Ask An Expert: Hybrid Introgression and BC Butterflies

Biodiversity and genetic diversity are influenced by many factors...

Question

What is hybrid introgression and does it occur in butterflies?

Answer (by Cris Guppy)

Hybrid introgression is the introduction of genes from the gene pool of one species into that of another, when the two species interbreed and produce offspring (hybridization) that are fertile, and the hybrid offspring continue to interbreed with one of the species.  An interesting case of hybrid introgression is the Propertius Duskywing butterfly (Erynnis propertius).  The overall range is the west coast of North America from San Diego north to central Vancouver Island, and DNA testing has found that the DNA is reasonably similar over that entire range (except for some subspecies-level variation).  However, populations from southern Vancouver Island and Puget Sound have two gene structures with about a 5% difference -- which is usually a large enough difference to indicate that two species are present. One gene structure matches the rest of the Propertius Duskywing and one matches Horace's Duskywing (E. horatius) of eastern North America.  At some undetermined time in the past, the range of the two species touched in the Puget Sound area, and they hybridized without merging into one species. The  range of Horace's Duskywing then retreated to east of the Rockies, but left behind some of its genetic material in the Propertius Duskywing gene pool.  The wing patterns and genitalia structure of the Propertius Duskywing all look the same, so the past hybridization is only detectable through DNA analysis. Quite cool!

Visit the E-Fauna BC atlas pages to learn about BC butterflies.
Read the E-Fauna BC Introduction to the Butterflies by Cris Guppy. 

Cris Guppy is a wildlife biologist and butterfly researcher based in the Yukon. He is co-author (with Jon Shepard) of Butterflies of British Columbia and is the butterfly advisor and butterfly photo reviewer on E-Fauna BC.