What caused the narrowing of the nenes' circumstances to the point of near-extinction? Was the isolation of island living to blame for draining their gene pool to a puddle, or was it caused by the 20th century population decline? How did they survive and recover when many other species of flightless Hawaiian birds disappeared altogether before recorded history?
Research reported in today's edition of the journal Science suggests that a boom in the human population between 900 and 350 years ago may have impacted and reduced the population size of the nene during that time, and consequently diminished the species' genetic variation.
A team of scientists from the Conservation and Research Center of the Smithsonian's National Zoological Park and National Museum of Natural History, along with a collaborator from the University of California, Los Angeles, examined DNA from nene on the island of Hawaii from four time periods: Extant captive and wild birds; museum specimens collected between 1833 and 1928; bones from archaeological middens radiocarbon dated at 160 to 500 years ago; and bones from paleontological sites dating from 500 to 2540 radiocarbon years before the present. They were surprised to find the levels of genetic variation typical of contemporary geese only in the paleontological samples.
"We were expecting to see evidence of the loss of genetic variation first in the museum specimens, coincident with the nene population decline that began in the 1800s," said Robert Fleischer, head of the Natural History Museum's genetics laboratory. "Instead, we found the precipitous drop much earlier, in the samples dating from between 500 and 850 years ago, coincident with the expansion of human settlements on the island."
Fleischer noted that the combination of new techniques and ancient specimens makes it possible to look at population genetics through time, as far back at 2,500 years ago.
It is widely believed that the ecological changes associated with human interference contributed to extinctions of many bird species in the islands 500 to a thousand years ago. These species, including the nene, likely were affected by habitat changes, introduced predators or directly by their consumption as food. The Smithsonian-led research goes a step further to implicate the spread of human settlements not just in the extinction of species, but also in the loss of one species' genetic diversity.
Moreover, the study demonstrates that surviving modern species still bear the imprint of human disruption in their genetic makeup.
"Our research also debunks the belief that Hawaii was a pristine paradise, and that prehistoric man lived in perfect harmony with nature," said Helen James, museum specialist in the Natural History Museum's Division of Birds.
James pointed out also that museum collections are vitally important to even the most cutting edge contemporary research. The Smithsonian team drew on specimens in its own collections, from the first U.S. exploring expeditions, as well as from the Bishop Museum in Hawaii and skins from Europe.