5.2.5-6 Speciation: Formation of New Species

Question 1

Define “species”

Answer 1

One or more populations of interbreeding organisms that are reproductively isolated in nature from all other organisms.

Question 2

Speciation is the formation of new species. How are new species formed?

Answer 2

Speciation: A population survives in an environment because it is “fit”. If differences build up within the population, the genetic divergence takes place, and new species form.

Genetic divergence occurs when adaptation, drift, and mutation act on populations.

Question 3

What cause “genetic divergence”?

Answer 3

Genetic divergence occurs when adaptation, drift, and mutation act on populations.

Question 4

When do two populations become new species?

Answer 4

When the populations no longer interbreed.

Question 5

Natural selection and speciation

Answer 5

As natural selection adapts populations to different environments, they may diverge into different races, subspecies, and finally separate species.

Question 6

Adaptive radiation

Answer 6

Several species of finches in the Galapagos islands is an example of “adaptive radiation”, because each one has adapted to a different way of life.

Question 7

Cladogenesis and Anagenesis

Answer 7

Cladogenesis: A small part of a parent species gives rise to a new species

Anagenesis: Evolution of one species into an entirely different descendant species

Question 8

Two types of speciation:

• Allopatric speciation
• Sympatric speciation

How are they different?

Answer 8

Allopatric speciation:

• Geographic isolation separates a population, and the different groups diverge from each other.

Sympatric speciation:

• Reproduction isolation mechanisms prevent members of a population from reproduction.
  
  • Example - Plants that fail to reduce chromosome number during meiosis results in polyploids that can reproduce only with themselves or other polypoids. Reproduction with their parent population produces sterile offspring.

Question 9

Reproductive isolation mechanisms prevent members of different species from reproducing.

What are the different types of the mechnism?

Answer 9

Pre-mating isolation mechnisms:

• geographical separation (mountain ranges, deserts, oceans, rivers, etc)
• ecological isolation (habitat isolation)
• differences in body structure (e.g., reproductive anatomy)
• differences in behavior (e.g., mating rituals)
• temporal or seasonal differences (e.g., groups reproduce in different times of the year)

Post-mating isolation mechnisms:

• developmental or physiological differences including:
  
  • incompatible gametes so that they cannot fuse to form a zygote (an egg may have receptors only for the sperms of its own species)
  • hybrid offspring of two different species are formed but are sterile (e.g., mules from donkey + horse)