Monogyne Populations Research Articles

Queen-worker ratio affects reproductive skew in a socially polymorphic ant.

The partitioning of reproduction among individuals in communally breeding animals varies greatly among species, from the monopolization of reproduction (high reproductive skew) to similar contribution to the offspring in others (low skew). Reproductive skew models explain how relatedness or ecological constraints affect the magnitude of reproductive skew. They typically assume that individuals are capable of flexibly reacting to social and environmental changes. Most models predict a decrease of skew when benefits of staying in the group are reduced. In the ant Leptothorax acervorum, queens in colonies from marginal habitats form dominance hierarchies and only the top‐ranking queen lays eggs (“functional monogyny”). In contrast, queens in colonies from extended coniferous forests throughout the Palaearctic rarely interact aggressively and all lay eggs (“polygyny”). An experimental increase of queen:worker ratios in colonies from low‐skew populations elicits queen–queen aggression similar to that in functionally monogynous populations. Here, we show that this manipulation also results in increased reproductive inequalities among queens. Queens from natural overwintering colonies differed in the number of developing oocytes in their ovaries. These differences were greatly augmented in queens from colonies with increased queen:worker ratios relative to colonies with a low queen:worker ratio. As assumed by models of reproductive skew, L. acervorum colonies thus appear to be capable of flexibly adjusting reproductive skew to social conditions, yet in the opposite way than predicted by most models.

Polygyny and strong genetic structuring within an isolated population of the wood ant Formica rufa

Social structuring of populations within some Formica species exhibits considerable variation going from monodomous and monogynous populations to polydomous, polygynous populations. The wood ant spe cies Formica rufa appears to be mainly monodomous and monogynous throughout most of its distribution area in central and northern Europe. Only occasionally it was mentioned that F. rufa can have both polygynous and monogynous colonies in the same geographical region. We studied an isolated polydomous F. rufa population in a deciduous mixed forest in the north-west of Belgium. The level of poly domy within the colonies varied from monodomous to 11 nests per colony. Our genetic analysis of eight variable microsatellites suggest an oligo- to polygynous structure for at least the major part of the sampled nests. Relatedness amongst nest mate workers varies considerable within the population and colonies but confirms in general a polygynous structure. Additionally high genetic diversity (e.g. up to 8 out of 11 alleles per nest for the most variable locus) and high within nest genetic variance (93%) indicate that multiple queens contribute to the gene pool of workers of the same nest. Moreover significant genetic struc turing among colonies indicates that gene flow between colonies is restricted and that exchange of workers between colonies is very limited. Finally we explain how possible factors as budding and the absence of Serviformica can explain the differences in genetic structure within this polygynous F. rufa population.

Is Increased Resistance to Parasitism at the Origin of Polygyny in a Mexican Population of the AntEctatomma tuberculatum(Hymenoptera: Formicidae)?

The Neotropical ant Ectatomma tuberculatum (Olivier) shows a polymorphic social organization with strictly monogynous or facultative polygynous populations along its distribution range. The causative factors of these variations in social organization are unknown but biotic and abiotic environmental factors might explain the differences. In particular, recent studies have suggested that parasites and parasitoids could have an impact on host colony phenotype. Here, we report on eucharitid wasps and mermithid nematodes that attack the only known Mexican polygynous population of E. tuberculatum in Veracruz, Mexico. The results were compared with those previously obtained from a monogynous population in Chiapas, Mexico; the aim being to investigate environmental influences on colony social organization. The rather similar prevalence of parasitism between the 2 populations suggests that the hypothesis of an increased resistance to parasites and parasitoids as one of the factors responsible for the emergence of polygyny in E. tuberculatum populations does not apply. More likely, other kinds of environmental stress or constraints facilitate the development of polygyny, such as nest site limitations, risks of dispersal and/or high rates of predation.

Workers determine queen inheritance of reproduction in a functionally monogynous ant population

In cooperatively breeding animals there is potential for conflict among group members over reproductive sharing (skew). The outcome of such conflict depends on which individuals have power. Theoretical treatments of skew generally assume that power rests with those directly reproducing, but in eusocial insects, an important group for testing skew theory, nonreproductive workers are known to be influential in other colony conflicts such as sex ratio. We investigated the role of queens and workers in determining queen inheritance of a newly vacant reproductive position in a functionally monogynous (only one queen reproduces) population of the ant Leptothorax acervorum. Multiple-queen colonies with an already established reproductive queen were split in half producing a fragment containing multiple, previously nonreproductive queens. Loss of the established queen simulates a queen turnover event as occurs in nature. We found that worker behaviour influenced which queen filled the vacant reproductive position, with this queen receiving on average less aggression and more grooming from workers than the other queens. This study shows that after loss of the established queen, workers can modify their behaviour towards individual queens, and, contrary to skew models, skew among queens remains high despite changes in relatedness asymmetry. Our results suggest workers collectively hold considerable power over skew among queens.

No evidence of volatile chemicals regulating reproduction in a multiple queen ant

Efficient cooperation in eusocial insect colonies requires effective communication, and there is abundant evidence of non-volatile chemicals playing a role in regulating reproduction within colonies. In contrast, there have been fewer studies investigating the role of volatile chemicals. This study investigated the potential role of volatile chemicals in regulating queen reproduction either by directly inhibiting queen reproduction or by honestly signalling queen fecundity to workers. We tested this using multiple queen colonies of the ant (Leptothorax acervorum) from a functionally monogynous population where one queen monopolizes all reproduction. Nine colonies, each with an established laying queen, were split to produce two colony fragments-one containing the reproducing queen (group 1) and one containing only previously non-reproducing queens (group 2). Each group was separated by a fine wire mesh preventing physical contact, but allowing volatile chemical contact. In each group 2 fragment, we found that a single formerly non-reproductive queen commenced reproduction and that the rate of egg laying and maximum number of eggs recorded did not significantly differ between groups 1 and 2, results that do not support volatile chemicals as playing a role in regulating queen reproduction. Instead, our findings suggest that physical contact is necessary to maintain functional monogyny.

Queen dominance and worker policing control reproduction in a threatened ant

BackgroundEfficient division of reproductive labor is a crucial characteristic of social insects and underlies their ecological and evolutionary success. Despite of the harmonious appearance of insect societies, nestmates may have different interests concerning the partitioning of reproduction among group members. This may lead to conflict about reproductive rights. As yet, few studies have investigated the allocation of reproduction among queens in multi - queen societies ("reproductive skew"). In the ant Leptothorax acervorum, reproductive skew varies considerably among populations. While reproduction is quite equally shared among nestmate queens in most populations from boreal Eurasia (low skew), colonies from populations at the edge of the species' range are characterized by "functional monogyny," i.e., high skew. The proximate mechanisms underlying high skew, in particular how workers influence which queen lays eggs, are not well understood. We investigated the behavior of queens and workers in functionally monogynous colonies of L. acervorum from two mountain ranges in central Spain.ResultsWe provide evidence for both queen and worker influence on the outcome of conflict over reproduction in colonies of L. acervorum from Spain. The patterns of queen - queen aggression and worker - queen grooming and feeding after hibernation allowed predicting, which queen later began to lay eggs. In contrast, worker aggression towards queens was not clearly associated with a queen's future reproductive success. Queen - queen and worker - queen aggression differed in quality: queens typically engaged in ritualized dominance behavior, such as antennal boxing, while workers also attacked queens by biting and prolonged pulling on their legs and antennae. In several cases, overt worker aggression led to the expulsion of queens from the nest or their death.ConclusionWe conclude that queens of L. acervorum from Spain establish rank orders by ritualized dominance interactions, such as antennal boxing. Workers may reinforce these hierarchies by preferentially feeding and grooming high ranking queens and attacking lower ranking queens. Aggressive worker policing may thus stabilize functional monogyny. Optimal skew models predict that high skew in ants is associated with high dispersal costs. In central Spain, L. acervorum is restricted to small patches at higher elevations, which presumably makes dispersal and colony founding difficult. Because of the ecological requirements of L. acervorum and the predicted large impact of global change on central Spain, the functionally monogynous populations of this ant must be considered as threatened.

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.

Polymorphic social organization in an ant

Identifying species exhibiting variation in social organization is an important step towards explaining the genetic and environmental factors underlying social evolution. In most studied populations of the ant Leptothorax acervorum, reproduction is shared among queens in multiple queen colonies (polygyny). By contrast, reports from other populations, but based on weaker evidence, suggest a single queen may monopolize all reproduction in multiple queen colonies (functional monogyny). Here we identify a marked polymorphism in social organization in this species, by conclusively showing that functional monogyny is exhibited in a Spanish population, showing that the social organization is stable and not purely a consequence of daughter queens overwintering, that daughter queen re-adoption is frequent and queen turnover is low. Importantly, we show that polygynous and functionally monogynous populations are not genetically distinct from one another based on mtDNA and nDNA. This suggests a recent evolutionary divergence between social phenotypes. Finally, when functionally monogynous and polygynous colonies were kept under identical laboratory conditions, social organization did not change, suggesting a genetic basis for the polymorphism. We discuss the implications of these findings to the study of reproductive skew.

Polygyny reduces rather than increases nestmate discrimination cue diversity in Formica exsecta ants

Although the majority of social insect colonies are headed by a single queen, some species possess nests that contain numerous reproductive queens (polygyny), a trait that is particularly widespread amongst the ants. Polygyny is often associated with a lack of conspecific inter-nest aggression between workers. This is hypothesised to result from increased nestmate cue diversity within nests, since polygynous nests are more genetically diverse than monogynous nests. Alternatively, it may reflect the common origin of polygynous nests that form polydomous networks. We exploit the recent discovery that the nestmate discrimination system in the ant Formica exsecta is based on cuticular hydrocarbons to investigate cue (Z9-alkenes) diversity in several monogynous and polygynous populations. Contrary to previous predictions, in all polygynous populations, the variation between nests in the Z9-alkene profiles was reduced relative to that found in monogynous populations. However, nest-specific Z9-alkene profiles with little variation amongst nestmate workers were still maintained irrespective of nest type or population. This suggests a very effective gestalt mechanism that homogenises the chemical discrimination cues, despite genetic diversity within colonies. Although the reduction in variation between nests was associated with reduced worker aggression on the population level, it cannot totally explain the weak aggression associated with polygynous populations.

Distribution Patterns of Imported Fire Ants (Hymenoptera: Formicidae) on a Sheep and Goat Farm in Oklahoma

Imported fire ant colonies were quantified in 1,000-m(2) circular subplots spaced approximately 125 m apart on a sheep and goat farm in Oklahoma. Social form (percent polygyny), mound density, cumulative above-ground mound volume, and average mound volume were subjected to multiple regression analyses to examine trends related to landscape metrics and habitat characteristics. Monogyne populations were spatially autocorrelated, and polygyne mounds tended to be smaller and more numerous. A model incorporating the effects of percent polygyny, canopy cover, and 1-d cumulative incident solar radiation explained 34% of the variation in mound density. Percent polygyny was not significantly related to cumulative mound volume, which provides a better estimate of overall ant biomass. A model incorporating the effects of 1-d cumulative incident solar radiation on the summer solstice, elevation, canopy cover, distance from cisterns, distance from water, and distance from trees explained 42% of the variation in cumulative mound volume. Monogyne mounds in areas that were flat and close to water in low-lying areas were largest. Results indicate that remotely sensed data in combination with publicly available U.S. Geological Survey data may be useful in predicting areas of high and low fire ant abundance at a field scale.

Population genetics and history of the introduced fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae), in Australia

Abstract The red imported fire ant, Solenopsis invicta, a damaging invasive pest, was discovered in February 2001 in Brisbane, Australia at two sites, Fisherman Islands and suburban Richlands‐Wacol. Using four microsatellite loci and the protein marker Gp‐9, we compared the two infestations with each other, and with potential source populations in North and South America to better understand the history of their introduction to Brisbane. Based on an analysis of molecular variance, as well as a maximum likelihood tree of colonies from the two Australian sites, we found that the two sites were genetically distinct and were almost certainly introduced separately. All of the colonies at Fisherman Islands were monogynous, headed by a single queen, while the Richlands‐Wacol site had a mixture of single‐queen monogynous and multiple‐queen polygynous colonies. However, the monogynous and polygynous colonies at the Richlands‐Wacol site were not genetically distinct from each other, and probably constitute a single, mixed introduction. Based on allele frequencies at the microsatellite loci, and Gp‐9, both Australian infestations were more similar to North American populations than to South American, though the Fisherman Islands infestation was intermediate, making it difficult to assign. Thus, there has been one introduction from either a North or South American monogynous population at Fisherman Islands, and one introduction from a mixed monogynous/polygynous North American population at Richlands‐Wacol. These findings have implications for the control of the current infestations, as well as for the quarantine regulations necessary to prevent additional introductions to Australia.

A formal assessment of gene flow and selection in the fire ant Solenopsis invicta.

Recent studies of the introduced fire ant Solenopsis invicta suggest that introduced polygyne (with multiple queens per nest) populations are strongly influenced by male-mediated gene flow from neighboring monogyne (single queen per nest) populations and selection acting on a single locus, general protein-9 (Gp-9). This investigation formally tests this hypothesis and determines if these processes can account for the genotypic structure of polygyne S. invicta. To increase the statistical power of this test, we considered the genotypes of polygyne queens and workers at both Gp-9 and the closely linked, selectively neutral locus Pgm-3. We then constructed and analyzed a novel mathematical model to delimit the effects of monogyne male gene flow and selection on the joint genotypes at the Pgm-3/Gp-9 superlocus. Using this framework, a hierarchical maximum-likelihood method was developed to estimate the best-fitting gene flow and selection parameters based on the fit of our model to data from both the current study and an earlier one of the same population. In each case, selection on polygyne queens and workers alone, with no monogyne male gene flow, provides the most parsimonious explanation for the observed genotype frequencies. The apparent discrepancy between this result and the empirical evidence for monogype male gene flow indicates that undocumented factors, such as other forms of selection in polygyne males or workers, are operating in introduced polygyne S. invicta.

A FORMAL ASSESSMENT OF GENE FLOW AND SELECTION IN THE FIRE ANT SOLENOPSIS INVICTA

Recent studies of the introduced fire ant Solenopsis invicta suggest that introduced polygyne (with multiple queens per nest) populations are strongly influenced by male-mediated gene flow from neighboring monogyne (single queen per nest) populations and selection acting on a single locus, general protein-9 (Gp-9). This investigation formally tests this hypothesis and determines if these processes can account for the genotypic structure of polygyne S. invicta. To increase the statistical power of this test, we considered the genotypes of polygyne queens and workers at both Gp-9 and the closely linked, selectively neutral locus Pgm-3. We then constructed and analyzed a novel mathematical model to delimit the effects of monogyne male gene flow and selection on the joint genotypes at the Pgm-3/Gp-9 superlocus. Using this framework, a hierarchical maximum-likelihood method was developed to estimate the best-fitting gene flow and selection parameters based on the fit of our model to data from both the current study and an earlier one of the same population. In each case, selection on polygyne queens and workers alone, with no monogyne male gene flow, provides the most parsimonious explanation for the observed genotype frequencies. The apparent discrepancy between this result and the empirical evidence for monogyne male gene flow indicates that undocumented factors, such as other forms of selection in polygyne males or workers, are operating in introduced polygyne S. invicta.Corresponding Editor: D. Wheeler

A morphological comparison of alates between monogynous and polygynous colonies of Myrmica kotokui in northernmost Japan

Social structure and sexual size of two populations of Myrmica kotokui were compared. Most of the colonies were polygynous in one population and monogynous in the other. Mean body size of the queens was larger in the monogynous population than in the polygynous population. Although the polygynous population contained many large queens, their wing length was significantly shorter than that of queens in the monogynous population. Some females in the polygynous population were intermorphic between typical workers and queens, while the females of the monogynous population were clearly divided into worker and queen castes without any intermorphic females. The body size of the males showed a large variation and the mean was not significantly different between the two populations.

Sex allocation in a facultatively polygynous ant: between-population and between-colony variation

We investigated sex allocation in three U.K. populations of the facultatively polygynous ant Leptothorax acervorum over 1–3 years. The first main finding was that, across sites, the population sex-investment ratio changed from significantly female biased to significantly male biased with increasing polygyny. This was consistent with workers controlling sex allocation and reacting to changes in their population-level relatedness asymmetry. It was also consistent with local resource competition due to reproduction by colony budding under polygyny. Worker control was supported by the finding that queen number had no effect on sex allocation among polygynous colonies. The second main result was that monogynous colonies consistently produced more female-biased sex-investment ratios than polygynous colonies in one site only (Santon). The results from Santon supported both the relative relatedness asymmetry hypothesis and the idea of sex ratio compensation due to colony budding. The workers’ response to their population-level relatedness asymmetry reinforced the case for relatedness asymmetry being influential at the colony level. The other populations could have lacked split sex ratios because polygynous colonies were either comparatively rare or common, making them behave as almost entirely monogynous (Aberfoyle) or polygynous (Roydon) populations. In Roydon, this was consistent with the inference from allozyme data that monogynous and polygynous colonies did not differ in their worker relatedness asymmetries. The final principal finding was that, of hypotheses linking the colony sex-investment ratio with sexual productivity, there was support for the constant female hypothesis but not for the constant male, cost variation, or multifaceted parental investment hypotheses.

Testing kin selection with sex allocation data in eusocial hymenoptera

Sex allocation data in eusocial Hymenoptera (ants, bees and wasps) provide an excellent opportunity to assess the effectiveness of kin selection, because queens and workers differ in their relatedness to females and males. The first studies on sex allocation in eusocial Hymenoptera compared population sex investment ratios across species. Female-biased investment in monogyne (= with single-queen colonies) populations of ants suggested that workers manipulate sex allocation according to their higher relatedness to females than males (relatedness asymmetry). However, several factors may confound these comparisons across species. First, variation in relatedness asymmetry is typically associated with major changes in breeding system and life history that may also affect sex allocation. Secondly, the relative cost of females and males is difficult to estimate across sexually dimorphic taxa, such as ants. Thirdly, each species in the comparison may not represent an independent data point, because of phylogenetic relationships among species. Recently, stronger evidence that workers control sex allocation has been provided by intraspecific studies of sex ratio variation across colonies. In several species of eusocial Hymenoptera, colonies with high relatedness asymmetry produced mostly females, in contrast to colonies with low relatedness asymmetry which produced mostly males. Additional signs of worker control were found by investigating proximate mechanisms of sex ratio manipulation in ants and wasps. However, worker control is not always effective, and further manipulative experiments will be needed to disentangle the multiple evolutionary factors and processes affecting sex allocation in eusocial Hymenoptera.

Frequency and origin of triploidy in the fire ant Solenopsis invicta

A large microsatellite survey of fire ants of both social forms (monogyne and polygyne) from both the native and introduced ranges (Argentina and the U.S.A.) revealed surprisingly high levels of triploidy (12%) in non-reproductive females from an introduced polygyne population in Georgia, U.S.A. Triploid females were not detected among reproductive (egg-laying) queens from this population, among females from monogyne populations in the introduced range or among females of either social form from the native range. The results of complementary analyses with allozyme markers were highly concordant with the individual microsatellite ploidy designations and confirmed the general patterns in the distribution of triploidy observed with microsatellites. Triploidy in the Georgia polygyne population is hypothesized to be linked to the high frequency of diploid males in this population; although most such males are sterile, 2.4% were found to possess functional reproductive tracts and presumably produce diploid sperm. Mating of such males with polygyne queens is expected to give rise to triploid females at levels close to those observed. Diploid males are absent in monogyne populations and uncommon in the introduced range, thus explaining the lack of triploid females in samples from these sources. The absence of triploid reproductive queens in the Georgia polygyne population may result from subviability of triploid queens or execution of such queens by workers. Our results suggest that triploid females of social Hymenoptera may be more common than appreciated and are most likely to be found in populations with substantial numbers of fertile diploid males.

The success of alternative reproductive tactics in monogyne populations of the ant Solenopsis invicta: significance for transitions in social organization

Newly produced queens from monogyne (single-queen) colonies of the ant Solenopsis invicta usually initiate reproduction independently, that is, without worker assistance. However, some recently mated queens attempt to bypass this risky phase of new colony foundation by entering established nests to reproduce, although it is unclear how often these queens are successful in natural populations. We surveyed a mature monogyne population of 5. invicta in both 1995 and 1996 for colonies headed by queens incapable of independent colony founding (diploid-male-producing queens) in order to estimate the frequency of colonies that are headed by queens that initiated reproduction within established nests (adopted queens). Using the frequency of diploid-male-producing queens among the recently mated queens in this population, we estimated that the overall rate of queen replacement by adopted queens is about 0.7% per colony per year. Although theory suggests that a change to a novel queen reproductive tactic could be associated with a fundamental change in social organization (queen number), this does not appear to be the case in monogyne S. invicta. However, the evolution of nest-infiltrating reproductive tactics by queens in a monogyne population and the evolution of multiple-queen societies may result from similar ecological pressures facing newly mated queens. We therefore incorporate this strategy into an existing theoretical framework that was developed to explain the evolution of alternative social organizations in ants, providing testable predictions regarding the distribution and frequency of queen adoption in other single-queen ant societies. Key uxrrds: alternative reproductive tactics, fire ants, polygyny, Solenopsis invicta. [Behav Ecol 9:130-135 (1998)]

Hierarchical analysis of genetic structure in native fire ant populations: results from three classes of molecular markers.

We describe genetic structure at various scales in native populations of the fire ant Solenopsis invicta using two classes of nuclear markers, allozymes and microsatellites, and markers of the mitochondrial genome. Strong structure was found at the nest level in both the monogyne (single queen) and polygyne (multiple queen) social forms using allozymes. Weak but significant microgeographic structure was detected above the nest level in polygyne populations but not in monogyne populations using both classes of nuclear markers. Pronounced mitochondrial DNA (mtDNA) differentiation was evident also at this level in the polygyne form only. These microgeographic patterns are expected because polygyny in ants is associated with restricted local gene flow due mainly to limited vagility of queens. Weak but significant nuclear differentiation was detected between sympatric social forms, and strong mtDNA differentiation also was found at this level. Thus, queens of each form seem unable to establish themselves in nests of the alternate type, and some degree of assortative mating by form may exist as well. Strong differentiation was found between the two study regions using all three sets of markers. Phylogeographic analyses of the mtDNA suggest that recent limitations on gene flow rather than longstanding barriers to dispersal are responsible for this large-scale structure.

Queen acceptance and nestmate recognition in monogyne and polygyne colonies of the antFormica truncorum

In ants permanent polygyny (the permanent presence of multiple reproducing queens) commonly arises secondarily through the adoption of daughter queens. Polygyny decreases the relatedness among nestmate workers and consequently the genetic benefits from helping close relatives. Hence, studies on nestmate recognition and queen adoption may shed light on how queen numbers are regulated as well as on causes of variation in queen number. In this study acceptance of nestmate and non-nestmate young queens in monogyne (single queen) and polygyne colonies of the antFormica truncorumwas compared. Queen number varies in this species: in some populations colonies have a single queen (monogyne populations), whereas in others all colonies contain several functional queens (polygyne populations). Young queens introduced into the experimental colonies varied with respect to female origin (nestmate versus non-nestmate), dispersal prospects as reflected by wing status (wingless versus winged) and mating status (mated versus virgin). Monogyne and polygyne colonies differed in one fundamental way in their responses to introduced females. Workers of monogyne colonies, but not those of polygyne colonies, discriminated between nestmate and non-nestmate females. In both monogyne and polygyne colonies mated females were destroyed to a higher extent than virgin ones, largely independently of wing status. None the less, mated females may have a reasonable chance of becoming adopted in their natal colony both in monogyne and polygyne colonies. If so, the single-queen status of monogyne colonies may be retained by a high rate of female dispersal in combination with few intra-nidal mating opportunities. Polygyne colonies are characterized by both a low degree of female rejection and low levels of discrimination between nestmates and non-nestmates. Nevertheless, previous genetic and behavioural data on female dispersal suggest that the majority of new queens adopted into polygyne colonies are their own daughters.