Reply to Ferlazzo and Foray: About the Space Pup project

We would like to thank Ferlazzo and Foray (1) for their very important comments and suggestions. We will keep in mind that “scientists should take particular care to justify their methodology and moderate their conclusions.”

One concern of Ferlazzo and Foray (1) is that our control experiment entailed exposure to the ground radiation of Japan, rather than to a high natural radiation background (NRB), such as Ramsar.

As the authors suggest, it would have been a good idea to expose our control sample to both Ramsar and Japan. When the control radiation level increases from 0.5 mSv/y (Japan) to 70 mSv/y (Ramsar) the difference between space and ground radiation will largely decrease. As mentioned in our paper, we concluded that regarding the use of a higher difference in radiation between space and a low-NRB location (Japan) “it does not affect the production of viable offspring after at least 9 mo of storage on the ISS [International Space Station].” (2) Thus, even if we use a high-NRB location as a control our conclusion will probably not change.

Ferlazzo and Foray (1) also point out the following: “Hence, when the authors report that the low dose rate in space is 100 times higher than on Earth, they omit the highest NRB where there is no evidence of significant hazard.” We regret not knowing the location. However, to find small effects derived from space radiation it might be better to make a comparison between a low-NRB location and space.

The authors were also concerned about how one can “extrapolate the risks for a 2.7-y mission that may be hazardous from the nonsignificant data obtained for a 9-mo mission.” We regret not being able to explain it very well in our paper. We had planned to conduct our Space Pup project for a longer period. However, our mission is still ongoing, as shown on a NASA web page (https://www.nasa.gov/mission_pages/station/research/experiments/893.html), and our sample will be returned to Earth after a longer exposure to space radiation.

Due to the restrictions placed on using the ISS we must demonstrate that our project is going well without any problems. For this reason, we need to publish our first data immediately to justify keeping the other space sample on the ISS for a longer period.

Another concern is the fertility of space-preserved sperm. The authors suggested that “aspermia may be permanent after more than 2,000 mGy” and that “exposure to 109.5 mSv is very far from these doses.”

We thank them for this suggestion. The effects of radiation on live animals and frozen cells are known to be different (3). Freeze-dried sperm cannot repair DNA damage during space flight; therefore, the damage will be greater than that in live animals. Nevertheless, our data (178 mSv) are inadequate to predict the actual effects of space radiation. Therefore, the authors’ following concern is perfectly valid: “Hence, to evaluate the impact of space radiation upon fertility, a much longer mission would have been more relevant.” As mentioned above, we are already conducting a longer preservation experiment and will publish our conclusion upon completing the experiment.