Week 17 L1 - Speciation

what is microevolution

Microevolution refers to small-scale changes in allele frequencies within a population over a short period of time. It occurs within a species and does not lead to new species formation.

Mechanisms:

1. Natural Selection

2. Mutation

3. Genetic Drift

4. Gene Flow

5. Non-Random Mating

what is macroevolution

Macroevolution refers to large-scale evolutionary changes that occur over long periods of time, resulting in the formation of new species or higher taxonomic groups.

Key Features:

• Happens over millions of years.

• Involves processes like speciation and extinction.

• Observable through fossil records and large phylogenetic changes.

Examples:

• The evolution of birds from dinosaurs.

• The diversification of mammals after the extinction of dinosaurs.

what was a species defined as before Darwin

a group of individuals sharing similar traits and they didn’t evolve

define the biological species concept

a species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; they do not breed successfully with other populations

What holds a population together, so that its members resemble each other more than they do other species?

gene flow

What stops Gene Flow from invading species from eroding a species barrier?

reproductive isolation

what is reproductive isolation

the existence of biological factors (barriers) that impede two species from producing viable, fertile offspring

• can be classified by whether factors act before or after fertilisation

what are prezygotic barriers

Prevent mating or fertilization from occurring.

• Types of Prezygotic Barriers:

  • Habitat Isolation: Live in different habitats

  • Temporal Isolation: Mating occurs at different times.

  • Behavioral Isolation: Differences in mating behaviors.

  • Mechanical Isolation: Physical differences prevent mating.

  • Gametic Isolation: Sperm and egg cannot fuse.

Example: Different frog species breed in different seasons.

what are postzygotic barriers

Occur after fertilization and prevent viable, fertile offspring.

• Types of Postzygotic Barriers:

  • Hybrid Inviability: Zygote does not develop properly.

  • Hybrid Sterility: Hybrid offspring are sterile (e.g., mule).

  • Hybrid Breakdown: Hybrid’s offspring are weak or infertile.

Example: A horse and donkey produce a sterile mule.

limitations of the biological species concept

cannot be applied to asexual organisms, this includes bacteria, single celled eukaryotes such as yeasts, a number of animals and vast numbers of plants

what can the mating of different species sometimes result in

result in vigorous offspring which may be fertile

• liger

• zorse (fertile on occasion)

What happens if species with incomplete reproductive barriers come into contact?

the formation of a hybrid zone

When closely related species meet in a hybrid zone, there are three possible outcomes:

• reinforcement - strengthening of reproductive barriers

• fusion - weakening of reproductive barriers

• stability - continued production of hybrid individuals

give an example of when the hybrid fusion zone has occurred

Grolar bear

• due to global warming there has been massive pack ice depletion and the hungry polar bears are increasingly interacting with grizzly bears as their habitats come into contact

• forms a hybrid zone and may lead to species fusion and polar bear extinction

2 types of speciation

• allopatric speciation - geographic barrier

• sympatric speciation - no geographic barrier

what is peripatric speciation

allopatric speciation + founder effect

small population becomes isolated at the edge of a larger population's range, leading to genetic divergence and the formation of a new species.

Key Points:

• Small isolated population experiences different selective pressures than the larger population.

• Often occurs in new environments (e.g., an island or a remote habitat).

• Founder effect: The small group may have different allele frequencies, accelerating divergence.

• Reproductive isolation develops over time due to genetic changes.

what is allopatric speciation

new species are formed due to geographic isolation. A population becomes geographically separated, leading to reproductive isolation and genetic divergence over time

can allopatric speciation be tested experimentally

yes

• A population of flies can be split into two isolated groups and given a different food source.

  After a few tens of generations we can see that flies from each food source start to preferentially mate with those raised on the same food source.

what is sympatric speciation

• Occurs without geographic isolation.

• Can result from factors like behavioral differences, dietary preferences, or temporal isolation (breeding at different times).

• Can be driven by disruptive selection, where individuals with extreme traits have higher fitness than those with intermediate traits.

sympatric speciation can occur if gene flow is reduced by factors including

• polyploidy

• sexual selection

• habitat differentiation

what is polyploidy

where an organism has more than two complete sets of chromosomes, resulting in multiple sets beyond the typical diploid number.

Key Points:

• Types of Polyploidy:

  • Autopolyploidy: Chromosome duplication within the same species.

  • Allopolyploidy: Combining chromosome sets from two different species (often through hybridization).

• Leads to Speciation: Polyploidy can result in reproductive isolation, leading to the formation of new species.

• More common in plants than animals.

how long ago was earth formed

4.6 billion years ago, along with the rest of the solar system

what did Earth’s early atmosphere likely contain

water vapour and chemicals released by volcanic eruptions

• nitrogen

• nitrogen oxides

• carbon dioxide

• methane

• ammonia

• hydrogen

• hydrogen sulfide

NO OXYGEN

what are the suggested defined events that led to the origins of life

• Abiotic synthesis of small organic molecules

• Joining of these small molecules into macromolecules

• Packaging of molecules into PROTOCELLS

• Origin of self-replicating molecules

what is abiogenesis

the study of how life on Earth emerged from inanimate organic and inorganic molecules

What was the first Miller-Urey experiment

The Miller-Urey experiment (1953) tested the hypothesis that organic molecules essential for life could be formed from simple inorganic compounds under conditions similar to those of early Earth.

Key Points:

• Simulated the early Earth's atmosphere: Methane (CH₄), Ammonia (NH₃), Hydrogen (H₂), and Water Vapor (H₂O).

• Electric sparks simulated lightning.

• After a week, the experiment produced amino acids and other organic molecules.

Conclusion:
This showed that prebiotic molecules (building blocks of life) could form spontaneously under early Earth conditions, supporting ideas about the origin of life.

What was the second Miller-Urey experiment

In a second experiment Miller simulated Volcanic Condition by spraying a jet of steam at the spark discharge.

Produced far more organic molecules.

Modern analysis of vials kept from Miller’s experiments show that he was able to produce more than 20 amino acids using these simple experimental approaches.

what do the Miller-Urey experiments not prove

His experiments DO NOT prove that life began this way but show how easily complex chemistry can take place using the compounds and energy sources available on earth.

what is the Panspermia hypothesis - Murchison Meteorite

The Murchison meteorite fell near Murchison, Victoria, Australia in 1969

It contain over 90 different amino acids, nineteen of which are found in Earth life.

We know the early Earth was bombarded heavily by comets, possibly providing a large supply of complex organic molecules along with the water and other volatiles they contributed.

Amino acids, nucleotide bases that make up DNA and RNA and many other compounds have been found in meteorites that have fallen on earth

Can the Central Dogma explain the origins of life?

No! The Central Dogma explains how genetic information flows in modern biological systems:

• DNA → RNA → Protein (DNA is transcribed to RNA, which is translated to proteins).

However, this cannot explain the origins of life due to a chicken-and-egg problem:

• Proteins are needed to replicate DNA, but DNA provides instructions to produce proteins.

Key Insight:

• The RNA World Hypothesis suggests that early life relied on RNA as the first molecule capable of storing information and catalyzing reactions (acting like an enzyme).

• Ribozymes (catalytic RNA) support the idea that RNA could perform the roles of both DNA and proteins in early life forms.

what is the abiotic (non-living) synthesis of macromolecules

• Definition: Refers to the formation of biological macromolecules (like amino acids, nucleotides, and lipids) from non-living, inorganic substances under early Earth conditions.

• Focus: How the building blocks of life were formed naturally, without biological processes.

• Examples:

  • The Miller-Urey experiment demonstrated the abiotic synthesis of amino acids.

  • Laboratory experiments have shown that nucleotides and fatty acids can form spontaneously under prebiotic conditions.

what is the RNA World Hypothesis

• Definition: Proposes that early life forms relied on self-replicating RNA molecules before DNA and proteins evolved.

• Focus: Describes a stage in the evolution of life where RNA served both as genetic material and as a catalyst for chemical reactions.

• Key Evidence: Discovery of ribozymes (RNA molecules that act as enzymes) supports the idea that RNA could carry out both information storage and catalysis.

how is the abiotic synthesis of macromolecules and the RNA world hypothesis linked

• Abiotic synthesis explains how organic molecules (amino acids, nucleotides) necessary for life could have formed on early Earth.

• The RNA World Hypothesis takes this further, suggesting that once nucleotides were available, they assembled into RNA molecules that could self-replicate and evolve, leading to the emergence of early life.

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🔹 Summary:

• Abiotic synthesis refers to the creation of basic building blocks (e.g., amino acids, nucleotides).

• The RNA World Hypothesis proposes that these building blocks led to the formation of self-replicating RNA molecules central to the origin of life.

Both concepts are essential to understanding how life could have originated, but they address different stages in the process.

in the 1980s, what was found regarding RNAs

research groups led by Sidney Altman and Thomas Cech independently found that RNAs can also act as catalysts for chemical reactions.

This class of catalytic RNAs are known as RIBOZYMES.

• Ribozymes can carry out catalytic reactions, such as cutting or splicing RNA

what did the discovery of ribozymes help to promote

helped to promote the RNA world hypothesis that was proposed in 1960s by Woese, Crick, and Orgel

what did Woese, Crick, and Orgel propose

proposed the RNA world hypothesis

• They thought that RNA could act as a catalyst as it was able to adopt different, sequence dependent conformations. 

• According to the RNA World Hypothesis, life later evolved to use DNA and proteins due to RNA's relative instability, and gradually, ribozymes became increasingly phased out. 

what strong evidence supports the RNA world hypothesis

the fact that the ribosome, a large molecular complex that assembles proteins, is a ribozyme

How could RNA be formed under prebiotic conditions on the early Earth?

Clays may have catalyzed long strands of RNA through polymerisation

• The charged clay surface attracts the nucleotides and the increased local concentration of nucleotides causes bond formation between nucleotides, forming a polymer of RNA

Two processes may account for how RNA became able to replicate itself:

1) Even in the absence of enzymatic catalysts, single-stranded RNAs may have been able to copy strands of RNA through template-directed polymerization

2) Eventually RNA replication is likely to have been replaced by a more reliable catalyst, such as a ribozyme. Scientists hypothesize that a ribozyme that was capable of making copies of other RNAs, called a REPLICASE, evolved very early in life's history.

What are protocells

Protocells are simple, membrane-bound structures that are considered precursors to living cells. They are thought to have formed on early Earth and provided a framework for the development of life.

• typically have a lipid membrane

• can trap organic molecules, such as RNA, amino acids, and other building blocks of life, inside their membrane.

how were fatty acids formed on early Earth

• 🌋 Geyser or Thermal Vent:

  • On early Earth, hydrothermal vents or geysers provided the necessary heat and a rich environment of gases such as hydrogen (H₂) and carbon monoxide (CO). These conditions were ideal for chemical synthesis.

• 🪨 Mineral Surfaces Catalyze Formation:

  • Inside the vent, metal-rich mineral surfaces (e.g., iron or nickel) acted as catalysts to facilitate the formation of fatty acid molecules from the hydrogen and carbon monoxide gases through Fischer-Tropsch-type reactions.

• 💧 Water Droplets Released Contain Fatty Acids:

  • As hot water from the vent or geyser is expelled into the cooler environment, it forms water droplets containing newly formed fatty acids.

  • These fatty acids can self-assemble into vesicles (membrane-like structures) in water, forming the basis for protocells.

The fatty acids produced in this manner may have accumulated through cycles of shrinkage by evaporation and growth by the delivery of additional dilute fatty acid solution.

This may also be a method for delivery of fatty acids to other locations

how do fatty acid vesicles grow

1. fatty acid vesicle

2. smaller vesicles arrive

3. smaller vesicles invade the lipid bilayer of the larger vesicles

4. vesicles gets bigger