Inbreeding butterflies – a problem for butterfly enthusiasts?

It is totally safe to breed sibling butterflies together for a couple of generations. The genetic diversity is great. Although continuing to breed siblings for quite a few generations in a row could lead to serious problems, a couple of generations is fine. If you want to know more of the details of why it is fine, read on!

Quite often enthusiasts gather eggs that are laid by one female (or assumed to be laid by one female). The question is often asked whether breeding the offspring together (siblings) is dangerous for the offspring. Will there be inbreeding problems? Inbreeding often causes unusual traits to occur when both the male and female parent passes a recessive gene to their offspring. Some recessive genes are delightful and do not cause damage or weakness to the offspring. Other recessive genes are deadly, causing death.

{Although this paragraph doesn’t answer the question, we do want to point out that in the wild, eggs laid in a single day, by one female, may not all be ‘full-blooded’ siblings. Female butterflies normally mate more than once and the sperm is stored in the female. The sperm that fertilizes eggs laid in the same hour may be from different males. There is a strong chance that eggs laid the same day have the same father, but it isn’t a hard fast rule. Now that we have the possibility of mixed parentage from a single female out of the way …}

Assuming that the offspring ARE from the same father, the offspring’s genetics are most likely quite diverse unless we are talking about a small-population species that always lives in the same area, never straying.

1) Let’s assume the species is the Monarch or one like the Monarch, a species that migrates. Monarch, Gulf Fritillary, Cloudless Sulphur, Buckeye, and many other species migrate south in the fall. Monarch butterflies are the species known to overwinter without mating or producing offspring until the spring. Other migrating species are known or assumed to continue producing offspring in the migration destination area throughout the winter and their offspring (or offspring several generations later) migrates back north in the spring. Either way, migrated butterflies mingle with no regard to place of origin. Males will mate with any female from any area, not simply with females only from one specific area. Each year, there is a huge mix of genetics as they gather in the winter and (for Monarchs only in the spring) mate and lay eggs. The eggs from a female may be from butterflies that originated (or their parents originated) over a thousand miles apart.

With such diversity of genetics, the chances of siblings producing first or second generation offspring that are damaged from inbreeding are low. If the adults are contained and the offspring are repeatedly bred without adding new genetics, each generation will increase the chance of inbreeding problems.

As always, if by extreme chance the parents have genes that match and produces a defective butterfly (due to genetics), it can cause problems in captivity as well as in the wild. In captivity, each generation will produce a greater number of defective butterflies if the defect does not end the life of the offspring before it can mate and lay eggs.

2) In a species that does not migrate, cross-breeding increases. Problems from inbreeding may increase or decrease, depending upon the species. We explain:

a] Genetic defects can increase because the genetics, although diverse, are more likely to be limited than with species that migrate and mix with adults from a huge area of the country or from more than one country.

OR

b} Genetic defects may not increase. In some species, the lack of mixing with a large number of butterflies can cause defective genes to ‘die out’ of the population. A small population that does not travel would lose the defective butterflies that physically manifest the defective gene. This may account for extinction of some species that began with a large extensive population. Once their numbers decline to a certain point, the defect could cause end of that population. Now assume a large population of butterfly X declines due to urbanization, pesticides, and loss of habitat due to storms. Once that population has shrunk to a small number of individuals in a small area, inbreeding may cause serious problems that could lead to its extinction.

Many ‘defects’ are not damaging. They may simply be a slight to major difference in color, change in color patterns, change in chrysalis color, or other non-life-threatening changes. Sometimes this leads to the development of a new species.

Other ‘defects’ are life-threatening, such as wing deformity that prevents the butterfly from flying.

Some types of recessive genes are in several species, causing the same type of appearance/change across species.

Deadly gene example:

One such defect is the lack of veining to the edges of the wings. Without veins to the edge of the wings, wings are weak and the butterfly cannot fly. Once the vein-less outer edge has broken off, if the remaining wings are large enough and are of normal strength, the butterfly will be able to fly. In nature, this defect won’t be noticed because the adult will quickly become lunch for a predator. They simply are rarely to never seen by humans. As more people bring in caterpillars and emerge them in protected areas, this genetic defect will be noticed more often simply because the adult will live long enough to be observed by a human. This specific recessive gene defect has been seen in and out of indoor breeding facilities and in more than one species. I have seen this in person and in photos with Monarch butterflies. I have seen it photos of a Giant Swallowtail butterfly that was collected from the wild by an enthusiast.

Not life-threatening example:

Blue Buckeyes in the US are rare. Photographed occasionally from naturally occurring mating in the wild, blue Buckeyes are usually a beautiful metallic blue or green only when they have been bred for several generations expressly for the color. In other countries, Junonia species are often metallic blue. One Junonia species, the Blue Pansy butterfly, closely resembles the Blue Buckeye that was created by inbreeding and is closely related to Buckeye butterflies. It naturally sports the metallic blue color on its wings.

Where do these non-threatening genes originate?

Yellow Monarch chrysalises are quite rare in the US. Queen butterflies, another Danaus species, can be green, pink, or nearly white. Plain Tiger butterflies, another Danaus species, have either green or pink-yellow chrysalises. The Striped Tiger, another Danaus species, has chrysalises that are yellow-orange. The Swamp Tiger, another Danaus species, has chrysalises that are orange.

Whether one believes in evolution, creation, or intelligent design, most of us believe that originally there was just one species of butterfly. As this original species spread out, speciation occurred. From that one species, many species developed. To find the very genes that create differences between species (such as chrysalis color) as recessive rare genes between related species should be expected. As with Danaus species, if all came from a common ancestor butterfly, it should not be surprising that the yellow/orange/pink recessive genes would exist in low percentages in each species.

So …

Can inbreeding cause problems? Yes and no. It can but in most cases, it would take quite a few generations for problems to occur.