Academic literature on the topic 'Primitively eusocial paper wasp'

In cooperatively breeding vertebrates, the existence of individuals that help to raise the offspring of non-relatives is well established, but unrelated helpers are less well known in the social insects. Eusocial insect groups overwhelmingly consist of close relatives, so populations where unrelated helpers are common are intriguing. Here, we focus on Polistes dominula— the best-studied primitively eusocial wasp, and a species in which nesting with non-relatives is not only present but frequent. We address two major questions: why individuals should choose to nest with non-relatives, and why such individuals participate in the costly rearing of unrelated offspring. Polistes dominula foundresses produce more offspring of their own as subordinates than when they nest independently, providing a potential explanation for co-founding by non-relatives. There is some evidence that unrelated subordinates tailor their behaviour towards direct fitness, while the role of recognition errors in generating unrelated co-foundresses is less clear. Remarkably, the remote but potentially highly rewarding chance of inheriting the dominant position appears to strongly influence behaviour, suggesting that primitively eusocial insects may have much more in common with their social vertebrate counterparts than has commonly been thought.

Abstract Nests of independent-founding primitively eusocial paper wasps are founded by one or a few females. Before worker emergence, foundresses must forage, sometimes leaving the nest unattended. Chemical defence - the application of ant repellent secretions of the Van der Vecht organ (VdVO) on the nest surface - allows brood protection when active defence is weak or not possible. After worker emergence, it is more likely that some wasps stay in the nest, so active nest defence may be more common. Given this constraint on the nest defence, selection for increasing the cuticular secretory area of the VdVO, to improve chemical defence, may be stronger in foundresses (queens) than in workers - morphological castes are hypothesized to evolve. We investigated the occurrence of morphological castes in the Neotropical paper wasp Mischocyttarus. Confirming our prediction, we found that in some (but not all) species, foundresses have a distinct increase in the secretory area of the VdVO in relation to workers; even though there is a strong overlap between caste phenotypes (incipient morphological castes). Implications of these findings for the evolution of morphological castes in primitively eusocial wasps are discussed.

Remarkable variation exists in the distribution of reproduction (skew) among members of cooperatively breeding groups, both within and between species. Reproductive skew theory has provided an important framework for understanding this variation. In the primitively eusocial Hymenoptera, two models have been routinely tested: concessions models, which assume complete control of reproduction by a dominant individual, and tug-of-war models, which assume on-going competition among group members over reproduction. Current data provide little support for either model, but uncertainty about the ability of individuals to detect genetic relatedness and difficulties in identifying traits conferring competitive ability mean that the relative importance of concessions versus tug-of-war remains unresolved. Here, we suggest that the use of social parasitism to generate meaningful variation in key social variables represents a valuable opportunity to explore the mechanisms underpinning reproductive skew within the social Hymenoptera. We present a direct test of concessions and tug-of-war models in the paper wasp Polistes dominulus by exploiting pronounced changes in relatedness and power structures that occur following replacement of the dominant by a congeneric social parasite. Comparisons of skew in parasitized and unparasitized colonies are consistent with a tug-of-war over reproduction within P. dominulus groups, but provide no evidence for reproductive concessions.

Abstract Relatively little is known about the processes shaping population structure in cooperatively breeding insect species, despite the long-hypothesized importance of population structure in shaping patterns of cooperative breeding. Polistes paper wasps are primitively eusocial insects, with a cooperative breeding system in which females often found nests in cooperative associations. Prior mark-recapture studies of Polistes have documented extreme female philopatry, although genetic studies frequently fail to detect the strong population structure expected for highly philopatric species. Together these findings have led to lack of consensus on the degree of dispersal and population structure in these species. This study assessed population structure of female Polistes fuscatus wasps at three scales: within a single site, throughout Central New York, and across the Northeastern United States. Patterns of spatial genetic clustering and isolation by distance were observed in nuclear and mitochondrial genomes at the continental scale. Remarkably, population structure was evident even at fine spatial scales within a single collection site. However, P. fuscatus had low levels of genetic differentiation across long distances. These results suggest that P. fuscatus wasps may employ multiple dispersal strategies, including extreme natal philopatry as well as longer-distance dispersal. We observed greater genetic differentiation in mitochondrial genes than in the nuclear genome, indicative of increased dispersal distances in males. Our findings support the hypothesis that limited female dispersal contributes toward population structure in paper wasps.

AbstractWe examined the queen's role in regulation of worker foraging in small field colonies of the primitively eusocial wasp, Polistes fuscatus (29 colonies; 148 h observation). Queen removal results in a significant reduction in worker departure rate. The placement of a cooled, inactive queen into her queenless nest produces a significantly greater reduction in worker departure rate than does queen removal, and the resumption of activity by an inactive queen causes a significant increase in worker departure rate. Removal or cooling of a single worker does not produce similar effects on worker foraging, suggesting that the queen is the central regulator of worker foraging in small P. fuscatus colonies. We present evidence that: (1) the queen's control of worker foraging is mediated primarily by her influence on worker nest activity, (2) queen aggression may be important in stimulating departures by workers with low tendencies to leave the nest (i.e., dominant workers), and (3) the magnitude of the queen's stimulatory influence on worker foraging is directly related to the number of workers on the nest. We integrate these results with evidence from our other studies of polistine colony dynamics in a feedback control model of the social regulation of foraging.

In primitively eusocial societies, all individuals can potentially reproduce independently. The key fact that we focus on in this paper is that individuals in such societies instead often queue to inherit breeding positions. Queuing leads to systematic differences in expected future fitness. We first discuss the implications this has for variation in behaviour. For example, because helpers nearer to the front of the queue have more to lose, they should work less hard to rear the dominant's offspring. However, higher rankers may be more aggressive than low rankers, even if they risk injury in the process, if aggression functions to maintain or enhance queue position. Second, we discuss how queuing rules may be enforced through hidden threats that rarely have to be carried out. In fishes, rule breakers face the threat of eviction from the group. In contrast, subordinate paper wasps are not injured or evicted during escalated challenges against the dominant, perhaps because they are more valuable to the dominant. We discuss evidence that paper-wasp dominants avoid escalated conflicts by ceding reproduction to subordinates. Queuing rules appear usually to be enforced by individuals adjacent in the queue rather than by dominants. Further manipulative studies are required to reveal mechanisms underlying queue stability and to elucidate what determines queue position in the first place.

Abstract Ropalidia marginata, traditionally regarded as a primitively eusocial wasp species appears to have acquired some features reminiscent of highly eusocial species. Queens are behaviorally passive individuals, yet maintain complete reproductive monopoly and probably use pheromones to achieve this. Regulation of worker foraging is achieved by the workers themselves in a decentralized, self-organized manner. If there are other species in the genus Ropalidia that do not show such relatively 'advanced' features, this genus can provide an attractive model system to investigate the evolutionary transition from the primitively eusocial to the highly eusocial state. Here, we therefore investigate the congeneric Ropalidia cyathiformis and demonstrate that in contrast to R. marginata, it appears to be a typical primitively eusocial species. As expected therefore, and in striking contrast with R. marginata, R. cyathiformis queens are the most, or among the most, dominant, active and interactive individuals and their behavior is consistent with the possibility that they suppress worker reproduction and regulate worker foraging in a relatively centralized manner. Upon removal of the queen, a potential queen with levels of aggression even higher than that of the queen, becomes apparent immediately. Such a potential queen appears to take over inhibition of worker reproduction and regulation of worker foraging by mechanisms similar to that used by the queen so that, there is no disruption in foraging and brood care. We suggest that comparative studies of

Many animals live in societies of varying degrees of organization. Some individuals in these societies seem to sacrifice their own fitness to increase the fitness of some others. Understanding the forces that mould the evolution of such altruistic behaviour has become a dominant theme in modern evolutionary biology. Primitively eusocial polistine wasps provide excellent model systems to study the evolution of altruism as they show high degrees of plasticity in their behaviour. Different individuals in the same population pursue different social strategies such as nesting alpne or nesting in groups. When wasps nest in groups, usually only one individual becomes the egg layer, while die rest assume the role of sterile workers. Why do the workers not become solitary foundresses and rear their own offspring instead of working to rear the brood of another individual? Here I have used the tropical primitively eusocial wasp Ropalidia marginata to explore some factors that might potentially favour the worker strategy over the solitary founding strategy. Workers in multiple foundress nests may benefit by rearing brood more closely related to them than their own offspring would be. However, from previous work on this species it is known that relatedness between sisters is rather low and that workers therefore rear quite distantly related brood. Therefore, I have concentrated on factors other than genetic relatedness that might potentially favour the worker strategy. A total of 145 naturally initiated nests with different numbers of foundresses was monitored over a period of 16 months, and their productivities were compared. Although the total colony productivity increased, the per capita productivity did not increase with increasing foundress numbers. Colonies with larger foundress numbers did not produce significantly heavier progeny and did not produce them significantly faster than colonies with fewer individuals. The conspecific usurpers preferred to usurp single foundress colonies more often than multiple foundress colonies. Therefore, protection from conspecific usurpers might be an advantage of multiple foundress associations. About 10% of the multiple foundress nests experienced queen turnovers. This provides a finite chance to reproduce and gain some individual fitness for workers, at some future point of time. Wasps may not be similar in their reproductive abilities and those who are less fertile might be joining others who are more fertile. Testing such a hypothesis would require that individuals who have chosen to be subordinate cofoundresses in multiple foundress associations are forced to nest alone. During this study a total of 77 nests was monitored. Cofoundresses forced to nest alone had significantly lower productivity than natural solitary foundresses and also queens of multiple foundress nests who were forced to nest alone. This suggested that wasps are not similar either in their reproductive ability or brood rearing ability or both. To ascertain which of the factors was responsible for lower productivity in cofoundresses, productivity of wasps isolated into laboratory cages was compared. There was no significant difference in the productivity of isolated cofoundresses and isolated queens. This suggests that wasps are not subfertile per se but probably differ in their foraging and brood rearing abilities. The certainty with which resources are brought into the nest and therefore, the certainty with which the mean per capita productivity is attained, provides an automatic benefit of group living according to the central limit theorem. This prediction was also tested. The coefficient of variation of mean per capita productivity decreased significantly with increasing foundress numbers. Behavioural observations on another 36 colonies, with different number of adults, showed that the coefficient of variation of food brought to the nest and the rate at which larvae were fed, decreased significantly with increasing number of adults. A computer simulation was used to find out the effect of group size on the variance in feed larva. Assuming that larvae cannot be starved for too long and cannot utilize more than a certain amount of food at a time, the fitness of larvae was found to increase with an increase in the number of adults attending the nest. Previous work on R. marginata has been largely confined to postemergence colonies. An attempt was made to look at and compare social organization in preemergence colonies with that of postemergence colonies. It was found that the egg layer was not the most dominant animal in the well-established preemergence colonies. There were no detectable differences in the social organization of the preemergence colonies (of this study) with that of postemergence colonies of the earlier studies. Perhaps my conclusions drawn from studying preemergence colonies are therefore applicable more widely to the species. It can be concluded that the apparent increased fitness of the worker strategy over solitary foundress strategy does not come from any increase in per capita productivity, but comes instead from (i) the greater predictability with which the mean per capita productivity is attained in larger colonies, (ii) the lower probabilities of usurpation of larger colonies, (iii) queen turnovers that provide opportunities for workers in multiple foundress colonies to gain some direct individual fitness and (iv) the lower brood rearing abilities of workers in multiple foundress nests that make the worker strategy the best of a bad job.

Many animals live in societies of varying degrees of organization. Some individuals in these societies seem to sacrifice their own fitness to increase the fitness of some others. Understanding the forces that mould the evolution of such altruistic behaviour has become a dominant theme in modern evolutionary biology. Primitively eusocial polistine wasps provide excellent model systems to study the evolution of altruism as they show high degrees of plasticity in their behaviour. Different individuals in the same population pursue different social strategies such as nesting alpne or nesting in groups. When wasps nest in groups, usually only one individual becomes the egg layer, while die rest assume the role of sterile workers. Why do the workers not become solitary foundresses and rear their own offspring instead of working to rear the brood of another individual? Here I have used the tropical primitively eusocial wasp Ropalidia marginata to explore some factors that might potentially favour the worker strategy over the solitary founding strategy. Workers in multiple foundress nests may benefit by rearing brood more closely related to them than their own offspring would be. However, from previous work on this species it is known that relatedness between sisters is rather low and that workers therefore rear quite distantly related brood. Therefore, I have concentrated on factors other than genetic relatedness that might potentially favour the worker strategy. A total of 145 naturally initiated nests with different numbers of foundresses was monitored over a period of 16 months, and their productivities were compared. Although the total colony productivity increased, the per capita productivity did not increase with increasing foundress numbers. Colonies with larger foundress numbers did not produce significantly heavier progeny and did not produce them significantly faster than colonies with fewer individuals. The conspecific usurpers preferred to usurp single foundress colonies more often than multiple foundress colonies. Therefore, protection from conspecific usurpers might be an advantage of multiple foundress associations. About 10% of the multiple foundress nests experienced queen turnovers. This provides a finite chance to reproduce and gain some individual fitness for workers, at some future point of time. Wasps may not be similar in their reproductive abilities and those who are less fertile might be joining others who are more fertile. Testing such a hypothesis would require that individuals who have chosen to be subordinate cofoundresses in multiple foundress associations are forced to nest alone. During this study a total of 77 nests was monitored. Cofoundresses forced to nest alone had significantly lower productivity than natural solitary foundresses and also queens of multiple foundress nests who were forced to nest alone. This suggested that wasps are not similar either in their reproductive ability or brood rearing ability or both. To ascertain which of the factors was responsible for lower productivity in cofoundresses, productivity of wasps isolated into laboratory cages was compared. There was no significant difference in the productivity of isolated cofoundresses and isolated queens. This suggests that wasps are not subfertile per se but probably differ in their foraging and brood rearing abilities. The certainty with which resources are brought into the nest and therefore, the certainty with which the mean per capita productivity is attained, provides an automatic benefit of group living according to the central limit theorem. This prediction was also tested. The coefficient of variation of mean per capita productivity decreased significantly with increasing foundress numbers. Behavioural observations on another 36 colonies, with different number of adults, showed that the coefficient of variation of food brought to the nest and the rate at which larvae were fed, decreased significantly with increasing number of adults. A computer simulation was used to find out the effect of group size on the variance in feed larva. Assuming that larvae cannot be starved for too long and cannot utilize more than a certain amount of food at a time, the fitness of larvae was found to increase with an increase in the number of adults attending the nest. Previous work on R. marginata has been largely confined to postemergence colonies. An attempt was made to look at and compare social organization in preemergence colonies with that of postemergence colonies. It was found that the egg layer was not the most dominant animal in the well-established preemergence colonies. There were no detectable differences in the social organization of the preemergence colonies (of this study) with that of postemergence colonies of the earlier studies. Perhaps my conclusions drawn from studying preemergence colonies are therefore applicable more widely to the species. It can be concluded that the apparent increased fitness of the worker strategy over solitary foundress strategy does not come from any increase in per capita productivity, but comes instead from (i) the greater predictability with which the mean per capita productivity is attained in larger colonies, (ii) the lower probabilities of usurpation of larger colonies, (iii) queen turnovers that provide opportunities for workers in multiple foundress colonies to gain some direct individual fitness and (iv) the lower brood rearing abilities of workers in multiple foundress nests that make the worker strategy the best of a bad job.

Altruism in its extreme form is seen in social insects where most individuals give up their own reproduction and work to rear the offspring of their queen. The origin and evolution of such sterile worker castes remains a major unsolved problem in evolutionary biology. Primitively eusocial polistine wasps are an attractive model system for investigating this phenomenon. Ropalidia marginata (Lep.) (Hymenoptera: Vespidae) is one such tropical primitively eusocial wasp, in which new nests are initiated either by a single foundress or by a group of female wasps. Worker behaviour in Ropalidia marginata cannot be satisfactorily explained by the haplodiploidy hypothesis due to the existence of polyandry and serial polygyny which reduce intra-colony genetic relatedness to levels lower than the value expected between a solitary foundress and her offspring. Besides, wasps appear to move frequently between newly initiated nests, perhaps further reducing intracolony genetic relatedness. To study social organization and examine the possibility of kin recognition and task specialization under conditions of low intra-colony relatedness, genetically mixed colonies were created by introducing alien one-day old wasps onto recipient nests. As a first step I have tried to determine the factors that influence the acceptance of foreign wasps onto established colonies. I have introduced wasps between 1 to 20 days of age from donor colonies located at least 10 km away onto 12 different recipient colonies, observed these wasps for a period of 10 hours and later dissected them to examine their ovarian condition. Observations were carried out in the blind i.e. the observer was unaware of the identity of the wasps. Wasps upto 6 days of age were accepted by the alien nests. Older wasps may have been rejected because their relatively better ovarian condition may have been perceived as a reproductive threat to the recipient nest. Alternatively, younger wasps may have been accepted because they may be more easily moulded to the desired roles or due to some other correlate of age per se independent of ovarian condition. Although ovarian condition appeared to influence the probability of acceptance, it was not statistically significant in the presence of age in multiple regression models, making a favourable case for the 'ease of moulding hypothesis' or 'age per se hypothesis' over the 'reproductive threat hypothesis'. In any case these findings gave me a method to create genetically mixed colonies. On 12 different nests Ropalidia marginata, I similarly introduced one-day old wasps and thus created genetically mixed colonies. Such an introduction simulates the eclosion of distantly related individuals which is quite common on nests of R. marginata due to the presence of serial polygyny. About 7 such wasps were introduced per colony and the introductions were so arranged as to matched with natural eclosions on the recipient nest. After 7 days following the last introduction, colonies were observed for 20 hours each. Alien wasps became well integrated and performed most of the behaviours and tasks shown by the natal wasps. There was no evidence of kin recognition or task specialization between natal and introduced wasps. The introduced wasps also sometimes became replacement queens. In an attempt to test the costs in terms of brood rearing efficiency, of living in such genetically variable groups, I created kin and non-kin pairs of wasps in plastic containers. They were provided with ad libitum food, water and building material. The nests initiated were monitored till an adult offspring eclosed. There were no detectable differences in either the productivities or the developmental periods of immature stages in the kin and nonkin pairs suggesting that there is no apparent cost of living with unrelated or distantly related individuals. To compare the extent of cooperation between the two wasps in kin and non-kin pairs, I conducted behavioural observations on 12 pairs each of kin and nonkin wasps. I found no difference in the rates at which the non-egg layers brought food and pulp, fed larvae and built the nest in the kin and nonkin pairs suggesting that cooperative nest building and brood rearing was common to the kin as well as non-kin pairs. The results reported here strengthen the idea that factors other than genetic relatedness must play a prominent role in the maintenance of worker behaviour in Ropalidia marginata.

Altruism in its extreme form is seen in social insects where most individuals give up their own reproduction and work to rear the offspring of their queen. The origin and evolution of such sterile worker castes remains a major unsolved problem in evolutionary biology. Primitively eusocial polistine wasps are an attractive model system for investigating this phenomenon. Ropalidia marginata (Lep.) (Hymenoptera: Vespidae) is one such tropical primitively eusocial wasp, in which new nests are initiated either by a single foundress or by a group of female wasps. Worker behaviour in Ropalidia marginata cannot be satisfactorily explained by the haplodiploidy hypothesis due to the existence of polyandry and serial polygyny which reduce intra-colony genetic relatedness to levels lower than the value expected between a solitary foundress and her offspring. Besides, wasps appear to move frequently between newly initiated nests, perhaps further reducing intracolony genetic relatedness. To study social organization and examine the possibility of kin recognition and task specialization under conditions of low intra-colony relatedness, genetically mixed colonies were created by introducing alien one-day old wasps onto recipient nests. As a first step I have tried to determine the factors that influence the acceptance of foreign wasps onto established colonies. I have introduced wasps between 1 to 20 days of age from donor colonies located at least 10 km away onto 12 different recipient colonies, observed these wasps for a period of 10 hours and later dissected them to examine their ovarian condition. Observations were carried out in the blind i.e. the observer was unaware of the identity of the wasps. Wasps upto 6 days of age were accepted by the alien nests. Older wasps may have been rejected because their relatively better ovarian condition may have been perceived as a reproductive threat to the recipient nest. Alternatively, younger wasps may have been accepted because they may be more easily moulded to the desired roles or due to some other correlate of age per se independent of ovarian condition. Although ovarian condition appeared to influence the probability of acceptance, it was not statistically significant in the presence of age in multiple regression models, making a favourable case for the 'ease of moulding hypothesis' or 'age per se hypothesis' over the 'reproductive threat hypothesis'. In any case these findings gave me a method to create genetically mixed colonies. On 12 different nests Ropalidia marginata, I similarly introduced one-day old wasps and thus created genetically mixed colonies. Such an introduction simulates the eclosion of distantly related individuals which is quite common on nests of R. marginata due to the presence of serial polygyny. About 7 such wasps were introduced per colony and the introductions were so arranged as to matched with natural eclosions on the recipient nest. After 7 days following the last introduction, colonies were observed for 20 hours each. Alien wasps became well integrated and performed most of the behaviours and tasks shown by the natal wasps. There was no evidence of kin recognition or task specialization between natal and introduced wasps. The introduced wasps also sometimes became replacement queens. In an attempt to test the costs in terms of brood rearing efficiency, of living in such genetically variable groups, I created kin and non-kin pairs of wasps in plastic containers. They were provided with ad libitum food, water and building material. The nests initiated were monitored till an adult offspring eclosed. There were no detectable differences in either the productivities or the developmental periods of immature stages in the kin and nonkin pairs suggesting that there is no apparent cost of living with unrelated or distantly related individuals. To compare the extent of cooperation between the two wasps in kin and non-kin pairs, I conducted behavioural observations on 12 pairs each of kin and nonkin wasps. I found no difference in the rates at which the non-egg layers brought food and pulp, fed larvae and built the nest in the kin and nonkin pairs suggesting that cooperative nest building and brood rearing was common to the kin as well as non-kin pairs. The results reported here strengthen the idea that factors other than genetic relatedness must play a prominent role in the maintenance of worker behaviour in Ropalidia marginata.

Reproductive division of labor is the most distinctive characteristic of the social Hymenoptera; some individuals reproduce and others forego their own reproduction to raise non-descendant offspring. In species where females are reproductively totipotent and lack morphologically distinct castes, there is potential for reproductive conflict because more than one female in a colony may attempt direct reproduction. I focused my dissertation research on a subtropical population of the primitively eusocial paper wasp, Mischocyttarus mexicanus, to investigate the initiation, establishment, and development of the colony before the emergence of adult offspring. Female M. mexicanus exhibit variation in behavior and task performance, and switch between reproductive and non-reproductive roles. These changes in behavior and reproduction may be influenced by social context. In three studies, I investigated the role of social context on reproduction, behavior, and brain structure. In the first study, I tested the role of body size, reproductive potential, and immediate egg-laying potential on the reproductive tactic employed by females. I found that large females either became solitary foundresses or became part of a group-initiated colony. In contrast, small females left their natal colony and pursued joining other colonies. This joiner tactic is unique to this population and has not been observed in temperate zone populations. I also found that subordinate females had the potential to lay eggs if given the opportunity. This suggests an incentive to remain in a colony for future opportunities of direct reproduction. In the second study, I investigated the effect of three variables on non-nestmate acceptance: non-nestmate age, stage of colony development, and non-nestmate aggressive behavior. I demonstrated that non-nestmate acceptance was context-dependent. Both non-nestmate age and stage of colony development had an effect on the proportion of accepted non-nestmates. Although, non-nestmate aggressive behavior did not affect non-nestmate acceptance, it did trigger an aggressive response from colony nestmates. In the third study, I assessed the relationship of Mushroom Bodies (MB) volume, the brain neuropils associated with learning and memory, to environmental conditions and social interactions. I compared MB volume of newly-established colonies initiated by solitary foundresses to groups of foundresses. In addition, I performed laboratory experiments to differentiate between the effect of environmental conditions and social interactions. I found a positive relationship between MB volume and environmental conditions including light intensity and foraging experience. In contrast to previous studies, I found no association between MB volume and social interactions. Ovary development was positively correlated with MB development. This result suggests that although reproductive dominance is established in newly-initiated colonies, social dominance may not yet be established. In summary, my studies found an effect of social context on behavior, adoption of reproductive tactics and brain structure in colonies of M. mexicanus during the offspring pre-emergence phase.

In my thesis, I found that queens and workers in the primitively eusocial paper wasp Ropalidia marginata use space on their nests non-randomly with a majority of individuals showing spatial fidelity to small core areas, in spite of the brood itself being randomly distributed. Such non-random space use appears to be a prophylactic measure against the spread of infection. I also found that centrally located larvae are preferably fed and wasps optimize feeding routes but do not spatially segregate when feeding larvae in parallel within a feeding bout probably to build-in redundancy and avoid larvae going hungry. Understanding the spatial organization of food transfer may be a key to understanding how insect societies achieve efficient social organization and division of labour.

Social insects are the most dominant terrestrial fauna for the last 50 million years. This tremendous ecological success is accompanied by the fact that sociality has evolved multiple times independently and achieved highest degree of complexity in insect lineages. The remarkable social organization found in insect societies is the result of finely balanced cooperation and conflict among the colony members. A typical hymenopteran colony is characterised by one or a few queens monopolizing reproduction and several sterile workers co-operatively raising brood and performing colony activities. The colonies are often conceptualized as superorganisms where groups of cooperative workers are compared with organs in the body, each of which accomplish a particular task like brood care, foraging and defence. The choice of tasks is often regulated by a systematic age polyethism. As the queens monopolize reproduction, they serve as the sole suppliers of eggs in the colony. Therefore, loss or death of the queen creates a crucial void which exposes the colony to potential reproductive conflict for the position of egg-layer. This crisis is expected to be extreme in monogynous colonies. The situation is rescued only after a new queen is established, and the whole process is known as queen succession. I am interested in this crisis management, and my thesis deals with potential and realized conflicts associated with queen succession and behavioural strategies involved in resolution of these conflicts. The queen can be replaced in two ways - either by a newly eclosed specialized reproductive individual, which happens in highly eusocial hymenopterans, or by an existing member of the colony (worker), as it happens in primitively eusocial hymenopterans. Unlike in highly eusocial species, the workers of primitively eusocial species retain their ancestral capability of mating and activating ovaries to produce both sons and daughters, which makes them suitable for taking up the role of queen in their lifetime. Hence, primitively eusocial species provide a unique situation where loss or death of the queen might result in severe reproductive conflict as the queen can be replaced by any one of the existing workers. Strictly monogynous colonies of the tropical primitively eusocial wasp Ropalidia marginata provide ideal opportunities to study the reproductive conflict and its resolution associated with queen succession because the queen is frequently replaced by one of her nestmates resulting in a serial polygyny. These queens have highly variable tenures of queenship ranging from seven to over 200 days, which, together with the fact that they are replaced by a variety of relatives such as daughters, niece and cousins, suggests a potential reproductive conflict with variable degrees of complexity. I have divided my thesis in three parts which are as follows -Natural queen turnover: Previous works from this lab have tried to characterize the queen succession in R. marginata colonies by experimentally removing the queen from the colony. As this design involves the experimenter intervening at a random point of the colony cycle, the colony might not respond in the similar way as it might have done to a natural succession necessitated by loss or death of the queen. But rarity and unpredictability of natural queen turnovers made them difficult to study. Therefore, in this section, we gathered a dataset of long-term and opportunistic quantitative behavioural observations on eleven natural queen turnovers and compared them with available data on queen removal experiments. All our queen removal experiments resulted in a hyper-aggressive potential queen who gradually reduced her aggression, activated her ovaries and went on to become the unanimously accepted new queen of the colony if the original queen was not returned. Here we found a similar phenomenon in natural colonies where a single un-challenged potential queen took over the colony as new queen after the old queen was lost, died or was driven out of the colony. In some of the natural colonies, the transition was preceded by aggression shown by the potential queens towards their nestmates including the queens, which indicates that they might have pre-empted the transition. The potential queens in natural colonies started laying eggs much faster than in experimental colonies suggesting their physiological readiness for the transition. How does a colony respond to a declining queen?: As we could show that some of the potential queens might perceive the upcoming queen turnover, a fair prediction would be that they sense it through the declining fertility status of the queens. Therefore, we tried to ex-perimentally induce situations where the queen appears to be declining, expecting that it might lead to a queen turnover. The growing evidence suggests that R. marginata queen maintains her status by applying a pheromone on the nest surface by rubbing the tip of her abdomen. We knocked down the nest to deny the queen the surface for applying her pheromone, and argued that the queen would be overthrown as the workers would sense her as infertile. To our surprise, the queen maintained her status in six out of seven colonies by applying her pheromone on the entire surface of the cage. However, the effectively insufficient concentration of pheromone elicited aggression from workers towards the queen, and the queen retaliated back with aggression. These results suggest that the pheromone, being an honest signal of fertility, is extremely important for the queen for maintaining her reproductive monopoly, and the workers are able to perceive the decline of the queen from her pheromone. Queen-successor conflict over access to reproduction: Here we more explicitly looked at the potential reproductive conflict between the queen and her successor over access to direct reproduction. We used the theory of parent-offspring conflict proposed by Robert Trivers (1974) as the conceptual framework and adapted it to unravel the pat-tern of queen-successor conflict in R. marginata colonies. According to this idea, we expected that there should be a pre-conflict zone where the queen and the successor both would agree that the queen should continue to reproduce, followed by a conflict zone where the successor would try to takeover but the queen would hang on, finally followed by post-conflict zone where they both would agree that the successor should reproduce. To test this expectation, we maintained the queen and the potential queen on either side of a wire-mesh partition, each with randomly chosen half of the workers. It allowed the potential queen (successor) to establish herself and then we reintroduced the queen to her side of the mesh daily till the queen gave up. We could behaviourally characterise all three zones which always appeared in the expected sequence. The pre and post-conflict zones had no aggressive interaction between the queen and the potential queen, whereas the conflict zone was characterized by aggressive falling fight between them. This is our first success in experimentally creating overt conflict between the queen and her successor. Overall we can say, that the queens and the potential queens of R. marginata show great behvioural plasticity which might have been shaped by natural selection as an adaptation for conflict resolution. We could show that the potential queens sometimes can predict the upcoming transition and pre-pare themselves accordingly, whereas they can also react to an experimentally created sudden loss of queen by hugely elevating their aggression. The docile queens, on the other hand, maintain their reproductive monopoly by a pheromone, which is essentially a feature of highly eusocial species. But these docile queens have not lost their capability to show aggression and can use that to complement the insufficient concentration of her pheromone. This and the behaviour of potential queens in their establishment phase are strongly reminiscent of typical primitively eusocial species. We conclude that Ropalidia marginata is, perhaps, a particularly advanced primitively eusocial hymenopteran situated on an evolutionary continuum from primitive to highly eusocial species.

Social insects are the most dominant terrestrial fauna for the last 50 million years. This tremendous ecological success is accompanied by the fact that sociality has evolved multiple times independently and achieved highest degree of complexity in insect lineages. The remarkable social organization found in insect societies is the result of finely balanced cooperation and conflict among the colony members. A typical hymenopteran colony is characterised by one or a few queens monopolizing reproduction and several sterile workers co-operatively raising brood and performing colony activities. The colonies are often conceptualized as superorganisms where groups of cooperative workers are compared with organs in the body, each of which accomplish a particular task like brood care, foraging and defence. The choice of tasks is often regulated by a systematic age polyethism. As the queens monopolize reproduction, they serve as the sole suppliers of eggs in the colony. Therefore, loss or death of the queen creates a crucial void which exposes the colony to potential reproductive conflict for the position of egg-layer. This crisis is expected to be extreme in monogynous colonies. The situation is rescued only after a new queen is established, and the whole process is known as queen succession. I am interested in this crisis management, and my thesis deals with potential and realized conflicts associated with queen succession and behavioural strategies involved in resolution of these conflicts. The queen can be replaced in two ways - either by a newly eclosed specialized reproductive individual, which happens in highly eusocial hymenopterans, or by an existing member of the colony (worker), as it happens in primitively eusocial hymenopterans. Unlike in highly eusocial species, the workers of primitively eusocial species retain their ancestral capability of mating and activating ovaries to produce both sons and daughters, which makes them suitable for taking up the role of queen in their lifetime. Hence, primitively eusocial species provide a unique situation where loss or death of the queen might result in severe reproductive conflict as the queen can be replaced by any one of the existing workers. Strictly monogynous colonies of the tropical primitively eusocial wasp Ropalidia marginata provide ideal opportunities to study the reproductive conflict and its resolution associated with queen succession because the queen is frequently replaced by one of her nestmates resulting in a serial polygyny. These queens have highly variable tenures of queenship ranging from seven to over 200 days, which, together with the fact that they are replaced by a variety of relatives such as daughters, niece and cousins, suggests a potential reproductive conflict with variable degrees of complexity. I have divided my thesis in three parts which are as follows -Natural queen turnover: Previous works from this lab have tried to characterize the queen succession in R. marginata colonies by experimentally removing the queen from the colony. As this design involves the experimenter intervening at a random point of the colony cycle, the colony might not respond in the similar way as it might have done to a natural succession necessitated by loss or death of the queen. But rarity and unpredictability of natural queen turnovers made them difficult to study. Therefore, in this section, we gathered a dataset of long-term and opportunistic quantitative behavioural observations on eleven natural queen turnovers and compared them with available data on queen removal experiments. All our queen removal experiments resulted in a hyper-aggressive potential queen who gradually reduced her aggression, activated her ovaries and went on to become the unanimously accepted new queen of the colony if the original queen was not returned. Here we found a similar phenomenon in natural colonies where a single un-challenged potential queen took over the colony as new queen after the old queen was lost, died or was driven out of the colony. In some of the natural colonies, the transition was preceded by aggression shown by the potential queens towards their nestmates including the queens, which indicates that they might have pre-empted the transition. The potential queens in natural colonies started laying eggs much faster than in experimental colonies suggesting their physiological readiness for the transition. How does a colony respond to a declining queen?: As we could show that some of the potential queens might perceive the upcoming queen turnover, a fair prediction would be that they sense it through the declining fertility status of the queens. Therefore, we tried to ex-perimentally induce situations where the queen appears to be declining, expecting that it might lead to a queen turnover. The growing evidence suggests that R. marginata queen maintains her status by applying a pheromone on the nest surface by rubbing the tip of her abdomen. We knocked down the nest to deny the queen the surface for applying her pheromone, and argued that the queen would be overthrown as the workers would sense her as infertile. To our surprise, the queen maintained her status in six out of seven colonies by applying her pheromone on the entire surface of the cage. However, the effectively insufficient concentration of pheromone elicited aggression from workers towards the queen, and the queen retaliated back with aggression. These results suggest that the pheromone, being an honest signal of fertility, is extremely important for the queen for maintaining her reproductive monopoly, and the workers are able to perceive the decline of the queen from her pheromone. Queen-successor conflict over access to reproduction: Here we more explicitly looked at the potential reproductive conflict between the queen and her successor over access to direct reproduction. We used the theory of parent-offspring conflict proposed by Robert Trivers (1974) as the conceptual framework and adapted it to unravel the pat-tern of queen-successor conflict in R. marginata colonies. According to this idea, we expected that there should be a pre-conflict zone where the queen and the successor both would agree that the queen should continue to reproduce, followed by a conflict zone where the successor would try to takeover but the queen would hang on, finally followed by post-conflict zone where they both would agree that the successor should reproduce. To test this expectation, we maintained the queen and the potential queen on either side of a wire-mesh partition, each with randomly chosen half of the workers. It allowed the potential queen (successor) to establish herself and then we reintroduced the queen to her side of the mesh daily till the queen gave up. We could behaviourally characterise all three zones which always appeared in the expected sequence. The pre and post-conflict zones had no aggressive interaction between the queen and the potential queen, whereas the conflict zone was characterized by aggressive falling fight between them. This is our first success in experimentally creating overt conflict between the queen and her successor. Overall we can say, that the queens and the potential queens of R. marginata show great behvioural plasticity which might have been shaped by natural selection as an adaptation for conflict resolution. We could show that the potential queens sometimes can predict the upcoming transition and pre-pare themselves accordingly, whereas they can also react to an experimentally created sudden loss of queen by hugely elevating their aggression. The docile queens, on the other hand, maintain their reproductive monopoly by a pheromone, which is essentially a feature of highly eusocial species. But these docile queens have not lost their capability to show aggression and can use that to complement the insufficient concentration of her pheromone. This and the behaviour of potential queens in their establishment phase are strongly reminiscent of typical primitively eusocial species. We conclude that Ropalidia marginata is, perhaps, a particularly advanced primitively eusocial hymenopteran situated on an evolutionary continuum from primitive to highly eusocial species.

Reproduction is the avenue for gaining direct fitness. But in certain species some individuals do not reproduce, instead gain indirect fitness by helping relatives to reproduce; the prime examples for this come from the worker caste of social insects like ants, bees and wasps. For explaining such a perplexing paradox, also known as altruism, W.D. Hamilton proposed that individuals can gain fitness in two ways: directly, by reproducing (direct fitness), and indirectly, by helping relatives to reproduce (indirect fitness). Indirect fitness has since been the main focus for explaining the evolution of workers while usually overlooking the fact that workers can also gain direct fitness. One of the avenues for gaining direct fitness by workers is nest foundation and we have studied this phenomenon in a primitively eusocial wasp Ropalidia marginata. We found that workers routinely leave their natal nests to initiate new nests either alone or with a few other wasps. Before leaving their natal nests, such workers prepare in several ways for nest foundation, like enhancing their nutrient reserves and forming outside nest aggregations to engage in dominance interactions. Next, we investigated the emergence of cooperation and division of labour in newly founded nests and how these affect the productivities of the new nests. We found that while two wasps are sufficient for the emergence of cooperation and reproductive division of labour (DOL), it takes three wasps for non-reproductive DOL to emerge; cooperation and reproductive DOL are not sufficient for increasing colony productivity which comes about only with the addition of non-reproductive DOL. Finally, we found that it is ageing and nutrition, and not work done towards gaining indirect fitness that affect workers’ potential of gaining future direct fitness by independent reproduction via nest foundation, in other words, current indirect fitness is not incompatible with future direct fitness.