules ("primordial soup") formed through chemical reactions, which eventually combined to form self-replicating organisms (with RNA considered the first self-replicating molecule).

Who proposed the Deep Sea Vent Theory, and what does it suggest?

Proposed by Cindy Van Dover, it suggests life originated in deep-sea hydrothermal vents where heat and minerals provided a suitable environment for organic molecules and early life. (Note: This is considered the most recent/updated theory).

What is the core idea of the Panspermia Theory and who initially suggested it?

Suggested by Hermann von Helmholtz, it proposes that life originated elsewhere in the universe and was transported to Earth on meteorites or other celestial bodies.

Who proposed the RNA World Hypothesis, and why is RNA unique in this context?

Proposed by Walter Gilbert, it suggests RNA was the first self-replicating molecule on Earth because it is capable of both carrying genetic information and catalyzing chemical reactions.

What does Graham Cairns-Smith’s Clay World Hypothesis suggest?

It suggests that clay minerals, with their catalytic properties, provided a surface for the assembly of organic molecules and the formation of early replicating systems.

What are some of the major problems/challenges encountered when classifying organisms?

• Morphological Variation

• Convergent Evolution

• Cryptic Species

• Transitional Forms

• Lack of Fossil Evidence

• Hybridization

• Parasitic Lifestyles

• Rapid Evolution

Define Monophyletic, Paraphyletic, and Polyphyletic groups, and explain which one is ideal.

• Monophyletic (Ideal): Includes a single common ancestor and all of its descendants; accurately represents evolutionary relationships.

• Paraphyletic (Problematic): Includes a single common ancestor and some, but not all, of its descendants.

• Polyphyletic (Problematic): Groups organisms from different ancestral sources based on superficial similarities, excluding their most recent common ancestor.

Define Cryptic Species and Apomorphy.

• Cryptic Species: Species that look very similar morphologically but are genetically/molecularly different.

• Apomorphy: A novel evolutionary trait that is unique to a particular species or group and its descendants.

What is Cladistic Vicariant Biogeography, and what are its main characteristics and criticisms?

• Starts with an area cladogram (taxa placed by places of origin).

• Regards vicariance (populations split by a new geographic barrier) as the primary mechanism of organism distribution rather than dispersal.

• Criticism: It is overly simplistic, heavily focused on patterns rather than process, acknowledges range expansion, and completely ignores dispersal even when it is the most likely explanation.

How does Dispersal-Vicariance Analysis work and what are its drawbacks?

• Infers ancestral areas at nodes by minimizing dispersal and extinction events using a 3D cost matrix.

• Drawbacks: It ignores branch lengths and fails to take divergence time into account, which handicaps the determination of true biogeographic history given that Earth's crust and sea/land distributions change over time.

What is Model-Based Biogeography?

It infers biogeographic history using mechanistic models of biogeographic processes with explicit parameters representing dispersal, extinction, and cladogenesis.

In Robert Smiles' 1982 revision, what genus was Polyura moved from, and what key morphological feature did he use?

Polyura used to be under Eulepis (and grouped closely with Charaxes). Smiles used underwing patterns (because genitalia, larval instars, and wing venation lacked clear apomorphies) to separate Polyura as a monophyletic sister group to the paraphyletic Charaxes, noting that Polyura has a completely open hindwing cell.

What gene markers and conclusions were established by modern molecular studies on Polyura?

• Gene Markers Used: CO1, ND5, Rps5, and Wingless.

• Conclusions: Confirmed Polyura is monophyletic and sister to Charaxes. Molecular tools successfully resolved cryptic lineages, described new species (e.g., Polyura paulettae, Polyura smilesi), and elevated several populations (like the Philippine representative Polyura luzonica) to full species status.

What is the difference between Microevolution and Macroevolution?

• Microevolution: Small-scale changes in allele frequencies within a population over a relatively short period, leading to changes in color, size, or behavior.

• Macroevolution: Large-scale evolutionary changes over long periods resulting in the formation of new species; driven by the same underlying mechanisms (mutation, gene flow, genetic drift, natural selection).

Compare Gene Flow and Genetic Drift in terms of population size and occurrence.

• Gene Flow: Movement of individuals/gametes between populations via migration; typically impacts larger populations by altering genetic composition.

• Genetic Drift: Random/chance fluctuations in allele frequencies (due to bottleneck or founder effects); has the most dramatic impact on smaller populations.

What are the key mechanisms driving macroevolution?

• Speciation (Allopatric, Peripatric, Parapatric, Sympatric)

• Vicariance

• Dispersal

• Adaptive Radiation (rapid diversification to fill ecological niches)

• Extinction

• Convergent Evolution (independent evolution of similar traits in unrelated organisms due to similar selective pressures)

Morphological Variation

Morphological variation is the difference in the physical form, outward appearance, or structural traits of organisms within a species or population.

Convergent Evolution

Convergent evolution is the independent evolution of similar features or traits in species of different, distantly related lineages.

Cryptic Species

Cryptic species are groups of individual organisms that look nearly or completely identical to one another (sharing the same physical appearance or morphology), but belong to separate, genetically distinct evolutionary lineages that cannot interbreed.

Transitional Forms

Transitional forms are fossils or organisms that display a combination of traits shared by an ancestral group and its later descendant groups.

Lack of Fossil Evidence

The fossil record is naturally incomplete representing less than 1% of all species that have ever lived.

Hybridization

Hybridization is the interbreeding of individuals from distinct species, subspecies, or divergent populations to produce offspring with admixed genomes.

Parasitic Lifestyle

Parasitic lifestyle reduces the host’s fitness while usually not killing it immediately. Traditional taxonomy relies heavily on physical traits (morphology) to group organisms. When a lineage adopts a parasitic lifestyle, it undergoes evolutionary reduction. Because the host provides locomotion, digestion, and protection, the parasite frequently sheds complex external features.

Rapid Evolution

Rapid evolution is a biological process where species show observable, heritable genetic and phenotypic changes over short timescales of decades, years, or even a single season, rather than millions of years.

Approaches in Understanding and Analyzing Species Phylogeny and Biogeography

• Cladistic Vicariant Biogeography

• Phylogeny

• Model-based Biogeography

Vicariance

An evolutionary and biogeographical process where continuous populations or species is physically split into isolated groups by the formation of a new geographic barrier.

• Nawab Butterflies

• Order: Lepidoptera Linnaeus

• Family: Nymphalida Rafinesque

• Subfamily: Charaxinae Doherty

• Tribe: Charaxini Guenèe

• Genus: Polyura Billberg