Comparisons of psychosomatic health and unhealthy behaviors between cleanroom workers in a 12-hour shift and those in an 8-hour shift

The General Health Questionnaire (GHQ12) and physical fitness tests were administered to 338 workers in clean rooms producing electronic parts in 12-h shifts. The results were compared to those in 95 workers in 8-h shifts and 284 daytime management, clerical and engineering workers. The 12-h shift workers complained of poor health, dissatisfaction with life and poor recuperation from fatigue more than the 8-h shift workers although the rates of complaints were highest in the daytime workers. The GHQ scores were similar in the two shift groups, and much better than those in the daytime workers. However, the 12-h shift workers showed significantly lower fitness levels than the 8-h shift workers, and the levels were even worse than the daytime workers who had higher mean age and BMI levels compared with the shift workers. The tendency to have sedentary freetime activities and larger alcohol and cigarette consumption were observed in the 12-h shift workers. The 12-h shift work may have contributed to the unhealthy behaviors resulting in lower physical fitness levels. Health promotion services at the workplace should devote greater attention to long-hour shift workers, together with devising the ways to improve working conditions and environments for reducing fatigue at work.     

Identification of vitellogenin in the ant, Camponotus festinatus: changes in hemolymph proteins and fat body development in workers.

Vitellogenin has been identified in the ant Camponotus festinatus, both in queens and workers. In the workers, it is already present before adult eclosion in low concentrations (less than 1 microgram/microliter hemolymph). Vitellogenin and vitellin are immunologically identical and are composed of a single type of apoprotein with an apparent Mr = 185,000. The molecular weight of the native molecules was estimated as approximately 460,000 by pore limiting gradient electrophoresis. Vitellogenin was detected as a major protein in the hemolymph of young workers, both under queenright and queenless conditions. Thus, in spite of their sterility in the presence of the queen, C. festinatus workers are able to synthetize vitellogenin which is identical both in size and immunologically to the queen vitellogenin. About 6-7 weeks after adult eclosion, however, vitellogenin was usually undetectable in the hemolymph of queenright workers, particularly the minor workers, while it constituted about 30% of total protein in queenless workers. Protein concentration in the hemolymph of queenless insects increased up to 20-fold as compared to 1-day-old insects. Queenless workers also developed large amounts of perivisceral fat body, while queenright workers, particularly the minor workers, showed a dramatic fat body regression about 6 weeks after emergence.     

Temporal behavioral variation and division of labor among workers in the primitively eusocial wasp,Polistes jadwigae Dalla Torre

The behavior of workers on 2 nests of the Japanese paper wasp,Polistes jadwigae, was recorded on video tape. Young workers performed pulp collection more frequently than middle-aged and old workers, while foraging of flesh (prey) was done mainly by middle-aged workers. Of the 26 behavioral categories, 7 showed negative, 2 concave, and 1 convex relationship to the workers age. Using behavioral profiles, workers could be classified into 3 age groups: 1) young workers (younger than 10 days old, active intranidal workers), 2) middle-aged workers (11–25 days old, extranidal workers) and 3) old workers (older than 26 days old, ‘idlers’). Idlers engaged in foraging and larval feeding significantly less frequency than the young and middle-aged workers, but they performed alerting toward many alien objects. Task specialization among workers irrespective of age polyethism was also suggested.     

Social parasitism by workers in queenless and queenright Apis cerana colonies

We examined worker reproduction in queenless and queenright Apis cerana colonies to determine if they are parasitized by workers from other nests. The results demonstrate that 2-6% of workers in queenright colonies are from another nest (non-natal), but these workers are not statistically more likely to have activated ovaries than natal workers, and are therefore unlikely to be active parasites. However, in queenless colonies we found a significant difference between the proportion of non-natal (72.7%) and natal (36.3%) workers with activated ovaries. Non-natal workers also had significantly higher reproductive success than natal workers: 1.8% of workers were non-natal, but these laid 5.2% of the eggs and produced 5.5% of the pupae. Unlike A. florea, the proportion of non-natal workers does not increase in queenless nests.     

Distribution and levels of dopamine and its metabolites in brains of reproductive workers in honeybees

To explore the role of dopamine and its metabolites for change of reproductive states of workers in honeybees (Apis mellifera), brain levels of dopamine relative substances were measured and localized in both normal workers and queenless workers. Dopamine and two possible metabolites of dopamine, N-acetyldopamine (NADA) and norepinephrine were detected in brain extracts. The brain levels of dopamine, NADA and norepinephrine were positively correlated with ovary development. Individuals with high dopamine levels had high levels of NADA or norepinephrine, suggesting that these metabolites might be involved in the change of reproductive sates of workers. Dopamine was distributed mainly in the protocerebrum, whereas NADA was in both the optic lobes and the protocerebrum. Dopamine levels in each distinct brain regions were higher in queenless workers than in normal workers, whereas there was a higher NADA level in the optic lobes in queenless workers than in normal workers. These results suggest that dopamine might be stored and/or released around the protocerebrum and the deutocerebrum, and also diffuse to the optic lobes where dopamine secretory cells are absent, resulting in high NADA levels in the optic lobes. The different manner of level changes of dopamine and its metabolites in each brain region might cause compound behavioural modulations in reproductive workers.     

Genome-wide analysis reveals differences in brain gene expression patterns associated with caste and reproductive status in honey bees (Apis mellifera)

A key characteristic of eusocial species is reproductive division of labour. Honey bee colonies typically have a single reproductive queen and thousands of sterile workers. Adult queens differ dramatically from workers in anatomy, physiology, behaviour and lifespan. Young female workers can activate their ovaries and initiate egg laying; these 'reproductive' workers differ from sterile workers in anatomy, physiology, and behaviour. These differences, however, are on a much smaller scale than those observed between the queen and worker castes. Here, we use microarrays to monitor expression patterns of several thousand genes in the brains of same-aged virgin queens, sterile workers, and reproductive workers. We found large differences in expression between queens and both worker groups (~2000 genes), and much smaller differences between sterile and reproductive workers (221 genes). The expression patterns of these 221 genes in reproductive workers are more queen-like, and may represent a core group of genes associated with reproductive physiology. Furthermore, queens and reproductive workers preferentially up-regulate genes associated with the nurse bee behavioural state, which supports the hypothesis of an evolutionary link between worker division of labour and molecular pathways related to reproduction. Finally, several functional groups of genes associated with longevity in other species are significantly up-regulated in queens. Identifying the genes that underlie the differences between queens, sterile workers, and reproductive workers will allow us to begin to characterize the molecular mechanisms underlying the evolution of social behaviour and large-scale remodelling of gene networks associated with polyphenisms.     

Specialization in policing behaviour among workers in the ant Pachycondyla inversa

Most animal societies are non-clonal and thus subject to conflicts. In social insects, conflict over male production can be resolved by worker policing, i.e. eating of worker-laid eggs (WLE) or aggression towards reproductive workers. All workers in a colony have an interest in policing behaviour being expressed, but there can be asymmetries among workers in performing the actual behaviour. Here, we show that workers of the ant Pachycondyla inversa specialize in policing behaviour. In two types of behavioural assays, workers developed their ovaries and laid eggs. In the first experiment, reproductive workers were introduced into queenright colonies. In the second experiment, WLE were introduced. By observing which individuals policed, we found that aggressive policing was highly skewed among workers that had opportunity to police, and that a similar tendency occurred in egg policing. None of the policing workers had active ovaries, so that policing did not incur a direct selfish benefit to the policer. This suggests that policing is subject to polyethism, just like other tasks in the colony. We discuss several hypotheses on the possible causes of this skew in policing tasks. This is the first non-primate example of specialization in policing tasks without direct selfish interests.     

Behavioral property of unusual large workers in the ant,<Emphasis Type="Italic"> Pristomyrmex pungens</Emphasis>

We surveyed the behavioral properties of unusual large workers in the parthenogenetic queenless ant, Pristomyrmex pungens. The majority of colonies mostly consist of monomorphic workers, which have two ovarioles (small workers). Large workers with four ovarioles are occasionally found in some colonies. We compared the behavior of small and large workers. Large workers performed brood care less frequently than small workers and almost never foraged. We set out three hypotheses of the adaptive significance of large workers: they are (1) reproductive castes, that is, functionally defined queens, (2) major workers, such as soldiers, and (3) of a socially parasitic lineage. Electronic Publication     

Genome-wide analysis of alternative reproductive phenotypes in honeybee workers

A defining feature of social insects is the reproductive division of labour, in which workers usually forego all reproduction to help their mother queen to reproduce. However, little is known about the molecular basis of this spectacular form of altruism. Here, we compared gene expression patterns between nonreproductive, altruistic workers and reproductive, non-altruistic workers in queenless honeybee colonies using a whole-genome microarray analysis. Our results demonstrate massive differences in gene expression patterns between these two sets of workers, with a total of 1292 genes being differentially expressed. In nonreproductive workers, genes associated with energy metabolism and respiration, flight and foraging behaviour, detection of visible light, flight and heart muscle contraction and synaptic transmission were overexpressed relative to reproductive workers. This implies they probably had a higher whole-body energy metabolism and activity rate and were most likely actively foraging, whereas same-aged reproductive workers were not. This pattern is predicted from evolutionary theory, given that reproductive workers should be less willing to compromise their reproductive futures by carrying out high-risk tasks such as foraging or other energetically expensive tasks. By contrast, reproductive workers mainly overexpressed oogenesis-related genes compared to nonreproductive ones. With respect to key switches for ovary activation, several genes involved in steroid biosynthesis were upregulated in reproductive workers, as well as genes known to respond to queen and brood pheromones, genes involved in TOR and insulin signalling pathways and genes located within quantitative trait loci associated with reproductive capacity in honeybees. Overall, our results provide unique insight into the molecular mechanisms underlying alternative reproductive phenotypes in honeybee workers.     

Effect ofNocardia rubra cell-wall skeleton on cancer prevention in humans

Summary The retired workers at the chemical weapons plant in Japan are regarded as a high-risk group for cancers. Under the Cancer Preventive Program,Nocardia rubra cell-wall skeleton (N-CWS) was administered to 80 workers directly involved in the production of sulfur mustard and 66 workers engaged in work related to sulfur mustard production. Untreated workers whose age, sex, duties and duration of work at this factory were individually matched to the N-CWS-treated workers were used as controls. During a 4.5-year observation period, development of cancers was found in 7 treated workers and 17 untreated controls. After elimination of the influence of the difference in smoking level, the incidence of subjects who developed cancers was compared statistically between the N-CWS-treated workers and the untreated controls and a significant suppression of development of cancers was noted in the N-CWS-treated workers. Thus, it was concluded that the administration of N-CWS could prevent cancer development in humans.     

Evaluation of Occupational Injuries among Young Workers in West Virginia

We compared workplace injuries between young (16 to 19 years of age) and adult workers using West Virginia Workers' Compensation database. All workers injured between January 1 and December 31, 1995 were included in the analysis. The industry-specific injury incidence rates between young and adults workers were significantly different with lower rates of injury in young workers in all sectors except service sector. In the service sector the young workers had significantly higher injury rates than adults (rate ratios for young workers were 2.28, 1.92, and 2.94 when compared with age groups 20-24, 25-34, and >34, respectively). Estimates of the proportional injury ratio (PIR) indicated significantly greater risk of finger (PIR 1.62) and hand (PIR 1.66) injuries and burns (PIR 3.27) and lacerations (PIR 1.69) in the young workers. The proportion of injuries occurring in the summer months was higher in the young than in the adults (35.2% vs. 27.0%), particularly in the service sector (79.6% vs. 25.9%). Higher injury rates in young workers compared to adults in the service sector may be explained by the seasonal employment of young workers in West Virginia.     

Reproductive conflict in social insects: male production by workers in a slave-making ant

In insect societies, workers cooperate but may also pursue their individual interests, such as laying viable male eggs. The case of obligatory slave-making ants is of particular interest because workers do not engage in maintenance activities and foraging. Therefore, worker egg laying is expected to be less detrimental for colony efficiency than in related, nonparasitic species. Furthermore, as slave-making workers usually do not perform brood care and thus might have little power in manipulating sex allocation, they might be more strongly selected to increase their direct fitness by producing their own sons than workers in nonparasitic species. In this study we investigated worker reproduction in four natural colonies of the slave-making ant Polyergus rufescens, using highly variable microsatellite markers. Our results show that workers produce up to 100% of the males. This study thus presents the first direct evidence of an almost complete takeover of male reproduction by workers in ants.     

Brain tyramine and reproductive states of workers in honeybees

To explore the role of tyramine in the transformation of reproductive states of honeybee workers, brain levels of tyramine and N-acetyltyramine were measured in both normal and queenless workers. Queenless workers had higher tyramine levels and lower N-acetyltyramine levels than normal workers did. Intermediate reproductive workers that were transferred into a normal colony from a queenless colony had intermediate levels of tyramine and N-acetyltyramine. Elevation of tyramine in the queenless workers occurred at an earlier adult stage than elevation of dopamine. Tyramine levels in intermediate reproductive workers returned to the levels seen in normal workers, but dopamine levels in intermediate reproductive workers remained elevated at the same level as in queenless workers. Thus, brain tyramine may be regulated by the colony condition with or without a queen. Injection of an amine uptake inhibitor, reserpine, depleted tyramine and elevated N-acetyltyramine. Distributions of tyramine and dopamine within the brain were distinctively different, whereas distributions of N-acetyltyramine and N-acetyldopamine were similar, suggesting that each functional amine is stored in specific neurosecretory cells and released to the relevant receptor sites but that metabolism into each N-acetylmetabolite is determined by diffusion.     

Sexual difference in juvenile-hormone titer in workers leads to sex-biased soldier differentiation in termites

In termites, the soldier caste, with its specialized defensive morphology, is one of the most important characteristics for sociality. Most of the basal termite species have both male and female soldiers, and the soldier sex ratio is almost equal or only slightly biased. However, in the apical lineages (especially family Termitidae), there are many species that have soldiers with strongly biased sex ratio. Generally in termites, since high juvenile hormone (JH) titer is required for soldier differentiation from a worker via a presoldier stage, it was hypothesized that the biased soldier-sex ratio was caused by differences in JH sensitivity and/or JH titer between male and female workers. Therefore, we focused on the presoldier differentiation and the worker JH titer in species with only male soldiers (Nasutitermes takasagoensis) and with both male and female soldiers (Reticulitermes speratus) in natural conditions. In the former species, there are four types of workers; male minor, male medium, female medium and female major workers, and presoldiers differentiate from male minor workers. First, we tried to artificially induce presoldiers from male and female workers. In N. takasagoensis, the presoldier differentiation rate and mortality was significantly higher in male minor workers. Morphological analyses showed that both male and female induced presoldiers possessed normal soldier-specific morphologies. It was suggested that female workers, from which soldiers do not differentiate under natural conditions, also maintained the physiological and developmental potential for soldier differentiation. In R. speratus, however, no differences were observed in solder differentiation rate and mortality between male and female workers. Second, the JH titers of each sex/type of workers were quantified by high performance liquid chromatography–mass spectrometry in two different seasons (April and December). The results showed that, in N. takasagoensis, JH titer in male minor workers was consistently higher than those in other worker types. In R. speratus, in contrast, there were no significant differences in JH titers between male and female workers. These results suggested that, in N. takasagoensis, male minor workers maintain JH titers at a high level throughout a year, and this may cause the male-biased presoldier differentiation.     

Caste specialization in food storage in the dimorphic antColobopsis nipponicus (Wheeler)

Summary Food-storage abilities of both minor and major workers of the dimorphic antColobopsis nipponicus were examined to prove the hypothesis that major workers of this species have a trophic role in addition to a defensive one. Both worker subcastes accumulated water, that was supplied with water-soluble food, as well as fat, that probably originated from food given. However, the major workers accumulated much larger amounts of water and fat than did the minor workers. Difference in water accumulation increased as food supply increased. In spite of their difference in body weight, the residual amount of fat after starvation did not differ between the two subcastes. Although the amount of stored fat increased with colony size in both subcastes, the stored fat per dry weight of the major worker was significantly larger than that of the minor worker regardless of the colony size. When workers of a colony were starved, minor workers with a single major worker survived significantly longer than those without a major worker. In addition, about half the behavioral acts of major workers were regurgitation for minor workers. These results demonstrate that major workers ofC. nipponicus functioned as a trophic caste. On the basis of the results, quantitative relationships of storage abilities between the two worker subcastes are discussed.     

Immunobiochemical profiles of workers differing in the degree of occupational exposure to vinyl chloride

The immunobiochemical studies were conducted in a group of 98 production workers engaged in polyvinyl chloride manufacture from ethylene (group A workers) and in a group of 59 vinyl chloride workers from a chemical plant employing classic production technology from acetylene (group B workers). Both groups of workers were matched by age (group A workers: 37.7 +/- 8.66 years; group B workers: 34.9 +/- 11.2 years) and average exposure length (group A workers: 8.6 +/- 3.0 years; group B workers: 10.7 +/- 8.4 years). All workers were examined for the serum concentrations of immunoglobulins IgG, IgA and IgM and acute reactants lysozyme (LYS), transferrin (TRF), ceruloplasmin (CPL), alpha-l-antitrypsin (AlAT), alpha-2-macroglobulin (A2M) and orosomucoid (ORO). The statistical analysis included calculations of means, standard deviations and 95% confidence intervals. Differences in means were evaluated by t-test, differences in the distribution pattern of values by F-test. Abnormality of values was assessed by comparisons to normal values valid in Czechoslovakia. Group A worked in conditions meeting the MAC 10 mg VC.m-3 comparing with group B workers had elevated levels of IgG (P less than 0.005), IgA and IgM (P less than 0.001 both). Group B workers differed from group A workers by exhibiting significantly elevated levels of AlAT, and CPL. (P less than 0.001). The differences in the frequency of abnormal values between group A and group B worked in substantially less favourable hygienic conditions were significant for immunoglobulins elevated in group A and for ORO (P less than 0.01) and CPL (P less than 0.001) elevated in group B. The possible relationship of these immunobiochemical findings with the degree of vinyl chloride exposure are critically analyzed.     

Effects of periodic administration ofNocardia rubra cell-wall skeleton on immunoglobulin production and B-cell-stimulatory factor activity in vitro in workers at a poison gas factory

Summary The former workers at the Okunojima poison gas factory (poison gas workers) are a high-risk group for malignant neoplasms and show abnormalities in cellular immunity. At the same time, poison gas workers often have chronic respiratory diseases, such as chronic bronchitis, and are highly susceptible to respiratory infections. To explore the possibility of immunological cancer prevention, we have periodically administered 200 µgNocardia rubra cell-wall skeleton (N-CWS) to poison gas workers once every 3 months since December 1978. During this period, we noted a significantly lower incidence of influenza among poison gas workers receiving N-CWS than in those not receiving the drug during the influenza epidemic. This finding suggested that the administration of N-CWS enhanced the resistance of these workers to infections. Therefore, periodical administration of N-CWS to poison gas workers was considered to enhance the reduced T-cell function of normalizing antibody production by stimulating the production of B-cell-stimulatory factor (BSF). In the present study, to clarify the mechanism of immunosuppression in the poison gas workers and to examine the effects of continual administration of N-CWS on this condition, we compared the immunoglobulin production and the proliferative and differentiative activities of B-cell-stimulatory factor (BSF) of peripheral blood mononuclear cells (PBMC), in poison gas workers treated or not treated with N-CWS. Comparisons were also made with age-matched healthy controls. In the untreated poison gas workers, immunoglobulin and BSF production of PBMC were reduced as compared with the control group. On the other hand, in the poison gas workers receiving N-CWS, immunoglobulin and BSF production of PBMC were restored nearly to the control level. These results show that in vitro antibody production in the poison gas workers was reduced and that a reduction in BSF production of T cells was one of its causes.     

Sex ratio determination by queens and workers in the ant Pheidole desertorum

Because workers in colonies of eusocial Hymenoptera are more closely related to sisters than to brothers, theory predicts workers should bias investment in reproductive broods to favour reproductive females over males. However, conflict between queens and workers is predicted. Queens are equally related to daughters and sons, and should act to prevent workers from biasing investment. Previous study of the ant Pheidole desertorum showed that workers are nearly three times more closely related to reproductive females than males; however, the investment sex ratio is very near equal, consistent with substantial queen control of workers. Near-equal investment is produced by an equal frequency of colonies whose reproductive broods consist of only females (female specialists) and colonies whose reproductive broods consist of only males or whose sex ratios are extremely male biased (male specialists). Because natural selection should act on P. desertorum workers to bias investment in favour of reproductive females, why do workers in male-specialist colonies rear only (or mostly) males? We tested the hypothesis that queens prevent workers from rearing reproductive females by experimentally providing workers with immature reproductive broods of both sexes. Workers reared available reproductive females, while failing to rear available males. Worker preference for rearing reproductive females is consistent with queens preventing their occurrence in colonies of male specialists. These results provide evidence that queens and workers will act in opposition to determine the sex ratio, a fundamental prediction of queen-worker conflict theory. Copyright 2000 The Association for the Study of Animal Behaviour.     

Sex ratio conflict and worker production in eusocial hymenoptera

The best known of the conflicts occurring in eusocial Hymenoptera is queen-worker conflict over sex ratio. So far, sex ratio theory has mostly focused on optimal investment in the production of male versus female sexuals, neglecting the investment in workers. Increased investment in workers decreases immediate sexual productivity but increases expected future colony productivity. Thus, an important issue is to determine the queen's and workers' optimal investment in each of the three castes (workers, female sexuals, and male sexuals), taking into account a possible trade-off between production of female sexuals and workers (both castes developing from diploid female eggs). Here, we construct a simple and general kin selection model that allows us to calculate the evolutionarily stable investments in the three castes, while varying the identity of the party controlling resource allocation (relative investment in workers, female sexuals, and male sexuals). Our model shows that queens and workers favor the investment in workers that maximizes lifetime colony productivity of sexual males and females, whatever the colony kin structure. However, worker production is predicted to be at this optimum only if one of the two parties has complete control over resource allocation, a situation that is evolutionarily unstable because it strongly selects the other party to manipulate sex allocation in its favor. Queens are selected to force workers to raise all the males by limiting the number of eggs they lay, whereas workers should respond to egg limitation by raising a greater proportion of the female eggs into sexual females rather than workers as a means to attain a more female-biased sex allocation. This tug-of-war between queens and workers leads to a stable equilibrium where sex allocation is between the queen and worker optima and the investment in workers is below both parties' optimum. Our model further shows that, under most conditions, female larvae are in strong conflict with queens and workers over their developmental fate because they value their own reproduction more than that of siblings. With the help of our model, we also investigate how variation in queen number and number of matings per queen affect the level of conflict between queens, workers, and larvae and ultimately the allocation of resource in the three castes. Finally, we make predictions that allow us to test which party is in control of sex allocation and caste determination.     

Social evolution: community policing in insects

A recent study shows that, in social insects where workers suppress or 'police' the reproduction of nestmate workers, only a subset of workers act as police. This confirms that policing can serve a collective rather than a selfish interest.