DESPITE the imposing name, the Great Eggfly butterfly, known in scientific circles as Hypolimnas bolina, isn?t quite as long as your index finger. The males have black wings with large white spot rimmed in pale blue. The females? markings are bit more varied, and can resemble a spread fan with a white band running down the center of each wing and several white dots along the wing edge.

For several decades between 1870 and 1930, these variations in wing markings made the H. bolina butterfly highly prized by entomologists who collected as many examples of both males and females of the species as possible.

British and French researchers have taken advantage of these century-old collections to track the evolution of the Great Eggfly species in the Philippines, Malaysia, Fiji and French Polynesia. In particular, they were interested in how the species was affected by the Wolbachia bacteria, which are transmitted from infected H. bolina mothers to offspring, significantly reducing the number of males that make it to adulthood in each generation.

Color patterns

In a statement, study senior author Greg Hurst from the University of Liverpool noted that the butterflies were widely collected for study at the turn of the century because their color patterns were useful for those reviewing Darwin?s theory of evolution.

?Today we can benefit from this early interest through museum collections, where we can now use the latest DNA technology to understand how species have evolved across time and geographical space,? he said.

Hurst and his colleagues used forensic DNA techniques to study the samples taken from the legs of both female and male butterfly specimens kept at Natural History Museum of London and the Oxford University Museum of Natural History to see if they had been infected with Wolbachia.

Based on the infection ratios, the researchers estimated the prevalence of the bacterial infection across the butterfly populations then, and compared the numbers to data gathered from genetic samples collected from Great Eggfly butterflies in the same 4 regions over the past decade.

Emily Hornett, the study?s first author and Hurst?s colleague at the University of Liverpool observed in a statement that recent breakthroughs in forensic science have allowed researchers to study the evolution of a species by extracting DNA samples from museum specimens.

?By analyzing DNA samples from the legs of butterflies living a century ago, and comparing these with contemporary samples,? she said, ?we were able to directly observe evolution between a butterfly and the bacteria that infects them.?

Gene vs Wolbachia bacteria

Based on the genetic information, Hornett and her colleagues found that as far back as 115 years ago, the Philippine H. bolina butterfly population had developed a gene that counters the Wolbachia bacteria so that the infected males survive. Other butterfly populations based in Malaysia, Independent Samoa and Fiji had varying male-to-female ratios, though none were as skewed toward a predominantly female population as the butterfly population in French Polynesia.

?All but one of our study populations has experienced extreme sex ratio conditions over the last 130 years, which is therefore likely to lead to reduced genetic variation and a lower capacity to respond to environmental change or coevolving antagonists,? Hornett and her colleagues wrote in their study.

The researchers are now trying to identify the so-called ?suppressor gene? in the H. bolani butterfly to better understand how the butterfly has adapted to counter the Wolbachia bacteria.

The study was published online September 10 in the journal Current Biology.

E-mail the author at massie@ massie.com.