Individual differences in the sleep/wake cycle of Arctic flexitime workers

Daytime workers tend to have shorter sleep duration and earlier sleep onset during work days than on days off. Large individual differences in sleep onset and sleep duration may be observed on work days, but work usually synchronizes sleep offset to a similar time. The present study describes individual differences in sleep behaviour of 48 daytime workers (25 men, aged 20–58 years) from an iron ore mine in Northern Sweden. The aim of the study was to determine whether differences in sleep patterns during work days were associated with the outcomes of sleepiness and sleep complaints. Cluster analysis was used to group workers into two categories of sleep onset and sleep duration. The “Late Sleep Onset” cluster comprised workers who slept 1.30 h later than the “Early Sleep Onset” cluster (p < 0.0001 for all weekdays). The “Long Sleep Duration” cluster slept 1.10 h longer than the “Short Sleep Duration” cluster (p < 0.0002 for work nights). The “Late Sleep Onset” cluster reported less refreshing sleep (p < 0.01) and had lower sufficient sleep scores (p < 0.01) than the “Early Sleep Onset” cluster. The “Short Sleep Duration” cluster also reported lower scores for sufficient sleep (p < 0.04) than the “Long Sleep Duration” cluster. For combined characteristics (phase and duration), workers with a late phase and short sleep duration reported greater sleep debt and sleepiness than workers with an early phase and short sleep duration (p < 0.02). Work schedule and commuting time modulate both sleep phase and sleep duration independently. Workers, classified as having an intermediate sleep phase preference, can organize their sleep time in order to minimize sleep debt and sleepiness symptoms. Individual differences in sleep phase and duration should be considered when promoting well-being at work even among groups with similar sleep needs. In order to minimize sleep debt and sleepiness symptoms, successful sleep behaviour could be promoted involving extend use of flexitime arrangement (i.e. later starting times) and reduce use of alarm clocks.     

Environmental Influences on Sleep Behavior in Captive Male Chimpanzees (Pan troglodytes)

Little is known as to the influence of captivity and stressful events on sleep patterns in primates. We investigated the sleep patterns of 19 male chimpanzees living under similar conditions at the Chimpanzee Sanctuary Uto (CSU) in Kumamoto, Japan, using a behavioral sleep index. We conducted nighttime observations of all subjects during a stable period and then observed three subjects after relocation to an unfamiliar facility at CSU. We estimated length of sleep and nonsleep periods over 13-h video recordings using instantaneous sampling at 1-min intervals to record sleep, which we defined operationally as an inactive posture with the body lying down with the head on the floor or on nesting materials. The 19 subjects slept for a mean ± SEM of 11.3?±?0.26?h during the stable period, and sleep patterns varied significantly among the subjects. The three relocated subjects all showed temporarily decreased sleep duration in the post-move period but subsequently recovered to the levels observed during the stable period when habituated to the new living quarters. These results suggest that a stressful event may induce temporary sleep shortage lasting for >1?wk in captive chimpanzees. Sleep patterns may serve as a useful behavioral index of the stress response, as it is less confounded by other behaviors and the actions of human caretakers than other indices.     

Day workers suffering from a wider range of sleep problems are more likely to experience suicidality

Both a higher suicide rate and widespread sleep problems are serious health concerns in Japan when compared with those of other countries. We investigated the relationship between suicidal ideation and sleep problems in Japanese day workers using the 3-dimensional sleep scale (3DSS), which measures three sleep elements (phase, quality, and quantity). Data from 635 Japanese day workers (461 mens and 174 womens) were included. The 3DSS was used to assess participants’ sleep condition. Participants were classified into eight sleep types based on scores of phase, quality, and quantity: All Good Sleep, Owl (poor phase), Inefficient (poor quality), Short (poor quantity), Owl + Inefficient (poor phase and quality), Owl + Short (poor phase and quantity), Inefficient + Short (poor quality and quantity), and All Poor Sleep. We assessed participants’ suicidal ideation using question 19 of the self-rating depression scale (SDS); 119 cases (18.7 %) had ratings of 2–4 for this question and were considered to have suicidal ideation. The higher the number of sleep problems, the higher the risk of suicidal ideation compared to sleep types not indicative of problems. All Poor Sleep had the highest risk of the eight sleep types. Individuals with Owl + Short, Inefficient + Short, or All Poor Sleep had a significant risk of suicidal ideation even after adjusting for hopelessness and nightmares. Our findings suggested that sleep problems assessed by the 3DSS were related to suicidal ideation. Analysis of various aspects of sleep could be helpful for suicide prevention.

     

Sleeping on the Job during Night Shifts May Be Associated with Extended Night Shifts and/or Variable Night Shift Onset Times

Continuous rotating shiftworkers temporarily working overtime slept at least once during the working hours of their night shifts. They worked at an electric power distribution plant in São Paulo (Brazil). In order to detect factors that could be associated with sleeping on the job, we compared those who slept (sleep group – S) with those who did not sleep (non-sleep group – NS) as to the number of night shifts, the average length of night shifts, the variability in night shift onset and offset times and the length of sleep episodes at home between consecutive night shifts. Data collection was based on dairies filled in by the workers for 30 consecutive days. For both S and NS groups, the number of night shifts for each worker varied from 5 to 9, no difference being found between groups. Individual means of night shifts length varied from 9.4 ± 0.3 hr to 14.2 ± 0.6 hr; they were significantly longer in the S than in the NS group. Night shift onset times were shown to be significantly more variable in the S than in the NS group, whereas offset times did not differ significantly between groups. Length of sleep episodes at home was not significantly different between groups. Workers who slept on the job were those who had longer working bouts and / or more variable night shift onset times. Differences among workers may be due to individual strategies to cope with a situation in which the work schedule included night shifts that were much longer than the established 8 hours, and with many changes in onset times from one night shift to the next.     

Photic resetting in night-shift work: impact on nurses' sleep

The objective of this study was to quantify daytime sleep in night-shift workers with and without an intervention designed to recover the normal relationship between the endogenous circadian pacemaker and the sleep/wake cycle. Workers of the treatment group received intermittent exposure to full-spectrum bright light during night shifts and wore dark goggles during the morning commute home. All workers maintained stable 8-h daytime sleep/darkness schedules. The authors found that workers of the treatment group had daytime sleep episodes that lasted 7.1 ± .1 h (mean?±?SEM) versus 6.6 ± .2 h for workers in the control group (p =?.04). The increase in total sleep time co-occurred with a larger proportion of the melatonin secretory episode during daytime sleep in workers of the treatment group. The results of this study showed reestablishment of a phase angle that is comparable to that observed on a day-oriented schedule favors longer daytime sleep episodes in night-shift workers. (Author correspondence: diane.boivin@douglas.mcgill.ca ).     

Absence of Within‐Colony Kin Discrimination in a Multiple‐Queen Ant,Leptothorax acervorum

Inclusive fitness theory predicts that, other things equal, individuals within social groups should direct altruistic behaviour towards their most highly related group‐mates to maximise indirect fitness benefits. In the social insects, most previous studies have shown that within‐colony kin discrimination (nepotism) is absent or weak. However, the number of studies that have investigated within‐colony kin discrimination at the level of individual behaviour remains relatively small. We tested for within‐colony kin discrimination in the facultatively multiple‐queen (polygynous) ant, Leptothorax acervorum. Specifically, we tested whether workers within polygynous colonies treated queens differently as a function of their relatedness to them. Colonies containing two egg‐laying queens were filmed to measure the rate at which individually marked workers antennated and groomed or fed each queen. Relatedness between individual queens and workers was calculated from their genotypes at four microsatellite loci. The results showed there were no differences in the rates at which workers antennated or groomed/fed their more related queen and their less related queen. Workers interacted preferentially with their potential mother queen with respect to grooming/feeding but not with respect to antennation. However, because of high queen turnover, the frequency of adult workers with their potential mother queen still present within the colony was relatively low. Overall, therefore, we found no evidence for within‐colony kin discrimination in the context of the average worker's treatment of queens in polygynous L. acervorum colonies.     

Estimates on the Duration of Sleep and Wakefulness Made in Isolation

Fifteen subjects who lived singly in an isolation unit without temporal cues were asked to note every day after awakening how many hours they thought they had slept, and in the evening before retiring how many hours they had been awake. These estimates of the duration of sleep and wakefulness were compared with the intervals between two signals given by the subjects by pressing a button at the time of waking up and when turning off their bedside reading lamp. The results can be summarized as follows: (a) the daily estimated durations of sleep and wakefulness were positively correlated with the actual durations in all but one subject; (b) sleep and wake times were better estimated in the presence of a light-dark cycle even if the subjects were not entrained by the zeitgeber; (c) for both episodes, there was a consistent trend from an overestimation of relatively short to an underestimation of long durations; (d) with equal durations in the two episodes, sleep was estimated to be shorter than wake time; (e) the most accurate estimates centered around 10.5 h of sleep and 13.5 h of wake time; (f) the sleep and wake times added up to 24 h in subjects who did not deliberately “compensate” for relatively long sleep estimates with a short wake estimate, with the full cycle being adjusted to 24 h.     

Unique habits of stomodeal trophallaxis in the ponerine antHypoponera sp.

Summary The present paper describes for the first time that adult-to-adult trophallaxis exists in ponerine ants. Furthermore, it shows that the adult castes of the ponerine andHypoponera sp. have different habits of trophallaxis. Workers display a soliciting behavior toward queens, males and workers, but receive regurgitated food only from workers. The workers are forced to stop soliciting for regurgitated food by the whipping behavior of the queen. Callow queens solicit regurgitated food from workers and ergatoid males and receive it, while mature queens do not solicit regurgitation from workers. Ergatoid males receive regurgitated food from workers and regurgitate it to queens. Alate males show no trophallactic food exchange with workers and queens. Trophallactic behavior was never observed between males of either winged or ergatoid types.     

Octopaminergic system in the brain controls aggressive motivation in the ant, Formica japonica

The ant, Formica japonica, is polyphagous and workers hunt other insects as foods. In this study, interspecific aggression was examined in the workers and queens. Behavior experiments demonstrated that interspecific aggressiveness was significantly higher in workers than queens. Workers showed predatory aggressive behavior towards crickets, on the other hand, queens elicited threat behavior but they didn't attack crickets. In order to investigate neuronal mechanisms underlying regulation of aggressive motivation, the role of biogenic amine in the brain in evoking aggressive behavior was examined by measuring biogenic amine using high-performance liquid chromatography (HPLC) with electrochemical detection (ECD). No significant difference in the octopamine (OA) level was found between workers and queens, but the level of N-acetyloctopamine (NacOA) in the brain of queens was significantly higher than that of workers. This study suggests that OAergic system in the brain must involve in controlling aggressive motivation in the ants.     

Photic Resetting in Night-Shift Work: Impact on Nurses' Sleep

The objective of this study was to quantify daytime sleep in night-shift workers with and without an intervention designed to recover the normal relationship between the endogenous circadian pacemaker and the sleep/wake cycle. Workers of the treatment group received intermittent exposure to full-spectrum bright light during night shifts and wore dark goggles during the morning commute home. All workers maintained stable 8-h daytime sleep/darkness schedules. The authors found that workers of the treatment group had daytime sleep episodes that lasted 7.1?±?.1?h (mean?±?SEM) versus 6.6?±?.2?h for workers in the control group (p?=?.04). The increase in total sleep time co-occurred with a larger proportion of the melatonin secretory episode during daytime sleep in workers of the treatment group. The results of this study showed reestablishment of a phase angle that is comparable to that observed on a day-oriented schedule favors longer daytime sleep episodes in night-shift workers. (Author correspondence: diane.boivin@douglas.mcgill.ca)     

红火蚁工蚁对绿僵菌侵染蛹的防御行为

研究了红火蚁工蚁感染绿僵菌后在蛹室的行为变化,以及健康工蚁对侵染蛹的行为保护机制.结果表明: 工蚁被绿僵菌侵染后,在蛹室的活动时间逐渐减少,由第1天的103.4 s降至第3天的38.5 s;而且育幼时间占蛹室活动时间的比例也下降,由第1天的13.6%降至第3天的3.5%.当蛹被绿僵菌侵染后,工蚁对侵染蛹的梳理总时间为对照组的5.3倍,每次梳理的平均持续时间为对照组的5.2倍.梳理行为能显著减少侵染蛹的体表分生孢子数量,在无工蚁、2只工蚁和10只工蚁存在条件下,蛹体表平均孢子数分别为103.1、51.6和31.3个.工蚁的存在能抑制蛹体表孢子的萌发,处理20 h后,无工蚁、2只工蚁和10只工蚁存在条件下,蛹体表孢子萌发率分别为95.1%、80.4%和59.9%.蛹的羽化率随着工蚁数量增加显著升高.红火蚁工蚁通过社会行为防御病原真菌侵染蛹的策略为种群的延续和发展提供了保障.     

Sleep on the Job Partially Compensates for Sleep Loss in Night‐Shift Nurses

Nursing personnel in Brazil are usually submitted to fixed 12 h shifts with no consecutive working days or nights. Moonlighting is common in this group, with a consequent increase in the number of working hours. The possibility of sleeping on the job during the night shift in the studied hospitals had already been described. The present study aims to analyze whether the time devoted to daily activities (sleep, rest, leisure, housework, commuting, personal needs, care of children or other people, non‐paid work, and study) is related to the number of worked hours and to nap‐taking during the night shift. The field study took place at two public hospitals in Rio de Janeiro, Brazil. Workers filled out a structured form on time devoted to the above‐mentioned activities for at least four consecutive days. The time devoted to sleep was analyzed according to its occurrence at home or on the job. Workers were classified according to the number of jobs (one job/two jobs) and the time dedicated to work according to the median of the whole series (below the median/above the median). All workers who had at least one working night were analyzed as to nap‐taking on the job. They were classified according to the sleep occurrence during the night shift—the sleep group and the non‐sleep group, both of which were compared to daytime workers. Statistical treatment of data included non‐parametrical procedures. The study group comprised 144 workers (mean age: 35.7±10.5 years old; 91% women; 78% nurse assistants, the remainder registered nurses). They recorded their daily activities for 4–11 days; 829 cumulative days were analyzed for the whole group. A total of 165 working nights were analyzed; sleep or rest occurred during 112 (68%) of them, with mean sleep/rest duration of 141±86 min. Time devoted to sleep and leisure varied according to the number of working hours, being significantly reduced in those submitted to longer work hours (p<0.001 and p=0.002, respectively). Results close to significance point to a reduction in the time dedicated to housework among workers with long work hours (p=0.053). The time spent on sleep/rest per working night did not differ according to the number of worked hours (p=0.490). A tendency was observed for those who have two jobs to devote more time to sleep/rest on the job (p=0.058). The time of personal needs was significantly lower among those who did not sleep on the job as compared to day workers (p=0.036). The total sleep time was significantly lower among those who did not sleep on the job, as compared to day workers and to those who slept on the job (p=0.004 and p=0.05, respectively). As to home sleep length, workers who slept and those who did not sleep on the job were similar and slept significantly less than exclusively daytime workers (p<0.001 and p=0.002, respectively). Sleeping on the job during the night shift seems to partially compensate for the shorter sleep at home among night workers and may play a beneficial effect in coping with two jobs.     

Optional gamergates in the queenright ponerine ant Gnamptogenys striatula Mayr

Summary: Ponerine ants display a number of social structures to which particular behaviours are associated. In the ponerine ant species Gnamptogenys striatula Mayr, queens occur and queenright colonies are functionally polygynous. However, some workers are capable to mate and to produce their own worker offspring. These gamergates appear several days after the queens are experimentally removed, allowing some workers to adopt a sexual calling posture inside the nest. At that time, other workers get outside the nest to collect males in the arena and carry them back into the colony. There, these males are groomed before they can mate with sexual calling workers. As for queens, several gamergates may coexist in a same colony. The social profile of gamergates is similar to those of nurses and they stay closer to the egg piles.     

Evolution of hybridogenetic lineages in Cataglyphis ants

In most social Hymenoptera, a diploid egg develops into either a queen or a worker depending on environmental conditions. Hybridogenetic Cataglyphis ants display a bizarre genetic system, where queen‐worker caste determination is primarily determined by genetic factors. In hybridogenetic populations, all workers are F1 hybrids of two distinct lineages, whereas new queens are nearly always pure‐lineage individuals produced by clonal reproduction. The distribution and evolutionary history of these hybridogenetic populations have not yet been thoroughly analysed. Here, we studied the phylogeographic distribution of hybridogenetic populations in two closely related Spanish species: Cataglyphis humeya and Cataglyphis velox. Hybridogenesis has been previously documented in a locality of C. velox, but whether this system occurs elsewhere within the range of the two species was yet unknown. Queens and workers from 66 localities sampled across the range of the species were genotyped at 18 microsatellite markers to determine whether queens were produced by parthenogenesis and whether workers were hybrids of divergent lineages. Populations with F1 hybrid workers were identified by combining genetic, geographical and mating assortments data. In most populations of C. velox, workers were found to be hybrids of two divergent lineages. Workers were however produced via random mating in two marginal populations of C. velox, and in all populations studied of its sister species C. humeya. High‐throughput sequencing data were obtained to confirm inferences based on microsatellites and to characterize relationships between populations. Our results revealed a complicated history of reticulate evolution that may account for the origin of hybridogenetic lineages in Cataglyphis.     

Queen reproduction, chemical signalling and worker behaviour in polygyne colonies of the ant Formica fusca

Potential reproductive conflicts are common in social insects and may occur between and within castes. In multiqueen (polygyne) colonies of ants, reproductive conflicts among coexisting queens may be resolved by aggressive interactions and/or by pheromonal signalling. Pheromonal signals may be directed at workers, which may adjust the reproductive shares of queens behaviourally. Workers are expected to favour a queen that is more likely to be their mother and to produce offspring of close kin to them. We used microsatellite markers to study reproductive partitioning between cobreeding Formica fusca queens in a laboratory experiment where workers received a choice between two queens. We expected queens of this species to communicate their reproductive status by chemical communication, because no aggressive interactions between queens have been observed. We found that queens of different reproductive status (with majority, minority or no production) differed in their cuticular hydrocarbon (CHC) profiles. The fecundity of a queen was associated with worker behaviour; the higher a queen's fecundity, the more attention she received from workers. Our results suggest that a queen fecundity signal is encoded in her CHC profile and acts as a pheromone for workers, which respond to the signal by discriminating between queens. Copyright 2002 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour     

Sleep/Wake Cycle Parameters and Sleep/Fatigue Complaints in Female Night Workers

Adaptation to shift-work is influenced by the way workers schedule their lives, including allocation of sleep episodes. Female workers (n = 29) engaged at an assembly line were studied as to individual differences in sleep parameters in order to verify whether those differences could be related to the manifestation of sleep and fatigue complaints. The sample was composed of women (20–40 y) working at night from Monday to Friday. Sleep data were based on daily sleep logs which were filled out by the workers for 10 consecutive weeks. In the analyses of sleep data both diurnal episodes between consecutive night shifts and noctural sleep episodes preceding working nights were taken into account. Worker's complaints were analyzed through questions extracted from an interview form encompassing questions on fatigue associated with the work schedule and on dissatisfaction with sleep on weekdays and weekends. The analysis of diurnal episodes showed no significant correlation between the total amount of sleep per day and the total number of complaints. Nevertheless, the latter was correlated to the length of the first sleep episode on a day, which usually began in the morning. As to sleep onset times, significant correlations were not detected concerning the first diurnal episodes. The analysis of nocturnal episodes did not reveal any significant correlation between sleep parameters and complaints. Results indicate that workers whose sleep onsets were allocated to the morning and were able to sleep for many consecutive hours, tended to show less complaints, suggesting that the temporal allocation of diurnal sleep and its length are relevant in the determination of how these workers perceive fatigue and sleep quality.     

Sleep on the job partially compensates for sleep loss in night-shift nurses

Nursing personnel in Brazil are usually submitted to fixed 12 h shifts with no consecutive working days or nights. Moonlighting is common in this group, with a consequent increase in the number of working hours. The possibility of sleeping on the job during the night shift in the studied hospitals had already been described. The present study aims to analyze whether the time devoted to daily activities (sleep, rest, leisure, housework, commuting, personal needs, care of children or other people, non-paid work, and study) is related to the number of worked hours and to nap-taking during the night shift. The field study took place at two public hospitals in Rio de Janeiro, Brazil. Workers filled out a structured form on time devoted to the above-mentioned activities for at least four consecutive days. The time devoted to sleep was analyzed according to its occurrence at home or on the job. Workers were classified according to the number of jobs (one job/two jobs) and the time dedicated to work according to the median of the whole series (below the median/above the median). All workers who had at least one working night were analyzed as to nap-taking on the job. They were classified according to the sleep occurrence during the night shift-the sleep group and the non-sleep group, both of which were compared to daytime workers. Statistical treatment of data included non-parametrical procedures. The study group comprised 144 workers (mean age: 35.7+/-10.5 years old; 91% women; 78% nurse assistants, the remainder registered nurses). They recorded their daily activities for 4-11 days; 829 cumulative days were analyzed for the whole group. A total of 165 working nights were analyzed; sleep or rest occurred during 112 (68%) of them, with mean sleep/rest duration of 141+/-86 min. Time devoted to sleep and leisure varied according to the number of working hours, being significantly reduced in those submitted to longer work hours (p < 0.001 and p = 0.002, respectively). Results close to significance point to a reduction in the time dedicated to housework among workers with long work hours (p = 0.053). The time spent on sleep/rest per working night did not differ according to the number of worked hours (p = 0.490). A tendency was observed for those who have two jobs to devote more time to sleep/rest on the job (p = 0.058). The time of personal needs was significantly lower among those who did not sleep on the job as compared to day workers (p = 0.036). The total sleep time was significantly lower among those who did not sleep on the job, as compared to day workers and to those who slept on the job (p = 0.004 and p = 0.05, respectively). As to home sleep length, workers who slept and those who did not sleep on the job were similar and slept significantly less than exclusively daytime workers (p < 0.001 and p = 0.002, respectively). Sleeping on the job during the night shift seems to partially compensate for the shorter sleep at home among night workers and may play a beneficial effect in coping with two jobs.     

Energetics of newly-mated queens and colony founding in the fungus-gardening ants Cyphomyrmex rimosus and Trachymyrmex septentrionalis (Hymenoptera: Formicidae)

Abstract.  The energetics of colony founding is investigated in the fungus gardening ants (Attini) Trachymyrmex septentrionalis and Cyphomyrmex rimosus . Similar to most ants, inseminated queens of these two species found nests independently unaccompanied by workers (haplometrosis). Whereas most ant founding queens seal themselves in a chamber and do not feed when producing a brood entirely from metabolic stores (claustral founding), the majority of fungus gardening ants must forage during the founding phase (semiclaustral founding). Laboratory-reared T. septentrionalis individuals comprise 84 dealate females collected after mating flights in June 2004. Twenty are immediately killed to obtain values for queen traits and another 20 after worker emergence for queen, fungus garden and worker traits. Cyphomyrmex rimosus comprise 22 dealate females collected in June 2005; ten of which are immediately killed and similarly prepared. Newly-mated T. septentrionalis queens have 25% of their dry weight as fat; whereas newly-mated C. rimosus queens contain 11% fat. These amounts are 50–75% less than most independently founding ant species. Trachymyrmex septentrionalis queens lose merely 5% of their energetic content during colony founding, whereas the total energetic content of their brood is more than three-fold the amount lost by the queen. Incipient T. septentrionalis colonies produce approximately half as much ant biomass per gram of fungus garden as do mature colonies. Similar to most ants, T. septentrionalis produces minim workers that are approximately 40% lighter than workers from mature colonies. Regardless of their size, T. septentrionalis workers contain much lower fat than do workers of claustral species. These data indicate that fungus gardening is adaptive because colonies can produce much cheaper offspring, making colony investment much lower.     

Sleep/Wake Cycle Parameters and Sleep/Fatigue Complaints in Female Night Workers

Adaptation to shift-work is influenced by the way workers schedule their lives, including allocation of sleep episodes. Female workers ( n = 29) engaged at an assembly line were studied as to individual differences in sleep parameters in order to verify whether those differences could be related to the manifestation of sleep and fatigue complaints. The sample was composed of women (20-40 y) working at night from Monday to Friday. Sleep data were based on daily sleep logs which were filled out by the workers for 10 consecutive weeks. In the analyses of sleep data both diurnal episodes between consecutive night shifts and noctural sleep episodes preceding working nights were taken into account. Worker's complaints were analyzed through questions extracted from an interview form encompassing questions on fatigue associated with the work schedule and on dissatisfaction with sleep on weekdays and weekends. The analysis of diurnal episodes showed no significant correlation between the total amount of sleep per day and the total number of complaints. Nevertheless, the latter was correlated to the length of the first sleep episode on a day, which usually began in the morning. As to sleep onset times, significant correlations were not detected concerning the first diurnal episodes. The analysis of nocturnal episodes did not reveal any significant correlation between sleep parameters and complaints. Results indicate that workers whose sleep onsets were allocated to the morning and were able to sleep for many consecutive hours, tended to show less complaints, suggesting that the temporal allocation of diurnal sleep and its length are relevant in the determination of how these workers perceive fatigue and sleep quality.     

Sex allocation conflict in ants: when the queen rules

Insect societies are paramount examples of cooperation, yet they also harbor internal conflicts whose resolution depends on the power of the opponents. The male-haploid, female-diploid sex-determining system of ants causes workers to be more related to sisters than to brothers, whereas queens are equally related to daughters and sons. Workers should thus allocate more resources to females than to males, while queens should favor an equal investment in each sex. Female-biased sex allocation and manipulation of the sex ratio during brood development suggest that workers prevail in many ant species. Here, we show that queens of Formica selysi strongly influenced colony sex allocation by biasing the sex ratio of their eggs. Most colonies specialized in the production of a single sex. Queens in female-specialist colonies laid a high proportion of diploid eggs, whereas queens in male-specialist colonies laid almost exclusively haploid eggs, which constrains worker manipulation. However, the change in sex ratio between the egg and pupae stages suggests that workers eliminated some male brood, and the population sex-investment ratio was between the queens' and workers' equilibria. Altogether, these data provide evidence for an ongoing conflict between queens and workers, with a prominent influence of queens as a result of their control of egg sex ratio.