Workers In Queenless Colonies Research Articles

The effect of DNA methylation on bumblebee colony development

BackgroundAlthough around 1% of cytosines in bees’ genomes are known to be methylated, less is known about methylation’s effect on bee behavior and fitness. Chemically altered DNA methylation levels have shown clear changes in the dominance and reproductive behavior of workers in queen-less colonies, but the global effect of DNA methylation on caste determination and colony development remains unclear, mainly because of difficulties in controlling for genetic differences among experimental subjects in the parental line. Here, we investigated the effect of the methylation altering agent decitabine on the developmental rate of full bumblebee colonies. Whole genome bisulfite sequencing was used to assess differences in methylation status.ResultsOur results showed fewer methylated loci in the control group. A total of 22 CpG loci were identified as significantly differentially methylated between treated and control workers with a change in methylation levels of 10% or more. Loci that were methylated differentially between groups participated in pathways including neuron function, oocyte regulation and metabolic processes. Treated colonies tended to develop faster, and therefore more workers were found at a given developmental stage. However, male production followed the opposite trend and it tended to be higher in control colonies.ConclusionOverall, our results indicate that altered methylation patterns resulted in an improved cooperation between workers, while there were no signs of abnormal worker dominance or caste determination.

Queens stay, workers leave: caste-specific responses to fatal infections in an ant

BackgroundThe intense interactions among closely related individuals in animal societies provide perfect conditions for the spread of pathogens. Social insects have therefore evolved counter-measures on the cellular, individual, and social level to reduce the infection risk. One striking example is altruistic self-removal, i.e., lethally infected workers leave the nest and die in isolation to prevent the spread of a contagious disease to their nestmates. Because reproductive queens and egg-laying workers behave less altruistically than non-laying workers, e.g., when it comes to colony defense, we wondered whether moribund egg-layers would show the same self-removal as non-reproductive workers. Furthermore, we investigated how a lethal infection affects reproduction and studied if queens and egg-laying workers intensify their reproductive efforts when their residual reproductive value decreases (“terminal investment”).ResultsWe treated queens, egg-laying workers from queenless colonies, and non-laying workers from queenright colonies of the monogynous (single-queened) ant Temnothorax crassispinus either with a control solution or a solution containing spores of the entomopathogenic fungus Metarhizium brunneum. Lethally infected workers left the nest and died away from it, regardless of their reproductive status. In contrast, infected queens never left the nest and were removed by workers only after they had died. The reproductive investment of queens strongly decreased after the treatment with both, the control solution and the Metarhizium brunneum suspension. The egg laying rate in queenless colonies was initially reduced in infected colonies but not in control colonies. Egg number increased again with decreasing number of infected workers.ConclusionsQueens and workers of the ant Temnothorax crassispinus differ in their reaction to an infection risk and a reduced life expectancy. Workers isolate themselves to prevent contagion inside the colony, whereas queens stay in the nest. We did not find terminal investment; instead it appeared that egg-layers completely shut down egg production in response to the lethal infection. Workers in queenless colonies resumed reproduction only after all infected individuals had died, probably again to minimize the risk of infecting the offspring.

Control of mandibular gland pheromone synthesis by alternative splicing of the CP-2 transcription factor gemini in honeybees (Apis mellifera carnica)

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.

Queen mandibular pheromone modulates hemolymph ecdysteroid titers in adult Apis mellifera workers

To test the hypothesis that exposure to queen mandibular pheromone (QMP) modulates ecdysteroid production in adult worker honey bees, ecdysteroids were measured in hemolymph and other tissues of individual adult worker honey bees reared with or without QMP in cages and field colonies. Ecdysteroid titers were higher in caged workers exposed to QMP continuously from the first day of adult life than in workers reared without QMP. Statistical cluster analysis suggested the possibility that a subgroup of workers (“responders”) is more sensitive to QMP in this regard than other workers. In 12-day-old workers, ecdysteroid titers in workers reared in queenright (QR) colonies were similar to those observed in cages with QMP, but lower than those in queenless (QL) colonies. Differences in number of ovarioles or degree of ovarian activation did not correlate with hemolymph ecdysteroids. Previous studies have demonstrated ecdysteroids in hemolymph in very young adult workers and in workers in QL colonies; the present study indicates that production of ecdysteroids occurs in older adult worker honey bees in the absence of morphological signs of ovarian activation, with cage studies revealing a modulatory role for QMP masked in the complex environment of the hive.

Reproduction of rebel workers in honeybee (Apis mellifera) colonies

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.

Consumption of tyrosine in royal jelly increases brain levels of dopamine and tyramine and promotes transition from normal to reproductive workers in queenless honey bee colonies

Dopamine (DA) and tyramine (TA) have neurohormonal roles in the production of reproductive workers in queenless colonies of honey bees, but the regulation of these biogenic amines in the brain are still largely unclear. Nutrition is an important factor in promoting reproduction and might be involved in the regulation of these biogenic amines in the brain. To test this hypothesis, we examined the effect of oral treatments of tyrosine (Tyr; a common precursor of DA, TA and octopamine, and a component of royal jelly) in queenless workers and quantified the resulting production of biogenic amines. Tyrosine treatments enhanced the levels of DA, TA and their metabolites in the brain. Workers fed royal jelly had significantly larger brain levels of Tyr, DA, TA and the metabolites in the brains compared with those bees fed honey or sucrose (control). Treatment with Tyr also inhibited the behavior of workers outside of the hive and promoted ovarian development. These results suggest that there is a link between nutrition and the regulation of DA and TA in the brain to promote the production of reproductive workers in queenless honey bee colonies.

Egg marking pheromones of anarchistic worker honeybees (Apis mellifera)

In honeybees, worker policing via egg eating enforces functional worker sterility in colonies with a queen and brood. It is thought that queens mark their eggs with a chemical signal, indicating that their eggs are queen-laid. Worker-laid eggs lack this signal and are, therefore, eaten by policing workers. Anarchistic worker honeybees have been hypothesized to circumvent worker policing by mimicking the queen egg-marking signal. We investigated this phenomenon by relating chemical profiles of workers and their eggs to egg acceptability. We found that the ability of some workers (anarchistic workers in queenright colonies and deviant workers from a queenless colony) to lay more acceptable eggs is due to them producing significant amounts of queen-like esters from their Dufour's gland. These esters appear to be transferred to eggs during laying and increase egg survival. However, these esters cannot be the normal queen egg-marking signal, as they are generally absent from queen-laid eggs and only increase the short-term persistence of worker-laid eggs, because only 7?30% of anarchistic worker-laid eggs persisted to hatching versus 91?92% of queen-laid eggs. All workers can produce some esters, but only workers that greatly increase their ester production lay more acceptable eggs. The production of esters appears to be a flexible response, as anarchistic workers reared in queenless colonies did not increase their ester production, while some deviant workers in queenless colonies did increase their ester production.

Conservation of Bio synthetic pheromone pathways in honeybees Apis.

Social insects use complex chemical communication systems to govern many aspects of their life. We studied chemical changes in Dufour's gland secretions associated with ovary development in several genotypes of honeybees. We found that C28-C38 esters were associated only with cavity nesting honeybee queens, while the alcohol eicosenol was associated only with their non-laying workers. In contrast, both egg-laying anarchistic workers and all parasitic Cape workers from queenright colonies showed the typical queen pattern (i.e. esters present and eicosenol absent), while egg-laying wild-type and anarchistic workers in queenless colonies showed an intermediate pattern, producing both esters and eicosenol but at intermediate levels. Furthermore, neither esters nor eicosenol were found in aerial nesting honeybee species. Both esters and eicosenol are biosynthetically similar compounds since both are recognizable products of fatty acid biosynthesis. Therefore, we propose that in honeybees the biosynthesis of esters and eicosenol in the Dufour's gland is caste-regulated and this pathway has been conserved over evolutionary time.

Patterns of male parentage in the fungus-growing ants

Ant queens from eight species, covering three genera of lower and two genera of higher attine ants, have exclusively or predominantly single mating. The ensuing full-sib colonies thus have a strong potential reproductive conflict between the queen and the workers over male production. This is because, all other things being equal, relatedness incentives should favour traits expressed in both workers and the queen to monopolise the production of the colony's male offspring. Microsatellite genotyping of males from these attine species shows that workers in queenless colonies are able to produce males, but that no worker-produced males were found in queenright colonies. Our results suggest that worker reproduction is rare or even absent in colonies with a fertile queen. This indicates that either the queen directly prevents the workers from raising their own sons, or that worker reproduction is absent in the presence of a fertile queen due to high ergonomic costs of this behaviour.

Worker age, size and social status in queenless colonies of the ant Leptothorax gredleri

Workers in queenless colonies of the ant Leptothorax gredleri form dominance hierarchies by antennation bouts and biting. The frequency of aggressive interactions peaked when the ants became active again after hibernation, a second time in summer, when new workers eclosed from overwintered brood, and a third time when we experimentally removed the queen. High-ranking individuals were more active and had greater ovarian development than their low-ranking nestmates. We investigated what proximately determines a worker's social status. Neither age, previously shown to affect hierarchy rank in several other social insects, nor levels of fluctuating asymmetry appeared to be important in worker rank orders inL.gredleri . High-ranking workers were on average larger than low-ranking individuals and body size and rank were correlated in four of five colonies investigated. However, individuals of similar age but different social status did not differ in size.

Development and behaviour of anarchistic honeybees

Anarchistic honeybees result from extremely rare behavioural mutations which allow workers to lay eggs despite the presence of the queen. We investigated the behavioural development of bees derived from a line in which ca. 5% of workers have developed ovaries and lay viable eggs. Other than their developed ovaries and proclivity to lay eggs, the anarchistic workers we studied are apparently normal, performing normal worker-like behaviour. Unlike many laying workers in queenless colonies, they are not queen-like and are apparently not the objects of aggression. When day-old workers from anarchistic colonies were cross-fostered into anarchistic and wild-type host colonies, the frequency of ovary development was an order of magnitude higher in the anarchistic host (9.1%) than in the wild-type host (0.7%). This suggests that there is a policing mechanism that affects ovary development in honeybees. Thus, worker reproduction is probably suppressed at the level of ovary development as well as by oophagy of worker-laid eggs. Other mechanisms, such as aggression towards individuals with developed ovaries, may also exist, but we found no evidence for this.

Effects of social conditions on Juvenile Hormone mediated reproductive development in Bombus terrestris workers

Abstract. During the annual life cycle of the bumble bee Bombus terrestris (L.) colony, there is a stage characterized by worker reproduction in the presence of the queen. It has been proposed that this is a result of a decrease in queen inhibition. This hypothesis was examined by studying the effects of queens taken from colonies at different stages of development on several aspects of worker physiology and behaviour: rates of Juvenile Hormone (JH) release in vitro, ovary development, and behaviour associated with reproduction. After optimizing and validating the radiochemical assay for JH release for bumble bee workers, we found that queenless workers had significantly more developed ovaries and higher rates of release of JH than did queenright workers, confirming and extending previous findings that suggest that bumblebee ovarian development is under JH control. Mated queens, separated from their colony and brood, can have the same inhibitory effect on the reproductive development of callow workers. In contrast, workers confined with virgin queens or in queenless groups demonstrated a significantly higher rate of release of JH, overt aggression and threatening behaviours. However, there were no differences in rates of release of JH between workers confined in groups in the laboratory with queens taken from colonies either before or after the onset of worker reproduction. Furthermore, overt aggression and threatening behaviours were similar and low in both types of groups. These results gave no support to the hypothesis that a decrease in queen inhibition is associated with the onset of worker reproduction. We also show that young workers reared in colonies either before or after worker reproduction occurs, or in queenless colonies, all demonstrated similar, low rates of release of JH. These results suggest that older workers may inhibit the corpora allata of younger workers in queenless colonies.

Emergency queen cell production in the honey bee colony

Emergency queen cell production was examined in honey bee colonies of mixed European races. Thirteen colonies were dequeened and followed on a daily basis until after queen emergence. Observations were made on the number of cells, the temporal sequence of queen cell construction, cell location within the nest, the age of larvae selected for queen rearing, mortality of immature queens and the scenting behavior of workers in queenless colonies.

Dynamics of Entry of Spermatozoa into the Spermatheca of Instrumentally inseminated Queen Honeybees

SummaryQueens were inseminated with 1, 2, 4 or 8 mm3 of semen, and either held, each with 250 workers, in an incubator at 34°C, or caged without workers in queenless colonies. In the first 4 h the amount of semen injected and the presence or absence of workers had little, if any, effect on the rate of entry of spermatozoa into the spermatheca, which was 200–300 thousand/h. In queens injected with 1 and 2 mm3 of semen, the process of entry had largely ended after 4–8 h, but in queens injected with 8 mm3 it continued, slowly, up to at least 40 h. The presence or absence of workers had little or no influence on the final number of spermatozoa in the spermatheca when 1 or 2 mm3 of semen were injected, but it clearly increased the final number when 4 or 8 mm3 were injected.

Separate protein body compartments of the worker honeybee ( Apis mellifera L.)

1. 1. Protein of adult worker bees are secreted from their exocrine glands in royal jelly and in venom or in eggs laid by laying workers in queenless colonies. 2. 2. The present report examines the protein composition of head and thoracic glands, venom glands, fat body and ovaries, the relation of these proteins to haemolymph proteins and the possible exchange of macromolecules between glandular compartments, the haemocoele and the organs located in the haemocoele. 3. 3. The identity of proteins from various compartments was established by double-diffusion, immunoelectrophoresis, gradient acrylamide slab gel electrophoresis and isoelectric focusing. 4. 4. Royal jelly is composed of proteins secreted from hypopharyngeal, mandibular and postcerebral, but not from thoracic glands. 5. 5. No immunological identity was found between the proteins of royal jelly, venom and haemolymph. The glands producing the two secretions seem to be separate compartments from the haemocoele with regards to macromolecular traffic. 6. 6. In contrast to the exocrine glands many of haemolymph proteins were shared by the fat body and the ovaries. 7. 7. Some aspects of macromolecular traffic between the body compartments in insects are discussed.