Mutated butterflies - caused by nuclear disaster.

Joji Otaki / EPA

This handout photo, released Tuesday, shows a healthy adult pale grass blue butterfly (top) and a mutated variety (bottom). Severe mutations were found in butterflies collected near Japan's Fukushima Daiichi nuclear power plant.

By Arata Yamamato, NBC News

TOKYO -- Researchers in Japan have found signs of mutation in butterflies, signaling one of the first indications of change to the local ecosystem as a result of last year's nuclear accident in Fukushima, according to one of the first studies on the genetic effects of the incident.
Joji Otaki from the University of the Ryukyus in Okinawa, who led the research, collected 144 commonly-found pale grass blue butterflies two months after the March 2011 accident at the Fukushima Dai-ichi nuclear plant.
Initial results indicated that roughly 12 percent of the butterflies showed signs of abnormalities, such as disfigurement in their antennas, smaller-sized wings, change in color patterns and indented eyes, Otaki said.
Even more alarming, when he collected another 238 samples six months later he found that those abnormalities had increased to 28 percent and the mutations had doubled to 52 percent in their offspring.