When explorers first reached Lord Howe Island off Australia's east coast they found it home to a truly remarkable creature, sometimes dubbed the "tree lobster". Also known as Lord Howe Island stick insects (Dryococelus australis), the bugs in question were subsequently wiped out. It seemed to be just another case in the sad catalog of human-induced extinction, until a similar creature was discovered on a nearby island. Doubts remained whether these were actually the same species as those that inhabited Lord Howe. New research, however, has definitively put that question to rest.
Islands support some very odd life forms, as the absence of competitors opens up evolutionary niches – particularly when the island is small and isolated. D. australis was a particularly good example, growing to 15 centimeters (6 inches) long and weighing 25 grams (0.9 ounces). Consequently, they were collected in abundance by naturalists. Unfortunately, by the 1920s museum collections were all that was left, as shipwrecked rats quickly changed the island's ecology and led to the insect being declared extinct.
Then in 1964, a similar-looking creature was discovered on Ball's Pyramid, an island as astonishing for its shape as its ecology. The first specimens were freshly dead but in 2001, a tiny population was found clinging precariously to the one spot on the bare island they can survive, most living in a single shrub. A breeding program at Melbourne Zoo has bolstered their numbers. Hopes rose that, if the Ball's Pyramid insects represented the lost species, they might be reintroduced to Lord Howe, after removing the rats of course.
Unfortunately, the living insects didn't look quite like the dead ones in museums, raising doubts about how closely related they might be.
Dr Alexander Mikheyev of the Okinawa Institute of Science and Technology sequenced the DNA of the Ball's pyramid stick insects. Although the museum specimens are not in good enough condition to provide a full sequence, Mikheyev reported in Current Biology that museum mitochondrial DNA has a better than 99 percent match with the living animals.
"We found what everyone hoped to find – that despite some significant morphological differences, these are indeed the same species," Mikheyev said in a statement. The conclusion removes ethical objections to introducing the Ball's Pyramid insects to Lord Howe.
Stick insects have much larger genomes than other invertebrates, but even by those standards, the D. australis is huge, its 4.2 gigabytes exceeding our own. It also appears to have six homologous chromosome sets, compared to our two, which is thought to reduce the effects of inbreeding in isolated populations.
Although Lord Howe Island and Ball's Pyramid were probably never joined, during the last Ice Age their edges probably approached each other, enabling the wingless insects to make the crossing.