Answer: Speciation in the same geographic location without physical isolation; most common mechanism: polyploidy in plants (chromosome doubling creates instant reproductive barrier); also: ecological specialization, sexual selection.
- A Speciation that generally and highly requires substantial, long-lasting physical geographic barriers separating the populations involved, such as mountain ranges, wide rivers, or expanses of open ocean between the diverging groups
- B Speciation in the same geographic location without physical isolation; most common mechanism: polyploidy in plants (chromosome doubling creates instant reproductive barrier); also: ecological specialization, sexual selection
- C Sympatric speciation is understood by evolutionary biologists to be largely impossible to actually occur anywhere in nature, despite well-documented cases in cichlid fish and apple maggot flies suggesting otherwise
- D Sympatric speciation is understood to occur mainly within animal populations, having rarely once been observed in plants, even though polyploidy-driven plant speciation is actually one of its best-known examples
Correct answer: B. Speciation in the same geographic location without physical isolation; most common mechanism: polyploidy in plants (chromosome doubling creates instant reproductive barrier); also: ecological specialization, sexual selection
Explanation: Sympatric speciation: new species form within the same geographic area as the parent species. Most documented in plants via polyploidy: allopolyploidy (hybridization + chromosome doubling) creates fertile polyploid that cannot breed with either parent - instant speciation. Example: bread wheat (Triticum aestivum, 6n) formed from hybridization of three diploid grasses. Rare in animals but documented in cichlids.
A simple phylogenetic tree: a common ancestor branches into several descendant lineages over time, with each branch point marking a speciation event.
Concept context
Origin of life, Darwin's theory, natural selection, speciation, and evidence for evolution.