9D: Speciation

Question 1

Species:

Answer 1

a group of individuals who are able to breed with each other and produce viable and fertile offspring

Question 2

Subspecies:

Answer 2

individuals phenotypically different from their original population which often arise from speciation

Question 3

Speciation:

Answer 3

the process by which populations genetically diverge until they become distinct species

Types of Speciation:
- Allopatric Speciation:
Sympatric Speciation:

Question 4

Isolating Mechanism:

Answer 4

mechanisms which prevent species from interbreeding to produce fertile and viable offspring

• Pre and post reproductive isolating mechanisms are also known as prezygotic and postzygotic

Question 5

Pre-reproductive Isolating Mechanism:

Answer 5

Geographical - individuals may not be able to interact with each other due to separation by barriers

Ecological - individuals may inhabit different ecological niches or habitats so they do not interact with each other

Temporal - the time of the day or year when individuals are ready to breed may differ

Behavioural - the type of mating behaviors, such as mating calls, of individuals may vary

Structural - the physical characteristics of individuals may drastically vary, physically preventing breeding

Question 6

Post-reproductive Isolating Mechanisms:

Answer 6

Gamete Mortality - the sperm may be unable to penetrate the ovum for fertilisation

Zygote Mortality - Fertilisation may occur and a zygote may be formed, however, it will not survive

Hybrid Sterility - A viable offspring may be formed and may survive until adulthood but will not be fertile

Question 7

Geographical Barrier:

Answer 7

a physical factor that prevents gene flow, and thereby stops two populations from breeding together

Question 8

Allopatric Speciation:

Answer 8

the geographical separation of a population from a parent population resulting in the formation of a new species

• Relies on the presence of a geographical barrier

Question 9

Process of Allopatric Speciation:

Answer 9

1. A geographical barrier separates a population, preventing gene flow
   2. Different selection pressures act upon each population, favouring different phenotypes and allowing for genetic differences to accumulate
   3. Eventually sufficient genetic differences accumulate so that the two populations can no longer interbreed to produce viable and fertile offspring

Question 10

Example of Allopatric Speciation:

Answer 10

• The Galapagos islands is a collection of 19 islands with 19 different ecological niches on each island(selection pressures and species) inhabited by Galapagos finches
  
  • Islands are also separated by the ocean which serves as a geographical barrier, preventing gene flow between them
  • As each different island has different food sources and selection pressures, different phenotypes(beak shape) are more advantageous, allow for genetic differences to accumulate and therefore for a new species to form

3 different species of Galapagos Finches:
Cactus Finch:
- Has a thin and elongated beak
- Primarily sources food from cacti using thin and elongated beak to prevent contact with spikes

Large-ground Finch:
- Thick and Short beak
- Primarily sources food from hard woody nuts with their thick and short beaks providing a significant amount of force to break open and extract the interior of woody nuts

Medium Ground Finches:
- Have moderate width and short beaks
- Primarily source their food from soft seeds

Question 11

Sympatric Speciation:

Answer 11

the divergence of a new species from an original species as a result of different selection pressures which act on different phenotypes

- Does not rely on the presence of a geographical barrier

• Can also arise from genetic abnormalities occurring during gamete formation which results in polyploid variants(more than 1 set of chromosomes) however this is only seen in plants

Question 12

Example of Sympatric Speciation:

Answer 12

• The differences in soil pH on the Lord Howe Island is a major catalyst for the sympatric speciation between the Howea Forsteriana and Howea Belmoreana
  
  • Howea Belmoreana inhabits neutral and acidic soils(Low pH) whereas Howea forsteriana inhabits a region of alkaline soil(high pH)
    The selection pressure of Howea Forsteriana inhabiting the alkaline soil resulted in the divergence of the sister species after the physiological differences began to develop, which after generations and generations, resulted in the formation of Howea Belmoreana