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In many social hymenopterans, workers of different ages engage in different tasks; younger workers remain inside the nest as intranidal workers, while older workers go outside the nest as extranidal workers (i.e., age polyethism). Previous studies have shown that ovarian activity is diminished in old, extranidal workers, but it remains unclear whether workers’ reproductive ability persists for life or whether they exhibit post-reproductive lifespans. In this study, we investigated the age-dependence of worker reproductive ability in a monomorphic ponerine ant Diacamma cf. indicum. In Diacamma ants, all females in a colony have reproductive ability, but effective reproduction is limited to one or a few dominant females, and the remaining females act as sterile helpers. Using long-term laboratory rearing, we investigated whether worker reproductive ability lasts throughout a worker’s lifetime. The ages of workers were accurately tracked, and the reproductive ability of young and old workers was examined by creating several gamergate-less sub-colonies. Results showed that at least one individual in each sub-colony developed ovaries, even in the sub-colonies that solely consisted of very old workers (> 252 days old). Interestingly, in the presence of younger workers, old workers rarely showed ovarian development. Besides age, we found a positive correlation between the amount of fat (i.e., nutritional condition) and ovarian development in old workers. Our data suggest that reproductive activity of old workers is low but maintained throughout their life in Diacamma. Significance statement: Females of social animals, such as cetaceans, are known to stop reproducing before the end of their lifespan. It is suggested that the reproductive ability of ant queens does not decline and is maintained throughout their lives; however, it is unclear whether this is also true in ant workers. We maintained ant colonies for more than 500 days and then tested whether the reproductive ability of ant workers is maintained throughout their lifespan. Even in small groups composed of only very old workers (> 252 days old), at least one individual in each group always reproduced actively. Interestingly, the presence of young workers seemed to suppress the reproduction of old workers. In addition, fat content was positively associated with the individual’s reproductive potential. [ABSTRACT FROM AUTHOR]

Eusocial insect colonies are vulnerable to exploitation by egg‐laying workers arising either as natal reproductive workers or as non‐natal reproductive 'drifting' workers (intraspecific social parasites). Worker egg‐laying is potentially costly to the colony, but queens and workers can counter its costs via egg eating (queen or worker policing). Bumblebee colonies exhibit egg laying by both natal and non‐natal workers: natal workers collectively lay more eggs but do so only after a specific point in the colony cycle, the 'competition point', whereas non‐natal workers potentially lay eggs throughout the colony cycle. These features create a special opportunity to investigate whether policing of worker‐laid eggs is context‐dependent (i.e. depends on worker origin of eggs and/or colony stage). We introduced artificial egg cells containing eggs laid by either natal or non‐natal workers into colonies of the bumblebee Bombus terrestris both before and after their competition points and observed the fate of introduced egg cells and eggs. In both colony stages, the majority of introduced egg cells and eggs were policed, demonstrating that policing was not activated only after the competition point. However, in the pre‐competition point stage alone, a smaller proportion of non‐natal workers' eggs (15%) remained after 20 h compared to the proportion of natal workers' eggs remaining (24%). More effective policing of non‐natal workers' eggs early in the colony cycle potentially represents an adaptive, context‐dependent response to the stage in the cycle when all worker‐laid eggs are normally unrelated to the natal colony. [ABSTRACT FROM AUTHOR]

Simple Summary: In honey bees, drones disperse to specific locations in order to mate before returning to their natal nests. However, in apiaries of Apis mellifera, drones have been witnessed returning to non-natal nests; this behavior may also sometimes occur at natural nests. This behavior could be due to the unnaturally high density of nests in apiaries. In this study, we genotyped colonies of the Apis cerana honey bee collected in its invasive range of Far North Queensland, Australia, to determine whether there is evidence of drone drift between colonies. We found no such evidence of drone drift. Some drones that do not match the resident queen's genotype are instead likely due to queen turnover or worker reproduction. The modes through which individuals disperse prior to reproduction has important consequences for gene flow in populations. In honey bees (Apis sp.), drones (males) reproduce within a short flight range of their natal nest, leaving and returning each afternoon within a narrow mating window. Drones are assumed to return to their natal nests as they depend on workers to feed them. However, in apiaries, drones are reported to regularly make navigation errors and return to a non-natal nest, where they are accepted and fed by unrelated workers. If such a "drone drift" occurred in wild populations, it could facilitate some further degree of dispersal for males, particularly if drones drift into host nests some distance away from their natal nest. Here, we investigated whether drone drift occurs in an invasive population of the Asian honey bee (Apis cerana). Based on the genotypes of 1462 drones from 19 colonies, we found only a single drone that could be considered a candidate drifter (~0.07%). In three other colonies, drones whose genotypes differed from the inferred queen were best explained by recent queen turnover or worker-laying. We concluded that drone drift in this population is low at best, and A. cerana drones either rarely make navigation errors in wild populations or are not accepted into foreign nests when they do so. We therefore confirm that drone dispersal distance is limited to the distance of daily drone flights from natal nests, a key assumption of both colony density estimates based on sampling of drone congregation areas and population genetic models of gene flow in honey bees. [ABSTRACT FROM AUTHOR]

In eusocial insects, the molecular basis of worker reproductivity, including how it changes with eusocial complexity, remains relatively poorly understood. To address this, we used mRNA-seq to isolate genes differentially expressed between ovary-active and ovary-inactive workers in the intermediately eusocial bumblebee Bombus terrestris. By comparisons with data from the advanced eusocial honeybee Apis mellifera, which shows reduced worker reproductivity, we characterised gene expression differences associated with change in worker reproductivity as a function of eusocial complexity. By comparisons with genes associated with queen-worker caste development in B. terrestris larvae, we tested the behavioural-morphological caste homology hypothesis, which proposes co-option of genes influencing reproductive division of labour in adults in morphological caste evolution. We conducted comparisons having isolated genes expressed in B. terrestris worker-laid eggs to remove the potential confound caused by gene expression in eggs. Gene expression differences between the B. terrestris worker phenotypes were mainly in fat body and ovary, not brain. Many genes (86%) more highly expressed in ovary of ovary-active workers were also expressed in worker-laid eggs, confirming egg-expressed genes were potentially confounding. Comparisons across B. terrestris and A. mellifera, and with B. terrestris larvae, returned significant percentage overlaps in differentially expressed genes and/or enriched gene ontology terms, suggesting conserved gene functions underpin worker reproductivity as it declines with increasing eusocial complexity and providing support for the behavioural-morphological caste homology hypothesis. Therefore, within bees, both a degree of conserved gene use and gene co-option appear to underlie the molecular basis of worker reproductivity and morphological caste evolution., (© The Author(s) 2024. Published by Oxford University Press on behalf of Society for Molecular Biology and Evolution.)

Abstract Workers in many species of social insects are capable of laying unfertilized eggs, which can develop into haploid males. This causes a conflict about male parentage between queens and workers. In a few species, this may result in matricide, that is, workers kill the colony's queen. Queen killing has so far been observed mainly in multi‐queen colonies or in annual species, when the queen's fecundity declines at the end of the reproductive period. Here, we report queen expulsion and matricide in a monogynous, monandrous ant with perennial societies. Workers were seen to aggressively expel both related and unrelated queens from their nest shortly after the end of hibernation. Queen expulsion and matricide led to a significant decrease in the number of workers and brood, but eventually increased the direct fitness of workers through significant male production. Long‐term observations revealed a short lifespan of queens, while workers in orphaned colonies survived and produced male offspring over several years.

The modes through which individuals disperse prior to reproduction has important consequences for gene flow in populations. In honey bees (Apis sp.), drones (males) reproduce within a short flight range of their natal nest, leaving and returning each afternoon within a narrow mating window. Drones are assumed to return to their natal nests as they depend on workers to feed them. However, in apiaries, drones are reported to regularly make navigation errors and return to a non-natal nest, where they are accepted and fed by unrelated workers. If such a “drone drift” occurred in wild populations, it could facilitate some further degree of dispersal for males, particularly if drones drift into host nests some distance away from their natal nest. Here, we investigated whether drone drift occurs in an invasive population of the Asian honey bee (Apis cerana). Based on the genotypes of 1462 drones from 19 colonies, we found only a single drone that could be considered a candidate drifter (~0.07%). In three other colonies, drones whose genotypes differed from the inferred queen were best explained by recent queen turnover or worker-laying. We concluded that drone drift in this population is low at best, and A. cerana drones either rarely make navigation errors in wild populations or are not accepted into foreign nests when they do so. We therefore confirm that drone dispersal distance is limited to the distance of daily drone flights from natal nests, a key assumption of both colony density estimates based on sampling of drone congregation areas and population genetic models of gene flow in honey bees.

Background: Worker reproduction has an important influence on the social cohesion and efficiency of social insect colonies, but its role in the success of invasive ants has been neglected. We used observations of 233 captive colonies, laboratory experiments, and genetic analyses to investigate the conditions for worker reproduction in the invasive Anoplolepis gracilipes (yellow crazy ant) and its potential cost on interspecific defence. We determined the prevalence of worker production of males and whether it is triggered by queen absence; whether physogastric workers with enlarged abdomens are more likely to be reproductive, how normal workers and physogastric workers compare in their contributions to foraging and defence; and whether worker-produced males and males that could have been queen- or worker-produced differ in their size and heterozygosity. Results: Sixty-six of our 233 captive colonies produced males, and in 25 of these, some males could only have been produced by workers. Colonies with more workers were more likely to produce males, especially for queenless colonies. The average number of days between the first appearance of eggs and adult males in our colonies was 54.1 ± 10.2 (mean ± SD, n = 20). In our laboratory experiment, queen removal triggered an increase in the proportion of physogastric workers. Physogastric workers were more likely to have yolky oocytes (37–54.9%) than normal workers (2–25.6%), which is an indicator of fertile or trophic egg production. Physogastric workers were less aggressive during interspecific aggression tests and foraged less than normal workers. The head width and wing length of worker-produced males were on average 4.0 and 4.3% greater respectively than those of males of undetermined source. Our microsatellite DNA analyses indicate that 5.5% of worker-produced males and 14.3% of males of undetermined source were heterozygous, which suggests the presence of diploid males and/or genetic mosaics in A. gracilipes. Conclusions: Our experimental work provides crucial information on worker reproduction in A. gracilipes and its potential cost to colony defence. The ability of A. gracilipes workers to produce males in the absence of queens may also contribute to its success as an invasive species if intranidal mating can take place between virgin queens and worker-produced males. [ABSTRACT FROM AUTHOR]

Workers in many species of social insects are capable of laying unfertilized eggs, which can develop into haploid males. This causes a conflict about male parentage between queens and workers. In a few species, this may result in matricide, that is, workers kill the colony's queen. Queen killing has so far been observed mainly in multi‐queen colonies or in annual species, when the queen's fecundity declines at the end of the reproductive period. Here, we report queen expulsion and matricide in a monogynous, monandrous ant with perennial societies. Workers were seen to aggressively expel both related and unrelated queens from their nest shortly after the end of hibernation. Queen expulsion and matricide led to a significant decrease in the number of workers and brood, but eventually increased the direct fitness of workers through significant male production. Long‐term observations revealed a short lifespan of queens, while workers in orphaned colonies survived and produced male offspring over several years. [ABSTRACT FROM AUTHOR]

Social insects can sense colony size-even without visual information in a dark environment. How they achieve this is yet largely unknown. We empirically tested a hypothesis on the proximate mechanism using ant colonies. In Diacamma colonies, the monogynous queen is known to increase the effort devoted to queen pheromone transmission behaviour (patrolling) as the colony grows, as if she perceives colony size. The negative feedback hypothesis assumes that, through repeated physical contact with workers, the queen monitors the physiological state (fertility) of workers and increases her patrolling effort when she encounters more fertile workers. Supporting this hypothesis, we found that the queen increased her patrolling effort in response to a higher ratio of fertile workers under the experimental condition of constant colony size. Furthermore, chemical analyses and bioassays suggested that cuticular hydrocarbons have queen pheromone activity and can mediate the observed queen-worker communication of fertility state. Such a self-organizing mechanism of sensing colony size may also operate in other social insects living in small colonies.

Hamilton's theory of inclusive fitness suggests that helpers in animal societies gain fitness indirectly by increasing the reproductive performance of a related beneficiary. Helpers in cooperatively breeding birds, mammals and primitively eusocial wasps may additionally obtain direct fitness through inheriting the nest or mating partner of the former reproductive. Here, we show that also workers of a highly eusocial ant may achieve considerable direct fitness by producing males in both queenless and queenright colonies. We investigated the reproductive success of workers of the ant Temnothorax crassispinus in nature and the laboratory by dissecting workers and determining the origin of males by microsatellite analysis. We show that workers are capable of activating their ovaries and successfully producing their sons independently of the presence of a queen. Genotypes revealed that at least one fifth of the males in natural queenright colonies were not offspring of the queen. Most worker‐produced males could be assigned to workers that were unrelated to the queen, suggesting egg‐laying by drifting workers. [ABSTRACT FROM AUTHOR]

In bumblebees, dominance behaviour contributes to the regulation of the reproductive division of labour between queens and workers. Towards the end of the colony cycle, at the onset of the competition phase, reproductive workers will establish a dominance hierarchy and challenge the reproductive monopoly of the queen by laying unfertilized, male-destined eggs. However, it has been suggested that the dominance and reproductive hierarchies in bumblebee workers are not completely aligned. By performing manipulative experiments and observing both aggressive behaviour and ovarian activation in Bombus terrestris workers, we aimed to elucidate how these two hierarchies interact and are modulated by the presence of the queen and other reproductive workers. We found that the reintroduction of a queen in a queenless colony not only caused worker ovary regression, but also decreased aggressive interactions between workers, thereby restoring the harmony in the colony. Furthermore, transplanting dominant reproductive workers from queenless colonies into queenright colonies induced the resident workers to activate their ovaries and aggressively compete over reproduction, thereby implying that positive feedback drives the onset of the competition phase. However, we did not see this result when subordinate reproductive workers from queenless colonies were added to queenright colonies, suggesting that ovary activation is mainly initiated in reaction to displays of dominance. Additionally, we observed that workers were attacked irrespective of their reproductive state, questioning the importance of signals that advertise either fertility or sterility in bumblebees. Finally, larger workers were significantly more aggressive and significantly more likely to be attacked, even though smaller workers were equally likely to have activated ovaries. This suggests that large workers resort to aggression to increase their chances of successfully reproducing due to their inherent fighting advantage, whereas small cheater workers could possibly reproduce by staying under the radar to evade nestmate aggression. • Dominance and reproductive hierarchies are not completely aligned in bumblebees. • Reintroduction of a queen causes worker ovary regression and restores harmony. • Worker competition is initiated by dominance displays of reproductive sisters. • Workers are aggressed based on their size rather than their reproductive state. • Subordinate, small reproductive workers avoid nestmate aggression. [ABSTRACT FROM AUTHOR]

Workers of many species of social Hymenoptera have functional ovaries and are capable of laying haploid, unfertilized eggs, at least in the absence of a queen. Except for honeybees, it remains largely unknown whether worker‐produced males have the same quality as queen‐produced males and whether workers benefit in direct fitness by producing their sons. Previous studies in the monogynous ant Temnothorax crassispinus revealed that a high proportion of males in natural and laboratory colonies are worker offspring. Here, we compare longevity, body size, sperm length and sperm viability between queen‐ and worker‐produced males. We either split queenright colonies into queenright and queenless halves or removed the queen from a fraction of the queenright colonies and then examined the newly produced males. Male quality traits varied considerably among colonies but differed only slightly between queen‐ and worker‐produced males. Worker‐produced males outnumbered queen‐produced males and also had a longer lifespan, but under certain rearing conditions sperm from queen‐produced males had a higher viability. [ABSTRACT FROM AUTHOR]

Honey bee workers can lay eggs that result in viable males (drones). In queenless colonies, workers activate their ovaries and lay eggs, both in their own colony and in other queenless colonies. While worker reproduction and reproductive parasitism are well demonstrated, the direct contribution of reproductive workers to the gene pool is unclear. Queenless workers mostly lay their eggs in worker-sized brood cells. The resulting drones are smaller than normal drones. We determined two measures of forewing size in drones reared in drone-sized cells (DC) and in worker-sized cells (WC). Forewing length and width were 5.78 ± 0.26 mm (± SD) and 1.27 ± 0.08 mm, respectively, for drones reared in DC, and 5.01 ± 0.21 mm and 1.11 ± 0.05 mm for drones reared in WC. Discriminant function analysis indicated that forewing length alone is sufficient to differentiate DC and WC drones. To determine the contribution of worker-laid drones to the mating population, we sampled males at a natural mating lek using a Williams' drone trap every month for 12 months. We used the discriminant function to assign drones as being DC or WC based on their forewing length and a strict classification criterion of ≥ 0.99% posterior probability of assignment to one or other group. We estimate that about 0.23% of sampled males were reared in WC and were, therefore, likely to have been laid by workers. Our results suggest that queenless workers and queenless colonies make a small contribution to the male mating population, and that this contribution may be sufficient to provide ongoing selection for worker reproductive parasitism. [ABSTRACT FROM AUTHOR]

Eusocial societies, in which egg laying is monopolized by one or a few females, have evolved multiple times during the evolution of insects but were always rooted in a simple family structure. Female reproduction in such families is often characterized by a trade-off between reproduction and brood care, yet most work on the regulation of reproduction in social insects has focused on signals and traits exhibited by adults: particularly on the behaviour and chemical signals produced by the queen and nestmate workers. Here we examined the role of brood in regulating worker reproduction in Bombus impatiens , an annual eusocial species whose reproduction is monopolized by the queen via an unknown mechanism. We found that the presence of young larvae reduced workers' egg laying, whereas the presence of pupae stimulated egg laying. The effect of young larvae was quantity dependent, with nearly complete suppression of egg laying in cages containing a pair of workers and more than 10 young larvae, and replicable regardless of worker age, relatedness to brood or brood parentage/sex. The findings that any larvae can regulate worker reproduction in this simple, yet eusocial, species highlight the role of brood in the evolution of advanced eusocial insects as a mechanism for regulating worker sterility. These findings also provide the first holistic explanation for the regulation of worker reproduction in B. impatiens , suggesting that the queen inhibits worker reproduction through her brood. • Presence of young larvae inhibited worker egg laying in B. impatiens. • Presence of pupae stimulated worker egg laying. • Larval effects were independent of relatedness, brood parentage or its sex. • Larval effect was quantity dependent. • Brood care plays an important role in the evolution of sociality. [ABSTRACT FROM AUTHOR]

In ants, reproductive division of labour is typically associated with queen-worker dimorphism. In some species with ergatoid queens (wingless worker-like queens), this polymorphism is drastically reduced and virgin queens may integrate the worker force. While ergatoid queens have been described in several species, their colony and population genetic structure remain largely unstudied. Here, we investigated the population structure and sociogenetic organisation of the desert ant Ocymyrmex robustior. All Ocymyrmex species have only ergatoid queens that are worker-sized. Workers, queens, and males from a large population were genotyped at ten polymorphic microsatellite loci. Our results show that the study population is genetically structured, consistent with dependent colony foundation. Genetic analyses revealed that 17.6% of the males were diploid; diploid males are fertile, siring triploid females. Nests were typically headed by a single queen, and queens were strictly monandrous. However, several nests in the population shared matrilines, indicating polygyny, polydomy, dependent colony foundation, serial polygyny, or a combination of these processes. Dissections reveal that workers lay eggs in both queenright and queenless nests, while virgin ergatoid queens lay eggs in queenright nests only. However, our genetic analyses show that male offspring in queenright nests are all queen-produced, suggesting worker policing and/or trophic egg laying. [ABSTRACT FROM AUTHOR]

The hallmark of eusociality is the division of labour between reproductive (queen) and nonreproductive (worker) females. Yet in many eusocial insects, workers retain the ability to produce haploid male offspring from unfertilized eggs. The reproductive potential of workers has well‐documented consequences for the structure and function of insect colonies, but its implications at the population level are less often considered. We show that worker reproduction in honey bees can have an important role in maintaining genetic diversity at the sex locus in invasive populations. The honey bee sex locus is homozygous‐lethal, and, all else being equal, a higher allele number in the population lead to higher mean brood survival. In an invasive population of the honey bee Apis cerana in Australia, workers contribute significantly to male production: 38% of male‐producing colonies are queenless, and these contribute one‐third of all males at mating congregations. Using a model, we show that such male production by queenless workers will increase the number of sex alleles retained in nascent invasive populations following founder events, relative to a scenario in which only queens reproduce. We conclude that by rescuing sex locus diversity that would otherwise be lost, workers' sons help honey bee populations to minimize the negative effects of inbreeding after founder events and so contribute to their success as invaders. [ABSTRACT FROM AUTHOR]

The evolution of altruism in complex insect societies is arguably one of the major transitions in evolution and inclusive fitness theory plausibly explains why this is an evolutionary stable strategy. Yet, workers of the South African Cape honey bee (Apis mellifera capensis) can reverse to selfish behavior by becoming social parasites and parthenogenetically producing female offspring (thelytoky). Using a joint mapping and population genomics approach, in combination with a time-course transcript abundance dynamics analysis, we show that a single nucleotide polymorphism at the mapped thelytoky locus (Th) is associated with the iconic thelytokous phenotype. Th forms a linkage group with the ecdysis-triggering hormone receptor (Ethr) within a nonrecombining region under strong selection in the genome. A balanced detrimental allele system plausibly explains why the trait is specific to A. m. capensis and cannot easily establish itself into genomes of other honey bee subspecies. [ABSTRACT FROM AUTHOR]

Resource inheritance is a major source of conflict in animal societies. However, the assumptions and predictions of models of conflict over resource inheritance have not been systematically tested within a single system. We developed an inclusive fitness model for annual eusocial Hymenoptera that predicts a zone of conflict in which future reproductive workers are selected to enforce nest inheritance before the queen is selected to cede the nest. We experimentally tested key elements of this model in the bumblebee Bombus terrestris. In colonies from which queens were sequentially removed, queen tenure was significantly negatively associated with worker male production, confirming that workers gain direct fitness by usurping the queen. In unmanipulated colonies, queen fecundity decreased significantly over the latter part of the colony cycle, confirming that workers' indirect fitness from maintaining queens declines over time. Finally, in an experiment simulating loss of queen fecundity by removal of queens' eggs, worker-to-queen aggression increased significantly and aggressive workers were significantly more likely to become egg layers, consistent with workers monitoring queen fecundity to assess the net benefit of future reproduction. Overall, by upholding key assumptions and predictions of the model, our results provide novel empirical support for kin-selected conflict over resource inheritance. [ABSTRACT FROM AUTHOR]

Parasites with complex life cycles regularly alter host traits in their own interest. In social hosts, phenotypic alterations induced by parasites can also affect uninfected group members. The tapeworm Anomotaenia brevis uses Temnothorax nylanderi ants as intermediate hosts, reducing host activity and behavioural repertoire, but increasing life span. Uninfected nestmates are less active and less aggressive and suffer from higher mortality. Next to parasites, the social environment, such as the queen, influences worker behaviour, reproduction and longevity. Here, we studied how tapeworm parasitism interacts with the queen to affect the behaviour and reproductive potential of ant workers. We collected naturally parasitized and unparasitized ant colonies, and experimentally removed the sole queen in half of each colony type to induce worker reproduction. We examined the behaviour and ovary development of tapeworm-infected workers, uninfected nurses and uninfected foragers from parasitized and unparasitized colonies living under queenright and queenless conditions. Remarkably, fertility induction was most pronounced in tapeworm-infected workers, which quickly responded to queen removal by developing their ovaries. The fertility of nurses, known to have the highest reproductive potential and to be in close contact with infected workers, was not reduced by tapeworm parasitism. However, their behaviour was impacted by an interaction between parasitism and queen removal: nurses from parasitized, queenless colonies became less active, whereas no behavioural changes were observed in nurses from unparasitized colonies. Behaviour and ovary development of foragers were unaffected by the presence of tapeworm-infected workers and the queen. Our findings indicate that parasitism by a tapeworm increases rather than decreases the reproductive potential of infected workers. We further show that parasites and the presence of dominant group members interactively shape fertility and behaviour of infected and healthy group members. [ABSTRACT FROM AUTHOR]

In contrast to honeybees, Bombus. terrestris workers are also capable of egg laying toward the end of the colony life even if in the presence of the queen. Males are produced from these unfertilized haploid eggs laid by both queens and workers. In a colony, males which produced from queen and reproductive worker eggs are not different morphologically. In mass rearing process under controlled conditions, all males which produced in colonies are collected and mated with young queens. This experiment was carried out to compare the development traits of colonies founded by queens mated with these two male groups. To produce two different male groups, old workers groups and virgin queens groups were formed and males were produced by these groups. Young B. terrestris queens produced by standard colonies were mated with males in two groups. After the hibernation period, queens were allowed to found colonies and some colony development characteristics were determined. Results showed that no significant differences in the all colony development characteristics except colony foundation ratio (P<0.05) were determined between colonies founded by queens mated with males produced by queens and reproductive workers. [ABSTRACT FROM AUTHOR]

Egg-laying behaviour of bumblebee workers is highly flexible and influenced by the bees’ social status and social environment. In this study, the dependence of the starting time of ovarian development in Bombus terrestris workers was determined under four different social conditions. The purpose was to test the effect of group stimulation and the presence of a queen on ovarian development. The relationship between weight and the commencement of ovarian development in workers was also investigated. We created four test groups: (1) 8 callow workers with a queen, (2) 8 callow workers without a queen, (3) 1 callow worker with a queen, and (4) 1 callow worker without a queen. Mated and hibernated (freshly awoken) B. terrestris queens made up Group 1 and 3. There was no significant difference between the starting times of ovarian development in the experimental groups composed of 8 callow workers in queenright (9.81 ± 2.44 days) and queenless (9.53 ± 2.53 days) conditions. However, ovaries of workers confined singly with a queen started to develop significantly earlier (11.77 ± 3.30 days) than workers confined singly without a queen (14.70 ± 3.56 days). The observations indicate that the presence of a queen does not inhibit the ovarian development of workers. The Point-Biserial Correlation Coefficient between the starting of ovarian development in workers and their weight was −0.013. However, there was a positive correlation between the weight and the ovarian developmental status of workers in groups containing 8 workers.

Kin selection and inclusive fitness are thought to be key factors explaining the reproductive altruism displayed by workers in eusocial insect species. However, when a colony’s queen has mated with Melophorus bagoti. Morphometric analyses revealed that workers belong to one of two distinct subcastes: they are either majors or minors. Using DNA microsatellite markers, we showed that all the colonies had a single, multiple-mated queen and that there was no relationship between worker patriline and worker subcaste. Furthermore, we found that workers were producing males in the presence of the queen, which contrasts with the predictions of inclusive fitness theory. Although our results are based on a small sample, they can serve as the foundation for future research examining worker reproduction in M. bagoti.

Reproductive division of labour is a defining feature of insect societies. Stingless bees (Meliponini) are an interesting exception among the highly eusocial insects in that workers of many species contribute significantly to the production of males. Since workers remain sterile in other species of this large tropical tribe, it has been hypothesized that, in the latter species, ancestral queens have won the conflict over who produces the males. The fact that sterile workers of some species lay trophic eggs to feed the queen and display ritualized behaviours towards her during oviposition has been interpreted as an evolutionary relic of this ancient conflict. Here, I used ancestral state estimation to test whether worker reproduction is indeed the ancestral condition and worker sterility a derived state in stingless bees. Contrary to this hypothesis, data suggest that trophic egg laying was the ancestral condition, whereas selfish worker reproduction in queenright colonies evolved subsequently during stingless bee diversification. The appearance of worker reproduction in queenright conditions was tightly linked to the laying of trophic eggs, which suggests that having activated ovaries in queen presence facilitates the evolution of worker reproduction. Worker reproduction is also linked to brood cell architecture, but surprisingly not to colony size or queen–worker dimorphism. The reason for this association between brood cell architecture and worker oviposition is currently unknown. These results suggest that trophic eggs are not a relic of an ancient conflict, but a sign of overlapping interests between the queen and workers about who produces the males. [ABSTRACT FROM AUTHOR]

Social insect colonies are organized by a reproductive division of labor, in which non-reproductive workers cooperate to rear the offspring of the queen. Queen pheromones, chemical compounds produced by queens that regulate worker fertility, have been identified in a handful of bees, ants, wasps, and termites. However, recent studies on bumblebee (Bombus spp.) queen signals have yielded conflicting findings. Here we provide an independent investigation of experiments to test the hypothesis that queen-produced non-volatile cuticular compounds influence worker’s reproductive behavior. We exposed small groups of Bombus impatiens workers to extracted cuticular compounds from queens collected from either mid-season (pre-reproductive) or late-season (reproductive) colonies and tracked worker reproduction and ovary development. We observed no difference in worker’s ovarian development or egg production when comparing among the mid-season queen extract, late-season queen extract and the solvent control treatments. Our data replicate the finding that body size positively correlates with ovarian development in workers. These results are consistent with recent studies showing that queen cuticular compounds do not inhibit worker reproduction in B. impatiens. [ABSTRACT FROM AUTHOR]

The honeybee queen’s mandibular gland pheromones (QMP) are essential for the suppression of worker reproduction. Worker ovary activation is regulated by alternative splicing of a CP2-transcription factor named gemini. Since workers with activated ovaries also produce QMP in their mandibular glands, we tested whether alternative splicing of gemini also controls mandibular gland pheromone biosynthesis in workers using RNA interference. Altering the splice pattern of gemini resulted in enhanced levels of the queen-specific components of the mandibular gland pheromone in queenless honeybee workers, suggesting that gemini functions as a pleiotropic regulatory switch influencing both ovary activation and resulting in QMP synthesis in workers. Because the QMP produced by these workers suppresses ovary activation in other workers, gemini seems to be a key regulatory gene affecting reproductive hierarchies among workers in queenless colonies. [ABSTRACT FROM AUTHOR]

Pollen feeding in the honeybee (Apis mellifera) is dependent on the caste, ethotype, and dominance status of individuals. Pollen is the near-exclusive external source of lipids for the colony. Lipids from pollen are rich in polyunsaturated fatty acyl residues, which, because of their sensitivity to lipid peroxidation, have been suggested to limit the lifespan of individual bees. We here investigated whether the spectrum of phosphatidylcholine (PC), the main class of membrane-constituting lipids in insects, is indeed, connected to pollen feeding. We further studied the relationship between pollen feeding, PC spectra, and fat-body stores of vitellogenin, an indicator of potential longevity in bees. For this, we determined the pollen consumption, PC spectra, abdominal vitellogenin stores, and behavioral as well as reproductive status of individuals in queenless groups of workers. In contrast to earlier studies, we found that reproduction in workers is not universally linked to trophallactic dominance alone, but can be accompanied by strong pollen consumption. Pollen consumption seemed connected to a strong remodeling of tissue PC spectra. There was no systematic link between these spectra and trophallactic activity, but individuals with strongly deviating spectra also showed extreme behavioral profiles. Abdominal vitellogenin was strongly and positively linked to pollen-influenced PC spectra and the prevalence of polyunsaturated fatty acyl residues, contradicting the hypothesis that pollen consumption is systematically leading to a shorter lifespan in workers. Our results suggest that the association between pollen consumption, short lifespan, and functional sterility that differentiates workers from queens cannot in all cases be extended to the situation within the worker caste. [ABSTRACT FROM AUTHOR]

Female eusocial sweat bees are capable of behaving as queens or workers. Relatively few females become queens, and those that do can directly manipulate the reproductive behaviour of other females in the nest. We collected Lasioglossum (Dialictus) laevissimum workers from nests with and without queens (queenright and queenless nests, respectively) to investigate the influence queens exert on worker behaviour via direct manipulation. Overall, very few L. laevissimum workers (17%) had developed ovaries in Ontario, but queenright and queenless workers were equally likely to have developed ovaries and worn mandibles. However, queenless workers were more likely to be mated than queenright workers. These results suggest first, that queens inhibit egg-laying in most, but not all workers, and second, that queen behaviour during the first few days of workers’ adult lives exerts a lasting influence on worker behaviour. We also compared social traits of L. laevissimum and other Dialictus species using principal components analysis. A strong correlation between worker reproduction and male availability suggests that queen manipulation of the worker brood sex ratio has evolved as an indirect mechanism for queens to discourage worker reproduction. [ABSTRACT FROM AUTHOR]

The honeybee is one of several eusocial species in which the queen is typically the only reproductive member of the colony; worker reproduction is mostly restricted to queenless colonies. Because workers cannot mate, they lay unfertilized eggs, which develop into males. A recent study showed that in queenless colonies, which arise after swarming, worker larvae develop into rebel workers that have greater reproductive potential than do workers reared in queenright colonies, as measured by the number of ovarioles and degree of ovary activation. However, there was no evidence that rebels had an opportunity to produce male offspring. Here, we show for the first time that rebel workers not only activate their ovaries but also produce significantly more male offspring in queenright colonies than do normal workers. Moreover, our results show that the level of rebel reproduction in queenright colonies is similar to the reproduction of normal workers in queenless colonies. This finding suggests that the ultimate factor favouring the evolution of the rebel strategy is the decrease in relatedness between the old-generation workers and the new queen’s offspring that occurs after queen exchange at swarming. [ABSTRACT FROM AUTHOR]

In some social insects, workers can produce females asexually through thelytokous parthenogenesis. This allows them to produce replacement queens (i.e. requeening) if the queen has died, but also to compete with the queen to produce females (i.e. reproductive cheating). For the first time, we experimentally tested the role of worker thelytoky under quasinatural conditions in the ant Cataglyphis cursor , where the queen uses both sexual and thelytokous reproduction. We reared pairs of orphaned and queenright colonies in enclosures for almost 3 months, during which they competed for resources. Orphaned colonies lost more workers than queenright colonies over the course of the experiment, presumably because of the costs of reproductive conflicts between workers. Nevertheless, they produced new queens through worker thelytoky and new colonies through colony fission. This is the first unambiguous demonstration that worker thelytoky allows requeening under natural conditions in this species. We further showed that worker thelytoky results in reproductive cheating in the form of a few workers reproducing in the presence of the queen (in queenright colonies) and a few worker lineages producing more new queens than other lineages (in orphaned colonies). In addition, it also results in rare instances of social parasitism, that is, workers entering and reproducing in foreign colonies. These benefits to workers seem too occasional and too low to drive the evolution of thelytoky in this species. We argue that thelytoky probably evolved in the queen caste, where it allows the production of young queens and confers frequent and large benefits by increasing gene transmission, but is also expressed in workers because of genetic correlations between the two castes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sexual maturation of small-sized honeybee males occurs earlier than in large-sized males. • Weight of reproductive organs and sperm count non-isometrically increased with body size. • Reproductive organs increase was relatively small to body size. • Sperm count increase was relatively large to body size. The body size of male honeybees (Apis mellifera L.) is a cause of skewed reproductive success. Large males are usually produced in colonies and have advantages in competition for mating and fertilisation. However, distinct small-sized males were produced depending on the colony conditions, particularly under queen-less conditions. Understanding the reproductive traits of small-sized males is currently limited, but it may provide insight into the developmental patterns and reproductive strategies that maximise reproductive success depending on body size and colony conditions. This study evaluated the process of sexual maturation in large- and small-sized males and the allometry between reproductive traits and body size. Changes in reproductive traits, including reproductive organs, number of spermatozoa, and sperm density, occurred earlier in small-sized males than in large-sized males after emergence. These results suggest that small males are precocious. The relatively early development of small-sized males would reflect the low developmental cost, which is likely to allow the production of many males and ensure reproductive success under circumstances in which available resources are limited. Furthermore, reproductive traits were positively correlated with body size, but allometry was different for these traits. Hence, the findings suggest that there is a given investment pattern toward reproductive traits with increasing body size, which would be responsible for high mating and fertilisation success in large males. [ABSTRACT FROM AUTHOR]

Worker reproduction in Apis mellifera typically leads to haploid males produced via arrhenotokous parthenogenesis. An exception are laying workers of the South African Cape honeybee Apis mellifera capensis. Due to an abnormal spindle rotation during meiosis A. m. capensis workers are able to produce female progeny via thelytokous parthenogenesis. This trait has been suggested to be genetically controlled by a recessive allele at the thelytoky locus ( th), but this conclusion was recently challenged by Chapman et al. (2015). To clarify the mode of inheritance for thelytokous parthenogenesis in Cape honeybees, we determined the sex of the offspring of 74 A. m. capensis workers of a single queen from a colony of the endemic wild population at the Cape of Good Hope Nature Reserve. When we tested individual worker reproduction, parthenogenesis was dimorphic, segregating in a Mendelian fashion supporting the single locus model. We could exclude maternal or paternal effects determining the mode of parthenogenesis. A careful re-analysis of the data of Chapman et al. (2015) also revealed that their data do not contradict the one locus model for the inheritance of thelytoky. [ABSTRACT FROM AUTHOR]

The human-mediated dispersal of species over geographical boundaries can bring previously isolated sister taxa into contact. Interspecific mating between closely related species may then occur, with various outcomes ranging from hybridization to reproductive interference. In the case of the Eastern honey bee Apis cerana and the Western honey bee Apis mellifera, an additional possible reproductive outcome has been posited: interspecific sperm triggers queens to produce daughters from unfertilized eggs via thelytokous parthenogenesis. Such an outcome would go unnoticed in natural population mergers, as queens, which are polyandrous, are likely to mate with both conspecific and interspecific males. We performed reciprocal crosses between A. mellifera and A. cerana via artificial insemination, plus control inseminations of saline (five queens per species per treatment), and genetically assessed the sex and origin of any resulting offspring. Neither A. cerana nor A. mellifera queens produced viable female brood after receiving interspecific semen, indicating a high cost of interspecific mating for both species. In two A. cerana colonies headed by cross-inseminated queens, workers responded by activating ovaries and laying eggs that were mainly male but occasionally female (i.e. thelytokous, 2% of brood), despite the queen's continued presence in the nest. We conclude that thelytoky is not a consistent response to interspecific mating by queens of A. mellifera or A. cerana. Rather, at least in A. cerana, when colonies are faced with 'mis-mated' queens, it may be up to the workers to secure the reproductive future of the colony. [ABSTRACT FROM AUTHOR]

In many colonies of social insects, the workers compete with each other and with the queen over the production of the colony's males. In some species of social bees and wasps with annual societies, this intra-colony conflict even results in matricide-the killing of the colony's irreplaceable queen by a daughter worker. In colonies with low effective paternity and high worker-worker relatedness, workers value worker-laid males more than queen-laid males, and thus may benefit from queen killing. Workers gain by eliminating the queen because she is a competing source of male eggs and actively inhibits worker reproduction through policing. However, matricide may be costly to workers if it reduces the production of valuable new queens and workers. Here, I test a theoretical prediction regarding the timing of matricide in a wasp, Dolichovespula arenaria, recently shown to have facultative matricide based on intra-colony relatedness. Using analyses of collected, mature colonies and a surgical manipulation preventing queens from laying female eggs, I show that workers do not preferentially kill queens who are only producing male eggs. Instead, workers sometimes kill queens laying valuable females, suggesting a high cost of matricide. Although matricide is common and typically occurs only in low-paternity colonies, it seems that workers sometimes pay substantial costs in this expression of conflict over male parentage. [ABSTRACT FROM AUTHOR]

Queen pheromones are essential for regulation of the reproductive division of labor in eusocial insect species. Although only the queen is able to lay fertilized eggs and produce females, in some cases workers may develop their ovaries and lay male-destined eggs, thus reducing the overall colony efficiency. As long as the queen is healthy, it is usually in the workers' collective interest to work for the colony and remain sterile. Queens signal their fertility via pheromones, which may have a primer effect, affecting the physiology of workers, or a releaser effect, influencing worker behavior. The queen pheromone of the ant Lasius niger was among the first queen pheromones of social insects to be identified. Its major component is 3-methylhentriacontane (3-MeC31), which is present in relatively large amounts on the queen's cuticle and on her eggs. 3-MeC31 regulates worker reproduction by inhibiting ovarian development. Most monomethyl-branched hydrocarbons can exist in two stereoisomeric forms. The correct stereochemistry is fundamental to the activity of most bioactive molecules, but this has rarely been investigated for methyl-branched hydrocarbons. Here, we tested the bioactivity of the (S)- and (R)-enantiomers of 3-MeC31, and found that whereas both enantiomers were effective in suppressing worker ovarian development, (S)-3-MeC31 appeared to be more effective at suppressing aggressive behavior by workers. This suggests that the natural pheromone may be a mixture of the two enantiomers. The enantiomeric ratio produced by queens remains unknown because of the small amounts of the compound available from each queen. [ABSTRACT FROM AUTHOR]

Studies of annual and geographic variation in eusocial bee populations suggest that more stringent environmental conditions result in stronger reproductive skew favouring queens, while moderate conditions favour increasing worker reproduction. To test these predictions, we compared the phenology and colony development of H. ligatus nesting in St. Catharines, Ontario, Canada to a previously studied aggregation 90 km north of St. Catharines, in Victoria, Ontario. Despite the close proximity of these two locations, St. Catharines has markedly shorter winters and longer summers. Comparisons between St. Catharines in 2006 and Victoria in the 1980s and 1990s incorporate both geographic differences in climate and temporal differences due to climate change. We predicted that St. Catharines foundress queens should emerge from hibernation and initiate nests earlier in spring, giving them time to produce more workers. Since earlier studies indicated that queens have difficulty suppressing worker reproduction in larger colonies, we also predicted higher rates of worker ovarian development in St. Catharines. In spring and summer 2006, we excavated 65 H. ligatus nests, comparing their contents to 713 specimens collected in pan traps. As predicted, nests were initiated about a month earlier in St. Catharines than in Victoria, but contrary to prediction, fewer workers were produced in St. Catharines. St. Catharines workers were just as likely to have developed ovaries as Victoria workers. About 40% of St. Catharines workers were classified as reproductive, and larger reproductive workers tended to have higher ovarian scores. Early queen mortality in the longer nest cycle of St. Catharines bees may have enhanced opportunities for worker reproduction despite their smaller numbers. Novel features of H. ligatus sociobiology in St. Catharines included evidence that queens can initiate new nests following the loss of their first brood, overlap between worker and gyne production within some nests, and high rates of independent nest founding by worker-sized females, suggesting that many worker-brood females overwinter. Overall, the distinctly warmer climate of St. Catharines compared to Victoria led to earlier nest initiation and lengthening of the flight season, but not to the predicted differences in colony social organisation or queen-worker reproductive skew. A second objective of our study was to assess how well pan trap collections capture important information about demographic and social parameters important in assessing social variability in sweat bees. Nest excavations and pan traps produced similar results, suggesting that pan traps are a good alternative when nest excavations are impossible. [ABSTRACT FROM AUTHOR]

In cooperatively breeding or eusocial societies, opportunities may arise for helper individuals to gain direct fitness by reproducing. However, the extent to which helpers respond differentially, in terms of their reproductive behaviour, to the probability that reproductive opportunities will arise is not fully known. In many eusocial Hymenoptera, workers lay eggs only in queenless conditions following the death of the queen or queens. Relative to polygyny (multiple queens per colony), monogyny (single queen per colony) increases the probability that queenless conditions arise. We therefore tested the hypothesis that ant workers respond differentially to queenless conditions as a function of the probability of queenlessness. We compared worker behaviour and reproduction before and after removal of queens from monogynous and polygynous colonies of the ant Leptothorax acervorum . We found that, in queenless conditions, workers from monogynous colonies were significantly more likely to lay eggs, showed a significantly reduced latency to egg laying and laid eggs at a significantly higher rate per capita than workers from polygynous colonies. In addition, before queen removal, workers that laid eggs in queenless conditions across both monogynous and polygynous colonies performed a range of behaviours associated with reproduction at significantly higher rates than nonreproductive, control workers. These ‘future reproductive’ workers also significantly reduced their rates of brood care following queen removal. These findings show that workers under monogyny reproduce more readily in queenless conditions than workers under polygyny, and that would-be reproductive workers alter their behaviour before they experience the opportunity for future reproduction. They therefore suggest that workers adaptively modulate their reproductive behaviour as a function of the likelihood of opportunities for direct reproduction arising, and that workers' behaviour is affected by the ability to gain direct fitness even when reproduction is currently not occurring. [ABSTRACT FROM AUTHOR]

It has been postulated that spatial organization of the colony, in addition to biological and social factors, influences colony life in honeybees. In this study, we examine the influence of workers' distance from the queen on their reproductive, pheromonal and behavioural characteristics. Our results demonstrate that with increasing distance from the queen, workers increasingly develop behavioural and reproductive traits characteristic of queenlessness, which are presumably the result of significant impairment in queen pheromone transmission. Having contemplated the alternative possibilities of inadequate transmission of queen signal and voluntary escape from queen control, we concluded, based on the behavioural and physiological data, that the former is far more probable than the latter. The dose-dependent manner of the queen pheromone action and its differential influence on various worker characteristics are discussed. [ABSTRACT FROM AUTHOR]

1. Workers in several bee species travel to conspecific nests ('drifting'), enter them, and produce male offspring inside them, so acting as intra-specific social parasites. This adds a new dimension to bees' reproductive behaviour and spatial ecology, but the extent to which drifting occurs over field scales, i.e. at natural nest densities in field conditions, has been unclear. 2. Using the bumble bee Bombus terrestris ( Linnaeus) as a model system, we sought to determine rates of worker drifting at field scales and the frequency of potential drifter workers in wild nests. 3. A field experiment with 27 colonies showed that workers travelled to, and became accepted in, conspecific nests that were up to 60 m away, although the number of accepted drifter workers within nests fell significantly with distance. The rate at which nests were entered by drifters was relatively high and significantly exceeded the rate at which drifters became accepted. 4. Microsatellite genotyping of eight field-collected nests from Greater London, U.K., showed that a low frequency (3%) of workers were not full sisters of nestmate workers and hence were likely to have been drifter workers. 5. It is therefore concluded that workers can drift to conspecific nests over field scales and confirmed that successful drifting occurs in natural populations. Drifting appears to be a natural but low-frequency behaviour permitting B. terrestris workers to gain direct fitness. [ABSTRACT FROM AUTHOR]

In colonies of primitively eusocial wasps, some dominant workers become successive queens and inherit queenship after the death of the foundress queens. Although workers in many species do not mate, workers of Polistes snelleni are capable of mating and female production. In this study, we removed foundress queens from colonies of P. snelleni to evaluate the effects of queen loss on the dominant-subordinate relationships among the remaining workers and the productivity of colonies in the species. The foundress queens were the sole egg layers in almost all of the queenright colonies. The frequency of dominance behaviour among the wasps in the queenright colonies was significantly less than in the orphan colonies. The frequency of dominance behaviour in the successive queens after queen removal was significantly more than in the foundress queens. Multiple workers had developed ovaries, including the successive queens in 66.7 % (10/15) of the orphan colonies after queen removal. The orphan colonies produced significantly more cells and eggs than the queenright colonies. Our results suggest that the reproductive potential of the successive queens in the orphan colonies is not lower than that of the foundress queens, and that the productivity of the orphan colonies is maintained rather than causing potential conflict over direct reproduction among workers. [ABSTRACT FROM AUTHOR]

Under the hymenopteran single-locus complementary sex-determination system, production of diploid males results from homozygosity at the sex-determiner locus. This arises when both parents transmit identical alleles at the locus to the offspring. In species reproducing asexually through thelytokous parthenogenesis, production of diploid males may also occur when the sex locus undergoes recombination and becomes homozygous in the offspring. Diploid males represent a substantial genetic load in hymenopteran populations because they often produce unviable sperm or sire sterile triploid female offspring. In the Mediterranean ant Cataglyphis cursor, the queen and workers can produce female offspring through automictic thelytokous parthenogenesis with central fusion, a mode of parthenogenesis that increases homozygosity. We report, for the first time, the presence of about 39 % of colonies producing adult diploid males (seven colonies out of 18). Overall, 8 % of adult males were diploid (12 diploid males out of the 146 males genotyped). Genotyping workers from the seven colonies producing diploid males showed that three diploid males were sons of queens and produced by thelytoky, six were probably sons of workers also produced by thelytoky and three were non-natal. Furthermore, the mating of a diploid male with two virgin queens in the laboratory led to the production of sterile triploid workers, which shows that diploid males in C. cursor are fertile, mate successfully and produce viable and functional but probably sterile female offspring. Because diploid males originate from thelytokous reproduction, they are only produced during sexual production and hence do not impair colony growth, which could explain why they are not removed at early brood stages. [ABSTRACT FROM AUTHOR]

Highlights: [•] Caste determination is induced by differential nutrition. [•] The TOR and insulin/insulin-like signaling pathways sense this signal. [•] Hormone levels [e.g., juvenile hormone (JH)] are altered in response to these signals. [•] JH in turn affects a wide range of gene expression levels. [•] Bidirectional pathways for female development lead to queens and workers. [ABSTRACT FROM AUTHOR]

Kin selection theory predicts that honeybee ( Apis mellifera) workers should largely refrain from producing their own offspring, as the workers collectively have higher inclusive fitness if they rear the sons of their mother, the queen. Studies that have quantified levels of ovary activation and reproduction among workers have largely supported this prediction. We sampled pre-emergent male pupae and adult workers from seven colonies at regular intervals throughout the reproductive part of the season. We show that the overall contribution of workers to male (drone) production is 4.2%, nearly 40 times higher than is generally reported, and is highest during reproductive swarming, when an average of 6.2% of the males genotyped are worker-produced. Similarly, workers in our samples were 100 times more likely to have active ovaries than previously assumed. Worker reproduction is seasonally influenced and peaks when colonies are rearing new queens. Not all worker subfamilies contribute equally to reproduction. Instead, certain subfamilies are massively over-represented in drone brood. By laying eggs within the period in which many colonies produce virgin queens, these rare worker subfamilies increase their direct fitness via their well-timed sons. [ABSTRACT FROM AUTHOR]