Hybrid Butterflies

Butterfly crossbreeding or hybridization isn't a very common thing in the world, but it does happen sometimes. In this post we will explore what stops most species from cross-species mating and what happens when cross species mating produces a hybrid. Science content ahead!

Female Polydamas Swallowtail (Battus polydamas) and male Pipevine Swallowtail (Battus philenor) mating. 

The Physical Barrier to Hybrids

Butterflies are often taxonomically classified by several points of reference, but one very important marker of a species is their very specific genitalia. In butterflies of the same species, their genitalia fit together like a lock (female) and a key (male) which generally prohibits much in the way of cross species breeding.

However, species of the same genus that are very closely related may have genetalia structure similar enough to allow mating. The first two pictures in this article show a Female Polydamas Swallowtail (Battus polydamas) and male Pipevine Swallowtail (Battus philenor) mating at MOSI Outside on May 19, 2015.

These species are from the same genus and therefore are closely related enough to make the mating process possible.

Learn more about butterfly courtship and mating

• Love Among the Butterflies: Courtship (MOSI Outside)
• Butterfly Lifecycle: Adult (Learn About Butterflies)
• Lepidoptera genitalia (Wikipedia)
• Heliconius (Wikipedia)

Hybrid Speciation: Sterile Hybrids and Fertile Hybrids

When species cross breed, the resulting offspring gain copies of their parent species' genes. If the parent species have an unequal number of chromosomes, this results in a Polyploid. For example, the mule is the offspring of a male donkey (Equus asinus) and female horse (Equus caballus). Each parent species possesses a different number of chromosomes. The horse has 64 chromosomes and the donkey possesses 62. Mules are born with 63 chromosomes that are of different structure and number which generally prevents them from pairing properly to produce a viable embryo. Because of this akward pairing of chromosomes, most mules are sterile and cannot reproduce.

Sometimes species are closely related enough that the offspring created through cross breeding can inheret the same number of chromosomes from both parent species. This creates a homopoloid hybrid and thus the new species is fertile and can reproduce. The Melissa Blue (Lycaeides melissa) and Idas Blue (Lycaeides idas) are North American butterflies that live on either side of the Sierra nevada mountain range. In the higher alpine regions of the mountain range, these species have been found to cross-breed to create a new species of Lycaeides, the Alpine Blue butterfly, that can reproduce and create a stable population of offspring. 

Learn more about sterile and fertile hybrids

• Hybrid Butterfly Found on Cold Mountain Tops (National Geographic)
• Homoploid speciation – what is it, and why does it matter? (Evolving Thoughts)
• Scientists May Have Found Those Nabokov Baby Blues (NY Times)

"Heliconius mimicry" by Repeating Patterns of Mimicry.
Meyer A, PLoS Biology, Vol. 4/10/2006,
e341 doi:10.1371/journal.pbio.0040341.
Licensed under CC BY 2.5 via Wikimedia Commons - 

Neotropical Butterfly Hybrids

In Central and South America, there live a collection of closely related species of the genus Heliconia. These species are often known for their bold aposomatic or warning colors and the variable wing patterns they display. These wing pattens and colors warn predators away from the poisonous species, using Mullarian mimicry to reinforce their distastefulness to predators. 

Learn more about Neotropical Heliconian mimicry and speciation

• Butterfly Hybrids (Natural History Museum)
• The stability and formation of  Neotropical butterfly hybrid zones (Tulane.edu)
• Mimicry (Heliconius Homepage)
• Hybrid speciation in Heliconiusbutterflies? A review and critique of the evidence (Andrew Brower)

A Hybrid Becomes a Species: Appalachain Tiger Swallowtail

The Appalachian Tiger Swallowtail (Papilio appalachiensis) is a species that is formed from such a hybridization. An estimated 100,000 years ago, Eastern Tiger Swallowtails (Papilio glaucus) and Cannadian Tiger Swallowtails (Papilio Canadensis) interbred and produced a hybrid that proved to be fertile.

This new species has retained traits of both parent species, sucha as being able to survive in colder climates which is a genetic gift of the Canadian Tiger Swallowtail. Also, they have the abaility to produce black form female offspring, like the Eastern Tiger Swallowtail.

Learn More about the Appalachain Tiger Swallowtail

• Common Butterfly is Hybrid of Two Species (LiveScience)
• Sex Chromosome Mosaicism and Hybrid Speciation among Tiger Swallowtail Butterflies (PLoS, Public Library of Science 2011)

Black form female Eastern Tiger Swallowtail