A group of University of Hawaii researchers has discovered a tiny Hawaiian moth is one of the islands’ oldest insects — at 15 million years old — an insight that helps show the barren Northwest Hawaiian Islands once brimmed with biological diversity.
"The Northwest Hawaiian Islands, which we now think of as these remote atolls and archipelagos, used to be as big as some of the main islands that we have now and they must have supported a huge diversity of organisms," said William Haines, one of three UH researchers who published an article on their findings last month in the online science journal Nature Communications.
"These moths are some of the ones that were able to survive the bottleneck when those islands sank into the sea," said Haines, who has a doctorate in entomology. "These things were able to make the jump onto the main islands when they arose."
The moth genus Hyposmocoma has more than 400 species in Hawaii, but only nine basic types that evolved before the main Hawaiian Islands were formed, the article says. The basic types provide evidence for the "environmental conditions and a reflection of habitats" on past high islands.
Haines said his group used a complex molecular dating technique, which looks at genetic mutations that occur at a clocklike rate, to determine when two species diverged. Working backward, the researchers calculated how long the moth has been in the islands.
Researchers can also tell the order in which mutations occurred in diverging species and use that data to get a glimpse of what their ecosystems were like, he said.
Haines estimates the moth arrived in Hawaii about 15 million years ago, alighting on Gardner Pinnacles, the largest target in the island chain at the time — at about 13,000 feet in elevation and matching Hawaii island in size. Today, only two barren rock outposts remain of the island.
About the time of the moth’s emergence, several now-vanished volcanoes in the Northwestern Hawaiian Islands were more than 3,280 feet above sea level, close to Oahu’s 4,000-foot elevation, the article says.
According to the article, the distance between Kauai and the older northwestern islands may have halted the spread of other ancient species to the younger islands. In addition, previous studies suggested that most native plants and animals in Hawaii are younger than Kauai, which formed about 5 million years ago.
Haines suspects the moth, whose wingspan averages less than 1 centimeter, was carried in the wind to Kauai.
On the bleak northwestern islands today, the moths surviving there are of the lichen-grazing groups. Researchers, however, believe the forest-dwelling Hyposmocoma species — such as those whose caterpillars feed on tree snails — developed in forests that once existed on islands in the northwest.
"We can show that the Northwestern Hawaiian Islands once supported a very diverse fauna and some of these groups depended on things like forests and streams," Haines said. "It just points out that these islands weren’t always so barren."
The Pacific plate carries the Hawaiian archipelago to the northwest at about 2 inches per year. The islands eventually erode and sink beneath the waves, often becoming flat-topped seamounts called guyots.
Beyond the Northwest Hawaiian Islands, the Emperor Seamounts extend almost all the way to Russia, representing 82 million years of tectonic history.
