Ionizing radiation affects the demography and the evolution of Caenorhabditis elegans populations.

Ionizing radiation can reduce survival, reproduction and affect development, and lead to the extinction of populations if their evolutionary response is insufficient. However, demographic and evolutionary studies on the effects of ionizing radiation are still scarce. Using an experimental evolution approach, we analyzed population growth rate and associated change in life history traits across generations in Caenorhabditis elegans populations exposed to 0, 1.4, and 50.0 mGy.h-1 of ionizing radiation (gamma external irradiation). We found a higher population growth rate in the 1.4 mGy.h-1 treatment and a lower in the 50.0 mGy.h-1 treatment compared to the control. Realized fecundity was lower in both 1.4 and 50.0 mGy.h-1 than control treatment. High irradiation levels decreased brood size from self-fertilized hermaphrodites, specifically early brood size. Finally, high irradiation levels decreased hatching success compared to the control condition. In reciprocal-transplant experiments, we found that life in low irradiation conditions led to the evolution of higher hatching success and late brood size. These changes could provide better tolerance against ionizing radiation, investing more in self-maintenance than in reproduction. These evolutionary changes were with some costs of adaptation. This study shows that ionizing radiation has both demographic and evolutionary consequences on populations.

Ionising Radiation Induces Promoter DNA Hypomethylation and Perturbs Transcriptional Activity of Genes Involved in Morphogenesis during Gastrulation in Zebrafish.

Embryonic development is particularly vulnerable to stress and DNA damage, as mutations can accumulate through cell proliferation in a wide number of cells and organs. However, the biological effects of chronic exposure to ionising radiation (IR) at low and moderate dose rates (< 6 mGy/h) remain largely controversial, raising concerns for environmental protection. The present study focuses on the molecular effects of IR (0.005 to 50 mGy/h) on zebrafish embryos at the gastrula stage (6 hpf), at both the transcriptomics and epigenetics levels. Our results show that exposure to IR modifies the expression of genes involved in mitochondrial activity from 0.5 to 50 mGy/h. In addition, important developmental pathways, namely, the Notch, retinoic acid, BMP and Wnt signalling pathways, were altered at 5 and 50 mGy/h. Transcriptional changes of genes involved in the morphogenesis of the ectoderm and mesoderm were detected at all dose rates, but were prominent from 0.5 to 50 mGy/h. At the epigenetic level, exposure to IR induced a hypomethylation of DNA in the promoter of genes that colocalised with both H3K27me3 and H3Kme4 histone marks and correlated with changes in transcriptional activity. Finally, pathway enrichment analysis demonstrated that the DNA methylation changes occurred in the promoter of important developmental genes, including morphogenesis of the ectoderm and mesoderm. Together, these results show that the transcriptional program regulating morphogenesis in gastrulating embryos was modified at dose rates greater than or equal to 0.5 mGy/h, which might predict potential neurogenesis and somitogenesis defects observed at similar dose rates later in development.

Transgenerational DNA Methylation Changes in Daphnia magna Exposed to Chronic γ Irradiation.

Our aim was to investigate epigenetic changes in Daphnia magna after a 25-day chronic external γ irradiation (generation F0 exposed to 6.5 µGy·h-1 or 41.3 mGy·h-1) and their potential inheritance by subsequent recovering generations, namely, F2 (exposed as germline cells in F1 embryos) and F3 (the first truly unexposed generation). Effects on survival, growth, and reproduction were observed and DNA was extracted for whole-genome bisulfite sequencing in all generations. Results showed effects on reproduction in F0 but no effect in the subsequent generations F1, F2, and F3. In contrast, we observed significant methylation changes at specific CpG positions in every generation independent of dose rate, with a majority of hypomethylation. Some of these changes were shared between dose rates and between generations. Associated gene functions included gene families and genes that were previously shown to play roles during exposure to ionizing radiation. Common methylation changes detected between generations F2 and F3 clearly showed that epigenetic modifications can be transmitted to unexposed generations, most likely through the germline, with potential implications for environmental risk.

In situ effects of metal contamination from former uranium mining sites on the health of the three-spined stickleback (Gasterosteus aculeatus, L.).

Human activities have led to increased levels of various pollutants including metals in aquatic ecosystems. Increase of metallic concentrations in aquatic environments represents a potential risk to exposed organisms, including fish. The aim of this study was to characterize the environmental risk to fish health linked to a polymetallic contamination from former uranium mines in France. This contamination is characterized by metals naturally present in the areas (manganese and iron), uranium, and metals (aluminum and barium) added to precipitate uranium and its decay products. Effects from mine releases in two contaminated ponds (Pontabrier for Haute-Vienne Department and Saint-Pierre for Cantal Department) were compared to those assessed at four other ponds outside the influence of mine tailings (two reference ponds/department). In this way, 360 adult three-spined sticklebacks (Gasterosteus aculeatus) were caged for 28 days in these six ponds before biomarker analyses (immune system, antioxidant system, biometry, histology, DNA integrity, etc.). Ponds receiving uranium mine tailings presented higher concentrations of uranium, manganese and aluminum, especially for the Haute-Vienne Department. This uranium contamination could explain the higher bioaccumulation of this metal in fish caged in Pontabrier and Saint-Pierre Ponds. In the same way, many fish biomarkers (antioxidant and immune systems, acetylcholinesterase activity and biometric parameters) were impacted by this environmental exposure to mine tailings. This study shows the interest of caging and the use of a multi-biomarker approach in the study of a complex metallic contamination.

Acclimation capacity of the three-spined stickleback (Gasterosteus aculeatus, L.) to a sudden biological stress following a polymetallic exposure.

To get closer to the environmental reality, ecotoxicological studies should no longer consider the evaluation of a single pollutant, but rather combination of stress and their interaction. The aim of this study was to determine if responses of a fish to a sudden biological stress could be modified by a prior exposure to a chemical stress (a polymetallic contamination). For this purpose, in situ experiment was conducted in three ponds in the Haute-Vienne department (France). One pond was chosen for its high uranium concentration due to uranium mine tailings, and the two other ponds, which were not submitted to these tailings. Three-spined sticklebacks (Gasterosteus aculeatus) were caged in these ponds for 14 days. After this period, fish were submitted to a biological stress, exerted by lipopolysaccharides injection after anesthesia, and were sacrificed 4 days after these injections for multi-biomarkers analyses (leucocyte viability, phagocytic capacity and reactive oxygen species production, antioxidant peptide and enzymes, lipid peroxidation and DNA damage). The pond which received uranium mine tailings had higher metallic concentrations. Without biological stress, sticklebacks caged in this pond presented an oxidative stress, with increasing of reactive oxygen species levels, modification of some parts of the antioxidant system, and lipid peroxidation. Caging in the two most metal-contaminated ponds resulted in an increase of susceptibility of sticklebacks to the biological stress, preventing their phagocytic responses to lipopolysaccharides and modifying their glutathione contents and glutathione-S-transferase activity.

In situ experiments to assess effects of constraints linked to caging on ecotoxicity biomarkers of the three-spined stickleback (Gasterosteus aculeatus L.).

The aim of this study was to evaluate the effects of caging constraints on multiple fish biomarkers used during ecotoxicological studies (biometric data, immune and antioxidant systems, and energetic status). Two of these constraints were linked to caging: starvation and fish density in cages, and one in relation to the post-caging handling: a short transport. Three in situ experiments were conducted with three-spined sticklebacks (Gasterosteus aculeatus). The first experiment compared the effects of three densities (low, medium, and high). The second experiment compared effects of starvation in fish fed every two days with fish that were not fed. Finally comparisons between sticklebacks which have suffered a short car transport after caging and sticklebacks killed without preliminary transport were made. The lack of food had no effect on fish energetic reserves but negatively affected their condition index and their immune system. Transport and high density induced oxidative stress, defined as an overproduction of reactive oxygen species and a stimulation of the antioxidant system. These two constraints also harmed the leucocyte viability. In order not to have any impact on ecotoxicity biomarkers during in situ experiments, it is preferable to decrease fish density in cages, prevent transport before dissections, and feed fish when the caging lasts more than two weeks.

Metrology supporting the European regulation for radiation protection.

The European Association of National Metrology Institutes (EURAMET) within its research programme European Metrology Programme for Innovation and Research (EMPIR) funded project EMPIR 19NET03 supportBSS that contributes to the establishment of a European Metrology Network (EMN) for Radiation Protection (RP). The EMN-RP was established in September 2021 with the intent to work as a meeting point for the metrology community and all stakeholders in the field of ionising radiation regulation, thus providing quality assurance for measurements in each of the exposure situations contemplated in the European Legislation. Within project EMPIR 19NET03, work package 3 aims at the preparation of a Strategic Research Agenda (SRA) by identifying the metrology needs to support the European legislation and regulation in Radiation Protection and of two Roadmaps for metrology services, one under the European Council Directive 2013/59/EURATOM and the other under the EURATOM Treaty. Following a Gaps Workshop held in September 2020 and a second internal workshop that took place in April 2022, a questionnaire was prepared for distribution to the stakeholders, e.g. RP platforms and authorities, academia, industry, among other, together with an accompanying paper. In this paper, the authors present the state of the art of European legislation in RP, address the importance of metrology, the practices and activities that need metrology to meet the requirements set in the regulations, emphasise the need for quality assured measurements in all fields, highlight the stakeholders contributions in their specific area and show their vision of the EMN-RP.

The ICRP, MELODI, and ALLIANCE workshop on effects of ionizing radiation exposure in offspring and next generations: a summary of discussions.

PURPOSE: Task Group 121 - Effects of ionizing radiation exposure in offspring and next generations - is a task group under the Committee 1 of the International Commission on Radiological Protection (ICRP), approved by the Main Commission on 18th November 2021. The main goals of Task Group 121 are to (1) review and update the scientific literature of relevance to radiation-related effects in the offspring of parent(s) exposed to ionizing radiation in both human and non-human biota; (2) to assess preconceptional and intrauterine effects of radiation exposure and related morbidity and mortality; and, (3) to provide advice about the level of evidence and how to consider these preconceptional and postconceptional effects in the system of radiological protection for humans and non-human biota. METHODS: The Task Group is reviewing relevant literature since Publication 90 'Biological effects after prenatal irradiation (embryo and fetus)' (2003) and will include radiation-related effects on future generations in humans, animals, and plants. This review will be conducted to account for the health effects on offspring and subsequent generations in the current system of radiological protection. Radiation detriment calculation will also be reviewed. Finally, preliminary recommendations will be made to update the integration of health effects in offspring and next generations in the system of radiological protection. RESULTS: A Workshop, jointly organized by ICRP Task Group 121 and European Radiation Protection Research Platforms MELODI and ALLIANCE was held in Budapest, Hungary, from 31st May to 2nd June 2022. Participants discussed four important topics: (1) hereditary and epigenetic effects due to exposure of the germ cell line (preconceptional exposure), (2) effects arising from exposure of the embryo and fetus (intrauterine exposure), (3) transgenerational effects on biota, and (4) its potential impact on the system of radiological protection. CONCLUSIONS: Based on the discussions and presentations during the breakout sessions, newer publications, and gaps on the current scientific literature were identified. For instance, there are some ongoing systematic reviews and radiation epidemiology reviews of intrauterine effects. There are newer methods of Monte Carlo simulation for fetal dosimetry, and advances in radiation genetics, epigenetics, and radiobiology studies. While the current impact of hereditary effects on the global detriment was reported as small, the questions surrounding the effects of radiation exposure on offspring and the next generation are crucial, recurring, and with a major focus on exposed populations. This article summarizes the workshop discussions, presentations, and conclusions of each topic and introduces the special issue of the International Journal of Radiation Biology resulting from the discussions of the meeting.

Comparative genotoxicity of aluminium and cadmium in embryonic zebrafish cells.

Aluminium is a toxic metal whose genotoxicity has been scarcely studied in aquatic species and more generally in mammals. Recently, human and ecological disaster caused by the discharge of red mud in Hungary has revived questions about the toxicity of this metal particularly for the environment. On the contrary, cadmium is a highly toxic metal whose genotoxicity has been well characterized in various mammalian cells. However on non-human cells, little is known about its impact on DNA damage and repair. In this study, the genotoxic potential of both metals on embryonic zebrafish cells ZF4 was analyzed and particularly the impairment of the major DNA double strand breaks (DSB)-repair pathway, i.e. non-homologous end-joining (NHEJ). To this aim, DNA single strand breaks (SSB) and DSB were evaluated using the comet assay and the immunodetection of γ-H2AX proteins, respectively, in AlCl(3) or CdCl(2) exposed ZF4 cells. These exposures result in the production of DSBs a few hours after incubation. The DNA-PK kinase activity, essential for NHEJ, is more affected by the presence of aluminium than cadmium. Altogether our data provide evidence of the high toxicity induced by aluminium in zebrafish and indicates the pertinence of genotoxicity evaluation in organisms living in contaminated water.

Genotoxic effects of exposure to waterborne uranium, dietary methylmercury and hyperoxia in zebrafish assessed by the quantitative RAPD-PCR method.

Release of chemicals and fluctuation in oxygen content in the aquatic environment represent hazards for fish health. The present study aims at assessing the genotoxic impact of low concentration exposures to waterborne uranium (U), dietary methyl mercury (MeHg) and hyperoxia in zebrafish by using the RAPD-PCR quantitative method. A significant increase of the number hybridization sites was observed in fish exposed to 30µgU/L and 100µgU/L and hyperoxia. In fish exposed to MeHg (13.5µg Hg/g, dry weight) no change in the number of hybridization sites were found, however, the frequency of PCR products showed significant variation. The mechanisms of toxicity leading to DNA damage in fish exposed to waterborne uranium, mercury and hyperoxia are discussed and the results from the literature given by the comet assay, micronucleus test and RAPD-PCR method compared. The study provides new data regarding the genotoxic effects of MeHg, hyperoxia and low U concentrations (30µgU/L) in fish. The present work highlights the use of the RAPD-PCR as a sensitive method in the assessment of chemically-induced DNA damage in animals.

Effects of depleted uranium on oxidative stress, detoxification, and defence parameters of zebrafish Danio rerio.

In this study, we investigated the effects of depleted uranium (DU), the by-product of nuclear enrichment of uranium, on several parameters related to oxidative stress, detoxification, and the defence system in the zebrafish Danio rerio. Several parameters were recorded: phenoloxidase-like (PO) activity, reactive oxygen species (ROS) production, and 7-ethoxyresrufin-O-deethylase (EROD) activity. Experiments were performed on adult and larvae D. rerio. Adult fish were exposed for 28 days at 20 µg U/L followed by a 27-day depuration period. Eggs of D. rerio were exposed for 4 days at 0, 20, 100, 250, 500, and 1,000 µg U/L. Results showed that DU increased ROS production both in adult and in larvae even at the low concentrations tested and even during the depuration period for adult D. rerio. DU also modified PO-like activity, both in the D. rerio adult and larvae experiments, but in a more transient manner. EROD activity was not modified by DU, but sex effects were shown. Results are discussed by way of comparison with other known effects of uranium in fish. Overall, these results show that the mechanisms of action of DU in fish tend to be similar to the ones existing for mammals. These results encourage the development and use of innate immune biomarkers to understand the effects of uranium and, more generally, radionuclides on the fish immune system.

Ionizing radiation exposure effects across multiple generations: evidence and lessons from non-human biota.

A Task Group (TG121) of the International Commission on Radiological Protection (ICRP) Committee 1 was launched in 2021 to study the effects of ionizing radiation in offspring and next generations. In this report, we summarize the evidence of multi- and trans-generational effects in non-human biota species that was discussed at the ICRP workshop entitled "Effects of Ionizing Radiation Exposure in Offspring and Next Generations" in June 2022. Epigenetic changes, including changes in DNA methylation, have been observed in trans- and multi-generational irradiation studies in both plants and animals. There were also reports of changes in offspring survival and reproduction. The reported evidence for altered reproduction is an area of potential concern, due to possible effects at the population or ecosystem level. Different considerations are also discussed regarding non-human biota data, such as transferability of data between different species or extending knowledge to humans, differences in species radiosensitivity, the presence of adaptive responses, and dose reconstruction for exposures that occur across multiple generations. Overall, there is a diverse range of available data of the effects in non-human biota, and it will require careful consideration when incorporating this evidence into the system of radiological protection of humans and of the environment.

Insights into the modes of action of tritium on the early-life stages of zebrafish, Danio rerio, using transcriptomic and proteomic analyses.

In the environment, populations are exposed to different kinds of ionizing radiation. Little is known about their modes of action on non-human species, and whether or not they are similar for alpha, beta and gamma radiations, considered as the reference. In this context, tritium effects (beta emitter) under the form of tritiated water (HTO) were investigated in zebrafish, a common model in toxicology and ecotoxicology with a fully sequenced genome. Experiments were conducted on early life stages, considered to be highly sensitive to pollutants, by exposing eggs to 0.4 mGy/h of HTO until 10 days post fertilization. Tritium internalization was quantified, and effects were investigated using a combined approach of transcriptomic and proteomic analyses. Results highlighted similarities in the biological pathways affected by HTO by both techniques, such as defence response, muscle integrity and contraction, and potential visual alterations. These results correlated well with previous data obtained on earlier developmental stages (1 and 4 dpf). Interestingly, HTO effects were partly overlapping those obtained after gamma irradiation, underlying potential common modes of action. This study, therefore, brought a body of evidence on the effects of HTO observed at the molecular level on zebrafish larvae. Further studies could investigate if the effects persist in adult organisms.

Targeted Central Nervous System Irradiation with Proton Microbeam Induces Mitochondrial Changes in Caenorhabditis elegans.

Fifty percent of all patients with cancer worldwide require radiotherapy. In the case of brain tumors, despite the improvement in the precision of radiation delivery with proton therapy, studies have shown structural and functional changes in the brains of treated patients with protons. The molecular pathways involved in generating these effects are not completely understood. In this context, we analyzed the impact of proton exposure in the central nervous system area of Caenorhabditis elegans with a focus on mitochondrial function, which is potentially implicated in the occurrence of radiation-induced damage. To achieve this objective, the nematode C. elegans were micro-irradiated with 220 Gy of protons (4 MeV) in the nerve ring (head region) using the proton microbeam, MIRCOM. Our results show that protons induce mitochondrial dysfunction, characterized by an immediate dose-dependent loss of the mitochondrial membrane potential (ΔΨm) associated with oxidative stress 24 h after irradiation, which is itself characterized by the induction of the antioxidant proteins in the targeted region, observed using SOD-1::GFP and SOD-3::GFP strains. Moreover, we demonstrated a two-fold increase in the mtDNA copy number in the targeted region 24 h after irradiation. In addition, using the GFP::LGG-1 strain, an induction of autophagy in the irradiated region was observed 6 h following the irradiation, which is associated with the up-regulation of the gene expression of pink-1 (PTEN-induced kinase) and pdr-1 (C. elegans parkin homolog). Furthermore, our data showed that micro-irradiation of the nerve ring region did not impact the whole-body oxygen consumption 24 h following the irradiation. These results indicate a global mitochondrial dysfunction in the irradiated region following proton exposure. This provides a better understanding of the molecular pathways involved in radiation-induced side effects and may help in finding new therapies.

Genotoxic and reprotoxic effects of tritium and external gamma irradiation on aquatic animals.

Aquatic ecosystems are chronically exposed to natural radioactivity or to artificial radionuclides released by human activities (e.g., nuclear medicine and biology,nuclear industry, military applications). Should the nuclear industry expand in the future, radioactive environmental releases, under normal operating conditions or accidental ones, are expected to increase, which raises public concerns about possible consequences on the environment and human health. Radionuclide exposures may drive macromolecule alterations, and among macromolecules DNA is the major target for ionizing radiations. DNA damage, if not correctly repaired, may induce mutations, teratogenesis, and reproductive effects. As such, damage at the molecular level may have consequences at the population level. In this review, we present an overview of the literature dealing with the effects of radionuclides on DNA, development, and reproduction of aquatic organisms. The review focuses on the main radionuclides that are released by nuclear power plants under normal operating conditions, γ emitters and tritium. Additionally, we fitted nonlinear curves to the dose-response data provided in the reviewed publications and manuscripts, and thus obtained endpoints commonly associated with ecotoxicological studies, such as the EDR(10). These were then used as a common metric for comparing the values and data published in the literature.The effects of tritium on aquatic organisms were reviewed for dose rates that ranged from 29 nGy/day to 29 Gy/day. Although beta emission from tritium decay presents a rather special risk of damage to DNA, genotoxicity-induced by tritium has been scarcely studied. Most of the effects studied have related to reproduction and development. Species sensitivity and the form of tritium present are important factors that drive the ecotoxicity of tritium. We have concluded from this review that invertebrates are more sensitive to the effects of tritium than are vertebrates.Because several calculated EDR10 values are ten times lower than background levels of γ irradiation the results of some studies either markedly call into question the adequacy of the benchmark value of 0.24 mGy/day for aquatic ecosystems that was recommended by Garnier-Laplace et al. (2006), or the dose rate estimates made in the original research, from which our EDR(10) values were derived, were under estimated, or were inadequate. For γ irradiation, the effects of several different dose rates on aquatic organisms were reviewed, and these ranged from 1 mGy/day to 18 Gy/day. DNA damage from exposure to y irradiation was studied more often than for tritium, but the major part of the literature addressed effects on reproduction and development. These data sets support the benchmark value of 0.24 mGy/day, which is recommended to protect aquatic ecosystems. RBEs, that describe the relative effectiveness of different radiation types to produce the same biological effect, were calculated using the available datasets. These RBE values ranged from 0.06 to 14.9, depending on the biological effect studied, and they had a mean of 3.1 ± 3.7 (standard deviation). This value is similar to the RBE factors of 2-3 recommended by international organizations responsible for providing guidance on radiation safety. Many knowledge gaps remain relative to the biological effects produced from exposure to tritium and y emitters. Among these are: Dose calculations: this review highlights several EDR(10) values that are below the normal range of background radiation. One explanation for this result is that dose rates were underestimated from uncertainties linked to the heterogenous distribution of tritium in cells. Therefore, the reliability of the concept of average dose to organisms must be addressed. Mechanisms of DNA DBS repair: very few studies address the most deleterious form of DNA damage, which are DNA DBSs. Future studies should focus on identifying impaired DNA DBS repair pathways and kinetics, in combination with developmental and reproductive effects. The transmission of genetic damage to offspring, which is of primary concern in the human health arena. However, there has been little work undertaken to assess the potential risk from germ cell mutagens in aquatic organisms, although this is one of the means of extrapolating effects from subcellular levels to populations. Reproductive behavior that is linked to alterations of endocrine function. Despite the importance of reproduction for population dynamics, many key endpoints were scarcely addressed within this topic. Hence, there is, to our knowledge,only one study of courtship behavior in fish exposed to γ rays, while no studies of radionuclide effects on fish endocrine function exist. Recent technical advances in the field of endocrine disrupters can be used to assess the direct or indirect effects of radionuclides on endocrine function. Identifying whether resistance to radiation effects in the field result from adaptation or acclimation mechanisms. Organisms may develop resistance to the toxic effects of high concentrations of radionuclides. Adaptation occurs at the population level by genetic selection for more resistant organisms. To date, very few field studies exist in which adaptation has been addressed, despite the fact that it represents an unknown influence on observed biological responses.

Assessing tritium internalisation in zebrafish early life stages: Importance of rapid isotopic exchange.

"It appeared that OBT content in organisms was low with an OBT/TFWT ratio of about 8% for both stages (24 hpf and 96 hpf)." Should be read as "It appeared that OBT content in organisms was low with an OBT/TFWT ratio of about 8% and 14% at 24 hpf and 96 hphf respectively".

Revealing the Increased Stress Response Behavior through Transcriptomic Analysis of Adult Zebrafish Brain after Chronic Low to Moderate Dose Rates of Ionizing Radiation.

High levels of ionizing radiation (IR) are known to induce neurogenesis defects with harmful consequences on brain morphogenesis and cognitive functions, but the effects of chronic low to moderate dose rates of IR remain largely unknown. In this study, we aim at defining the main molecular pathways impacted by IR and how these effects can translate to higher organizational levels such as behavior. Adult zebrafish were exposed to gamma radiation for 36 days at 0.05 mGy/h, 0.5 mGy/h and 5 mGy/h. RNA sequencing was performed on the telencephalon and completed by RNA in situ hybridization that confirmed the upregulation of oxytocin and cone rod homeobox in the parvocellular preoptic nucleus. A dose rate-dependent increase in differentially expressed genes (DEG) was observed with 27 DEG at 0.05 mGy/h, 200 DEG at 0.5 mGy/h and 530 DEG at 5 mGy/h. Genes involved in neurotransmission, neurohormones and hypothalamic-pituitary-interrenal axis functions were specifically affected, strongly suggesting their involvement in the stress response behavior observed after exposure to dose rates superior or equal to 0.5 mGy/h. At the individual scale, hypolocomotion, increased freezing and social stress were detected. Together, these data highlight the intricate interaction between neurohormones (and particularly oxytocin), neurotransmission and neurogenesis in response to chronic exposure to IR and the establishment of anxiety-like behavior.

Male frequency in Caenorhabditis elegans increases in response to chronic irradiation.

Outcrossing can be advantageous in a changing environment because it promotes the purge of deleterious mutations and increases the genetic diversity within a population, which may improve population persistence and evolutionary potential. Some species may, therefore, switch their reproductive mode from inbreeding to outcrossing when under environmental stress. This switch may have consequences on the demographic dynamics and evolutionary trajectory of populations. For example, it may directly influence the sex ratio of a population. However, much remains to be discovered about the mechanisms and evolutionary implications of sex ratio changes in a population in response to environmental stress. Populations of the androdioecious nematode Caenorhabditis elegans, are composed of selfing hermaphrodites and rare males. Here, we investigate the changes in the sex ratio of C. elegans populations exposed to radioactive pollution for 60 days or around 20 generations. We experimentally exposed populations to three levels of ionizing radiation (i.e., 0, 1.4, and 50 mGy.h-1). We then performed reciprocal transplant experiments to evaluate genetic divergence between populations submitted to different treatments. Finally, we used a mathematical model to examine the evolutionary mechanisms that could be responsible for the change in sex ratio. Our results showed an increase in male frequency in irradiated populations, and this effect increased with the dose rate. The model showed that an increase in male fertilization success or a decrease in hermaphrodite self-fertilization could explain this increase in the frequency of males. Moreover, males persisted in populations after transplant back into the control conditions. These results suggested selection favoring outcrossing under irradiation conditions. This study shows that ionizing radiation can sustainably alter the reproductive strategy of a population, likely impacting its long-term evolutionary history. This study highlights the need to evaluate the impact of pollutants on the reproductive strategies of populations when assessing the ecological risks.

Unusual evolution of tree frog populations in the Chernobyl exclusion zone.

Despite the ubiquity of pollutants in the environment, their long-term ecological consequences are not always clear and still poorly studied. This is the case concerning the radioactive contamination of the environment following the major nuclear accident at the Chernobyl nuclear power plant. Notwithstanding the implications of evolutionary processes on the population status, few studies concern the evolution of organisms chronically exposed to ionizing radiation in the Chernobyl exclusion zone. Here, we examined genetic markers for 19 populations of Eastern tree frog (Hyla orientalis) sampled in the Chernobyl region about thirty years after the nuclear power plant accident to investigate microevolutionary processes ongoing in local populations. Genetic diversity estimated from nuclear and mitochondrial markers showed an absence of genetic erosion and higher mitochondrial diversity in tree frogs from the Chernobyl exclusion zone compared to other European populations. Moreover, the study of haplotype network permitted us to decipher the presence of an independent recent evolutionary history of Chernobyl exclusion zone's Eastern tree frogs caused by an elevated mutation rate compared to other European populations. By fitting to our data a model of haplotype network evolution, we suspected that Eastern tree frog populations in the Chernobyl exclusion zone have a high mitochondrial mutation rate and small effective population sizes. These data suggest that Eastern tree frog populations might offset the impact of deleterious mutations because of their large clutch size, but also question the long-term impact of ionizing radiation on the status of other species living in the Chernobyl exclusion zone.

Development of an adverse outcome pathway for radiation-induced microcephaly via expert consultation and machine learning.

BACKGROUND: Brain development during embryogenesis and in early postnatal life is particularly complex and involves the interplay of many cellular processes and molecular mechanisms, making it extremely vulnerable to exogenous insults, including ionizing radiation (IR). Microcephaly is one of the most frequent neurodevelopmental abnormalities that is characterized by small brain size, and is often associated with intellectual deficiency. Decades of research span from epidemiological data on in utero exposure of the A-bomb survivors, to studies on animal and cellular models that allowed deciphering the most prominent molecular mechanisms leading to microcephaly. The Adverse Outcome Pathway (AOP) framework is used to organize, evaluate and portray the scientific knowledge of toxicological effects spanning different biological levels of organizations, from the initial interaction with molecular targets to the occurrence of a disease or adversity. In the present study, the framework was used in an attempt to organize the current scientific knowledge on microcephaly progression in the context of ionizing radiation (IR) exposure. This work was performed by a group of experts formed during a recent workshop organized jointly by the Multidisciplinary European Low Dose Initiative (MELODI) and the European Radioecology Alliance (ALLIANCE) associations to present the AOP approach and tools. Here we report on the development of a putative AOP for congenital microcephaly resulting from IR exposure based on discussions of the working group and we emphasize the use of a novel machine-learning approach to assist in the screening of the available literature to develop AOPs. CONCLUSION: The expert consultation led to the identification of crucial biological events for the progression of microcephaly upon exposure to IR, and highlighted current knowledge gaps. The machine learning approach was successfully used to screen the existing knowledge and helped to rapidly screen the body of evidence and in particular the epidemiological data. This systematic review approach also ensured that the analysis was sufficiently comprehensive to identify the most relevant data and facilitate rapid and consistent AOP development. We anticipate that as machine learning approaches become more user-friendly through easy-to-use web interface, this would allow AOP development to become more efficient and less time consuming.