Social parasitism of queens and workers in the Cape honeybee (<Emphasis Type="Italic">Apis mellifera capensis</Emphasis>)

Workers of a queenless honeybee colony can requeen the colony by raising a new queen from a young worker brood laid by the old queen. If this process fails, the colony becomes hopelessly queenless and workers activate their ovaries to lay eggs themselves. Laying Cape honeybee workers (Apis mellifera capensis) produce female offspring as an additional pathway for requeening. We tested the frequency of successful requeening in ten hopelessly queenless colonies. DNA genotyping revealed that only 8% of all queens reared in hopelessly queenless colonies were the offspring of native laying worker offspring. The vast majority of queens resulted from parasitic takeovers by foreign queens (27%) and invading parasitic workers (19%). This shows that hopelessly queenless colonies typically die due to parasitic takeovers and that the parasitic laying workers are an important life history strategy more frequently used than in providing a native queen to rescue the colony. Parasitism by foreign queens, which might enter colonies alone or accompanied by only a small worker force is much more frequent than previously considered and constitutes an additional life history strategy in Cape honeybees.     

Queen acceptance and the complexity of nestmate discrimination in the Argentine ant

In most social insect species, individuals recognize and behave aggressively towards non-nestmate conspecifics to maintain colony integrity. However, introduced populations of the invasive Argentine ant, Linepithema humile, exhibit pronounced variation in intraspecific aggression denoting diversity in nestmate recognition behavior, which possibly shapes their social structure and the varying levels of unicoloniality observed among these populations. One approach to better understand differential aggression behaviors towards conspecifics and recognition cue perception and response in L. humile is to examine variation in nestmate discrimination capability among genetically distinct colonies under different social contexts. Consequently, we investigated the dynamics of queen and worker recognition in southeastern US L. humile queenless and queenright colonies by measuring rates of non-nestmate worker and queen adoption and intercolony genetic similarity. Aggression levels between colony pairs differed and were associated with non-nestmate worker, but not queen adoption. Adoption of queens and workers was a function of host colony origin, while colony queen number affected adoption of queens, but not workers, with queens more readily accepted by queenless hosts. Fecundity of adopted non-nestmate queens was comparable to that of rejected non-nestmate and host colony queens, suggesting that queen fecundity did not affect adoption decisions. Genetic similarity between colonies ranged from 30 to 77% alleles shared, with more genetically similar colonies showing lower levels of intraspecific aggression. Non-nestmate queens and workers that were more genetically similar to host colony workers were more likely to be adopted. We provide the first evidence for the role of L. humile colony queen number on queen discrimination and suggest an effect of resident queens on worker conspecific acceptance thresholds. Our findings indicate a role for genetically based cues in L. humile nestmate recognition. However, subtle discrimination capability seems to be influenced by the social context, as demonstrated by more frequent recognition errors in queenless colonies.     

Patterns of male parentage in the fungus-growing ants

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

The dissolution of cooperative groups: mechanisms of queen mortality in incipient fire ant colonies

In several species of ants, queens often form temporary cooperative associations during colony foundation. These associations end soon after the eclosion of the first workers with the death or expulsion of all but one of the queens. This study examined competition between foundress queens of the fire ant Solenopsis invicta. Although attacks by the workers contributed to queen mortality, queens gained no advantage by producing more workers than their co-foundresses. Restriction fragment length polymorphism analysis of mitochondrial DNA showed that the queen producing more workers during colony founding was no more likely to survive than the less productive queen. In experimentally manipulated colonies in which all the workers were daughters of only one of the queens, the mother of the workers was no more likely to survive than the unrelated queen. Queens producing diploid males reared fewer offspring but were as likely to survive as queens producing only workers. These results suggest that workers do not discriminate between related and unrelated queens within colonies. Aggressive encounters between queens were common. Queens were more likely to die or be expelled if paired with heavier queens or if they lost more weight than their co-foundress during the claustral period. Finally, when queens were separated by screens through which workers could pass, the workers usually attacked and killed the queen farther from the brood. These results suggest that queen survival is promoted by a high fighting ability relative to co-foundresses, rather than by increased worker production, and that workers respond to queen differences that are independent of kinship. Received: 8 September 1995/Accepted after revision: 5 March 1996     

Control of reproduction in social insect colonies: individual and collective relatedness preferences in the paper wasp, Polistes annularis

Social insect colonies often have one or a few queens. How these queens maintain their reproductive monopoly, when other colony members could gain by sharing in the reproduction, is not generally known. DNA microsatellite genotyping is used to determine reproductive interests of various classes of colony members in the paper wasp, Polistes annularis. The relatedness estimates show that the best outcome for most individuals is to be the reproductive egg-layer. For workers, this depends on the sex of offspring: they should prefer to lay their own male eggs, but are indifferent if the queen lays the female eggs. The next-best choice is usually to support the current queen. As a rule, subordinates and workers should prefer the current queen to reproduce over other candidates (though subordinates have no strong preference for the queen over other subordinates, and workers may prefer other workers as a source of male eggs). This result supports the theory that reproductive monopoly stems from the collective preferences of non-reproductives, who suppress each other in favor of the queen. However, we reject the general hypothesis of collective worker control in this species because its predictions about who should succeed after the death of the present queen are not upheld. The first successor is a subordinate foundress even though workers should generally prefer a worker successor. If all foundresses have died, an older worker succeeds as queen, in spite of a collective worker preference for a young worker. The results support the previous suggestion that age serves as a conventional cue serving to reduce conflict over queen succession. Received: 3 May 1996 / Accepted after revision: 22 September 1996     

Queen fertility, egg marking and colony size in the ant Camponotus floridanus

In ant societies, workers do not usually reproduce but gain indirect fitness benefits from raising related offspring produced by the queen. One of the preconditions of this worker self-restraint is sufficient fertility of the queen. The queen is, therefore, expected to signal her fertility. In Camponotus floridanus, workers can recognize the presence of a highly fertile queen via her eggs, which are marked with the queen's specific hydrocarbon profile. If information on fertility is encoded in the hydrocarbon profile of eggs, we expect workers to be able to differentiate between eggs from highly and weakly fertile queens. We found that workers discriminate between these eggs solely on the basis of their hydrocarbon profiles which differ both qualitatively and quantitatively. This pattern is further supported by the similarity of the egg profiles of workers and weakly fertile queens and the similar treatment of both kinds of eggs. Profiles of queen eggs correspond to the cuticular hydrocarbon profiles of the respective queens. Changes in the cuticular profiles are associated with the size of the colony the queen originates from and her current egg-laying rate. However, partial correlation analysis indicates that only colony size predicts the cuticular profile. Colony size is a buffered indicator of queen fertility as it is a consequence of queen productivity within a certain period of time, whereas daily egg-laying rate varies due to cyclical oviposition. We conclude that surface hydrocarbons of eggs and the cuticular profiles of queens both signal queen fertility, suggesting a major role of fertility signals in the regulation of reproduction in social insects.     

Regulation of reproduction by dominant workers in bumblebee (Bombus terrestris) queenright colonies

The mechanisms of regulating worker reproduction in bumblebees were studied by direct behavioral observations and by measuring ovarian development and juvenile hormone (JH) biosynthesis rates in workers under different social conditions. Workers in the last stage of Bombus terrestris colony development (the competition phase) had the lowest ovarian development and JH biosynthesis rates. Callows introduced into colonies immediately after queen removal (dequeened colonies) demonstrated a significant increase in ovarian development before, but not during, the competition phase. These findings differ from the higher ovarian development in colonies during the competition phase predicted by the prevailing hypothesis that worker reproduction starts in response to a decrease in queen inhibition. Reproduction of callows housed with dominant workers in small queenless groups was inhibited as in queenright colonies. This suggests that the reduced ovarian development and JH biosynthesis rates observed in dequeened and normally developing colonies during the competition phase also reflect inhibition by dominant workers. Thus, two distinct stages of inhibition of reproduction seem to exist: (1) before the competition phase, when the queen slows down worker ovarian development and prevents oviposition; (2) during the competition phase, when dominant workers inhibit ovarian development of other workers. Between these stages there seems to be a temporal “window” of enhanced worker reproductive development. The queen's typical switch to haploid egg production was not associated with changes in worker ovarian development or JH biosynthesis rates. These findings suggest that regulation of worker reproduction in B. terrestris is not determined by simple changes in the queen's inhibition capacity or by the sex of offspring and that the worker's role is more important than previously believed. Received: 18 March 1998 / Accepted after revision: 18 July 1998     

Reproductive decision-making in semelparous colonies of the bumblebee bombus terrestris

Queen and worker Bombus terrestris have different optima for the timing of gyne production. Workers, being more related to their gyne-sisters than to their sons, should ascertain that gyne production has started before attempting to reproduce. Their optimal timing for gyne production will be as early as possible, while allowing sufficient ergonomic colony growth to support gyne rearing. Queen optimum, on the other hand, should be to postpone gyne production toward the end of colony life cycle, in order to minimize the time-window available for worker reproduction. Thus, the timing of gyne production may profoundly affect the outcome of queen–worker competition over male production. In this study we investigated some of the social correlates possibly affecting this timing. It was found that neither keeping colony size constant and as low as 20 workers, nor decreasing worker average age, influenced the onset of gyne production. To test the effect of queen age we created young colonies with old queens and vice versa. When colony social composition remained unchanged, in young colonies headed by old queens gynes were produced earlier than predicted, but in the inverse situation gyne production was not delayed. When colony social composition was completely standardized queen age had a decisive effect, indicating that the timing of gyne production is both under queen influence and affected by queen age. Furthermore, queens assess colony age from the time of first worker emergence rather than from their own first oviposition. In these experiments the factors affecting gyne production also affected the onset of queen–worker conflict for male production, suggesting that both are regulated by the same causal effect. Postponing gyne production as much as possible provides another mechanism, in addition to extensive oophagy, for the queen to outcompete her workers in male production.     

Social influences on body size and developmental time in the bumblebee Bombus terrestris

In many social insects, including bumblebees, the division of labor between workers relates to body size, but little is known about the factors influencing larval development and final size. We confirmed and extend the evidence that in the bumblebee Bombus terrestris the adult bee body size is positively correlated with colony age. We next performed cross-fostering experiments in which eggs were switched between incipient (before worker emergence) and later stage colonies with workers. The introduced eggs developed into adults similar in size to their unrelated nestmates and not to their same-age full sisters developing in their mother colony. Detailed observations revealed that brood tending by the queen decreases, but does not cease, in young colonies with workers. We next showed that both worker number and the queen presence influenced the final size of the developing brood, but only the queen influence was mediated by shortening developmental time. In colonies separated by a queen excluder, brood developmental time was shorter in the queenright compartment. These findings suggest that differences in body size are regulated by the brood interactions with the queen and workers, and not by factors inside the eggs that could vary along with colony development. Finally, we developed a model showing that the typical increase in worker number and the decrease in brood contact with the queen can account for the typical increase in body size. Similar self-organized social regulation of brood development may contribute to the optimization of growth and reproduction in additional social insects.     

Queen primer pheromone affects conspecific fire ant (<Emphasis Type="Italic">Solenopsis invicta</Emphasis>) aggression

Monogyne fire ant, Solenopsis invicta, colony workers are territorial and are aggressive toward members of other fire ant colonies. In contrast, polygyne colony workers are not aggressive toward non-nestmates, presumably due to broader exposure to heritable and environmentally derived nestmate recognition cues (broad template). Workers from both monogyne and polygyne fire ant colonies execute newly mated queens after mating flights. We discovered that monogyne and polygyne queens have a remarkable effect on conspecific recognition. After removal of their colony queen, monogyne worker aggression toward non-nestmate conspecifics quickly drops to merely investigative levels; however, heterospecific recognition/aggression remains high. Queenless monogyne or polygyne worker groups were also not aggressive toward newly mated queens. Queenless worker groups of both forms that adopted a monogyne-derived newly mated queen became aggressive toward non-nestmate workers and newly mated queens. We propose that the powerful effect of fire ant queens on conspecific nestmate recognition is caused by a queen-produced recognition primer pheromone that increases the sensitivity of workers to subtle quantitative differences in nestmate recognition cues. This primer pheromone prevents the adoption of newly mated queens (regulation of reproductive competition) in S. invicta and when absent allows queenless workers to adopt a new queen readily. This extraordinary discovery has broad implications regarding monogyne and polygyne colony and population dynamics.     

Mixed messages: fertility signaling interferes with nestmate recognition in the monogynous ant Camponotus floridanus

Chemical communication is crucial for the organization of social insect colonies. However, with the heavy use of one communication modality, problems may arise such as the interference of different types of information. This study investigated how information about fertility and colony membership is integrated in the ant Camponotus floridanus. We introduced into mature, queenright colonies (a) the nestmate queen, (b) a nestmate worker, (c) a foreign, high-fertility queen, (d) a foreign, low-fertility queen, and (e) a foreign worker. As expected, workers did not attack their nestmate queen or a nestmate worker but responded aggressively to foreign workers and foreign, low-fertility queens. Surprisingly, workers did not attack foreign, high-fertility queens. Chemical analysis demonstrated that the cuticular hydrocarbon profile of C. floridanus encodes information about fertility status in queens and workers and colony membership in workers. We suggest that ants respond to this information in the cuticular hydrocarbon profile: individuals with strong fertility signals are accepted regardless of their colony membership, but individuals without strong fertility signals are tolerated only if their cuticular hydrocarbon profile matches that of colony members. Learning how social insects respond to multiple types of information presented together is critical to our understanding of the recognition systems that permit the complex organization of social insect colonies.     

Dominance orders,worker reproduction,and queen-worker conflict in the slave-making ant Harpagoxenus sublaevis

Summary In a queenright colony of the monogynous slave-making ant Harpagoxenus sublaevis, a subset of workers formed a linear dominance order in which dominance was corrlated with ovarian development, frequency of trophallaxis, length of time spent in the nest, but not body size. Identical dominance orders occurred in queenless colonies. Experiments in which the top-ranking workers were removed from queenless colonies demonstrated that worker dominance behaviour inhibits egg-laying in subordinates. A similar removal experiment showed queens restrict dominance behaviour and egg-laying in workers, probably pheromonally. Observations of slave raids indicated ovary-developed workers spent significantly less time scouting for slaves, and tended to participate less in slave raids, than workers without ovarian development. These findings suggest that potentially fertile H. sublaevis workers aggressively compete for egg-laying rights, consume extra food for egg development, and safeguard their reproductive futures by avoiding risks outside the nest. Hence worker reproduction in this species strongly influences the colony's social structure, nutrient flow, and division of labour, even though all workers in a colony are full sisters. I hypothesize that worker reproduction was formerly even more prevalent in H. sublaevis, with workers following the strategy of raising sisters and producing sons predicted by kinship theory. Its continued existence despite queen opposition conceivably results from selection on orphaned workers to reproduce, and the inability of slave-maker workers to raise female-biased broods. The social organization of H. sublaevis therefore highlights the importance both of worker reproduction and of the concomitant queen-worker conflict over male parentage in Hymenopteran social evolution.     

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.     

Regulation of worker reproduction in bumblebees (Bombus terrestris): workers eavesdrop on a queen signal

In the annual bumblebee Bombus terrestris, the onset of queen-worker conflict over male production is seasonally and socially constrained. Workers will do better if they start to reproduce (the so-called competition phase) only after ascertaining that larvae are committed to gyne development but before the season ends because they gain more by rearing sister-gynes than their own sons. Here, we tested two nonmutually exclusive hypotheses as to what triggers the onset of worker reproduction: Workers can directly monitor larval development and/or workers eavesdrop on the queen signal that directs gyne development. Exposing workers to gyne larvae through a double mesh did not advance the competition phase compared to control colonies. However, when workers, but not the queen, were allowed contact with gyne larvae, both the competition phase and gyne production were advanced. Thus, while larvae do not emit a volatile pheromone that discloses their developmental route, the physical contact of workers with such larvae triggers early competition phase. However, workers exclusively exposed to worker larvae (colonies prevented from producing gyne larvae) started to reproduce at the same time as control colonies. Replacing the resident queen with an older queen (from gyne-rearing colonies) advanced the competition phase, irrespective of worker age. The results are consistent with the hypothesis that workers eavesdrop on the queen pheromones. This is adaptive because it allows workers a broader time-window for reproduction and thus to gain fitness from rearing both sister-gynes and sons before the season ends without affecting colony development.     

Reproductive plasticity in bumblebee workers (<Emphasis Type="Italic">Bombus terrestris</Emphasis>)—reversion from fertility to sterility under queen influence

Worker sterility in the bumblebee Bombus terrestris is conditional and is linked to the social development of the colony. Workers refrain from reproducing or overtly challenging the queen until gyne production has initiated, at the so-called competition point (CP). It is not known whether this behavior is hard-wired or workers show reproductive plasticity. It also remains unclear whether worker reproductive decision is under queen and/or worker control. In this study, we tested worker reproductive plasticity in an attempt to assess whether and under which conditions worker sterility/fertility are reversible. We introduced egg-laying workers into colonies with different social structures for 1 week then monitored their reproductive status. We revealed a remarkable reproductive plasticity in the introduced workers that was social-condition-dependent. In the presence of a pre-CP queen, the introduced workers reverted to sterility, whereas in the presence of a post-CP queen, such workers remained egg-layer. Reversion to sterility does not occur when direct contact with the queen is prevented, as the introduced workers remained egg-layer in the queenright colonies with a confined queen. Egg-laying workers that were introduced into queenless colonies mostly maintained their fertility regardless of colony social phase. This shows that worker transition from cooperative to selfish behavior is reversible depending on the social context.     

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     

The effect of queen-worker conflict on caste determination in the bumblebee Bombus terrestris

Endocrine analyses were used to investigate the well-known association between queen production and the onset of worker reproduction (termed the competition phase, CPh) in Bombus terrestris. Larvae that reached the age of 5 days before the CPh had a worker-like profile: low juvenile hormone (JH) biosynthesis rates and low JH hemolymph titers. In contrast, larvae that reached the age of 5 days during the CPh had a queen-like profile: high JH biosynthesis rates and high hemolymph JH levels. Larval fate could be manipulated by transplanting egg cells into host colonies with different social structures. There was a steep rise in JH production in larvae transplanted into colonies near or during the CPh. This indicates that during colony development, larvae switch from the ”worker developmental pathway” to the ”queen developmental pathway,” and that the switch is socially regulated. In small rearing groups, larvae reared with queens before the CPh developed into workers, whereas those reared with queens after the CPh developed into queens. Variation in worker type (naive or experienced) did not affect caste determination. Therefore, we hypothesize that queens produce a pheromone that directly inhibits queen differentiation by larvae. We also present two alternative scenarios that explain the timing of gyne production in B. terrestris, one based on ecological constraints and the other based on queen-worker competition. Received: 20 October 1999 / Received in revised form: 18 December 1999 / Accepted: 23 January 2000     

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.     

Behavioral regulation of genetic caste determination in a Pogonomyrmex population with dependent lineages

The fate of a social insect colony is partially determined by its ability to allocate individuals to the caste most appropriate for the requirements for growth, maintenance, and reproduction. In pairs of dependent lineages of Pogonomyrmex barbatus, the allocation of individuals to the queen or worker caste is constrained by genotype, a system known as genetic caste determination (GCD). In mature GCD colonies, interlineage female eggs develop into sterile workers, while intralineage eggs become reproductively capable queens. Although the population-level consequences of this system have been intensively studied, the proximate mechanisms for GCD remain unknown. To elucidate these mechanisms, we brought newly mated queens into the laboratory and allowed them to establish colonies, nearly half of which unexpectedly produced virgin queens only seven months after colony founding. We genotyped eggs, workers, and the virgin queens from these colonies. Our results showed that queens in young colonies produce both interlineage and intralineage eggs, demonstrating that queens of GCD colonies indiscriminately use sperm of at least two lineages to fertilize their eggs. Intralineage eggs were more frequent in colonies producing virgin queens. These findings suggest that intralineage eggs are predetermined to become queens and that workers may cull these eggs when colonies are not producing queens. Virgin queens produced by young GCD colonies were smaller than field-caught virgin queens, and often had developmental problems. Hence, they are probably nonfunctional and represent an intense resource drain for developing colonies, not a contribution to colony fitness.     

Prior experience with eggs laid by non-nestmate queens induces egg acceptance errors in ant workers

We studied the effect of prior experience to eggs laid by nestmate and non-nestmate queens on the acceptance of queen-laid eggs by worker wood ants, Formica fusca. We transferred eggs from a non-nestmate queen into colonies during early spring, when their own queen was recommencing egg laying. A few weeks later, workers from these “experienced” colonies accepted eggs of both familiar (44% acceptance) and unfamiliar (40%) non-nestmate queens much more than workers from control colonies (2%) that had only had previous contact with their own queen’s eggs. Thus, prior exposure to eggs laid by a non-nestmate queen induces much greater acceptance of all non-nestmate queen-laid eggs. Mechanistically, we hypothesize that exposure to eggs from several queens may increase acceptance by causing a highly permissive acceptance threshold of non-nestmate queen-laid eggs rather than by widening the template for acceptable queen-laid eggs. These novel results show that egg-discrimination behaviour in F. fusca is flexible and that workers respond to the diversity of eggs experienced in their colony.