Investigating the impacts of Chernobyl-level radiation exposure on insect life history traits

Abstract

The majority of our understanding of the effects of radiation are extrapolated from acute high-dose exposures or originate from human based studies. For example, chronic human exposures are well studied from external sources as well as internal e.g. radon in drinking water. We know comparatively less about the effects of radiation on non-human biota, especially those exposed to lower dose rates. This thesis consequently focused on the effects of dose rates found in some areas of the Chernobyl Exclusion Zone (CEZ), a heterogeneously radiologically contaminated landscape where dose rates range from 0.1 to 250 μGy h-1. This thesis primarily used the bumblebee Bombus terrestris as a model study system, to investigate whether low dose rates affect key life history traits in a vital pollinator. The dose rates used in these laboratory-based studies were between 40 and 200 μGy h-1. I focused on key life history traits in order to provide a generalisable measure that could be used to investigate the effects of these dose rates in a consistent way across different species. I found low dose radiation exposure causes a substantial change in bumblebee energy budgets through an upregulation in resource acquisition and metabolic rate. This change is further evidenced by a dramatic increase in haemolymph sugar concentrations at dose rates as low as 40 μGy h-1. The gut microbiome was however largely unchanged by this increase in nectar, but did show an increase in microbial species richness in response to radiation. A response to chronic low doses of radiation was not unique to bumblebees as they also led to a significant increase in the number of eggs produced by Drosophila melanogaster within just 18 hours of radiation exposure. This was followed by a dramatic decrease in fecundity. This thesis provides clear evidence that invertebrates experience substantial physiological effects as a result of low dose rates of radiation. I argue this result has ecological relevance because the dose rates at which these impacts were recorded can be currently found in the CEZ. This work could have implications for international policy as the dose rates that are currently considered safe for insects are set at 417 μGy h-1 by the International Commission on Radiological Protection. Whilst this thesis did not identify an exact mechanism driving physiological change in these species, I propose a possible explanation of an energetically costly recovery mechanism being activated by these lower doses.