Concept 24.2: Speciation can take place with or without geographic separation

Flashcards from Concept 24.2 of Pearson's Campbell Biology, Twelfth Edition.

Speciation

The separation of a species into two different species, the two major types being:

• Allopatric (geogrpahical isolation)

• Sympatric (no geographical isolation)

It may also occur through mutation, natural selection, and genetic drift — which can result in reproductive isolation

Allopatric speciation

Speciation where gene flow is interrupted when a population is divided into geographically isolated subpopulations, eventually creating barriers to reproduction with genetic changes

• Depends on the ability of organisms to move about

  • The water in a lake may subside and form two lakes with separated populations if fish are unable to bypass it

• Individuals colonizing a remote area can lead to this without geographical change

  • Seen in the flightless cormorant of the Galapagos originating from a flying mainland species

Sympatric speciation

Speciation where the two populations are not geographically isolated; is less common than allopatric speciation

Occurs if gene flow is reduced by factors such as:

• Polyploidy

• Reproductive selection

• Habitat differentiation

Polyploidy

Type of sympatric speciation with the accidental presence of extra sets of chromosomes during cell division

• Can form a new species within a single generation without geographic separation

• Common in plants but rare in animals, as seen in the genus Tragopogon and many important agricultural crops

  • New species can be produced using chemicals to induce errors in cell division

Reproductive selection

Type of sympatric speciation with female mate choice being influenced by male characteristics or behaviors

Habitat differentiation

Type of sympatric speciation resulting from the exploitation of new habitats or resources

• Apple maggot flies evolved in North America after switching hosts from hawthorn to apple — this resulted in isolation between groups using different hosts and the advancement of apple maggot flies accelerating