HOW TO SOLVE A BIOLOGICAL MYSTERY USING MUSEUM COLLECTIONS AND DNA TECHNOLOGY
By Rebecca Whitla, PhD student at Oxford Brookes University
The Black-veined white butterfly (Aporia crataegi) was a large, charismatic butterfly with distinctive black venation on its wings. Once commonly found in the UK, the species unfortunately went extinct here in around 1925, with the last British specimens collected from Herne Bay in Kent. It isn’t fully understood why the species disappeared from the UK, but climate change, predation, parasites, and disease have all been suggested to have caused its disappearance — perhaps with several of these factors contributing to its decline. Central to solving the mystery of the disappearance of the Black-veined white will be the collections of butterflies that are stored in museums like OUMNH.
Butterflies tend to be well-represented in museum collections, and the Black-veined white is no exception. While the species has now been extinct in the UK for around 100 years, Lepidoptera enthusiasts from previous centuries often captured wild Black-veined white specimens for their personal collections. The abundance of Black-veined white butterflies in museum collections, like the collections at OUMNH, serve as a valuable repository for scientific research — including my own!
Between June and December 2021, I undertook a research project using OUMNH’s Black-veined white butterflies. My task was to extract enough DNA from the butterflies to use for ‘whole genome sequencing’ — in other words, I was attempting to extract DNA from butterfly specimens to decode their complete DNA sequence. Getting DNA sequences from the historical specimens that are kept in Museums is no easy task, as DNA degrades over time. Nonetheless, animal specimens from natural history museums have successfully been used for whole genome sequencing and genetic analysis in the past, including species as diverse as longhorn beetles and least Weasels.
In order to work out how to extract DNA from the specimens, I had to try a variety of methods. This included experimenting to find out whether butterfly legs or abdomen fragments yielded more DNA, and whether non-destructive methods of DNA extraction were as effective as destructive methods. An example of a non-destructive method of DNA extraction would be a process like soaking a sample overnight and using the leftover liquid for DNA extraction, whereas a destructive method might involve mashing a whole leg or abdomen segment to use as a DNA source.
Overall, I found that destructively sampling the legs of the butterflies gave the most reliable results, and also had the added benefit of not destroying the wings or abdomen of the specimens. Keeping the wings and abdomens of the butterflies intact will likely prove useful for conducting morphological studies in future.
Now that I have a reliable DNA extraction method, the next step in my research will be to analyse more Black-veined white specimens from a span of different time periods leading up to the species’ disappearance. I will then compare samples collected from each time period to calculate the genetic diversity of the species at each point in time, leading up to its disappearance. If I find a steady decline in the species’ genetic diversity over time, this may indicate a gradual extinction of the species. This is because we expect that, as numbers of a species decrease, inbreeding will become common, resulting in less diversity in the species’ DNA. However, if the populations of Black-veined white butterflies went extinct very suddenly, the decline in genetic diversity will probably be less pronounced. Learning more about the fate of the Black-veined White could not only help us unlock the historical mystery of the species’ decline in Britain, but will also help us understand more about the species’ decline in other parts of the world.