Evaluating Fukushima: fallout from a butterfly controversy


Research conducted in the area around the Fukushima nuclear power plant in the months following the devastating tsunami and nuclear meltdown suggested that the radioactive fallout had substantial effects on a local butterfly species. After their research attracted both considerable attention and considerable criticism, the authors have responded to their critics and the controversy surrounding their work in a new article published this month in BMC Evolutionary Biology.


Vimeo.comThe Fukushima Daiichi nuclear disaster, caused by the failure and meltdown of the Fukushima nuclear power plant following the massive earthquake and tsunami in March 2011, was the biggest nuclear incident since the Chernobyl disaster in 1986. Substantial amounts of radiation were released into the surrounding area; recent news shows that this problem continues, as contaminated water leaks from the crippled power plant.

As the initial concerns about short-term dangers posed by the disaster fade, the focus has moved to the long-term implications for both human health and the wider environment. While humans evacuate the worst affected areas, the local wildlife continue on with their lives obliviously. As in Chernobyl then, animals and plants living in the affected areas can act as indicators of the environmental impact of the disaster.

The damage done

It was in this vein that Atsuki Hiyama and colleagues at the University of the Ryukyus in Japan conducted a study, published in August 2012 in the journal Scientific Reports, on the effect of the Fukushima disaster on the pale blue grass butterfly. This butterfly is common throughout Japan, including the Fukushima area. The authors collected a number of adult butterflies in Fukushima and surrounding areas in May 2011; two months earlier at the time of the disaster these individuals were larvae overwintering underground.

Many of the butterflies collected from Fukushima and other areas contaminated by radioactive fallout suffered from abnormalities not seen elsewhere in Japan; mainly changes in this species distinctive wing-patterns, but also abnormalities in the shape of the legs, appendages, eyes and wings. These were relatively mild; however when butterflies were collected four months later in September 2011, the abnormalities were much more severe and widespread (38.5% of butterflies collected in Fukushima were abnormal).

Given the short lifespan of the adult butterflies (just one week) it could not be the case that this was due to prolonged exposure to radiation; none of these September butterflies were alive when the disaster first happened. This suggests that the radiation is causing mutations to the germline as well as somatic cells; that is, these abnormalities are being inherited.

The authors confirmed this by raising the captured butterflies offspring in their lab; the number and severity of abnormalities increased with each generation. Finally, to confirm that radiation was capable of causing these changes, the authors exposed larvae caught in non-contaminated parts of Japan to radiation, both externally (by exposure to 137Cs radiation) and internally (by feeding them with plants taken from Fukushima and thus contaminated with radioactive molecules). These butterflies showed the same kinds of abnormalities the authors had found in the wild.

Responding to controversy

These were provocative results and it is no surprise that the study attracted considerable attention both inside and outside Japan; not every scientific paper gets downloaded over 300,000 times. However, a lot of the feedback the authors received was decidedly negative, with many criticising the design and the conclusions of the study. This led the authors to write a new article, published recently in BMC Evolutionary Biology, to address these criticisms.


The arguments against Hiyama and colleagues study took several lines, but were all based around the same question: can we really be sure the abnormalities were caused by the radiation emanating from the Fukushima plant? After all, populations will always vary considerably in different geographic areas – perhaps these apparent abnormalities were always present in pale-blue grass butterflies in the Fukushima area, due to temperature, geography or some unknown variable.

The authors are well placed to answer such questions, having studied this species for over a decade, including the variation in its morphology across Japan. They clearly describe in their new article the reasons why radiation is by far the most plausible reason for the observed abnormalities. Of course, ideally the authors would have collected butterflies from the Fukushima area before the disaster, to allow a direct comparison with individuals collected post-disaster; a clear limitation of the original study. However, in a nice example of the benefits of communicating scientific research to the wider public, two amateur butterfly collectors contacted the authors, offering to share specimens they had collected from Fukushima in the years before the disaster. All of these specimens were normal, with none of the abnormalities so common post-disaster.

All well and good, but some doubted if it was even theoretically possible for radiation to cause such mutations in insects. After all, we all know that if the nuclear apocalypse ever arrives, cockroaches and ants will inherit the earth; insects are especially resistant to radiation damage, correct? As Hiyama and co-authors point out, this is an idea based on little evidence. Most research exposing insects to radiation has involved high doses over short time spans, not the low doses over a long period that the Fukushima butterflies have experienced. While admitting that more research is needed into this area, the authors are confident that radiation is capable of causing the mutations seen in the butterflies.

The wider meaning

As the dust settles, what is the wider significance of these findings? The authors speculate that radiation resistance will quickly evolve in the Fukushima butterfly populations. If the pale-blue butterflies are a good indicator of the likely effect of the radiation on other wildlife in the region (and the authors believe they are), then the disaster could have a substantial evolutionary effect for some time to come.

The results also of course suggest that the area around Fukushima is liable to remain uninhabitable by humans for some time; it is perhaps this implication that is in large part the cause of the controversy surrounding the study. Atsuki Hiyama and his colleagues should be commended for engaging with their critics and strengthening our knowledge of the wider impacts of the Fukushima disaster.

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