Asexually produced Cape honeybee queens (Apis mellifera capensis) reproduce sexually

Unmated workers of the Cape honeybee Apis mellifera capensis can produce female offspring including daughter queens. As worker-laid queens are produced asexually, we wondered whether these asexually produced individuals reproduce asexually or sexually. We sampled 11 colonies headed by queens known to be the clonal offspring of workers and genotyped 23 worker offspring from each queen at 5 microsatellite loci. Without exception, asexually produced queens produced female worker offspring sexually. In addition, we report the replacement of a queen by her asexually produced granddaughter, with this asexually produced queen also producing offspring sexually. Hence, once a female larva is raised as a queen, mating and sexual reproduction appears to be obligatory in this subspecies, despite the fact that worker-laid queens are derived from asexual lineages.     

Foreign ant queens are accepted but produce fewer offspring

Understanding social evolution requires us to understand the processes regulating the number of breeders within social groups and how they partition reproduction. Queens in polygynous (multiple queens per colony) ants often seek adoption in established colonies instead of founding a new colony independently. This mode of dispersal leads to potential conflicts, as kin selection theory predicts that resident workers should favour nestmate queens over foreign queens. Here we compared the survival of foreign and resident queens as well as their relative reproductive share. We used the ant Formica exsecta to construct colonies consisting of one queen with workers related to this resident queen and introduced a foreign queen. We found that the survival of foreign queens did not differ from that of resident queens over a period of 136 days. However, the genetic analyses revealed that resident queens produced a 1.5-fold higher number of offspring than introduced queens, and had an equal or higher share in 80% of the colonies. These data indicate that some discrimination can occur against dispersing individuals and that dispersal can thus have costs in terms of direct reproduction for dispersing queens.     

The genetic structure of swarms and the timing of their production in the queen cycles of neotropical wasps

Kin selection theory has received some of its strongest support from analyses of within-colony conflicts between workers and queens in social insects. One of these conflicts involves the timing of queen production. In neotropical wasps, new queens are only produced by colonies with just one queen while males are produced by colonies with more queens, a pattern favoured by worker interests. We now show that new colonies, or swarms, have few queens and variable within-colony relatednesses which means that their production is not tied to new queen production. The queens in these swarms are seldom the mothers of the workers in the swarm. Therefore, either colonies producing swarms have very many queens, or queens joining daughter swarms are reproductive losers on the original colonies. As new colony production is not linked to queen production, it can occur at the ecologically optimum time, i.e. the rainy season. This disassociation between queen production and new colony production allows worker interests in sex ratios to prevail without hampering new colony production at the most favourable season, an uncoupling that may contribute to the ecological success of the Epiponini.     

Kin structure and colony male reproduction in the hornet<Emphasis Type="Italic"> Vespa crabro</Emphasis> (Hymenoptera: Vespidae)

We estimated queen mating frequency, genetic relatedness among workers, and worker reproduction in Vespa crabro flavofasciata using microsatellite DNA markers. Of 20 colonies examined, 15 contained queens inseminated by a single male, 3 colonies contained queens inseminated by two males, and 2 colonies contained queens inseminated by three males. The genetic relatedness among workers was estimated to be 0.73±0.003 (mean±SE). For this high relatedness, kin selection theory predicts a potential conflict between queens and workers over male production. To verify whether males are derived from queens or workers, 260 males from 13 colonies were genotyped at four microsatellite loci. We found that all of the males were derived from the queens. This finding was further supported by the fact that only 33 of 2,990 workers dissected had developed ovaries. These workers belonged to 2 of the 20 colonies. There was no relationship between queen mating frequency and worker reproduction, and no workers produced male offspring in any of the colonies. These results suggest that male production dominated by queens in V. crabro flavofasciata is possibly due to worker policing.     

Experimentally induced variation in the physical reproductive potential and mating success in honey bee queens

In honeybee colonies, reproduction is monopolized by the queen while her daughter workers are facultatively sterile. Caste determination is a consequence of environmental conditions during development, during which female larvae may become either queens or workers depending on their larval diet. This bipotency introduces significant variation in the reproductive potential of queen bees, with queens raised from young worker larvae exhibiting high reproductive potential and queens raised from older worker larvae exhibiting lower reproductive potential. We verify that low-quality queens are indeed produced from older worker larvae, as measured morphometrically (e.g., body size) and by stored sperm counts. We also show, for the first time, that low-quality queens mate with significantly fewer males, which significantly influences the resultant intracolony genetic diversity of the worker force of their future colonies. These results demonstrate a reproductive continuum of honeybee queens and provide insights into the reproductive constraints of social insects.     

No intracolonial nepotism during colony fissioning in honey bees

Most species of social insects have singly mated queens, but in some species each queen mates with numerous males to create a colony whose workers belong to multiple patrilines. This colony genetic structure creates a potential for intracolonial nepotism. One context with great potential for such nepotism arises in species, like honey bees, whose colonies reproduce by fissioning. During fissioning, workers might nepotistically choose between serving a young (sister) queen or the old (mother) queen, preferring the former if she is a full-sister but the latter if the young queen is only a half-sister. We examined three honeybee colonies that swarmed, and performed paternity analyses on the young (immature) queens and samples of workers who either stayed with the young queens in the nest or left with the mother queen in the swarm. For each colony, we checked whether patrilines represented by immature queens had higher proportions of staying workers than patrilines not represented by immature queens. We found no evidence of this. The absence of intracolonial nepotism during colony fissioning could be because the workers cannot discriminate between full-sister and half-sister queens when they are immature, or because the costs of behaving nepotistically outweigh the benefits.     

Mating frequency and genetic relatedness of workers in the hornet Vespa analis (Hymenoptera: Vespidae)

Mating frequency of Vespa analis queens and the genetic relatedness of their workers was analyzed by DNA microsatellite genotyping. Of 20 colonies studied, 18 had a queen inseminated by a single male and two had queens each inseminated by two males. The estimated effective number of matings was 1.05 ± 0.037 (mean ± SE), with 75–85% of the offspring of the two multiply mated queens sired by a single male. The pedigree relatedness between nestmate workers averaged over the 20 colonies was estimated to be 0.74 ± 0.008, almost identical to the predicted value of 0.75 for colonies headed by a singly mated queen. Multiple matrilines; that is, the presence of workers not related to the current queens, were detected in six colonies, suggesting that queen replacement occurred via usurpation of the founding queens in these six colonies. These results demonstrate that the kin structure of V. analis is similar to that reported in other vespid species.     

No evidence that reproductive bumblebee workers reduce the production of new queens

Kin selection theory predicts potential conflict between queen and workers over male parentage in hymenopteran societies headed by one, singly mated queen, because each party is more closely related to its own male offspring. In ‘late-switching’ colonies of the bumblebee Bombus terrestris, i.e. colonies whose queens lay haploid eggs relatively late in the colony cycle, workers start to lay male eggs shortly after the queen lays the female eggs that will develop into new queens. It has been hypothesized that this occurs because workers recognize, via a signal given by the queen instructing female larvae to commence development as queens, that egg laying is now in their kin-selected interest. This hypothesis assumes that aggressive behaviour in egg-laying workers does not substantially reduce the production of new queens, which would decrease the workers' fitness payoff from producing males. We tested the hypothesis that reproductive activity inB. terrestris workers does not reduce the production of new queens. We used microsatellite genotyping to sex eggs and hence to select eight size-matched pairs of ‘late-switching’ colonies from a set of commercial colonies. From one colony of each pair we removed every egg-laying or aggressive worker observed. From the other colony, we simultaneously removed a nonegg-laying, nonaggressive worker. Removed workers were replaced with young workers from separate colonies at equal frequencies within the pair. There was no significant difference in queen productivity between colonies with reduced or normal levels of egg-laying or aggressive workers. Therefore, as predicted, reproductive B. terrestris workers did not significantly reduce the production of new queens.     

Maternity of emergency queens in the Cape honey bee,Apis mellifera capensis

During reproductive swarming, some workers of the Cape honey bee, Apis mellifera capensis, lay eggs in queen cells, many of which are reared to maturity. However, it is unknown if workers are able to lay in queen cells immediately after queen loss during an episode of emergency queen rearing. In this study we experimentally de‐queened colonies and determined the maternity of larvae and pupae that were reared as queens. This allowed us to determine how soon after queen loss workers contribute to the production of new queens. We were further interested to see if workers would preferentially raise new queens from queen‐laid brood if this was introduced later. We performed our manipulations in two different settings: an apiary setting where colonies were situated close together and a more natural situation in which the colonies were well separated. This allowed us to determine how the vicinity of other colonies affects the presence of parasites. We found that workers do indeed contribute to queen cell production immediately after the loss of their queen, thus demonstrating that some workers either have activated ovaries even when their colony has a queen or are able to activate their ovaries extremely rapidly. Queen‐laid brood introduced days after queen loss was ignored, showing that workers do not prefer to raise new queens from queen brood when given a choice. We also detected non‐natal parasitism of queen cells in both settings. We therefore conclude that some A. m. capensis genotypes specialize in parasitizing queen cells.     

QUEEN SIGNALING IN SOCIAL WASPS

Social Hymenoptera are characterized by a reproductive division of labor, whereby queens perform most of the reproduction and workers help to raise her offspring. A long‐lasting debate is whether queens maintain this reproductive dominance by manipulating their daughter workers into remaining sterile (queen control), or if instead queens honestly signal their fertility and workers reproduce according to their own evolutionary incentives (queen signaling). Here, we test these competing hypotheses using data from Vespine wasps. We show that in natural colonies of the Saxon wasp, Dolichovespula saxonica, queens emit reliable chemical cues of their true fertility and that these putative queen signals decrease as the colony develops and worker reproduction increases. Moreover, these putative pheromones of D. saxonica show significant conservation with those of Vespula vulgaris and other Vespinae, thereby arguing against fast evolution of signals as a result of a queen–worker arms race ensuing from queen control. Lastly, levels of worker reproduction in these species correspond well with their average colony kin structures, as predicted by the queen signaling hypothesis but not the queen control hypothesis. Altogether, this correlative yet comprehensive analysis provides compelling evidence that honest signaling explains levels of reproductive division of labor in social wasps.     

Mode of colony foundation influences the primary sex ratio in ants

In ants, young queens can found new colonies independently (without the help of workers) or dependently (with the help of workers). It has been suggested that differences in the mode of colony founding strongly influence queen survival and colony development. This is because independent queens are constrained to produce a worker force rapidly, before they deplete their body reserves and to resist the intense intercolony competition during the founding stage. By contrast, queens that found colonies dependently remain with the workers, which probably results in a lower mortality rate and earlier production of reproductive offspring. Consequently, in species that found independently, queens of incipient colonies are expected to produce mostly worker brood by laying a lower fraction of haploid (male) eggs than queens in mature colonies; such a difference would not occur in species founding dependently. We compared the primary sex ratio (proportion of male-determined eggs) laid by queens in incipient and mature colonies of two ant species Lasius nigerLinepithema humile, showing independent and dependent modes of colony founding, respectively. As predicted L. niger queens of incipient colonies laid a lower proportion of haploid eggs than queens from mature colonies. By contrast, queens of L. humile laid a similar proportion of haploid eggs in both incipient and mature colonies. These results provide the first evidence that (1) the primary sex ratio varies according to the mode of colony foundation, and (2) queens can adjust the primary sex ratio according to the life history stage of the colony in ants. Copyright 1999 The Association for the Study of Animal Behaviour.     

Ant queens adjust egg fertilization to benefit from both sexual and asexual reproduction

An enduring problem in evolutionary biology is the near ubiquity of sexual reproduction despite the inherent cost of transmitting only half the parent's genes to progeny. Queens of some ant species circumvent this cost by using selectively both sexual reproduction and parthenogenesis: workers arise from fertilized eggs, while new queens are produced by parthenogenesis. We show that queens of the ant Cataglyphis cursor maximize the transmission rate of their genes by regulating the proportion of fertilized and parthenogenetic eggs laid over time. Parthenogenetic offspring are produced in early spring, when workers raise the brood into sexuals. After the mating period, queens lay mostly fertilized eggs that will be reared as the non-reproductive caste.     

Workers influence royal reproduction

Understanding which parties regulate reproduction is fundamental to understanding conflict resolution in animal societies. In social insects, workers can influence male production and sex ratio. Surprisingly, few studies have investigated worker influence over which queen(s) reproduce(s) in multiple queen (MQ) colonies (skew), despite skew determining worker-brood relatedness and so worker fitness. We provide evidence for worker influence over skew in a functionally monogynous population of the ant Leptothorax acervorum. Observations of MQ colonies leading up to egg laying showed worker aggressive and non-aggressive behaviour towards queens and predicted which queen monopolized reproduction. In contrast, among-queen interactions were rare and did not predict queen reproduction. Furthermore, parentage analysis showed workers favoured their mother when present, ensuring closely related fullsibs (average r = 0.5) were reared instead of less related offspring of other resident queens (r ≤ 0.375). Discrimination among queens using relatedness-based cues, however, seems unlikely as workers also biased their behaviour in colonies without a mother queen. In other polygynous populations of this species, workers are not aggressive towards queens and MQs reproduce, showing the outcome of social conflicts varies within species. In conclusion, this study supports non-reproductive parties having the power and information to influence skew within cooperative breeding groups.     

Genetic caste determination in Pogonomyrmex harvester ants imposes costs during colony founding

Some populations of Pogonomyrmex harvester ants comprise genetically differentiated pairs of interbreeding lineages. Queens mate with males of their own and of the alternate lineage and produce pure-lineage offspring which develop into queens and inter-lineage offspring which develop into workers. Here we tested whether such genetic caste determination is associated with costs in terms of the ability to optimally allocate resources to the production of queens and workers. During the stage of colony founding, when only workers are produced, queens laid a high proportion of pure-lineage eggs but the large majority of these eggs failed to develop. As a consequence, the number of offspring produced by incipient colonies decreased linearly with the proportion of pure-lineage eggs laid by queens. Moreover, queens of the lineage most commonly represented in a given mating flight produced more pure-lineage eggs, in line with the view that they mate randomly with the two types of males and indiscriminately use their sperm. Altogether these results predict frequency-dependent selection on pairs of lineages because queens of the more common lineage will produce more pure-lineage eggs and their colonies be less successful during the stage of colony founding, which may be an important force maintaining the coexistence of pairs of lineages within populations.     

Worker reproduction and related behavior in orphan colonies of a Japanese paper wasp,Polistes jadwigae (Hymenoptera,Vespidae)

Worker reproduction and related behavior in 2 orphan colonies ofPolistes jadwigae, one of which had been maintained by a queen and 5 artificially introduced alien workers, were observed. After the queen loss, a dominance hierarchy was established among workers, and several workers laid eggs without physical interference from other workers. Only males emerged from worker-laid eggs, however, a few new queens were produced from queen-laid eggs. Investment sex ratio of queenright (=normal) colonies (0.27) fell between the 2 theoretical values, corresponding to worker control (0.20 or 0.18) and queen control (0.48 or 0.46) of the sex ratio, both being calculated by considering the excess of males produced in the orphan colonies.     

Queen adoption in the polygynous and polydomous ant, Leptothorax curvispinosus

Alate female reproductives of the facultatively polygynous andpolydomous ant, Lepiothorax curuispinosus, were reared fromfield-collected nests, mated, and introduced into either theirparental nests or alien conspecific nests. The 41 queens introducedinto alien nests were usually attacked and rejected (97. 6%),but one queen was accepted after initial aggression. The 27queens introduced into their parental nests received a variableresponse. Some were accepted without any apparent aggression(59. 3%), but others were strongly attacked and rejected (40.7%). Sequential introductions of up to four queens into particularparental nests indicated that nests consistently either acceptor reject their mated offspring. The presence or absence ofresident queens in parental nests had no apparent influenceon the acceptance of offspring queens. Nests that accepted queenshad significantly fewer workers than those that did not, butthis slight difference is unlikely to explain these dichotomousresults and could be spurious. Dissections of the introducedqueens revealed that 79. 0% were inseminated and 98. 3% haddeveloping, yolked eggs in their ovarioles, but these variableshad no apparent effect on acceptability. Similarly, the sizeof the introduced queens and the time that elapsed between matingand introduction had no apparent effect. The consistent responseof parental nests in either accepting or rejecting their matedoffspring indicates a mechanism of queen number regulation inthis species that involves characteristics of the colony ornest rather than variability among offspring queens. This mechanismcould be responsible for maintaining relatively low numbersof queens and high genetic relatedness in colonies (or individualnests) while promoting flexibility in colony reproduction bycolony fission ("budding") and the dispersal of young queens.This mechanism could also involve an important conflict of interestbetween parental colonies and their mated offspring and mightcontribute to the evolution of socially parasitic colony foundationstrategies. Acceptance of mated offspring by their parentalcolonies might only occur during certain periods in colony development,depend on the level of genetic diversity within the colony (ornest), reflect the condition of the colony, nest, queen(s),brood, or local habitat, or result from a genetic polymorphism.     

Queen execution in a monogynous ant

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

Facultative polygyny in Ectatomma tuberculatum (Formicidae, Ectatomminae)

Summary. Polygyny, the presence of several mated queens within the same colony, is widespread in insect societies. This phenomenon is commonly associated with ecological constraints such as limited nest sites. In habitats where solitary nest foundation is risky, monogynous colonies can reintegrate young daughter queens (secondary polygyny). We studied the reproductive structure (i.e. queen number) of the ectatommine ant Ectatomma tuberculatum from Bahia State, Brazil. This species was found to present facultative polygyny: out of a total of 130 colonies collected, 39.2% were monogynous, while 43.8% were polygynous. Polygynous colonies had significantly more workers than monogynous ones. Queen number in polygynous colonies ranged from 2 to 26, with an average of 4 ± 4 queens per colony. All nestmate queens were egg-layers with no apparent dominance hierarchy or agonistic behavior. Non-nestmate queens were adopted by monogynous colonies suggesting that polygyny is secondary, originating through queen adoption. This species is characterized by an open recognition system, which probably allows a switch from monogynous to polygynous colonies. The behavioral acts of queens showed that resident queens remained frequently immobile on or near the brood, contrarily to alien or adopted queens and gynes. In addition, monogynous queens showed no behavioral or physiological (i.e. by ovarian status) differences in comparison with polygynous ones. Secondary or facultative polygyny, probably associated with queen adoption, may have been favored in particular environmental conditions. Indeed, by increasing colony productivity (i.e. number of workers) and territory size (by budding and polydomy), polygyny could uphold E. tuberculatum as a dominant species in the mosaic of arboreal ants in Neotropical habitats.Received 7 April 2004; revised 11 November 2004; accepted 15 November 2004.     

Genetic determination of female castes in a hybridogenetic desert ant

In most social insects, the brood is totipotent and environmental factors determine whether a female egg will develop into a reproductive queen or a functionally sterile worker. However, genetic factors have been shown to affect the female's caste fate in a few ant species. The desert ant Cataglyphis hispanica reproduces by social hybridogenesis. All populations are characterized by the coexistence of two distinct genetic lineages. Queens are almost always found mated with a male of the alternate lineage than their own. Workers develop from hybrid crosses between the genetic lineages, whereas daughter queens are produced asexually via parthenogenesis. Here, we show that the association between genotype and caste in this species is maintained by a ‘hard‐wired’ genetic caste determination system, whereby nonhybrid genomes have lost the ability to develop as workers. Genetic analyses reveal that, in a rare population with multiple‐queen colonies, a significant proportion of nestmate queens are mated with males of their own lineage. These queens fail to produce worker offspring; they produce only purebred daughter queens by sexual reproduction. We discuss how the production of reproductive queens through sexual, intralineage crosses may favour the stability of social hybridogenesis in this species.     

On the relationship between queen number and fecundity in polygyne colonies of the fire ant Solenopsis invicta

ABSTRACT. The reproductive status of individual queens in relation to the number of queens in polygyne colonies of Solenopsis invicta Buren was investigated under both field and laboratory conditions. In field colonies, the weight of individual queens is inversely related to the number of resident queens present. The weight of a queen is positively correlated with fecundity, as measured by the number of eggs laid in 5 h in isolation. Thus increasing queen number has a strong negative effect on the fecundity of individual queens in these colonies. A similar relationship was established in standardized laboratory colonies using queens from a single experimental population. Colony size by itself had no significant effect on queen weight in either the field or laboratory colonies, suggesting that the inverse relationship between queen number and fecundity results from mutual inhibition among queens, possibly involving pheromones, rather than reduced nutrition through lower worker/queen ratios. While uninseminated queens can comprise up to 50% of the functional (i.e. egglaying) queens in polygyne colonies of this ant, they tend to be less fecund than their inseminated nestmates; uninseminated queens within a given colony generally weigh 5–25% less.