5.5 Speciation
2026-05-19 06:24
Status: #new
Tags: #biology #evolution
5.5 Speciation
Defining KEY terms
Microevolution
- Small changes such as shifts in allele frequencies
Macroevolution
- Large changes, like the formation of new species will lead to speciation
Species
- Groups of organisms that can interbreed and produce fertile offspring
Reproductive Isolation
- Two populations may become reproductively isolated when there is little to no gene flow.
- The prevention of gene flow between populations is key to speciation
Gene flow
- The transfer of genetic material from one population to another through interbreeding or migration
Pre-zygotic and Post-zygotic Isolation
- Preventing gene flow from different populations which will help lead to speciation
Pre-zygotic Isolation
- Ways in which organisms are prevented from mating
Types of Pre-zygotic Isolation
Temporal
- Occurs when two species mate at different times of the year
Ecological
- Occurs when two species occupy different habitats
Behavioural
- Occurs when two species have different courtship (behaviour that leads to mating) behaviours
Mechanical
- Occurs when physic differences prevent copulation or pollination
Gametic Isolation
- If gametes (sperm and egg) from different species meet, they will rarely fuse to form a zygote
Post-zygotic Isolation
- After zygotes are produced, modes which prevent the development of offspring
Hybrid Inviability
- Hybrids are produced but fail to develop reproductive maturity
Zygotes between incompatible species do not continue to develop Molecular signals that are required for successful organism development cannot occur. Therefore, no hybrid organism is created. - This results in a spontaneous abortion by the body
Hybrid Infertility
- Hybrids fail to produce functional gametes (defined as: Sterility)
- Development proceeds as normal and complete organisms are created
- Suggests that chromosomes are sufficiently close
- However, these hybrid animals are sterile as issues with meiosis could arrive
Hybrid Breakdown
- When F1 Hybrids are healthy and could reproduce (fertile), however the F2 generation is Sterile, due to worsened chromosomes
- The key difference is that Hybrid Infertility has F1 Generations being Sterile, while in Hybrid Breakdown it is the F2 Generation
Types of Speciation
Sympatric
- As a Population splits into separate gene pools, but occupy the same geographical location
Sympatric Speciation
- When populations that live in the same geographical area but become reproductive isolated
Can lead to the evolution of new species due to reproductive isolation
Allopatric
- Large geographical barriers that can separate populations
Allopatric Speciation
- Due to physical separation of populations (geographic isolation)
- Can lead to the evolution of new species
Evolutionary Types and Theory
Divergent Evolution
- Evolution from a common ancestor that results in diverse species adapted to different environments
- Also known as Adaptive Radiation
Convergent Radiation
- Distantly related species that live in similar environments develop similar adaptations
- For example: Wings evolved in bats, birds, insects, etc. independently (analogous structures) and share similar structure and function
Two Theories for How Speciation Occurs
Gradualism
- Small changes over long periods of time
Punctuated Equilibrium
- Sudden changes with long periods of stability in between
Human Impact on Speciation
Habitat Fragmentation
- Damage to the natural habitat due to:
- Croplands, Recreational areas, Roads, Dams for hydroelectric power generation
Consequences
- Leads to the isolation of population and promotes allopatric speciation
- Could be more disruptive than natural geographic behaviours since populations may not adapt in the same manner as they would under natural conditions
There is a increased risk of extinction Small isolated populations suffer from reduced genetic diversity,inbreeding, and higher risk of extinction, reducing the chance for speciation to occur.