DNA damage in barn swallows (Hirundo rustica) from the Chernobyl region detected by use of the comet assay

We investigated levels of DNA damage in blood cells of barn swallows (Hirundo rustica) inhabiting the Chernobyl region to evaluate whether chronic exposure to low-level radioactive contamination continues to induce genetic damage in free-living populations of animals. Blood samples were obtained from barn swallows collected at sites with different background levels of radiation, including a relatively uncontaminated area. The extent of DNA damage was evaluated using the alkaline (pH = 12.1) comet assay, a robust and sensitive electrophoresis-based technique widely employed in research ranging from biomonitoring to clinical studies. We found that levels of DNA damage, as indexed by the extent of DNA migration, were increased in barn swallows living in areas surrounding Chernobyl when compared to swallows sampled at low-level sites. The results we obtained are consistent with previous findings on this same species, which showed that swallows breeding in areas heavily contaminated with radionuclides have increased mutation rates, higher oxidative stress and incidence of morphological aberrations and tumors. Overall, these results indicate that chronic exposure to radioactive contaminants, even 20 years after the accident at the Chernobyl nuclear power plant, continues to induce DNA damage in cells of free-living animals.     

Carotenoids, sexual signals and immune function in barn swallows from Chernobyl.

Carotenoids have been hypothesized to facilitate immune function and act as free-radical scavengers, thereby minimizing the frequency of mutations. Populations of animals exposed to higher levels of free radicals are thus expected to demonstrate reduced sexual coloration if use of carotenoids for free-radical scavenging is traded against use for sexual signals. The intensity of carotenoid-based sexual coloration was compared among three populations of barn swallows Hirundo rustica differing in exposure to radioactive contamination. Lymphocyte and immunoglobulin concentrations were depressed, whereas the heterophil:lymphocyte ratio, an index of stress, was enhanced in Chernobyl swallows compared to controls. Spleen size was reduced in Chernobyl compared to that of two control populations. Sexual coloration varied significantly among populations, with the size of a secondary sexual character (the length of the outermost tail feathers) being positively related to coloration in the two control populations, but not in the Chernobyl population. Thus the positive covariation between coloration and sexual signalling disappeared in the population subject to intense radioactive contamination. These findings suggest that the reliable signalling function of secondary sexual characters breaks down under extreme environmental conditions, no longer providing reliable information about the health status of males.     

Increased oxidative stress in barn swallows from the Chernobyl region

The Chernobyl nuclear accident produced the largest unintended release of radionuclides in history, with dramatic consequences for humans and other organisms. Exposure to ionizing radiation is known to reduce circulating and stored levels of specific antioxidants in birds and humans, thus potentially increasing oxidative stress. However, overall effects of radioactive exposure on oxidative status have never been investigated in any free ranging vertebrate. We measured plasma antioxidant capacity and concentration of reactive oxygen metabolites in adult barn swallows (Hirundo rustica) from colonies with variable background radiation levels in the Chernobyl region in Ukraine and Belarus. We predicted that antioxidants would decrease while reactive oxygen metabolites would increase with exposure to increasing levels of radiation at the breeding sites. Consistent with this expectation, radiation level positively predicted plasma concentration of reactive oxygen metabolites, whereas no significant covariation was found with non-enzymatic plasma antioxidant capacity. An index of oxidative stress was also larger in barn swallows exposed to high contamination levels. Thus, radioactive contamination appeared to be responsible for the increased generation of reactive oxygen metabolites and the imbalance between reactive oxygen metabolites and non-enzymatic plasma antioxidant capacity.     

Impaired swimming behaviour and morphology of sperm from barn swallows Hirundo rustica in Chernobyl

We investigated the motility and morphology of live sperm from barn swallows Hirundo rustica breeding in radioactively contaminated areas around Chernobyl and control areas in Ukraine in order to test the hypothesis that swimming behaviour and morphology of sperm was impaired by radioactive contamination. We obtained sperm samples from 98% of sampled birds, thus avoiding sampling bias due to the fraction of males not producing sperm samples. Analyses of within- and between-sample repeatability revealed significant and intermediate to large estimates for all sperm parameters. There were significant differences between the Chernobyl area and the control area for two of 11 sperm behaviour parameters, and significant interactions between area and year for six of these parameters. The proportion of sperm with abnormal morphology was elevated in barn swallows from Chernobyl. A principal component (PC) analysis revealed four significant axes that explained 88% of the variance in sperm behaviour parameters. One of these principal components differed between areas, and three components showed significant year by area interactions. PC2 representing the frequency of slow sperm increased with increasing radiation in one year, but not another. PC3 representing sperm with high linearity, small amplitude of lateral head displacement and low track velocity decreased with increasing background radiation level. PC4 reflecting a large proportion of static sperm with high beat cross frequency increased with increasing background radiation level. Sperm behaviour as reflected by principal components was predictable among years from information on level of radiation, and it was predictable among sites in different years. These results are consistent with the hypothesis that sperm behaviour and morphology have been affected by radiation due to the Chernobyl accident.     

Impaired swimming behaviour and morphology of sperm from barn swallows Hirundo rustica in Chernobyl

We investigated the motility and morphology of live sperm from barn swallows Hirundo rustica breeding in radioactively contaminated areas around Chernobyl and control areas in Ukraine in order to test the hypothesis that swimming behaviour and morphology of sperm was impaired by radioactive contamination. We obtained sperm samples from 98% of sampled birds, thus avoiding sampling bias due to the fraction of males not producing sperm samples. Analyses of within- and between-sample repeatability revealed significant and intermediate to large estimates for all sperm parameters. There were significant differences between the Chernobyl area and the control area for two of 11 sperm behaviour parameters, and significant interactions between area and year for six of these parameters. The proportion of sperm with abnormal morphology was elevated in barn swallows from Chernobyl. A principal component (PC) analysis revealed four significant axes that explained 88% of the variance in sperm behaviour parameters. One of these principal components differed between areas, and three components showed significant year by area interactions. PC2 representing the frequency of slow sperm increased with increasing radiation in one year, but not another. PC3 representing sperm with high linearity, small amplitude of lateral head displacement and low track velocity decreased with increasing background radiation level. PC4 reflecting a large proportion of static sperm with high beat cross frequency increased with increasing background radiation level. Sperm behaviour as reflected by principal components was predictable among years from information on level of radiation, and it was predictable among sites in different years. These results are consistent with the hypothesis that sperm behaviour and morphology have been affected by radiation due to the Chernobyl accident.     

Sexual selection in the barn swallow Hirundo rustica. VI. Aerodynamic adaptations

Secondary sexual characters are assumed to be costly to produce and maintain, and this will select for morphological modifications that reduce the magnitude of such costs. Here we test whether a feather ornament, the sexually exaggerated outermost tail feathers of male barn swallows Hirundo rustica, a trait currently subject to a directional female mate preference, and other aspects of the morphology used for flight have been modified to increase aerodynamic performance. This was done by making comparisons among sexes within populations, among individuals varying in tail length within populations, and among populations from different parts of Europe. Male barn swallows experienced reduced drag from their elongated tail feathers by morphological modifications of the ornamental feathers as compared to females. Morphological features of the outermost tail feathers were unrelated to tail length in both males and females within populations. Wing and tail morphology (length of central tail feathers and wings, wing span, wing area, wing loading, and aspect ratio) was modified in males compared to females. Barn swallows with long tails had morphological tail and wing modifications that reduced the cost of a large ornament, and similar modifications were seen among populations. The costs of the exaggerated secondary sexual character were therefore reduced by the presence of cost-reducing morphological modifications. The assumptions of reliable signalling theory, that signals should be costly, but more so to low than to high quality individuals, were not violated because long-tailed male barn swallows had the largest cost-reducing morphological characters.     

Microorganisms Associated with Feathers of Barn Swallows in Radioactively Contaminated Areas Around Chernobyl

The Chernobyl catastrophe provides a rare opportunity to study the ecological and evolutionary consequences of low-level, environmental radiation on living organisms. Despite some recent studies about negative effects of environmental radiation on macroorganisms, there is little knowledge about the effect of radioactive contamination on diversity and abundance of microorganisms. We examined abundance patterns of total cultivable bacteria and fungi and the abundance of feather-degrading bacterial subset present on feathers of barn swallows (Hirundo rustica), a colonial migratory passerine, around Chernobyl in relation to levels of ground level environmental radiation. After controlling for confounding variables, total cultivable bacterial loads were negatively correlated with environmental radioactivity, whereas abundance of fungi and feather-degrading bacteria was not significantly related to contamination levels. Abundance of both total and feather-degrading bacteria increased with barn swallow colony size, showing a potential cost of sociality. Males had lower abundance of feather-degrading bacteria than females. Our results show the detrimental effects of low-level environmental radiation on total cultivable bacterial assemblage on feathers, while the abundance of other microorganism groups living on barn swallow feathers, such as feather-degrading bacteria, are shaped by other factors like host sociality or host sex. These data lead us to conclude that the ecological effects of Chernobyl may be more general than previously assumed and may have long-term implications for host–microbe interactions and overall ecosystem functioning.     

Searching for potential wintering and migration areas of a Danish Barn Swallow population in South Africa by correlating NDVI with survival estimates

On the basis of correlation analyses between annual Normalised Difference Vegetation Index (NDVI) values in Africa and the annual survival rate estimated for a breeding population of barn swallows Hirundo rustica from Denmark, we identified potential wintering and migration areas in South Africa during December–February and March–May, when barn swallows commonly occur in South Africa. During December–February we identified potential wintering areas only in the western part of South Africa, in the Karoo. Potential areas in the central and eastern parts of the country were only identified during March–May. NDVI values in the Karoo during March–May explained most of the variance in annual adult survival rate of the population. The high ratio of European ringed barn swallows among controlled individuals in the Karoo was similar to the ratio that would be expected based on the number of ringed barn swallows and the population sizes of barn swallows in north-western European breeding populations. The level of this ratio in the Karoo was higher than in any other locality in the central and eastern parts of South Africa and Botswana, indicating that ringed birds from the eastern flyway are absent to a much smaller extent than ringed birds from the western flyway. This approach shows that the NDVI and survival method can focus ringing efforts to regions and areas that are likely to harbour specific breeding populations, thereby helping to identify potential wintering and migration areas for breeding populations of migratory birds.     

6-Thioguanine-resistant T-lymphocyte autoradiographic assay. Determination of variation frequencies in individuals suspected of radiation exposure

We used the autoradiographic assay to assess human in vivo somatic cell gene mutation at the hypoxanthine guanine phosphoribosyl transferase (HGPRT) locus in T-lymphocytes. Cells able to incorporate tritiated thymidine in vitro in the presence of 6-thioguanine were enumerated in order to determine 6-thioguanine-resistance (TGr) variant frequencies in cryopreserved lymphocytes from 17 normal control individuals, from 3 persons suspected to have been exposed to 60Co in an accident in Cd. Juárez (Mexico), studied 24 months after the accident, and from 4 individuals who were in Kiev during the radiation accident in Chernobyl (U.S.S.R.); 2 of them were studied 1 month after the accident, and again 1 year after the first sampling, the other 2 were studied 13 months after the accident. The data obtained indicate that this assay may be useful in any laboratory of cytogenetics for human population monitoring and that its use following accidental exposure to ionizing radiation should be further evaluated.     

Genetic monitoring of natural Drosophila populations in radiation contaminated regions of Belarus

Genetic monitoring of natural Drosophila melanogaster populations inhabiting regions of Belarus with different radiation background (Vetka and Svetilovichi villages), radonuclide-contaminated after the Chernobyl accident, compared with populations from the Berezinsky biosphere reserve (the control area) were conducted. The dominant and recessive lethal mutation levels and genetic structure of the populations were analyzed for frequencies of F- and S-alleles of Adh (alcohol dehydrogenase) of Gpdh (glycerinophosphate dehydrogenase) and Sod (superoxide dismutase) loci. Populations inhabiting the regions with high radiation background exhibited higher frequency of lethal mutations and higher heterozygosity than those from the control area. Moreover, higher frequency of polymorphous Sod locus S-allele was detected in these populations. Apparently, Sod S-alleles are more adaptively valuable under conditions of high radiation background, because as is known, superoxide dismutase is an effective radioprotector at all levels molecular, cellular and organism. Adaptation of populations to stress impacts was analyzed, since 1998. Nonspecific adaptation of natural Drosophila melanogaster populations from Vetka and Svetilovichi villages of Gomel region was reveled. They are higher adapted than the control population from the Berezinsky biosphere reserve to both ionizing radiation effect and to chemical mutagen EMS. After laboratory cultivation within 6-8 generations without irradiation adaptation to radiation in the population from radiocontaminated regions remained. The content of samples from the control natural drosophila population in the laboratory conditions is an environmental stress that led to the formation of nonspecific adaptation within 6-8 generations to unfavorable factors, including ionizing radiation. It should be taken into account that the population adaptation is formed via death of sensitive genotypes at various ontogenesis stages.     

Morphological abnormalities among the offspring of irradiated pines (pinus sylvestris L.) from chernobyl populations

The significant changes of the quantitative signs and the increase in the frequency of morphological abnormalities were found among the offspring of pines (Pinus sylvestris L.) exposed as a result of the Chernobyl accident. We have detected that the typical effects of radiation exposure (stimulation, inhibition, abnormalities of morphogenesis) are transmitted to the offspring of irradiated pine trees. The mechanisms of their occurrence are discussed.     

Trends in infant leukaemia in West Germany in relation to in utero exposure due to the Chernobyl accident

A temporary increase in the incidence of infant leukaemia in Greece was reported by Petridou et al., which was attributed to in utero exposure to ionising radiation resulting from the Chernobyl accident. We performed a similar analysis based on the data of the German Childhood Cancer Registry in order to check whether the observation could be confirmed by means of independent data. Applying the same definitions as Petridou et al., we also observed an increased incidence of infant leukaemia in a cohort of children born after the Chernobyl accident. More detailed analyses, regarding areas with different contamination levels and dose rate gradients over time after the accident, showed, however, no clear trend with regard to exposure. It would therefore appear less likely that the observed effect was caused by exposure to ionising radiation due to the Chernobyl accident. Received: 30 January 1998 / Accepted in revised form: 23 April 1998     

A quantitative measure of migratory connectivity

The study of the extent of the connection between areas where populations of birds breed and areas where they winter has flourished in recent years mainly thanks to the development of new techniques, but also due to traditional ringing and recovery schemes, which allow tracking of individuals or populations linking wintering and breeding distributions. Currently, studies on migratory connectivity focus on retention of breeding population spatial structure on the non-breeding grounds and vice versa.Here we propose a method to quantify migratory connectivity based on Mantel correlation coefficients and to statistically test for deviations of the observed connectivity from a random mix of individuals. In addition, we propose a procedure, based on clustering algorithms, to identify whether observed connectivity depends on aggregation of individuals or on rigid transference of distribution patterns between areas.We applied this method to a large dataset of ringing recoveries of barn swallows (Hirundo rustica L) migrating from their Western Palearctic breeding areas to sub-Saharan winter quarters. We show that migration of barn swallow populations connects specific breeding and wintering areas, and that the “sub-populations” quantitatively identified by our method are consistent with qualitative patterns of migratory connectivity identified by studies of individual geographical populations based on other methods. Finally, we tested the performance of the method by running simulations under different scenarios. Such simulations showed that the method is robust and able to correctly detect migratory connectivity even with smaller datasets and when a strong geographical pattern is not present in the population. Our method provides a quantitative measure of migratory connectivity and allows for the identification of populations showing high connectivity between the breeding and wintering areas. This method is suitable for a generalized application to diverse animal taxa as well as to large scale analyses of connectivity for conservation purposes.     

Barn swallows before barns: population histories and intercontinental colonization

The barn swallow (Hirundo rustica) is one of most widely distributed swallows, owing in part to its recent switch from natural nest sites to human structures. We conducted phylogenetic analysis of mitochondrial (mt) and nuclear DNA to explore the recent evolutionary history of this species. Strongly supported mtDNA clades corresponded to Europe, Asia and North America plus the Baikal region of Asia. Analysis of sequence data from a sex-linked nuclear gene was unable to recover the phylogenetic splits in the mtDNA tree, confirming that the main clades evolved recently. The phylogenetic pattern suggests that the ancestral area of the barn swallow was the holarctic; most divergence events are consistent with vicariance. Most unexpectedly, analyses show that barn swallows from North America colonized the Baikal region in the recent past (one fixed substitution). This dispersal direction is opposite of that for most nearctic-palearctic taxon exchanges. Although this invasion was envisioned to coincide with the appearance of new types of human dwelling in the Baikal region, calibration of molecular divergence suggests an older dispersal event. A recent history of gene flow within the main palearctic clades is consistent with range and population expansion owing to new nesting opportunities provided by human settlements. Contrary to expectation, populations in North America appear historically larger and more stable than those in the palearctic. The Baikal population apparently has not increased greatly since colonization.     

Study on genetic radioresistance of natural Drosophila Melanogaster population from radionuclide contaminated regions of Byelarus

Over the period from 1998 to 2000 adaptation to unfavorable ecological factors was revealed to be formed in natural Drosophila melanogaster populations from various regions of Belarus with increased radiation background due to the Chernobyl accident. This adaptation was shown to be of non-specific character, since the populations from radiation regions were more resistant to the effect of not only factors of physical nature (irradiation), but also to that of chemical mutagen ethylmethanesulphonate. Assessment of population resistance was carried out by means of tests of dominant lethal mutations and recessive sex-linked lethal mutations.     

Chromosome alterations in cleanup workers sampled years after the Chernobyl accident

Cytogenetic analysis performed 4-13 years after the Chernobyl accident showed an elevated frequency of acentrics, chromatid exchanges, dicentrics and rings in Chernobyl cleanup workers compared to the control group. Cytogenetic data were analyzed according to the information on exposure to radiation (the year when the cleanup workers worked at the Chernobyl station, doses rates, time elapsed since exposure to radiation, and cytogenetic examination) and some lifestyle factors. The data obtained suggested that some types of chromosome aberrations could be influenced by the action of different environmental factors or lifestyle factors. The frequency of acentrics was correlated with the age of the cleanup workers, and the increased chromatid exchange frequency was attributed to smoking. The numbers of dicentrics and rings suggested a genotoxic effect of ionizing radiation that is still present over 13 years after the exposure.     

The effects of radiation on sperm swimming behavior depend on plasma oxidative status in the barn swallow (Hirundo rustica)

Sperm are highly susceptible to reactive oxygen species (ROS) that can damage sperm DNA and structure, resulting in reduced fertilizing capacity. Exposure to radioactive contamination can also impair sperm swimming behavior and fertilizing ability, both through a reduction of sperm DNA integrity and via an increased generation of reactive oxygen species (ROS). However, the relationship between individual oxidative status and sperm swimming behavior has never been investigated in any wild population of animals exposed to radioactive contamination. We studied the motility of sperm collected from barn swallows, Hirundo rustica, breeding under different levels of radioactive contamination following the Chernobyl accident in 1986, in relation to individual oxidative status. We tested the hypothesis that the degree of impairment of sperm swimming behavior by radioactive contamination depended on plasma antioxidant capacity, the level of reactive oxygen metabolites (ROMs) and oxidative stress (sensu Costantini et al. 2006), a better oxidative status being associated with higher sperm motility. Sperm behavior parameters were subjected to principal component (PC) analysis, which extracted four PCs explaining 86% of the variance in sperm motility. PC2, representing sperm with high track velocity and ample lateral head displacement, was significantly predicted by the interaction between radiation level and either oxidative damage or oxidative stress. Contrary to our predictions, the highest values of PC2 were associated with relatively high radiation levels, particularly for high levels of either ROMs or oxidative stress. In addition, there was a tendency for values of PC3 (representing the percent of motile sperm) and PC4 (representing slow sperm with high beat cross frequency) to depend on the interaction between radiation level and total plasma antioxidant protection. Our results confirm the importance of oxidative status in determining the genetic and physiological outcome of exposure to radioactive contamination, complementing previous studies relating sperm abnormality to circulating levels of specific antioxidants. Our results also complement previous evidence that oxidative damage of sperm was negatively related to sperm motility, thus indicating a possible trade-off in quenching pro-oxidant compounds in the plasma and the seminal fluid.     

A Continent-Wide Migratory Divide in North American Breeding Barn Swallows (Hirundo rustica)

Populations of most North American aerial insectivores have undergone steep population declines over the past 40 years but the relative importance of factors operating on breeding, wintering, or stopover sites remains unknown. We used archival light-level geolocators to track the phenology, movements and winter locations of barn swallows (Hirdundo rustica; n = 27) from populations across North America to determine their migratory connectivity. We identified an east-west continental migratory divide for barn swallows with birds from western regions (Washington State, USA (n = 8) and Saskatchewan, Canada (n = 5)) traveling shorter distances to wintering areas ranging from Oregon to northern Colombia than eastern populations (Ontario (n = 3) and New Brunswick (n = 10), Canada) which wintered in South America south of the Amazon basin. A single swallow from a stable population in Alabama shared a similar migration route to eastern barn swallows but wintered farther north in northeast Brazil indicating a potential leap frog pattern migratory among eastern birds. Six of 9 (67%) birds from the two eastern populations and Alabama underwent a loop migration west of fall migration routes including around the Gulf of Mexico travelling a mean of 2,224 km and 722 km longer on spring migration, respectively. Longer migration distances, including the requirement to cross the Caribbean Sea and Gulf of Mexico and subsequent shorter sedentary wintering periods, may exacerbate declines for populations breeding in northeastern North America.     

Effects of livestock farming on birds of rural areas in Europe

In the last decades, profound modifications of agricultural practices occurred in Europe, including the introduction of modern livestock farming. These modifications negatively affected the fauna of rural areas, as indicated by the large demographic declines suffered by several populations of birds typical of these habitats. The impact of agricultural practices on bird populations has been widely investigated, while the effect of livestock farming has seldom been assessed. To fill this gap, we carried out a quantitative meta-analysis of the existing scientific literature and evaluated the size of the effects of livestock farming on birds of rural areas in Europe. We only found 26 papers on this topic, from which 72 effect sizes could be estimated. The barn swallow (Hirundo rustica) was the species on which most studies focused. Livestock farming positively influenced presence and distribution of barn swallows in breeding habitats, while it did not significantly affect reproduction of this species. Effects on other bird species typical of rural habitats were non-significant. The positive effect on the insectivorous barn swallow might be mediated by the enhanced insect abundance where livestock is reared. In addition, habitat features typical of rural settings where livestock is reared (e.g. cattle-sheds or large hayfields) positively affected barn swallows independently of actual presence of livestock at a setting. Presence of livestock at rural setting therefore seems beneficial to barn swallows, but not significantly to other bird species typical of rural habitats. The effect of livestock farming on birds of rural habitats has been under-investigated to date.     

Latency in response of barn swallow Hirundo rustica populations to changes in breeding habitat conditions

Inclusion of past, in addition to current ecological conditions can improve the realism of animal‐habitat models, because populations may show delayed responses to changing environments. We studied the relationships between the distribution of barn swallows (Hirundo rustica L.) in 2001 and ecological factors between 1986 and 2001. Livestock farming was the best predictor of swallow distribution. Maximum predictive power of swallow abundance was achieved by livestock farming data 7 years before the census and significantly earlier than 2001, as shown by a bootstrap analysis. Breeding philopatry, social facilitation of breeding habitat choice may delay response of barn swallow populations to rapidly changing ecological conditions in anthropogenic habitats. By bootstrapping the set of farms and applying our predictive distribution models to livestock farming data in the past and those predicted for the near future we forecast no significant change in swallow populations until 2015. This study suggests that population studies should incorporate historical ecological data.