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Essay: The Queen Bee

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  • Published: 23 January 2019*
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One individual, the queen bee, typically dominates reproduction in eusocial bee species. However, worker bees refrain from reproductive activity unless it benefits their own interests. The controversy at hand is who has more control over reproduction in the hive between the queen and the workers. Multiple experiments are analyzed with variables such as ovary activation, pheromones, policing, and distance. Evidence points to the worker bees have more methods to control reproduction in the hive.
 
Introduction

Many bees fit into a category called eusocial species. Eusocial is the highest level of organization in a species. Organization includes division of labor such as brood care, overlapping of generations, and reproductive division. For this reason, bees are studied in depth to understand the interactions between the queen and her worker bees.

The division of labor in a beehive is broken up into three groups; queen bee, worker bees, and drone bees. The queen bee lays eggs for the hive. She has a sex-determining mechanism called haplodiploidy, in which she can control the gender of her offspring. Male and female are determined by the ploidy of her offspring. The diploid worker bees typically clean the hive, care for queen larvae, and police their sister worker bees. The haploid drone bees are the males in the hive and sole purpose is to breed. Between these groups of bees, studies specifically are concerned in the reproductive aspect within the hive. Who has more control over reproduction – the queen bee or worker bees? Are male reproductive made to queens optimum or workers optimum? Contrary to common belief, worker bees have shown to escape the queen’s full control. Currently, there are two main hypotheses arguing who has more reproductive power (Figure 1). According to the ‘queen control’ hypothesis, the queen turns on the workers sterility by emission of her pheromones, actively inhibiting reproduction. In addition to this, workers police their sister bees to increase their inclusive fitness. This will benefit the queen by maintaining her power over reproduction. On the contrary, in the ‘queen signal’ hypothesis, selfish worker bees can have offspring for their own benefit. If a worker reproduces, they do not have to work for the hive for the duration of reproduction. This lengthens the workers life span, considering that the highest mortality for worker bees is due to work exhaustion (Alves et al. 2009). The problem with selfish reproduction is that it is risky because other worker bees can police the reproducing bee by eating her egg(s). Policing carried out by the workers shows that they have another aspect of control over the reproduction, even if it is defending the queen. The purpose of this article is to show evidence that the ‘queen signal’ hypothesis has stronger support for reproductive control.

Evidence for Queen Control Hypothesis

Ovary Activation

The queen has a mandibular pheromone (QMP) that suppresses development in workers ovaries. QMP is transferred from the queen to worker bees, and then dispersed throughout the hive via physical contact between the bees (Orlova & Hefetz 2014). This hormone is very effective in attracting males during mating flight, inhibiting queen rearing, attracting workers, and most importantly, inhibiting reproduction in workers (Oi 2015). QMP will significantly, if not completely, inhibit ovary activation in the workers. A colony that had a fecund queen was observed to see how workers carried on normal tasks, and results show that in this specific colony, almost all workers had inactive ovaries and reared the queen’s offspring (Peso et al. 2013). This favors the ‘queen control’ because workers are manipulated to remain sterile against their own reproductive interest.

Sex Allocation

The queen’s mechanism haplodiploidy allows for sex allocation. This control was found to be endogenous to the queen bee. The queen determines the sex of her offspring by exhibiting a “switch-point” where she will either lay an unfertilized haploid egg (drone bee) or a fertilized diploid egg (potential queen or worker bee). Workers have no control over this mechanism (Holland 2018). This mechanism permits queen to exercise control in kin-selected conflict over sex allocation.

Worker Policing

The worker bees have multiple ways to control reproduction in the hive including policing. Policing is any action done by the worker bees that interferes with reproductive output of their sister bees (Holmes et at. 2014). Actions include initially detecting the worker’s eggs and then eating them. This study demonstrated the significance of policing mechanisms in order to avoid the cost for the colony as a whole associated with selfish behavior. When an effective policing method is in place, reproductive acquiesce is predicted to take place (Yagound et al. 2017). This is when the incentive for worker reproduction, kin selection (Box 1), is nearly lost (Holmes et al. 2014). If their eggs will be policed, the energy and time will not be worth it. Studies were done for a 24-hour period to examine policing done to both worker-laid and queen-laid cells. It was shown that highest policing was done to worker cells and after the 24 hours, all worker eggs were removed by sister workers. This shows that policing is very effective in keeping the workers offspring to a minimum and allowing queen’s offspring to thrive.

Evidence for Queen Signal Hypothesis

Worker Policing

Although worker policing is a factor in queen control, it also is one of the strongest argument in favor of queen signal. Experiments have shown that policing is effective by removing ~98% of worker laid eggs (Karcher & Ratneiks 2013). Policing is carried out using a recognition system. This recognition system is effective and typically only 2% of eggs are mistakenly not destroyed. This is minimal compared to the 50/50 chance it would be if the workers just guessed. Kin selection explains why worker bees will sacrifice their own well being to rear queen’s offspring. Workers are twice as related to sons of the queen than sons of other workers. Therefore, workers can increase their inclusive fitness by rearing the queen’s offspring (Holmes et al. 2014). The inclusive fitness theory predicts that the worker bees as a whole want to minimize selfish behavior in their sisters. Refraining from personal reproduction and increase reproductive output of queen will increase worker inclusive fitness.

Distance

In a hive, there will always be remote and peripheral areas that will potentially be without a queen. These can be considered queenless or just far enough away to be out of her control. In these areas, a worker bee can be less affected by the queen’s pheromones and thus activate their own ovaries. Movement towards and away from the queen was studied and found that moving far away allowed for increase in ovary size (Figure 2) (Orlova & Hefetz 2014). Therefore, if a worker has the means to deter the queen’s pheromones simply by distance, her control is not as strong as previously thought.

Life Span

The typical life span of a worker bee is 31 days. This life span is much shorter than the average queen’s span of 175 days (Alves et al. 2009). The biggest factor of this low life span is exhaustion. Worker bees carry out all the risky and costly tasks that ultimately end in being over worked. This leads to selfish reproduction because if a worker is laying eggs, she will not be participating in hive maintenance for the duration of reproducing. Typically 21 days is required from the day the egg is laid until it is fully-grown (Naeger et al. 2013). This is nearly the number of days for a full-expected worker life span. An experiment took place looking at workers with ovaries either resting, partly developed, or fully developed (Mattila et al 2012). The bees with partly developed ovaries were said to be in reproductive “readiness”. This meant that they were not reproducing but ready to jump on the opportunity if one was to arise. The study looked at task performances and tested for correlation with ovary development. Task performances are behaviors such as walking, grooming, feeding brood, maintaining hive,
enter/exit hive, and guarding. Results showed that the work
er bees with fully developed ovaries were motionless more often than actively participating in hive tasks (Figure 3).

Another study was done looking at the offspring in a hive and testing their DNA to see if the offspring was that of a worker or the queen (Alves et al. 2009). Surprising results demonstrated that 80% of workers sons had genotypes that were incompatible with them being sons of workers of the present queen. This means the particular larvae they were looking at had DNA from a superseded queen. These workers that reproduced were found to increase their lifespan to 110 days, which is almost 3.5 times expected (Alves et al. 2009). This shows that the worker bees who were reproductive surpassed their initial queen and parasitized the next generation. This benefits the worker because when a new queen comes in, the new queen’s offspring will be less related to her, therefore the incentive of inclusive fitness decreases. The bees that are able to take advantage of this opportunity are typically the bees that are in reproductive “readiness” (Mattila et al. 2012).

Ovary Activation

Workers have the ability to activate their own ovaries when they perceive that their colony is queenless or headed by a failing queen. In addition, they can detect when brood size is decreasing. The strength of the QMP pheromone diminishes with distance, which can give the worker a false idea that there is no queen (Orlova & Hefetz 2014) The problem with the false impression (thinking that the queen is no longer in power) worker bees have no choice but to rear a new queen. The queues initiate a response that they need to reproduce and rear their colony a new queen bee. Ovaries will then activate and the queen will no longer be the sole reproductive source.

Hypotheses Collide

Worker policing is used to defend both queen signal and queen control hypotheses. It is hard to draw the line between the bees policing to maintain the queen’s monopoly or to simply have control over offspring to increase their own inclusive fitness. Comparison of all experiments shows that majority favors queen signal hypothesis (Table 1).

Caveats

Nearly all data collected on worker reproduction has been under conditions that either removed the queen completely in power, or used a queen excluder to put a barrier in between the workers and the queen. In these circumstances, observed worker bees act according to how they would if their colony was queenless. However, with a strong powerful queen in a natural setting, reproductive activity in workers may not be as evident as seen in experiments. There have also been fluctuations in different studies based on if the queen is mated or unmated (Peso et al. 2013). The mated queen is shown to have higher effectiveness. Therefore, depending on what type of queen is being studied the overall results could be affected.

Conclusion

Evidence shows the Queen Signal Hypothesis is stronger and worker bees have more power over reproduction in the hive. Both the queen bee and worker bees have effective measures for controlling the population in a beehive. However, with the queen’s strongest trait being her pheromones, and considering they are subject to being weak based on distance, it falls short to the many ways workers control reproduction. Worker bees can make decisions based on their own fitness and the queen does not have ability to control them completely. Even if she is responsible for majority of the offspring, the workers decide what eggs live and what eggs are removed.

Importance and Future Studies

Bees are the most critical pollinators humans have and without them we would lose a significant number of crops and biodiversity. Understanding how they maintain structure and facilitate jobs in the hive can help us protect them and allow them to thrive.

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