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.     

Plumage coloration, not length or symmetry of tail-streamers, is a sexually selected trait in North American barn swallows

Sexual adornments often vary markedly across a species' range,which presumably is owing to differences in local environmentalconditions and the associated selection pressures, such as naturalversus sexual selection or the relative signaling value of differentornamental traits. However, there are only a few reported examplesin which the information content of mating signals varies geographically,and even fewer in which a set of secondary sexual traits servesdifferent signaling functions in different populations. Classicstudies of sexual selection in the European barn swallow (Hirundorustica rustica) demonstrate that elongate tail-streamers provideseveral reproductive advantages to males and females and areused as reliable signals of mate quality. Here, we show thattail-streamers do not appear to confer these same benefits ina population of barn swallows from North America (Hirundo rusticaerythrogaster). Instead, ventral plumage coloration, which ismore exaggerated in North American swallows compared with theirEuropean counterparts, predicts patterns of assortative matingand annual reproductive success in H. r. erythrogaster. Theseobservations support the idea that ornamental traits can servedifferent functions among animal populations and suggest thatgeographic variation in different sexual signals may facilitatepopulation divergence, which may ultimately lead to speciation.     

Elevated frequency of abnormalities in barn swallows from Chernobyl

Ever since the Chernobyl accident in 1986, that contaminated vast areas in surrounding countries with radiation, abnormalities and birth defects have been reported in human populations. Recently, several studies suggested that the elevated frequency of such abnormalities can be attributed to poverty and stress in affected human populations. Here, we present long-term results for a free-living population of barn swallows, Hirundo rustica, demonstrating the presence of 11 morphological abnormalities in populations around Chernobyl, but much less frequently in an uncontaminated Ukrainian control population and three more distant control populations. The presence of these abnormalities in barn swallows is associated with reduced viability. These findings demonstrate a link between morphological abnormalities and radiation in an animal population that cannot be attributed to poverty and stress. The most parsimonious hypothesis for abnormalities in animal and human populations alike is that the effects are caused by the same underlying cause, viz. radiation derived from the Chernobyl accident.     

Proximate mechanisms of variation in the carotenoid-based plumage coloration of nestling great tits (Parus major L.)

Many vertebrates use carotenoid-based signals in social or sexual interactions. Honest signalling via carotenoids implies some limitation of carotenoid-based colour expression among phenotypes in the wild, and at least five limiting proximate mechanisms have been hypothesized. Limitation may arise by carotenoid-availability, genetic constraints, body condition, parasites, or detrimental effects of carotenoids. An understanding of the relative importance of the five mechanisms is relevant in the context of natural and sexual selection acting on signal evolution. In an experimental field study with carotenoid supplementation, simultaneous cross-fostering, manipulation of brood size and ectoparasite load, we investigated the relative importance of these mechanisms for the variation in carotenoid-based coloration of nestling great tits (Parus major). Carotenoid-based plumage coloration was significantly related to genetic origin of nestlings, and was enhanced both in carotenoid-supplemented nestlings, and nestlings raised in reduced broods. We found a tendency for ectoparasite-induced limitation of colour expression and no evidence for detrimental effects of carotenoids on growth pattern, mortality and recruitment of nestlings to the local breeding population. Thus, three of the five proposed mechanisms can generate individual variation in the expression of carotenoid-based plumage coloration in the wild and thus could maintain honesty in a trait potentially used for signalling of individual quality.     

Rapid divergence of social signal coloration across the White Sands ecotone for three lizard species under strong natural selection

Animal social signals are important for population recognition, communication, and mate choice. Although natural selection often favours cryptic coloration, sexual selection can underlie patterns of coloration that function in inter- or intrasexual communication. We compared social signal coloration of three lizard species across a substrate colour ecotone in New Mexico. These species exhibit cryptic blanched dorsal coloration on the gypsum dunes of White Sands and dark coloration on the surrounding desert soils. We detected corresponding population divergence in colour used for intra- ( Aspidoscelis inornata , Sceloporus undulatus ) or inter- ( Holbrookia maculata ) sexual signalling. Although the magnitude and direction of change in coloration varied among taxa, differences in hue and chroma accounted for more variation in social coloration than for dorsal coloration. The relative conspicuousness of social signals also varied across the ecotone. We discuss the possibilities that divergent signalling colours in this system are the result of: (1) stochastic processes, (2) direct selection, and/or (3) a correlated response to natural selection on dorsal coloration.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 98 , 243–255.     

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.     

Genome‐wide differentiation in closely related populations: the roles of selection and geographic isolation

Population divergence in geographic isolation is due to a combination of factors. Natural and sexual selection may be important in shaping patterns of population differentiation, a pattern referred to as ‘isolation by adaptation’ (IBA). IBA can be complementary to the well‐known pattern of ‘isolation by distance’ (IBD), in which the divergence of closely related populations (via any evolutionary process) is associated with geographic isolation. The barn swallow Hirundo rustica complex comprises six closely related subspecies, where divergent sexual selection is associated with phenotypic differentiation among allopatric populations. To investigate the relative contributions of selection and geographic distance to genome‐wide differentiation, we compared genotypic and phenotypic variation from 350 barn swallows sampled across eight populations (28 pairwise comparisons) from four different subspecies. We report a draft whole‐genome sequence for H. rustica, to which we aligned a set of 9493 single nucleotide polymorphisms (SNPs). Using statistical approaches to control for spatial autocorrelation of phenotypic variables and geographic distance, we find that divergence in traits related to migratory behaviour and sexual signalling, as well as geographic distance, together explain over 70% of genome‐wide divergence among populations. Controlling for IBD, we find 42% of genomewide divergence is attributable to IBA through pairwise differences in traits related to migratory behaviour and sexual signalling alone. By (i) combining these results with prior studies of how selection shapes morphological differentiation and (ii) accounting for spatial autocorrelation, we infer that morphological adaptation plays a large role in shaping population‐level differentiation in this group of closely related populations.     

Geographic variation in sexual selection among populations of an iguanid lizard,Sauromalus obesus (=ater)

Abstract.— Geographic variation in selection pressures may result in population divergence and speciation, especially if sexual selection varies among populations. Yet spatial variation in targets and intensity of sexual selection is well studied in only a few species. Even more rare are simultaneous studies of multiple populations combining observations from natural settings with controlled behavioral experiments. We investigated how sexual selection varies among populations of the chuckwalla, Sauromalus obesus. Chuckwallas are sexually dimorphic in color, and males vary in coloration among populations. Using field observations and multiple regression techniques, we investigated how sexual selection acts on various male traits in three populations in which males differed in coloration. The influence of sexual selection on male coloration was then investigated in more detail using controlled experiments. Results from field observations indicate that phenotypic selection was acting on territory quality in all three populations. In two populations, selection was also acting either directly or indirectly on male coloration. Male color likely functions as an indicator of food resources to females because male color is based partly on carotenoid pigments. In controlled experiments, significantly more females from these two populations chose males with brighter colors over dull males, a result consistent with studies on carotenoid pigments in other taxa. In a third population, no evidence of sexual selection on male coloration was found in either the field study or controlled experiment. Lack of female preferences for male color in this population, in which chuckwalla densities are low and home ranges are large, may result from searching costs to females.     

Heritability of male secondary sexual traits in feral guppies in Japan

Secondary sexual traits of male guppies show remarkable geographic variation, and male guppies can flexibly change the conspicuousness of their sexual traits within a few generations when they are introduced into new habitats. We examined the degree of conspicuousness and heritabilities of male secondary sexual traits in a feral guppy population in Okinawa, a subtropical island of Japan. Male guppies in this population showed high variation of their sexual traits such as dorsal and caudal fin lengths and red-orange color spot patterns on their bodies. Offspring–parent regressions revealed significant heritabilities of male body size, dorsal and caudal fin lengths, and the number and relative area of orange spots. Especially, the high heritability of the relative orange spot area of sons compared to that of fathers suggests some Y chromosome-linked contribution of the trait. On the other hand, coloration (hue and saturation) of orange spots did not show significant inheritance, probably because most components of orange spot coloration may be condition-dependent traits. These results compared with previous work in native guppy populations suggest female mate preferences based upon these male secondary sexual traits and low predation pressure in this population. Received: June 19, 2000 / Accepted: September 18, 2000     

Sexual Dimorphism and Population Differences in Structural Properties of Barn Swallow (Hirundo rustica) Wing and Tail Feathers

Sexual selection and aerodynamic forces affecting structural properties of the flight feathers of birds are poorly understood. Here, we compared the structural features of the innermost primary wing feather (P1) and the sexually dimorphic outermost (Ta6) and monomorphic second outermost (Ta5) tail feathers of barn swallows (Hirundo rustica) from a Romanian population to investigate how sexual selection and resistance to aerodynamic forces affect structural differences among these feathers. Furthermore, we compared structural properties of Ta6 of barn swallows from six European populations. Finally, we determined the relationship between feather growth bars width (GBW) and the structural properties of tail feathers. The structure of P1 indicates strong resistance against aerodynamic forces, while the narrow rachis, low vane density and low bending stiffness of tail feathers suggest reduced resistance against airflow. The highly elongated Ta6 is characterized by structural modifications such as large rachis width and increased barbule density in relation to the less elongated Ta5, which can be explained by increased length and/or high aerodynamic forces acting at the leading tail edge. However, these changes in Ta6 structure do not allow for full compensation of elongation, as reflected by the reduced bending stiffness of Ta6. Ta6 elongation in males resulted in feathers with reduced resistance, as shown by the low barb density and reduced bending stiffness compared to females. The inconsistency in sexual dimorphism and in change in quality traits of Ta6 among six European populations shows that multiple factors may contribute to shaping population differences. In general, the difference in quality traits between tail feathers cannot be explained by the GBW of feathers. Our results show that the material and structural properties of wing and tail feathers of barn swallows change as a result of aerodynamic forces and sexual selection, although the result of these changes can be contrasting.     

Haemosporidian parasites depress breeding success and plumage coloration in female barn swallows Hirundo rustica

Parasites are major effectors of natural selection and also play a role in sexual selection processes. Haemosporidian blood parasites are common in vertebrates and have been shown to vary in their effects depending on both the parasite and host species, on the host trait investigated as well as on host condition and stage of infection. Here we investigated infection of adult barn swallows Hirundo rustica by Plasmodium, Leucocytozoon and Haemoproteus species during the chronic stage of infection and the consequences for host fitness traits. Prevalence was higher than 10% only for Plasmodium. Chronic stage infection by Plasmodium was associated with reduced female breeding success, but did not affect breeding dates. Infection did not affect the expression of male secondary sexual traits (tail length and melanin‐based plumage coloration), but was associated with paler coloration of females. Finally, we found a negative effect of infection by Plasmodium on feather growth rate in older but not in yearling individuals. Because feathers are moulted during wintering in sub‐Saharan Africa where infection of barn swallows by Plasmodium occurs, our results suggest that male secondary sexual traits have little potential to reveal acute‐stage infection whereas plumage coloration of females may advertise their infection status. In addition, these results suggest that infection by Plasmodium can influence the course of plumage moult. Thus, our results add to the observations of negative effects of haemosporidian infection on fitness traits in birds and provides evidence that these effects can vary among traits and in relation to age and sex.     

Gape coloration reliably reflects immunocompetence of barn swallow (Hirundo rustica) nestlings

In some passerines, parents allocate more food to offspringwith the brightest red gapes, but the function of parental decisionsbased on offspring gape coloration is unknown. We hypothesizethat gape coloration is part of a communication system wherenestlings reveal their condition to attending parents, whichmay thus base their decisions on reliable signals of offspringreproductive value. We analyze the effects of brood size manipulation,injection with an immunogen and food deprivation, on gape coloration,morphology, and T-cell–mediated immunocompetence of nestlingbarn swallows (Hirundo rustica). For each gape we measured threecomponents of coloration (hue, saturation, and brightness) andobtained an overall color score by principal component analysis.Enlargement of brood size and injection with an antigen resultedin less red and less saturated and brighter gape color. Nestlingsin enlarged broods had smaller body mass and T-cell–mediatedimmunocompetence compared to those in reduced broods. A positivecovariation existed between redness and saturation of gape colorand T-cell–mediated immunocompetence. Gape color siblingsraised in different nests did not depend on parentage. Thus,condition-dependent gape coloration can reveal different componentsof nestling state on which parents may base their adaptive decisionsabout allocation of care to the offspring.     

Selection on multiple sexual signals in two Central and Eastern European populations of the barn swallow

Variation in intensity and targets of sexual selection on multiple traits has been suggested to play a major role in promoting phenotypic differentiation between populations, although the divergence in selection may depend on year, local conditions or age. In this study, we quantified sexual selection for two putative sexual signals across two Central and East European barn swallow (Hirundo rustica rustica) populations from Czech Republic and Romania over multiple years. We then related these differences in selection to variation in sexual characters among barn swallow populations. Our results show that tail length and ventral coloration vary between populations, sexes, and age classes (first‐time breeders vs. experienced birds). We found that selection on tail length was stronger in first‐time breeders than in experienced birds and in males than in females in the Romanian population, while these differences between age groups and sexes were weak in Czech birds. We suggest that the populational difference in selection on tail length might be related to the differences in breeding conditions. Our results show that ventral coloration is darker (i.e., has lower brightness) in the Romanian than in the Czech population, and in experienced birds and males compared with first‐time breeders and females, respectively. The sexual difference in ventral coloration may suggest sexual selection on this trait, which is supported by the significant directional selection of ventral coloration in first‐time breeding males on laying date. However, after controlling for the confounding effect of wing length and tarsus length, the partial directional selection gradient on this trait turned nonsignificant, suggesting that the advantage of dark ventral coloration in early breeding birds is determined by the correlated traits of body size. These findings show that ventral coloration may be advantageous over the breeding season, but the underlying mechanism of this relationship is not clarified.     

ALBINISM AND PHENOTYPE OF BARN SWALLOWS (HIRUNDO RUSTICA) FROM CHERNOBYL

Abstract The effects of mutation on phenotypic expression are supposed to be mainly deleterious because mutations disrupt the expression of genes that function relatively well under current environmental conditions. Thus, mutations are assumed to give rise to deviant phenotypes that are generally selected against. Radioactive contamination in the Chernobyl region of Ukraine is associated with a significant increase by a factor two to 10 in mutation rate in microsatellite markers of the barn swallow, Hirundo rustica. Barn swallows from Chernobyl had a temporally constant, elevated frequency of partial albinism compared to the situation before radioactive contamination and compared to birds from a control area. Albinism disproportionately affected the carotenoid‐based plumage of the head, suggesting that carotenoid metabolism is particularly susceptible to the effects of radiation. Individuals with partially albinistic plumage had, on average, lower mean phenotypic values than other birds, and this was particularly the case for males. Furthermore, differences in phenotypic variation, as determined using Levene's test, were significantly larger in partial albinos compared to nonalbinos in males, but not in females, even though the null expectation would be the opposite due to the lower mean phenotypic values of partial albinos. Although small phenotypes were commonly associated with germline mutations, there was no general decrease in overall body size during the period 1991–2000, implying that small individuals were selected against. Because partial albinism is disfavored by natural selection, the effects of mutations are deleterious, giving rise to a balance between mutation and selection.     

Carotenoid‐based bill coloration functions as a social,not sexual,signal in songbirds (Aves: Passeriformes)

Many animals use coloration to communicate with other individuals. Although the signalling role of avian plumage colour is relatively well studied, there has been much less research on coloration in avian bare parts. However, bare parts could be highly informative signals as they can show rapid changes in coloration. We measured bill colour (a ubiquitous bare part) in over 1600 passerine species and tested whether interspecific variation in carotenoid‐based coloration is consistent with signalling to potential mates or signalling to potential rivals in a competitive context. Our results suggest that carotenoid bill coloration primarily evolved as a signal of dominance, as this type of coloration is more common in species that live in social groups in the nonbreeding season, and species that nest in colonies; two socio‐ecological conditions that promote frequent agonistic interactions with numerous and/or unfamiliar individuals. Additionally, our study suggests that carotenoid bill coloration is independent of the intensity of past sexual selection, as it is not related to either sexual dichromatism or sexual size dimorphism. These results pose a significant challenge to the conventional view that carotenoid‐based avian coloration has evolved as a developmentally costly, condition‐dependent sexual signal. We also suggest that bare part ornamentation may often signal different information than plumage ornaments.     

Aerodynamic costs of long tails in male barn swallows Hirundo rustica and the evolution of sexual size dimorphism

Exaggerated tail feathers of birds constitute a standard exampleof evolution of extravagant characters due to sexual selection.Such secondary sexual traits are assumed to be costly to produceand maintain, and they usually are accompanied by morphologicaladaptations that tend to reduce their costs. The aerodynamiccosts for male barn swallows Hirundo rustica of having longtails were quantified using aerodynamics theory applied to morphologicaldata from seven European populations. Latitudinal differencesin tail length were positively correlated with differences inflight costs predicted by aerodynamics theory. A positive relationshipbetween aerodynamic costs of long tails and the degree of sexualsize dimorphism was found among populations. Latitudinal differencesin foraging costs may result in tail length being relativelysimilar in males and females in southern populations, whereasthe low foraging costs for males in northern populations mayallow them to cope with higher aerodynamic costs, giving riseto large sexual size dimorphism. Enlargement of wingspan inmales can alleviate but not eliminate the costs of tail exaggeration,and therefore differences in aerodynamic costs of male ornamentswere maintained among populations. Sexual size dimorphism in thebarn swallow arises as a consequence of latitudinal differencesin the advantages of sexual selection for males and the costsof long tails for males and females.     

Non-gradual variation in colour morphs of the strawberry poison frog Dendrobates pumilio: genetic and geographical isolation suggest a role for selection in maintaining polymorphism

The relative roles that geographical isolation and selection play in driving population divergence remain one of the central questions in evolutionary biology. We approached this question by investigating genetic and morphological variation among populations of the strawberry poison frog, Dendrobates pumilio, in the Bocas del Toro archipelago, Panama. We found significant population genetic structure and isolation by distance based on amplified fragment length polymorphism markers. Snout vent length (SVL), coloration and the extent and size of dorsal black spots showed large variation among the studied populations. Differences in SVL correlated with genetic distance, whereas black spot patterns and other coloration parameters did not. Indeed, the latter characters were observed to be dramatically different between contiguous populations located on the same island. These results imply that neutral divergence among populations may account for the genetic patterns based on amplified fragment length polymorphism markers and SVL. However, selective pressures need to be invoked in order to explain the extraordinary variation in spot size and coverage, and coloration. We discuss the possibility that the observed variation in colour morphs is a consequence of a combination of local variation in both natural selection on an aposematic signal towards visual predators and sexual selection generated by colour morph-specific mate preferences.     

Multimodal signals in male European treefrog (Hyla arborea) and the influence of population isolation on signal expression

In nocturnal treefrogs, mate choice implies the use of acoustic and visual signals. Multimodality is suspected to have evolved for either information redundancy or information complementariness. It is essential to explore multimodality in a natural context to understand the selection pressures operating on the signals. In the present study, we investigated calling and coloration in relation to male biometry and condition in four populations of European treefrog (Hyla arborea) varying in size and genetic isolation. We compared the signal intensity between core and satellite populations to estimate the impact of genetic diversity on male secondary sexual traits. The results obtained show important regional variations in both traits, likely as a result of local adaptations. Call and coloration are weakly correlated within an individual, implying that these traits likely convey different information about the signaller's identity or quality, thus supporting the hypothesis of complementariness of multiple messages. By contrast to the experimental evidence, we find that call and coloration are not related to male condition (as estimated by the residual of mass over size), suggesting that the condition‐dependence of these traits may be mediated by complex mechanisms not accurately reflected by the chosen estimator. Finally, male call and colour phenotypes present no robust pattern of variation with isolation status, probably because of variation in local selective pressures and in history of population dynamics. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 633–647.     

Offspring sexual dimorphism and sex-allocation in relation to parental age and paternal ornamentation in the barn swallow

We analysed the morphology of nestling barn swallows (Hirundo rustica) in relation to their sex, and laying and hatching order. In addition, we studied sex-allocation in relation to parentage, parental age and expression of a secondary sexual character of fathers. Molecular sexing was conducted using the sex chromosome-linked avian CHD1 gene. Sex of the offspring was not associated with laying or hatching order. None of nine morphological, serological and immunological variables varied in relation to offspring sex. Sexual dimorphism did not vary in relation to parental age and expression of a paternal secondary sexual character. The proportion of sons declined with brood size. Individual males and females had a similar proportion of sons during consecutive breeding years. The proportion of sons of individual females declined with age, but increased with the expression of a secondary sexual character of their current mate. The generalized lack of variation in sexual dimorphism among nestlings may suggest that barn swallows do not differentially invest in sons vs. daughters. Alternatively, male offspring may require different parental effort compared to their female siblings in order to attain the same morphological state. The lack of variation in offspring sexual dimorphism with paternal ornamentation suggests no adjustment of overall parental effort in relation to reproductive value of the two sexes. However, male-biased sex ratio among offspring of highly ornamented males may represent an adaptive sex-allocation strategy because the expression of male ornaments is heritable and highly ornamented males are at a sexual selection advantage.     

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.