Stable relatedness structure of the large-colony swarm-founding wasp Polybia paulista

In social-insect colonies, cooperation among nestmates is generally stabilized by their high genetic similarity. Thus, fitness gained through cooperation drops quickly as the number of reproductive females (queens) increases. In this respect, wasps of the tribe Epiponini have attracted special attention, because the colonies have tens, or even hundreds of queens. It has been empirically or genetically confirmed that relatedness within nestmates can be elevated by a mechanism known as cyclical monogyny, under which new queens are produced only after the number of old queens is reduced to one. Another likely factor that can increase relatedness within nestmates under polygyny is comb partitioning by queens. If queens concentrate their egg laying on one or a subset of the available combs, then workers may be able to rear closer relatives by focusing their work on the comb where they emerged. Using microsatellite markers, we tested the hypotheses of cyclical monogyny and comb partitioning by queens increasing relatedness within nestmates under polygyny in the large-colony epiponine wasp, Polybia paulista. There were no significant differences between relatedness within combs and between combs, and thus we ruled out the possibility that each queen partitions reproduction between combs. However, as cyclical monogyny predicts, a lower effective number of queens contributed to queen production than to worker production. Cyclical monogyny explained well the observed smaller effective number of queens for new queens than that for workers, but failed to explain the stable relatedness values throughout colony cycles.Communicated by L. Keller     

Sociogenetic organization of the red ant Myrmica rubra

Knowledge of the sociogenetic organization determining the kin structure of social insect colonies is the basis for understanding the evolution of insect sociality. Kin structure is determined by the number and relatedness of queens and males reproducing in the colonies, and partitioning of reproduction among them. This study shows extreme flexibility in these traits in the facultatively polygynous red ant Myrmica rubra. Relatedness among worker nestmates varied from 0 to 0.82. The most important reason for this variation was the extensive variation in the queen number among populations. Most populations were moderately or highly polygynous resulting in low relatedness among worker nestmates, but effectively monogynous populations were also found. Polygynous populations also often tend to be polydomous, which is another reason for low relatedness. Coexisting queens were positively related in two populations out of five and relatedness was usually similar among workers in the same colonies. Due to the polydomous colony organization and short life span of queens, it was not possible to conclusively determine the importance of unequal reproduction among coexisting queens, but it did not seem to be important in determining the relatedness among worker nestmates. The estimates of the mating frequency by queens remained ambiguous, which may be due to variation among populations. In some populations relatedness among worker nestmates was high, suggesting monogyny and single mating by queens, but in single-queen laboratory nests relatedness among the worker offspring was lower, suggesting that multiple mating was common. The data on males were sparse, but indicated sperm precedence and no relatedness among males breeding in the same colony. A comparison of social organizations and habitat requirements of M. rubra and closely related M. ruginodis suggested that habitat longevity and patchiness may be important ecological factors promoting polygyny in Myrmica. Received: 15 May 1995/Accepted after revision: 17 October 1995     

Lack of evidence for nepotism by workers tending queens of the polygynous termite <Emphasis Type="Italic">Nasutitermes corniger</Emphasis>

Kin selection theory predicts that workers in social insect colonies should preferentially aid close relatives over less related or unrelated individuals if such behaviors increase inclusive fitness. For example, a worker in a polygynous (multiple-queen) colony is predicted to tend its own mother rather than an unrelated queen if this nepotistic behavior increases its mother’s reproductive success in excess of costs. Despite predictions, experimental tests conducted in the social Hymenoptera have found no clear evidence of nepotism. No tests for nepotism have been carried out in the Isoptera (termites), another major insect taxon showing highly developed sociality. We tested for nepotistic behavior in the termite Nasutitermes corniger by determining if workers preferentially fed and groomed their mothers in a laboratory assay. We collected workers from nine naturally occurring multiple-queen colonies as they tended queens and determined their parentage using highly variable microsatellite markers. Our results provide no evidence that workers tend their mothers in preference to co-occurring queens. The absence of evidence for nepotism is consistent with previous results reported from numerous studies of eusocial hymenopterans.     

Queen longevity,queen adoption,and posthumous indirect fitness in the facultatively polygynous ant Myrmica tahoensis

In many polygynous ant species, established colonies adopt new queens secondarily. Conflicts over queen adoption might arise between queens and workers of established colonies and the newly mated females seeking adoption into nests. Colony members are predicted to base adoption decisions on their relatednesses to other participants, on competition between queens for colony resources, and on the effects that adopted queens have on colony survivorship and productivity. To provide a better understanding of queen-adoption dynamics in a facultatively polygynous ant, colonies of Myrmica tahoensis were observed in the field for 4 consecutive years and analyzed genetically using highly polymorphic microsatellite DNA markers. The extreme rarity of newly founded colonies suggests that most newly mated queens that succeed do so by entering established nests. Queens are closely related on average (rˉ = 0.58), although a sizable minority of queen pairs (29%) are not close relatives. An experiment involving transfers of queens among nests showed that queens are often accepted by workers to which they are completely unrelated. Average queen numbers estimated from nest excavations (harmonic mean = 1.4) are broadly similar to effective queen numbers inferred from the genetic relatedness of colony members, suggesting that reproductive skew is low in this species. Queens appear to have reproductive lifespans of only 1 or 2 years. As a result, queens transmit a substantial fraction of their genes posthumously (through the reproduction of related nestmates), in comparison to direct and indirect reproduction while they are alive. Thus queens and other colony members should often accept new queens when doing so will increase colony survivorship, in some cases even when the adopted queens are not close relatives. Received: 20 February 1996/Accepted after revision: 25 May 1996     

Colony life history and demography of a swarm-founding social wasp

Colonies of social insects are sometimes viewed as superorganisms. The birth, reproduction, and death of colonies can be studied with demographic measures analogous to those normally applied to individuals, but two additional questions arise. First, how do adaptive colony demographies arise from individual behaviors? Second, since these superorganisms are made up of genetically distinct individuals, do conflicts within the colony sometimes modify and upset optima for colonies? The interplay between individual and superindividual or colony interests appears to be particularly complex in neotropical, swarm-founding, epiponine wasps such as Parachartergus colobopterus. In a long-term study of this species, we censused 286 nests to study colony-level reproduction and survivorship and evaluated individual-level factors by assessing genetic relatedness and queen production. Colony survivorship followed a negative exponential curve very closely, indicating type II survivorship. This pattern is defined by constant mortality across ages and is more characteristic of birds and other vertebrates than of insects. Individual colonies are long-lived, lasting an average of 347 days, with a maximum of over 4.5 years. The low and constant levels of colony mortality arise in part from colony initiation by swarming, nesting on protected substrates, and an unusual expandable nest structure. The ability to requeen rapidly was also important; relatedness data suggest that colonies requeen on average once every 9–12 months. We studied whether colony optima with respect to the timing of reproduction could be upset by individual worker interests. In this species, colonies are normally polygynous but new queens are produced only after a colony reaches the monogynous state, a result which is in accord with the genetic interests of workers. Therefore colony worker interests might drive colonies to reproduce whenever queen number happens to cycled down to one rather than at the season that is otherwise optimal. However, we found reproduction to be heavily concentrated in the rainy season. The number of new colonies peaked in this season as did the percentages of males and queens. Relatedness among workers reached a seasonal low of 0.21–0.27, reflecting the higher numbers of laying queens. This seasonality was achieved in part by a modest degree of synchrony in the queen reduction cycle. Worker relatedness reached peaks of around 0.4 in the dry season, reflecting a decrease to a harmonic mean queen number of about 2.5. Thus, a significant number of colonies must be approaching monogyny entering the rainy season. Coupled with polygynous colonies rearing only males (split sex ratios), this makes it possible for a colony cycle driven by selfish worker interests to be consistent with concentrating colony reproduction during a favorable season.     

Oligogyny by unrelated queens in the carpenter ant, Camponotus ligniperdus

Multilocus DNA fingerprinting and microsatellite analysis were used to determine the number of queens and their mating frequencies in colonies of the carpenter ant, Camponotus ligniperdus (Hymenoptera: Formicidae). Only 1 of 61 analyzed queens was found to be double-mated and the population-wide effective mating frequency was therefore 1.02. In the studied population, 8 of 21 mature field colonies (38%) contained worker, male, or virgin queen genotypes which were not compatible with presumed monogyny and therefore suggested oligogyny, i.e., the cooccurrence of several mutually intolerant queens within one colony. Estimated queen numbers in oligogynous colonies ranged between two and five. According to the results of the genetic analysis, most of the queens coexisting in oligogynous colonies were not closely related. Pleometrosis is very rare and queenless colonies adopt mated queens both in the laboratory and field. Therefore, the most plausible explanation for the origin of oligogynous colonies in C. ligniperdus is the adoption of unrelated queens by orphaned mature colonies. The coexistence of unrelated, but mutually intolerant queens in C. ligniperdus colonies demonstrates that oligogyny should be considered as a phenomenon distinct from polygyny. Received: 18 December 1997 / Accepted after revision: 20 June 1998     

Dual mechanism of queen influence over sex ratio in the ant Pheidole pallidula

Social Hymenoptera are general models for the study of parent-offspring conflict over sex ratio, because queens and workers frequently have different reproductive optima. The ant Pheidole pallidula shows a split distribution of sex ratios with most of the colonies producing reproductives of a single sex. Sex ratio specialization is tightly associated with the breeding system, with single-queen (monogynous) colonies producing male-biased brood and multiple-queen (polygynous) colonies female-biased brood. Here, we show that this sex specialization is primarily determined by the queens influence over colony sex ratio. Queens from monogynous colonies produce a significantly more male-biased primary sex ratio than queens from polygynous colonies. Moreover, queens from monogynous colonies produce a significantly lower proportion of diploid eggs that develop into queens and this is associated with lower rate of juvenile hormone (JH) production compared to queens from polygynous colonies. These results indicate that queens regulate colony sex ratio in two complementary ways: by determining the proportion of female eggs laid and by hormonally biasing the development of female eggs into either a worker or reproductive form. This is the first time that such a dual system of queen influence over colony sex ratio is identified in an ant.     

The evolution of worker–queen polymorphism in Cataglyphis ants: interplay between individual- and colony-level selections

In many ants, young queens disperse by flying away from their natal nest and found new colonies alone (independent colony founding, ICF). Alternatively, in some species, ICF was replaced by colony fission, in which young queens accompanied by workers found a new colony at walking distance from the mother nest. We compared the queen morphology of Cataglyphis floricola, which disperses by fission, with that of its most likely living ancestor, Cataglyphis emmae, which disperses by ICF. As in other species, the transition from ICF to fission is associated with queen miniaturization. Interestingly, C. floricola presents two types of small queens: brachypters (with short non-functional wings) and ergatoids (worker-like apterous queens). Ergatoids are, on average, 2.8 mg lighter and have half the number of ovarioles than brachypters, which limits the advantage for a colony to produce ergatoids instead of brachypters. Furthermore, more ergatoids are produced than brachypters, but their individual survival rate is lower. During colony fission, 96% of the cocoons containing brachypters but only 31% of those containing ergatoids are transferred to the daughter nests where, after emergence, they compete for becoming the next queen. The remaining queen cocoons, which stay in the mother queen's nest, are eliminated by workers upon emergence, probably to maintain monogyny. This waste of energy suggests that producing ergatoids instead of brachypters is unlikely to increase colony efficiency. We argue that the evolution of ergatoids could derive from a selfish larval strategy, developing into worker-like queens in spite of the colony interest.     

Phenotypic plasticity and “cultural transmission” of alternative social organizations in the fire ant Solenopsis invicta

Summary We investigated the process of sexual maturation in winged queens of the fire ant Solenopsis invicta, a species with two distinct forms of social organization. We found that queens of the monogynous social form (single reproductive queen per colony) differ little or not at all from queens of the polygynous form (multiple reproductive queens per colony) in weight and fat content when these are pupae or newly-eclosed adults. Furthermore, the size of a sclerotized region of the adult thorax, which is set during larval growth, does not differ between queens of the two forms. In contrast, winged queens of the two social forms differ dramatically in their physiological phenotypes once they have matured, with monogynous queens weighing more and having greater fat reserves than polygynous queens. A crossfostering experiment revealed that the different maturation processes of queens of the two forms are induced largely by the type of colony in which a queen matures (monogynous or polygynous) rather than being due to intrinsic genetic differences between the forms. However, genetic variation at a single locus does appear to play some role in determining physiological phenotype in queens of the polygynous form, providing an example of genotype-environment interaction in the expression of these physiological traits. Differences between the social forms in the mature phenotypes that are produced constrain the reproductive options of queens, so that the characteristic social organization of a colony is perpetuated by virtue of the social environment in which new queens are reared. Correspondence to: L. Keller     

Seasonal polydomy and unicoloniality in a polygynous population of the red wood ant Formica truncorum

Ant colonies may have a single or several reproductive queens (monogyny and polygyny, respectively). In polygynous colonies, colony reproduction may occur by budding, forming multinest, polydomous colonies. In most cases, budding leads to strong genetic structuring within populations, and positive relatedness among nestmates. However, in a few cases, polydomous populations may be unicolonial, with no structuring and intra-nest relatedness approaching zero. We investigated the spatial organisation and genetic structure of a polygynous, polydomous population of Formica truncorum in Finland. F. truncorum shifts nest sites between hibernation and the reproductive season, which raises the following question: are colonies maintained as genetic entities throughout the seasons, or is the population unicolonial throughout the season? Using nest-specific marking and five microsatellite loci, we found a high degree of mixing between individuals of the population, and no evidence for a biologically significant genetic structuring. The nestmate relatedness was also indistinguishable from zero. Taken together, the results show that the population is unicolonial. In addition, we found that the population has undergone a recent bottleneck, suggesting that the entire population may have been founded by a very limited number of females. The precise causes for unicoloniality in this species remain open, but we discuss the potential influence of intra-specific competition, disintegration of recognition cues and the particular hibernation habits of this species.     

High genetic relatedness among nestmate queens in the polygynous ponerine ant Gnamptogenys striatula in Brazil

Gnamptogenys striatula is a polygynous ant species, in which all workers are potentially able to mate. The reproductive status, relatedness and pedigree relationships among nestmate queens and winged females in a Brazilian population were investigated. We collected all the sexual females of 12 colonies (2–44 queens per colony, plus 2–18 winged females in 3 colonies). Dissections revealed that 98% of the queens were inseminated and that the queens in the most polygynous colonies did not lay equal numbers of eggs. The sexual females and a sample of the population were genotyped using eight microsatellite markers. Relatedness among nestmate queens was among the highest recorded to date (0.65±0.25), and tests of pedigree relationship showed that they were likely to be full-sisters, and sometimes cousins. Mated winged females were always full-sisters, the estimated genetically effective queen numbers were low and tests of pedigree relationship showed that only a few queens in the colony could be the mothers. These results suggest that the high queen-queen relatedness in polygynous colonies of G. striatula is maintained by an unusual mechanism: winged females are mostly produced by only one or a few queens, and these groups of full-sisters are recruited back into their original nest after mating. Received: 26 November 1999 / Revised: 7 September 2000 / Accepted: 7 September 2000     

Extended family structure in the ant Formica paralugubris: the role of the breeding system

In populations of various ant species, many queens reproduce in the same nest (polygyny), and colony boundaries appear to be absent with individuals able to move freely between nests (unicoloniality). Such societies depart strongly from a simple family structure and pose a potential challenge to kin selection theory, because high queen number coupled with unrestricted gene flow among nests should result in levels of relatedness among nestmates close to zero. This study investigated the breeding system and genetic structure of a highly polygynous and largely unicolonial population of the wood ant Formica paralugubris. A microsatellite analysis revealed that nestmate workers, reproductive queens and reproductive males (the queens' mates) are all equally related to each other, with relatedness estimates centring around 0.14. This suggests that most of the queens and males reproducing in the study population had mated within or close to their natal nest, and that the queens did not disperse far after mating. We developed a theoretical model to investigate how the breeding system affects the relatedness structure of polygynous colonies. By combining the model and our empirical data, it was estimated that about 99.8% of the reproducing queens and males originated from within the nest, or from a nearby nest. This high rate of local mating and the rarity of long-distance dispersal maintain significant relatedness among nestmates, and contrast with the common view that unicoloniality is coupled with unrestricted gene flow among nests. Received: 8 February 1999 / Received in revised form: 15 June 1999 / Accepted: 19 June 1999     

A test of reproductive skew models in a field population of a multiple-queen ant

Determining the evolutionary basis of variation in reproductive skew (degree of sharing of reproduction among coexisting individuals) is an important task both because skew varies widely across social taxa and because testing models of skew evolution permits tests of kin selection theory. Using parentage analyses based on microsatellite markers, we measured skew among female eggs (n=32.3 eggs per colony, range=20–68) in 17 polygynous colonies from a UK field population of the ant Leptothorax acervorum. We used skew among eggs as our principal measure of skew because of the high degree of queen turnover in the study population. Queens within colonies did not make significantly unequal contributions to queen and worker adult or pupal offspring, indicating that skew among female eggs reflected skew among daughter queens. On average, both skew among female eggs (measured by the B index) and queen–queen relatedness proved to be low (means±SE=0.06±0.02 and 0.28±0.08, respectively). However, contrary to current skew models, there was no significant association of skew with either relatedness or worker number (used as a measure of productivity). In L. acervorum, predictions of the concession model of skew may hold between but not within populations because queens are unable to assess their relatedness to other queens within colonies. Additional phenomena that may help maintain low skew in the study population include indiscriminate infanticide in the form of egg cannibalism and split sex ratios that penalize reproductive monopoly by single queens within polygynous colonies.     

Levels of selection in a social insect: a review of conflict and cooperation during honey bee (<Emphasis Type="Italic">Apis mellifera</Emphasis>) queen replacement

The extended phenotype of a social insect colony enables selection to act at both the individual level (within-colony selection) and the colony level (between-colony selection). Whether a particular trait persists over time depends on the relative within- and between-colony selection pressures. Queen replacement in honey bee colonies exemplifies how selection may act at these different levels in opposing directions. Normally, a honey bee colony has only one queen, but a colony rears many new queens during the process of colony reproduction. The replacement of the mother queen has two distinct phases: queen rearing, where many queens develop and emerge from their cells, and queen elimination, where most queens die in a series of fatal duels. Which queens are reared to adulthood and which queens ultimately survive the elimination process depends on the strength and direction of selection at both the individual and colony levels. If within-colony selection is predominant, then conflict is expected to occur among nestmates over which queens are produced. If between-colony selection is predominant, then cooperation is expected among nestmates. We review the current evidence for conflict and cooperation during queen replacement in honey bees during both the queen rearing and queen elimination phases. In particular, we examine whether workers of different subfamilies exhibit conflict by acting nepotistically toward queens before and after they have emerged from their cells, and whether workers exhibit cooperation by collectively producing queens of high reproductive quality. We conclude that although workers may weakly compete through nepotism during queen rearing, workers largely cooperate to raise queens of similar reproductive potential so that any queen is suitable to inherit the nest. Thus it appears that potential conflict over queen replacement in honey bees has not translated into actual conflict, suggesting that between-colony selection predominates during these important events in a colonys life cycle.Communicated by A. Cockburn     

Polygyny,relatedness and nest founding in the polygynous myrmicine ant Leptothorax acervorum (Hymenoptera; Formicidae)

Summary There is high within-nest relatedness for functional queens (with corpora lutea), nonfunctional queens (without corpora lutea), and workers in polygynous nests of Leptothorax acervorum. The high functional queen relatedness suggests that young mated queens are adopted back to their mother nest. Functional queen relatedness does not change with the number of queens present in the nest, suggesting that the number of generations of queens, on average two to three, is rather stable. Worker relatedness decreases with increasing number of functional queens per nest (Tables 5, 6). The number of queens contributing offspring to the nest (mothers), estimated from worker and functional queen relatedness, is lower than the number of functional queens, particularly in highly polygynous nests. Estimates of number of mothers in monogynous nests indicate that these nests previously were polygynous (Table 7). There is no correlation between nest relatedness and distance between nests, and budding-off, if present, thus appears to be a rare mode of nest founding (Table 8). There are no indications of inbreeding in the two populations studied since the frequency of heterozygotes is as high as expected from random mating (Table 4). Most likely, polygyny is the rule in L. acervorum and serves to secure the presence of queens in the nest.     

Colony founding,queen dominance and oligogyny in the Australian meat ant Iridomyrmex purpureus

Summary Field observations and laboratory experiments demonstrate that in the Australian meat ant, Iridomyrmex purpureus, the modes of colony founding are remarkably diverse. New colonies can originate from single foundresses (haplometrosis), or foundress associations (pleometrosis), or by colony budding, or the adoption of newly-mated queens that dig founding chambers next to mature nests (probably their natal nests, as workers protect them and may help them dig). Readoption of foundresses and pleometrosis lead to the coexistence of several queens in one nest. We discovered a striking antagonistic behavior among coexisting queens in young colonies, in the form of ritualized antennation bouts. These interactions result in a reproductive rank order in which dominant queens inhibit egg-laying by subordinates, but escalation into physical fighting is rare. Workers ignore queen dominance interactions and treat all queens equally. The first quantitative ethogram of dominance display behavior between multiple ant queens, and its reproductive consequences, is presented. As a colony grows, queens become intolerant of each other's presence and permanently separate within the nest. Once separated, queens appear to be equal in status, laying approximately equal numbers of eggs. All queens continue to be tolerated by workers, even when the colony has reached a size of several thousand workers and begun to produce reproductives. Such mature nests of I. purpureus fulfill the criteria of oligogyny, defined by worker tolerance toward more than one queen and antagonism among queens, such that a limited number of fully functional queens are spaced far apart within a single colony. Oligogynous colonies can arise in this species by pleometrotic founding (primary oligogyny) or by adoption of queens into existing nests (secondary oligogyny). The adaptive significance of the complex system of colony founding, queen dominance and oligogyny in I. purpureus is discussed.     

Replacement of reproductives in Nasutitermes princeps (Desneux) (Isoptera: Termitidae)

Summary The production of replacement reproductives in experimentally orphaned societies was investigated in Nasutitermes princeps (Desneux). From 1 to 180 replacement queens and multiple kings, all adultoids, were found in the 13 nests that were re-collected. Normal imagos, microimagos, or a mixture of the two forms were present, depending on colony composition at the time of orphaning. In colonies with alates, the corresponding forms were found as replacement reproductives. Where only young nymphs were present, microimagos differentiated. Neither the number of queens nor their level of physogastry was correlated with the time elapsed since orphaning, but the total egg-laying rates were. We suggest that competition among queens rather than time determines individual physogastric development. Observations show that the most likely cause of accidental queen death in nature is probably nest fall from the supporting tree. Even in this case, the queen may be able to migrate to a newly rebuilt nest. An experimental simulation of this situation showed that colony migration can occur. The data indicate that the replacement of the primary queen after her accidental death cannot by itself account for the high rate of polygyny (60%) encountered in N. princeps. Two other possible causes are the replacement of the ageing foundress as a normal event of colony life, and colony reproduction by budding off new nests with adultoid reproductives.King Léopold III Biological Station, Laing Island, Papua New Guinea, contribution no. 84Research Assistant of the National Fund for Scientific Research (Belgium)     

Multiple mating increases the sperm stores of Atta colombica leafcutter ant queens

Multiple mating is likely to be costly for ant queens and yet it is common. Whether multiple mating brings benefits to queens that outweigh the costs has, therefore, received considerable theoretical attention. Empirical tests of hypotheses have been scarce and no clear evidence has been reported. We tested the “multiple-mating-for-more-sperm” hypothesis on individual young queens in a natural population of the leafcutter ant Atta colombica, a monogynous ant characterised by very large colonies and high colony longevity. We found that the number of sperm stored by queens was positively correlated with the number of mates per queen estimated through mother-offspring analysis with microsatellite DNA markers. Queen sperm stores increased on average by 30 million sperm for each additional mate. Life-history information for Atta indicate that the number of stored sperm observed is likely to constrain the reproductive lifespan of queens in nature. Multiple mating, despite costs, may therefore enhance the fitness of Atta queens because it enables them to store more sperm. Received: 19 September 1997 / Accepted after revision: 7 December 1997     

Unequal resource allocation among colonies produced by fission in the ant Cataglyphis cursor

How organisms allocate limited resources to reproduction is critical to their fitness. The size and number of offspring produced have been the focus of many studies. Offspring size affects survival and growth and determines offspring number in the many species where there is a trade-off between size and number. Many social insects reproduce by colony fission, whereby young queens and accompanying workers split off from a colony to form new colonies. The size of a new colony (number of workers) is set at the time of the split, and this may allow fine tuning size to local conditions. Despite the prevalence of colony fission and the ecological importance of social insects, little is known of colony fission except in honey bees. We studied colony fission in the ant Cataglyphis cursor. For clarity, "colony" and "nest" refer to colonies before and after colony fission, respectively (i.e., each colony fissions into several nests). The reproductive effort of colonies was highly variable: Colonies that fissioned varied markedly in size, and many colonies that did not fission were as large as some of the fissioning colonies. The mother queen was replaced in half of the fissioning colonies, which produced 4.0 +/- 1.3 (mean +/- SD) nests of markedly varied size. Larger fissioning colonies produced larger nests but did not produce more nests, and resource allocation among nests was highly biased. When a colony produced several nests and the mother queen was not replaced, the nest containing the mother queen was larger than nests with a young queen. These results show that the pattern of resource allocation differs between C. cursor and honey bees. They also suggest that C. cursor may follow a bet-hedging strategy with regard to both the colony size at which fission occurs and the partitioning of resources among nests. In addition, colony fission may be influenced by the age and/or condition of the mother queen, and the fact that workers allocating resources among nests have incomplete knowledge of the size and number of nests produced. These results show that the process of colony fission is more diverse than currently acknowledged and that studies of additional species are needed.     

Worker self-restraint and policing maintain the queen’s reproductive monopoly in a pseudomyrmecine ant

Division of reproductive labor in insect societies is often based on worker self-restraint and both queen and worker policing. Workers of many hitherto studied wasps, bees and ants do not lay eggs in the presence of a queen. However, it is presently unclear how far these observations in a few select clades can be generalized. We investigated if and how queens maintain a reproductive monopoly in colonies of the elongate twig ant, Pseudomyrmex gracilis, a member of the previously unstudied ant subfamily Pseudomyrmecinae. Colonies are usually headed by a single, singly mated queen (monogyny, monandry). Workers therefore would be more closely related to males produced by other workers (r?=?0.375) than to the sons of queens (r?=?0.25). Nevertheless, workers appear to refrain from laying male-destined eggs in the presence of the queen. In queenless conditions, workers form dominance hierarchies by antennal boxing, and only one or a few high-ranking individuals readily begin to lay eggs. When returned into a queenright colony, egg-laying workers are immediately bitten, stung and expelled or killed by other workers. While the composition of cuticular hydrocarbons clearly differed between castes, it less clearly reflected worker ovarian development. An association with worker ovarian development that would allow workers to monitor the reproductive status of nestmates could only be tentatively postulated for certain substances. Our study broadens our knowledge about reproductive conflict in social Hymenoptera and shows that worker sterility in the presence of a queen is more common in monogynous, monandrous ants than expected from relatedness alone.