Page "Speciation" Paragraph 44

However, the DNA evidence cited above is from mitochondrial DNA ( mtDNA ), which can often move easily between closely related species (" introgression ") when they hybridize.

A more recent study, using genetic markers from the nuclear genome, shows that limnetic forms in different lakes are more closely related to each other ( and to marine lineages ) than to benthic forms in the same lake.

The three-spine stickleback is now usually considered an example of " double invasion " ( a form of allopatric speciation ) in which repeated invasions of marine forms have subsequently differentiated into benthic and limnetic forms.

The three-spine stickleback provides an example of how molecular biogeographic studies that rely solely on mtDNA can be misleading, and that consideration of the genealogical history of alleles from multiple unlinked markers ( i. e. nuclear genes ) is necessary to infer speciation histories.