Three swallowtail species and hybridization.

 

At first glance, the Canadian and pale tiger butterflies above look to be the same species.  A third butterfly (below), the western tiger swallowtail, is similar in many ways to both of the above species.  The three species live in British Columbia and their ranges overlap to some degree.  It is in those places that the species may interbreed producing hybrids.

There is an interesting post on the website E-Fauna BC that discusses the hybridization; I have included the paragraph below.

All the tiger swallowtails (subgenus Pterourus) hybridize in the wild to some extent. In southern BC there is a broad zone of hybridization between Canadian Tiger Swallowtails and Western Tiger Swallowtails from Manning Provincial Park east to Creston. In the areas where their ranges overlap, Western Tiger Swallowtails prefer low-elevation deciduous forest habitats whereas Canadian Tiger Swallowtails prefer higher-elevation boreal forest habitats. Hybridization between Pale Swallowtails and Western Tiger Swallowtails is rare, but Wagner (1978) collected a perfectly intermediate male hybrid in the wild in Idaho. Jon and Sigrid Shepard found a male hybrid of the Pale Swallowtail and the Canadian Swallowtail 10 km south of Galloway, BC. lt is intermediate in appearance between the two species.

The whole idea of hybridization between species has value as it could promote an exchange of genetic information to ensure the survival of the genus.  The problem with most hybridization within close species is that the offspring are often infertile and not capable of producing viable offspring.  The reason often has to do with the number of chromosomes each species has.  Donkeys, for example, have 62 chromosomes while horses have 64.  The mule, a hybrid, has 63 and thus is deficient in some genetic material which renders them sterile (incapable of producing viable offspring).  There is a very interesting website discussing butterfly hybridization here.

Thanks to the various websites and authors for putting together the information.  I found it very interesting.

Thanks for reading.

Eric Svendsen     www.ericspix.com

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