Radiation can have extremely negative effects on an individual. But is it as easy to measure its effects on an entire population? (Image Credit: Hnapel, CC BY-SA 4.0, Image Cropped)

Variation in chronic radiation exposure does not drive life history divergence among Daphnia populations across the Chernobyl Exclusion Zone (2019) Goodman et al., Ecology and Evolution, DOI: 10.1002/ece3.4931

The Crux

As anyone who has recently watched HBO’s Chernobyl can tell you, large doses of radiation are capable of doing some pretty serious damage to an organism. But whilst examining the effect of radiation on an individual might be simple, monitoring those effects on a population can be difficult. Whilst radiation negatively effects fitness, it can also help individuals with higher radiation tolerance to reproduce and dominate within the population of a single species, making it difficult to monitor the exact effects of radiation on that population. If a population is filled with only those who were strong enough to survive, you don’t get an idea of the variation in the radiation’s effects.

This week’s researchers tried to break through that problem by looking at different populations of a water flea in Chernobyl’s Exclusion Zone (CEZ) – the area still barred from entry in eastern Europe.

What They Did

The researchers sampled populations of the water flea Daphnia pulex (see below) from 8 lakes within the CEZ, all of which had experienced different doses of radiation since the Chernobyl disaster. Information on how much radiation those lakes were subject to was taken from Ukraine’s radiation databases and water samples collected at the site. The 38 types of Daphnia from the 8 lakes were then transported back to a laboratory and bred for three generations. The survival and reproductive success of this third generation was then modelled against radiation dose.

Did You Know: Daphnia as Study Organisms

Some species are frequently used across different ecological disciplines as model organisms. One example is the genus Daphnia, a genus of water fleas. They have a short life cycle, and can reproduce asexually. This means that scientists have the opportunity to disentangle environmental effects on populations of genetically similar individuals, as well as between populations of different genetic backgrounds.

What They Found

Whilst reproductive success and survival varied between the populations of Daphnia at different lakes, this did not seem to occur as a result of radiation dose. Radiation did not have a pronounced effect on any fitness variable.

Problems?

Sample size is of course an issue here. Only having 8 lakes to compare the effects of radiation on populations was always going to make an effect of radiation dose hard to find. It was made more difficult by the fact that the effects of one lake were significantly different to the others, skewing results considerably. This is of course no fault of the authors, and hopefully technology in the future will allow us to expand the data used in these projects.

So What?

It’s important to note here that these results do not necessarily mean that radiation has no effect on Daphnia populations. Radiation is known to have negative effects on individual fitness, so what this study could tell us is that we need to view radiation as an environmental process which acts in concert with a variety of other biotic factors. Perhaps a study which takes into account further environmental variables and more lake populations would be able to further advance the work done in this paper.