Long-distance Dispersal Research Articles

The global pattern of epiphytic liverwort disparity: insights from Frullania

The geographical and ecological patterns of morphological disparity are crucial to understand how species are assembled within communities in the context of the evolutionary history, morphological evolution and ecological interactions. However, with limited exceptions, rather few studies have been conducted on the global pattern of disparity, particularly in early land plants. Here we explored the spatial accumulation of disparity in a morphologically variable and species rich liverwort genus Frullania in order to test the hypothesis of latitude disparity gradient. We compiled a morphological data set consisting of eight continuous traits for 244 currently accepted species, and scored the species distribution into 19 floristic regions worldwide. By reconstructing the morphospace of all defined regions and comparisons, we identified a general Gondwana-Laurasia pattern of disparity in Frullania. This likely results from an increase of ecological opportunities and / or relaxed constraints towards low latitudes. The lowest disparity occurred in arid tropical regions, largely due to a high extinction rate as a consequence of paleoaridification. There was weak correlation between species diversity and disparity at different spatial scales. Furthermore, long-distance dispersal may have partially shaped the present-day distribution of Frullania disparity, given its frequency and the great contribution of widely distributed species to local morphospace. This study not only highlighted the crucial roles of paleoenvironmental changes, ecological opportunities, and efficient dispersal on the global pattern of plant disparity, but also implied its dependence on the ecological and physiological function of traits.

Gone with the waves: the role of sea currents as key dispersal mechanism for Mediterranean coastal and inland plant species.

Thalassochory, the dispersal of propagules through marine currents, is a key long-distance dispersal (LDD) mechanism with implications for global biogeography and particularly for island colonization. The propagules of coastal plant species are generally assumed to be better adapted for sea dispersal than those of inland plants, but this hypothesis remains largely untested. We conducted experiments on four genera (Juniperus, Daucus, Ferula, and Pancratium) and compared traits among nine species with different habitats and distributions. Our results showed that Juniperus spp. and P. maritimum have strong thalassochorous potential within the Mediterranean Basin. Interestingly, we did not find a clear association on the thalassochorous potential of coastal versus inland species within all the tested genera, apart from P. maritimum compared withthe endemic inland P.illyricum. These findings suggest that thalassochory may be a more common dispersal mechanism than previously assumed. The apparently weak link of dispersal syndrome with species ecology broadens the possibility of dispersal by the sea also for inland plants, although considered to be poorly salt-tolerant. Moreover, our results reveal significant differences in sea dispersal between endemic and widespread species, but do not rule out an important role of thalassochory in shaping the distribution patterns of archipelago endemic flora. The presented method is largely replicable and could be used for further studies with a larger set of species to better delineate trends of sea dispersal syndrome among species with different ecology or dispersal traits.

Distribution and ecological aspects of sand fly species from Kousseri, an endemic focus of visceral leishmaniasis in Northern Cameroon

IntroductionKousseri in the Far North Region of Cameroon has long been known as an endemic focus of visceral leishmaniasis (VL), although the study on sand flies in this focus is scarce. The present study investigates the spatial distribution, seasonality, and ecological aspects of sand flies from Kousseri. This study is based on the need to optimize the effectiveness of leishmaniasis control programs in the northern part of the country. MethodsSand flies were sampled monthly over 12 months in five selected sites using CDC light traps. Only captured females were morphologically identified at species level based on valid keys. Results and discussionOverall, 4,214 sand fly specimens were collected during 360 trapping nights. The male/female sex ratio slightly favored females (1:1.04). The eudominant Sergentomyia antennata followed by both dominant Sergentomyia schwetzi and Sergentomyia squamipleuris were the most common and abundant species, accounting for 76.1% of the collection. Phlebotomus duboscqi, the confirmed vector of cutaneous leishmaniasis (CL) in West African foci, although rare in the collection, was found in four of the five surveyed sites. This sand fly species with Se. schwetzi abounded in peri-urban areas and, respectively, in animal shed and in uninhabited house biotopes, while Se. antennata and Se. squamipleuris prevailed in rural areas and, respectively, in animal shelter biotopes and outside dwellings. All caught sand fly species except Se. schwetzi, Sergentomyia clydei, Sergentomyia inermis, and Sergentomyia adleri prevailed during the dry season. The highest Shannon–Wiener index of sand flies due to the maximal richness and evenness was found in the urban area, in outdoor biotopes, and during the rainy season (H′ = 1.68, 1.80, and 1.74, respectively). These data provide evidence that less urbanized areas, animal shelters around the compounds, and the absence of precipitation (dry season) favored the dispersion of abundant sand fly species in Kousseri. Based on previous reports on Leishmania transmission, a surveillance plan is required to prevent an outbreak of VL or an establishment of CL or canine leishmaniasis (CnL) in this focus. Further research identifying the blood meal source and the Leishmania parasites in these insects is critical for providing insightful data to fight leishmaniasis in Northern Cameroon.

GhiPLATZ17 and GhiPLATZ22, zinc-dependent DNA-binding transcription factors, promote salt tolerance in upland cotton.

The utilization of transcriptome analysis, functional validation, VIGS, and DAB techniques have provided evidence that GhiPLATZ17 and GhiPLATZ22 play a pivotal role in improving the salt tolerance of upland cotton. PLATZ (Plant AT-rich sequences and zinc-binding proteins) are known to be key regulators in plant growth, development, and response to salt stress. In this study, we comprehensively analyzed the PLATZ family in ten cotton species in response to salinity stress. Gossypium herbaceum boasts 25 distinct PLATZ genes, paralleled by 24 in G. raimondii, 25 in G. arboreum, 46 in G. hirsutum, 48 in G. barbadense, 43 in G. tomentosum, 67 in G. mustelinum, 60 in G. darwinii, 46 in G. ekmanianum, and a total of 53 PLATZ genes attributed to G. stephensii. The PLATZ gene family shed light on the hybridization and allopolyploidy events that occurred during the evolutionary history of allotetraploid cotton. Ka/Ks analysis suggested that the PLATZ gene family underwent intense purifying selection during cotton evolution. Analysis of synteny and gene collinearity revealed a complex pattern of segmental and dispersed duplication events to expand PLATZ genes in cotton. Cis-acting elements and gene expressions revealed that GhiPLATZ exhibited salt stress resistance. Transcriptome analysis, functional validation, virus-induced gene silencing (VIGS), and diaminobenzidine staining (DAB) demonstrated that GhiPLATZ17 and GhiPLATZ22 enhance salt tolerance in upland cotton. The study can potentially advance our understanding of identifying salt-resistant genes in cotton.

Plant-level establishment can result from a single female Acanthococcus lagerstroemiae propagule

AbstractCrapemyrtle bark scale (CMBS), Acanthococcus lagerstroemiae (Kuwana) (Hemiptera: Eriococcidae), is a non-native scale insect that has spread throughout many urban areas of the Southeast and Middle Atlantic regions of the United States following its initial detection near Dallas, Texas in 2004, severely reducing the aesthetic value and health of the popular ornamental crapemyrtle tree (Lagerstroemia spp.). We infested crapemyrtles with known numbers of CMBS to determine the minimum number of individuals required for establishment after initial arrival on plants. We also investigated how netting—implemented to understand differences in establishment when scale dispersal and predation are inhibited—influenced population growth. We determined that one female CMBS egg sac can successfully establish a new population ~ 92% of the time and that netting had negligible effects on establishment. Our results underscore the importance of surveying and managing CMBS and scale insects with similar biology when attempting to prevent infestation of nursery stock, which is widely implicated as a vector for long-distance dispersal of scale insects.

Linking Seed Traits and Germination Responses in Caribbean Seasonally Dry Tropical Forest Species

Understanding the relationships between seed traits and germination responses is crucial for assessing natural regeneration, particularly in threatened ecosystems like the seasonally dry tropical forest (SDTF). This study explored links between seed traits (mass, volume, moisture content, and dispersal type), germination responses (germinability, germination speed (v¯), time to 50% of germination (T50), synchrony, and photoblastism), and physical dormancy (PY) in 65 SDTF species under experimental laboratory conditions. We found that species with smaller seeds (low mass and volume) had higher v¯ and reached T50 faster than species with larger seeds. For moisture content, species with lower moisture content had higher germinability and reached the T50 faster than seeds with high moisture content. Abiotic dispersed species germinated faster and reached the T50 in fewer days. Most of the SDTF species (60%) did not present PY, and the presence of PY was associated with seeds with lower moisture content. As for photoblastism (germination sensitivity to light), we classified the species into three ecological categories: generalists (42 species, non-photoblastic), heliophytes (18 species, positive photoblastic, germination inhibited by darkness), and sciadophytes (5 species, negative photoblastic, light inhibited germination). This study intends to be a baseline for the study of seed ecophysiology in the SDTF.

Tailored Metal-Organic Frameworks for Water Purification: Perfluorinated Fe-MOFs for Enhanced Heterogeneous Catalytic Ozonation.

An industrially viable catalyst for heterogeneous catalytic ozonation (HCO) in water purification requires the characteristics of good dispersion of active species on its surface, efficient electron transfer for ozone decay, and maximum active species utilization. While metal-organic frameworks (MOFs) represent an attractive platform for HCO, the metal nodes in the unmodified MOFs exhibit low catalytic activity. Herein, we present a perfluorinated Fe-MOF catalyst by substituting H atoms on the metalated ligands with F atoms (termed 4F-MIL-88B) to induce structure evolution. The Lewis acidity of 4F-MIL-88B was enhanced via the formation of Fe nodes, tailoring the electron distribution on the catalyst surface. As a result of catalyst modification, the rate constant for degradation of the target compounds examined increased by ∼700% compared with that observed for the unmodified catalyst. Experimental evidence and theoretical calculations showed that the modulated polarity and the enhanced electron transfer between the catalyst and ozone molecules contributed to the adsorption and transformation of O3 to •OH on the catalyst surface. Overall, the results of this study highlight the significance of tailoring the metalated ligands to develop highly efficient and stable MOF catalysts for HCO and provide an in-depth mechanistic understanding of their structure-function evolution, which is expected to facilitate the applications of nanomaterial-based processes in water purification.

Using biophysical modelling and marine connectivity to assess the risk of natural dispersal of non-indigenous species to comply with the Ballast Water Management Convention

AbstractThe introduction of Marine Non-Indigenous Species (NIS) poses a significant threat to global marine biodiversity and ecosystems. To mitigate this risk, the Ballast Water Management Convention (BWMC) was adopted by the UN International Maritime Organisation (IMO), setting strict criteria for discharges of ballast water. However, the BWMC permits exemptions for shipping routes operating within a geographical area, known as a Same-Risk-Area (SRA). An SRA can be established in areas where a risk assessment (RA) can conclude that the spread of NIS via ballast water is low relative to the predicted natural dispersal. Despite the BWMC's requirement for RAs to be based on modelling of the natural dispersal of NIS, no standard procedures have been established. This paper presents a methodology utilizing biophysical modelling and marine connectivity analyses to conduct SRA RA and delineation. Focusing on the Kattegat and Øresund connecting the North Sea and Baltic Sea, we examine two SRA candidates spanning Danish and Swedish waters. We provide an example on how to conduct an RA including an RA summary, and addressing findings, challenges, and prospects. Our study aims to advance the development and adoption of consistent, transparent, and scientifically robust SRA assessments for effective ballast water management.

Capture of single Ag atoms through high-temperature-induced crystal plane reconstruction

The “terminal hydroxyl group anchoring mechanism” has been studied on metal oxides (Al2O3, CeO2) as well as a variety of noble and transition metals (Ag, Pt, Pd, Cu, Ni, Fe, Mn, and Co) in a number of generalized studies, but there is still a gap in how to regulate the content of terminal hydroxyl groups to influence the dispersion of the active species and thus to achieve optimal catalytic performance. Herein, we utilized AlOOH as a precursor for γ-Al2O3 and induced the transformation of the exposed crystal face of γ-Al2O3 from (110) to (100) by controlling the calcination temperature to generate more terminal hydroxyl groups to anchor Ag species. Experimental results combined with AIMD and DFT show that temperature can drive the atomic rearrangement on the (110) crystal face, thereby forming a structure similar to the atomic arrangement of the (100) crystal face. This resulted in the formation of more terminal hydroxyl groups during the high-temperature calcination of the support (Al-900), which can capture Ag species to form single-atom dispersions, and ultimately develop a stable and efficient single-atom Ag-based catalyst.

Ancient mitogenomes reveal evidence for the Late Miocene dispersal of mergansers to the Southern Hemisphere

Abstract Mergansers are riverine and coastal piscivorous ducks that are widespread throughout North America and Eurasia but uncommon in the Southern Hemisphere. One species occurs in South America and at least two extinct species are known from New Zealand. It has been proposed that these Southern Hemisphere merganser lineages were founded by at least two independent dispersal events from the Northern Hemisphere. However, some morphological and behavioural evidence suggests that Southern Hemisphere mergansers may form a monophyletic clade that descended from only a single dispersal event from the Northern Hemisphere. For example, Southern Hemisphere mergansers share several characteristics that differ from Northern Hemisphere mergansers (e.g. non-migratory vs. migratory, sexual monochromatism vs. sexual dichromatism, long vs. short pair bonds). We sequenced complete mitogenomes from the Brazilian merganser and an extinct merganser from New Zealand—the Auckland Island merganser. Our results show that the Brazilian and Auckland Island mergansers are not sister-taxa, and probably descend from two separate colonization events from the Northern Hemisphere at least 7 Mya. Nuclear (palaeo)genomic data may help to further resolve the relationship between living and extinct mergansers, including merganser fossils from New Zealand that have not been subjected to palaeogenetic analysis.

Asymmetric drift in MaNGA: Mass and radially-dependent stratification rates in galaxy disks

Abstract We measure the age-velocity relationship from the lag between ionized gas and stellar tangential speeds in ∼500 nearby disk galaxies from MaNGA in SDSS-IV. Selected galaxies are kinematically axisymmetric. Velocity lags are asymmetric drift, seen in the Milky Way’s (MW) solar neighborhood and other Local Group galaxies; their amplitude correlates with stellar population age. The trend is qualitatively consistent in rate ($\dot{\sigma }$) with a simple power-law model where σ ∝ tb that explains the dynamical phase-space stratification in the solar neighborhood. The model is generalized based on disk dynamical times to other radii and other galaxies. We find in-plane radial stratification parameters σ0, r (dispersion of the youngest populations) in the range of 10-40 km s−1 and 0.2 < br < 0.5 for MaNGA galaxies. Overall br increases with galaxy mass, decreases with radius for galaxies above 10.4 dex (M⊙) in stellar mass, but is ∼constant with radius at lower mass. The measurement scatter indicates the stratification model is too simple to capture the complexity seen in the data, unsurprising given the many possible astrophysical processes that may lead to stellar population dynamical stratification. Nonetheless, the data show dynamical stratification is broadly present in the galaxy population, with systematic trends in mass and density. The amplitude of the asymmetric drift signal is larger for the MaNGA sample than the MW, and better represented in the mean by what is observed in the disks of M31 and M33. Either typical disks have higher surface-density or, more likely, are dynamically hotter (hence thicker) than the MW.

Assessing the Conservation Value of Artificial and Natural Reefs via Ichthyoplankton Spatio-Temporal Dynamics

Assessing the Conservation Value of Artificial and Natural Reefs via Ichthyoplankton Spatio-Temporal Dynamics

Towards document-level event extraction via Binary Contrastive Generation

In this study, we explored the complexities of document-level event extraction, a process that involves identifying multiple events and their associated arguments within a document. The primary challenges include (1) the distribution of event arguments across numerous sentences, resulting in long-distance dependencies, and (2) the complex relationships between multiple events due to the overlapping and dispersion of event arguments throughout the document. To address these issues, we propose the Binary Contrastive Generation (BCG) method. BCG utilizes binary auto-regressive generation in both the original and reversed sequences to learn binary-directed interdependency, thereby capturing the long-distance dependency of dispersed event arguments. To handle intricate multi-event relationships, BCG enhances the global semantic representation of multiple events by extraction-oriented contrastive learning. Specifically, event representations derived from identical event arguments in varying sequences are deemed positive pairs, while those from different event arguments in the same sequence are classified as negative pairs. Experimental results on three public datasets demonstrate that BCG outperforms existing methods, achieving an increase of 2.6 in absolute F1 score. Further analysis revealed that BCG effectively models the dependency of dispersed event arguments and enhances the semantic representation of multiple events.

Primer registro del coral copo de nieve, Carijoa riisei (Cnidaria: Anthozoa: Octocorallia) en una laguna costera del Pacífico sur de México

A small colony of the snowflake coral, Carijoa riisei, was collected from Corralero Lagoon in June 2015. This species is native to the Indo-West Pacific and, as invasive species, spread into Tropical Western Atlantic, Hawaii, Western Africa and Tropical Eastern Pacific. This record suggests that the invasion of C. riisei in the Mexican Pacific could be earlier than inferred and by means other than biofou-ling or ballast water, as Corralero Lagoon at least 190 km away from any port. Monitoring is recommended in the reefs, coastal lagoons, ports and marinas of the Mexican Pacific to evaluate the dispersion of this inva-sive species, in addition to proposing mitigation and management measures.

Non-invasive surveillance of shared pathogens in the Eurasian brown bear (Ursus arctos) human interface

Multi-host communities are perfect scenarios for the emergence and spread of pathogens, threatening the recovery of endangered, isolated, or inbred populations, such as the brown bear (Ursus arctos) in northwestern Spain. The population recovery in recent years has forced bears to occupy highly anthropized areas, increasing their interaction with human and domestic animals, with potential consequences for global health. During 2022–2023 a survey of parasites, bacteria and viruses shared between wildlife, domestic animals and humans was performed in this population using non-invasive surveillance, i.e., bear fecal samples (n = 73) and sponge-based sampling of trees (n = 42; 14 rubbed trees and 28 control trees). Pathogen detection rates were defined as the percentage of qPCR or culture-positive samples. Generalized linear models were fitted to assess their relationship with environmental variables including dispersion of the human population, and percentage of agricultural and periurban habitats in a 6 km-buffer around each sample. Canine Adenovirus type 1 (45.2%), Giardia spp. (15.1%), Salmonella spp. (12.3%), and extended-spectrum-beta-lactamases (ESBL) Escherichia coli (1.4%) were identified in fecal samples. In contrast, only five sponges from three rubbed and two control trees resulted positive to E. coli (14.3%). The results suggest that several pathogens are common in the Cantabrian brown bear population and that anthropization of the territory modulates their prevalence and richness.The effective design of management programs for bear conservation will require a one-health approach, in which genetic analysis of non-invasive samples can be key tools for the sanitary surveillance at the wildlife-livestock-human interface.

Plant dispersal in the Devonian world (c. 419–359 Ma)

AbstractDispersal, whether active or passive, plays a crucial role in biogeography by facilitating the movement of propagules away from their original location. Botanical geographical zonation, resulting from the co‐evolution of plants and their environment, has been established since the remarkable plant diversification during the Devonian Period (c. 419–359 Ma). However, a significant knowledge gap exists in understanding plant dispersal between living and fossil organisms due to the rarity of opportunities for tracing plant dispersal in geological history. In this study, we present evidence of two plant dispersal routes and verify their occurrence through the examination of geographical zonation, changes in plant diversity, and latitudinal and longitudinal gradients during the Devonian. We analyse global occurrence data from widely‐distributed and extensively‐studied Devonian plants. The two dispersal routes, namely clockwise and anticlockwise, connect the South China and Euramerica–Siberia realms. These routes clearly demonstrate inland and inter‐land dispersal models, closely linked to Devonian sea–land topography and dispersal vectors such as wind and ocean currents. Moreover, these models probably apply to all Devonian plants. Our comprehensive synthesis of plant dispersal in deep time reveals that propagule diversity and dispersal vectors have progressively increased and become more complex over time, facilitating plant colonization and diversity changes. Importantly, our study unveils the dispersal models of fossil plants, demonstrating the equivalent models observed in extant plants that have been established since the Devonian Period.

Deactivation of nickel/biochar catalyst through metal-volatiles interaction in pyrolysis of poplar sawdust loaded with nickel salt

Metal/biochar is an important category of catalyst that can be prepared via direct impregnation of metal salt to a biomass feedstock. However, during pyrolysis of metal salt@biomass for catalyst preparation, metal-volatiles interaction might affect exposure or dispersion of metal species. To verify this, loading of nickel acetate to poplar sawdust directly and to the sawdust-derived biochar was conducted to prepare Ni/biochar and biochar/Ni at 500 or 750 °C, aiming to understand the effect of metal-volatiles interaction on exposure of nickel species in resulting Ni/biochar. The results indicated Ni species catalyzed cracking, dehydrogenation, and reforming reactions in sawdust pyrolysis, producing more bio-oil/gases at the expense of biochar and also making biochar of higher aromatic degree with improved thermal stability. The in-situ IR characterizations also evidenced high activity of Ni towards dehydration and cracking of carbonyls for enhancing aromatization of biochar. In biochar/Ni catalysts prepared via loading nickel to biochar, little metal-volatiles interaction existed and nickel species weakly interacted with the biochar, resulting in remarkable migration and agglomeration of nickel, forming nickel size of 2–3 times larger than that in Ni/biochar. However, biochar/Ni possessed higher capability for adsorption/activation of H2, thus exhibiting superior catalytic activity than Ni/biochar for hydrogenation of phenolics.

Spatial distribution of benthic taxonomic and functional diversity in the Yellow River Basin: From ecological processes to associated determinant factors

One of the fundamental objectives in ecology is to investigate the ecological processes and associated factors governing the abundance and spatial distribution patterns of biodiversity. However, the reaction of biological communities to environmental degradation remains relatively unknown, even for ecologically crucial communities like macroinvertebrates in aquatic ecosystems. Here, we sampled 117 locations to quantify relative contributions of geographical and environmental factors, including water quality, land use, climate, and hydrological factors, to determine the absolute and relative compositions of macroinvertebrate communities and their spatial distribution in the Yellow River Basin (YRB), the sixth-longest river system on Earth. We assessed relative roles of species sorting and dispersal in determining macroinvertebrate community structure along YRB. Our results demonstrated that alpha and beta diversity indices showed an increase from the up- to low-reaches of YRB. The middle and low-reaches exhibited elevated species diversity and both regions exhibited relatively stable community compositions. The biodiversity of macroinvertebrates was influenced by a combination of geographical factors and environmental variables, with environmental factors predominantly serving as the principal determinants. Results of multiple linear regression and variance decomposition showed that the effect of environmental factors was approximately three times greater than that of spatial factors. These findings provide support for the hypothesis that species sorting, driven by environmental gradients, plays a significant role in shaping the community structure of macroinvertebrates in running water ecosystems at the basin scales. Moreover, the factors contributing to substantial shifts in biodiversity across different segments of YRB indicate that distinct river sections have been influenced by varying stressors, with downstream areas being more susceptible to the impacts of water pollution and urbanization resulting from human activities.

Unique role of silica in MOF-Derived High-Loading Palladium-on-Ceria single atom catalysts with excellent efficiency and durability

In most cases, the sintering tendency of supported metal single atoms could be attributed to the unstable structural characteristics of supports in demanding operating conditions, particularly for high-loading single-atom catalysts (SACs), ultimately resulting in deactivation. To address this issue, SiO2 is employed to enhance the structural stability of both supports and the supported Pd single atoms. SiO2 serves not only to prevent the collapse of support structures but also to promote the activation of surface oxygen species by facilitating electron transfer with the supports. This, in turn, establishes strong metal-support interactions (MSIs) to stabilize and activate atomically dispersed Pd species. Additionally, the electrons donated from Ce-O and Si-O to Pd atoms further catalyze the formation of oxygen vacancies, ultimately leading to significantly improved activity and durability in CO oxidation. Without SiO2, the instability of support structure, coupled with the weak MSIs, promotes the aggregation of Pd atoms, resulting in relatively lower catalytic activity and durability.

Enhanced Sulfur-resistance in Fe-based catalysts with secondary crystallization growth for the removal of odorous S-VOCs (CH3SH)

Sulfur poisoning is a major challenge in the design of high-performance heterogeneous catalysts. In this study, an effective sulfur-resistant catalyst for the catalytic decomposition of CH3SH was prepared by a secondary crystallization method. Compared with the conventional impregnation method, this method can effectively regulate the position of iron on the S-1 support and the property of the acidic site. The strong redox properties, strong acidity and highly dispersed iron species on the modified 2.5% Fe@S-1 catalyst contributed to the improvement of the low-temperature activity of the catalytic decomposition of CH3SH, and increased the sulfur- and coke-resistant properties of the catalyst. As expected, the 2.5% Fe@S-1 catalyst maintained 90% CH3SH conversion within 80h of TOS. By contrast, Fe particles in 2.5% Fe/S-1 catalysts was large and prone to agglomeration, resulting in poor catalyst stability. It was shown that Fe-based catalysts prepared by the secondary crystallization method have potential applications in CH3SH degradation.