Biased sperm use by polyandrous queens of the ant<Emphasis Type="Italic"> Proformica longiseta</Emphasis>

The occurrence and genetic effects of polyandry were studied in the ant Proformica longiseta using three microsatellite markers. The average queen mating frequency (QMF) estimated from the sperm dissected from the spermathecae of 61 queens was 2.4 with 69% of the queens being multiply mated. QMF estimated from worker offspring in a subsample of eight monogynous colonies was 3.5, but the effective paternity (m_e,p) was only 1.23. The difference between these values reflected unequal sperm use by the queens. Most colonies of P. longiseta were polygynous and the average relatedness among workers was 0.35. Polyandry thus added only marginally to the genetic diversity of colonies, and our results gave little support to the genetic-variability hypothesis for explaining polyandry. Diploid male load was low, as only 1% of males were diploid. A large majority (92%) of nests produced one sex only, with males produced in colonies that had higher than average worker relatedness. This contradicted the predictions derived from worker control of sex ratios. Males produced enough sperm to fill the spermathecae of several queens. Thus, the results indicated that diploid male load, sperm limitation and sex ratio conflict are also unlikely explanations of polyandry. Plausible hypotheses for polyandry include mating by convenience, as the sex ratio is male biased and the mating costs to a female can be low because the females are wingless and have no mating flight. The observed unequal sperm use furthermore points to sperm choice and sperm competition as important factors in the evolution of polyandry.     

Low queen mating frequency in the seed-harvester ant Pogonomyrmex (Ephebomyrmex) pima: implications for the evolution of polyandry

The evolution of polyandry is a central problem in the study of insect mating systems, and both material and genetic benefits have been proposed to offset the presumed costs of multiple mating. Although most eusocial Hymenoptera queens mate with just one or occasionally two males, high levels of polyandry are exhibited by several taxa, including seed-harvester ants of the genus Pogonomyrmex. Previous studies of queen mating frequency in Pogonomyrmex have focused on monogynous (one queen per colony) species in the subgenus Pogonomyrmex. We performed a genetic mother–offspring analysis of mating frequency in Pogonomyrmex (Ephebomyrmex) pima, a queen-dimorphic species with dealate and intermorph queens that differ in colony structure (intermorph colonies contain multiple queens). Our results demonstrate that both dealate and intermorph queens of P. (E.) pima are typically single maters, unlike their congeners analyzed thus far. Polyandry appears to be a derived trait in Pogonomyrmex, but comparative tests between P. (E.) pima queen morphs and across the genus provide no evidence that it evolved as an adaptation to increase genetic diversity within colonies or to obtain more sperm, respectively.     

Incest avoidance,fluctuating asymmetry,and the consequences of inbreeding in Iridomyrmex humilis,an ant with multiple queen colonies

Summary Inbreeding may have important consequences for the genetic structure of social insects and thus for sex ratios and the evolution of sociality and multiple queen (polygynous) colonies. The influence of kinship on mating preferences was investigated in a polygynous ant species, Iridomyrmex humilis, which has within-nest mating. When females were presented simultaneously with a brother that had been reared in the same colony until the pupal stage and an unrelated male produced in another colony, females mated preferentially with the unrelated male. The role of environmental colony-derived cues was tested in a second experiment where females were presented with two unrelated males, one of which had been reared in the same colony until the pupal stage (i.e., as in the previous experiment), while the other had been produced in another colony. In this experiment there was no preferential mating with familiar or unfamiliar males, suggesting that colony-derived cues might not be important in mating preferences. Inbreeding was shown to have no strong effect on the reproductive output of queens as measured by the number of worker and sexual pupae produced. The level of fluctuating asymmetry of workers produced by inbreeding queens was not significantly higher than that of non-inbreeding queens. Finally, colonies headed by inbreeding queens did not produce adult diploid males. Based on the current hypotheses of sex-determination the most plausible explanations for the absence of diploid-male-producing colonies are that (i) workers recognized and eliminated these males early in their development, and/or (ii) there are multiple sex-determining loci in this species. It is suggested that even if inbreeding effects on colony productivity are absent or low, incest avoidance mechanisms may have evolved and been maintained if inbreeding queens produce a higher proportion of unviable offspring. Correspondence to: L. Keller at the present address     

Multiple mating and facultative polygyny in the Panamanian leafcutter ant Acromyrmex echinatior

Queen mating frequency of the facultatively polygynous ant Acromyrmex echinatior was investigated by analysing genetic variation at an (AG)_n repeat microsatellite locus in workers and sexuals of 20 colonies from a single Panamanian population. Thirteen colonies were found to be monogynous, 5 colonies contained multiple queens, whereas the queen number of 2 colonies remained unresolved. Microsatellite genotypes indicated that 12 out of 13 queens were inseminated by multiple males (polyandry). The mean queen mating frequency was 2.53 and the mean genetically effective paternity frequency was 2.23. These values range among the highest found in ants, and the results are in keeping with the high mating frequencies reported for other species of leafcutter ants. Consistent skew in the proportional representation of different patrilines within colonies was found, and this remained constant in two consecutive samples of offspring. Dissections showed that all examined queens from multiple-queen colonies were mated egg-layers. The mean relatedness value among nestmate workers in polygynous colonies was lower than that for monogynous colonies. No diploid males were detected in a sample of 70 genotyped males. Worker production of males was detected in one queenless colony. We discuss our findings in relation to known patterns of multiple maternity and paternity in other eusocial Hymenoptera. Received: 2 September 1998 / Received in revised form: 3 February 1999 / Accepted: 7 February 1999     

Polyandry in the genus Apis, particularly Apis andreniformis

Using four polymorphic microsatellite loci, we found that four Apis andreniformis queens collected in Thailand each mated at least 10–20 times, producing an average relatedness, g _ww, of workers of 0.30 ± 0.007, and an average effective number of matings of 9.1 ± 2.2. The degrees of polyandry and intra-colonial genetic relatedness in A. andreniformis are similar to those in A. mellifera, slightly more than in A. florea, and up to 6 times less than in A. dorsata. We argue that while presently favoured hypotheses for the evolution of polyandry in monogynous social insects may adequately explain the evolution of up to five or six matings, they are inadequate to explain the extreme polyandry (10–60 matings) observed in Apis. One alternative possibility is that colony fitness is a non-additive function of the fitness of individual subfamilies. Such behavioral over-dominance may mean that queen fitness is increased by high levels of polyandry, which increase the probability of desirable combinations of worker genotypes occurring in one colony. The special attributes of honey bees which may lead to behavioral over-dominance include colony aggregation (which may increase the incidence of disease), and frequent long-distance migration. Received: 8 May 1996/Accepted after revision: 9 August 1996     

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     

Genetic analysis of parentage within experimental populations of a male dimorphic beetle,<Emphasis Type="Italic"> Onthophagus taurus</Emphasis>, using amplified fragment length polymorphism

We used the multilocus DNA fingerprinting technique, amplified fragment length polymorphism, to examine parentage of 902 offspring from eight experimental populations of the dung beetle, Onthophagus taurus. The males of this species exhibit a suit of morphological and behavioural traits that characterise alternative mating tactics. Hornless minor males sneak copulations with females that are guarded by horned major males. Our aims were to provide a prospective assessment of the potential role of frequency dependence in the maintenance of alternative mating tactics, to assess the levels of polyandry, and to determine the patterns of sperm usage by multiply mated females. The average proportion of offspring sired by major and minor males did not co-vary with the relative frequency of each morph present in experimental populations. However, there was some indication that the effective mating frequency (number of females producing offspring sired by a given male) of major and minor males may exhibit frequency dependence. Mating success of both male types declined with increasing numbers of major males. Paternity was positively associated with effective mating frequency. Females produced offspring sired from between one and eight males and, on average, paternity was distributed equally amongst a females mates, regardless of the number of males mated. Differences in fertilisation success among males were not associated with alternative male phenotypes. Neither did a males fertilisation success depend on his genetic dissimilarity with the female. These results are discussed in the context of the evolution of alternative mating strategies, and mechanisms of postcopulatory sexual selection.Communicated by N. Wedell     

Polyandry, multiple mating, and female fitness in a water strider Aquarius paludum

Contrary to Bateman’s principle, polyandry appears to be a common female mating strategy. Several hypotheses have been proposed to explain the evolution of polyandry. It is assumed that females gain either material or genetic benefits from multiple matings, or that they are coerced into mating by males. In water striders, mating is generally assumed to be costly to females, and they are thought to mate for reasons of convenience, adjusting their resistance to mating according to male harassment. Here, we tested the effect of number of matings (with the same male) and number of partners on female fitness in a water strider Aquarius paludum. In the first experiment, we regulated the time females spent with a male and found that females’ egg production increased with multiple matings up to a point. The result supports the existence of an optimal female mating frequency. In the second experiment, we tested how polyandry affects the number of eggs laid and egg hatching success. We conducted three different trials: females mated four times with either a single male, two different males, or with four different males. Females that mated with four different males laid the lowest number of eggs and had the lowest egg hatching success, suggesting that polyandry reduces females’ egg production and egg hatching success in A. paludum. We conclude that A. paludum females probably gain material benefits from mating but no genetic benefits were found in this study.     

Male butterfly investment in successive ejaculates in relation to mating system

In Lepidoptera, female mating systems range from strict monandry to strong polyandry. Males transfer an ejaculate during copulation that contains both sperm and accessory gland substances. In butterflies the male ejaculate has at least three effects: it (1) contains sperm that can fertilize the eggs of the male’s mating partner, (2) influences the refractory period of the mated female, and (3) contains nutrients that can be used by the female to increase her reproductive output. A number of recent studies have shown that males in polyandrous mating systems are endowed with adaptations to increase mating capabilities. Relative to males in more monandrous species they transfer larger first ejaculates which contain relatively more protein, and allocate proportionally more resources to reproduction. The objective of this study was to compare male reproductive investment in successive ejaculates, in terms of both mass and quality, to determine if males of polyandrous species are capable of maintaining the production of larger and more nutritious ejaculates than males of more monandrous species. We used three species of pierid butterfly, with mating systems ranging from relative monandry to polyandry. The degree of polyandry had a substantial effect on the reproductive performance of males. The cumulative protein content of ejaculates increased with the degree of polyandry. Only males of the most polyandrous species, Pieris rapae, produced three successive ejaculates of similar mass and protein content. In the relatively monandrous species, Aporia crataegi and P. brassicae, males in subsequent matings never produced another ejaculate as large as that transferred by males mating for the first time, although the protein content (mg) of ejaculates did not differ in second and third ejaculates. Moreover, the ability to remate varied with the degree of polyandry. Given the opportunity to remate, the majority of P. rapae males mated three times, whereas relatively few A. crataegi and P. brassicae males were able to perform three matings. These results suggest that male capacity to produce large, nutritious ejaculates is limited in relatively monandrous species. In this study only males belonging to the most polyandrous species had the ability to recuperate quickly from a mating event and remate. Our results suggest that males in polyandrous systems are better adapted to mating more than once. Received: 3 November 1995/Accepted after revision: 13 July 1996     

Evolution of extreme polyandry in the honeybee Apis mellifera L.

A number of hypotheses have been proposed to explain the evolution of multiple mating in the honeybee queen. In particular, the consequences of reduced intracolonial relatedness provide plausible explanations for multiple mating with up to ten drones, but fail to account for the much higher mating frequencies observed in nature. In this paper, we propose an alternative mechanism which builds on non-linear relationships between intracolonial frequencies in genotypic worker specialization and colony fitness. If genes for any worker specialization confer an advantage on colony fitness only when they are rare, this would require a stable mix of sperm from a few drones which contribute that trait, and many which do not. To ensure both specific, low within-colony proportions of “rare specialist” genes, and to reduce random variation of these proportions would require mating with high numbers of drones. The quantitative implementation shows that moderate to very high numbers of matings are required to exploit colony advantages from genotypic allocation of workers to rare tasks. Extreme polyandry thus could result from colony selection dependent on the intracolonial frequency of rare genetic specialists. Received: 30 January 1998 / Accepted after revision: 7 October 1998     

Sex ratio determination and worker reproduction in the slave-making ant Harpagoxenus sublaevis

Summary In a population of the monogynous slave-making ant Harpagoxenus sublaevis in S.E. Sweden, the mean proportion of dry weight investment in queens was 0.54. This result differed significantly from 0.75 but not from 0.5, matching the prediction from the genetic relatedness hypothesis of sex ratio applied to slave-makers, given (as confirmed by this study) single mating of queens, population-wide mate competition, and relatively low levels of worker male production. Sex investment appeared unaffected by resource availability. In the same 47 colony population sample, fertile slave-maker workers were found in every queenless colony (ca. 30% of all colonies), and in 58% of queen-right colonies. Fertile workers occurred at a significantly higher frequency in the queenless colonies (19.2%) than in the queenright ones (9.8%), confirming that queenless conditions promote worker fertility. Fertile and sterile workers were similar in size. Electrophoretic allozyme analysis of ants from 49 colonies showed that: 1) queens mated singly; 2) female nestmates were full sisters (their regression coefficient of relatedness (±SE) was 0.735±0.044); 3) inbreeding did not occur; 4) queen and worker siblings were not genetically differentiated. Worker male production in queenright colonies was neither confirmed nor ruled out by the genetic data. However, production data indicated that queenless workers produced between 4.4 and 21.6% of all males. Overall colony productivity was largely determined by slave number, itself positively correlated with the number of slave-maker workers. There was an abrupt switch from all worker to all sexual production as colony size rose, as predicted by life history models. In queenright colonies, fertile slave-makers did not discernibly reduce colony productivity. Such workers occurred in queenright colonies with most slaves, suggesting they exploited energetic surpluses. Worker reproduction in H. sublaevis therefore appears to have greater influence at the level of individual behaviour than at colony or population level.     

Sperm limitation and the evolution of extreme polyandry in honeybees (Apis mellifera L.)

Honeybee queens (Apis mellifera) show extreme levels of polyandry, but the evolutionary mechanisms underlying this behaviour are still unclear. The sperm-limitation hypothesis, which assumes that high levels of polyandry are essential to get a lifetime sperm supply for large and long-lived colonies, has been widely disregarded for honeybees because the semen of a single male is, in principle, sufficient to fill the spermatheca of a queen. However, the inefficient post-mating sperm transfer from the queens lateral oviducts into the spermatheca requires multiple matings to ensure an adequate spermatheca filling. Males of the African honeybee subspecies A. m. capensis have fewer sperm than males of the European subspecies A. m. carnica. Thus, given that sperm limitation is a cause for the evolution of multiple mating in A. mellifera, we would expect A. m. capensis queens to have higher mating frequencies than A. m. carnica. Here we show that A. m. capensis queens indeed exhibit significantly higher mating frequencies than queens of A. m. carnica, both in their native ranges and in an experiment on a North Sea island under the same environmental conditions. We conclude that honeybee queens try to achieve a minimum number of matings on their mating flights to ensure a sufficient lifetime sperm supply. It thus seems premature to reject the sperm-limitation hypothesis as a concept explaining the evolution of extreme polyandry in honeybees.Communicated by R.E. Page     

A genetic component to size in queens of the ant,<Emphasis Type="Italic"> Formica truncorum</Emphasis>

The genetic basis of morphological traits in social insects remains largely unexplored. This is even true for individual body size, a key life-history trait. In the social insects, the size of reproductive individuals affects dispersal decisions, so that small size in queens is often associated with reduced dispersal, and large size with long-range dispersal and independent colony founding. Worker size is connected to division of labour when workers specialize in certain tasks according to their size. In many species, variation in worker size has been shown to increase colony performance. In this study, we present the first evidence of an additive genetic component to queen size in ants, using maternal half sib analysis. We also compared intra-colony size variation in colonies with high (queen doubly mated) versus low (queen singly mated) genetic variability. We found a high and significant heritability (h²=0.51) for queen size in one of the two study years, but not in the other. Size variation among queens was greater in colonies headed by a doubly mated queen in one of the study years, but not in the other. This indicates that genetic factors can influence queen size, but that environmental factors may override these under some circumstances. The heritability for worker size was low (h²=0.09) and non-significant. Increased genetic diversity did not increase worker size variation in the colonies. Worker size appeared largely environmentally determined, potentially allowing colonies to adjust worker size ratios to current conditions.Communicated by J. Heinze     

Multiple paternity and colony homeostasis in<Emphasis Type="Italic"> Lasius niger</Emphasis> ants

Multiple mating by social insect queens is a common phenomenon despite likely imposing substantial costs on queens. Mating with several males could be adaptive if a more genetically diverse worker force is better able to always handle any task sufficiently well, leading to a higher colony homeostasis. If multiple-paternity colonies are more homeostatic, then I propose that they may constitute less stressful rearing environments for developing sexuals. The effective stress levels experienced by developing males and queens may, however, also depend on colony productivity and sex-ratio preferences. I tested these hypotheses in the ant Lasius niger by examining whether the fluctuating asymmetry, means and coefficients of variation of a set of phenotypic traits in males and new queens co-varied with the effective number of patrilines per colony, colony productivity or sex ratio.Little support was found that the level of intra-colonial genetic diversity affects the variation of phenotype in sexuals. In 1 out of 2 years, however, females from colonies with high effective patriline numbers were heavier relative to their head width than were females from colonies with few patrilines. Support was found for the hypothesis that colonies with more resources may invest more in individual sexuals, and tendencies suggested that sexuals may receive better treatment when they belong to the majority sex of their colony.Communicated by J. Heinze     

Oligogyny by unrelated queens in the carpenter ant, Camponotus ligniperdus

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

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.     

Correlates of male mating success in two species of Anthidium bees (Hymenoptera : Megachilidae)

Summary Field observations were made on the mating behavior of two congeneric species of solitary bees, Anthidium porterae in an arid grassland and A. palliventre in a coastal sand dune habitat. Males of both species exhibited resource defence polygyny and defended hostplants to gain access to females foraging for nectar and pollen. The mating frequencies of marked and measured resident (territorial) males were monitored during periods of continuous observation, following which measurements of territory size and floral resources were obtained. Mating success of A. palliventre males was strongly influenced by territory characteristics: Males that defended small areas with a few rich hostplant patches mated more often than males that held larger territories containing many hostplant patches of low floral density. Large males generally held high-quality sites and thus had a mating advantage over smaller individuals. In A. porterae, on the other hand, male mating success was unrelated to any measure of territory quality. Copulation frequency and male size were positively correlated, however, apparently due to the increased ability of large males to seize and hold females for mating. The two species also differed in the incidence of non-territorial, sneaky males. While absent in A. palliventre, sneaky males accounted for 12% of all mating observed in A. porterae. Males of A. porterae that displayed sneaky tactics mated, on average, as often as resident males. Offprint requests to: E.M. Villalobos     

Levels of polyandry and intracolonial genetic relationships in Apis florea

DNA was extracted from worker and drone pupae of each of five colonies of the dwarf honey bee Apis florea. Polymerase chain reactions (PCR) were conducted on DNA extracts using five sets of primers known to amplify microsatellite loci in A. mellifera. Based on microsatellite allele distributions, queens of the five colonies mated with at least 5–14 drones. This is up to 3 times previous maximum estimates obtained from sperm counts. The discrepancy between sperm count and microsatellite estimates of the number of matings in A. florea suggests that despite direct injection of semen into the spermatheacal duct, either A. florea drones inject only a small proportion of their semen, or queens are able to rapidly expel excess semen after mating. A model of sexual selection (first proposed by Koeniger and Koeniger) is discussed in which males attempt to gain reproductive dominance by increasing ejaculate volume and direct injection of spermatozoa into the spermatheca, while queens attempt to maintain polyandry by retaining only a small fraction of each male's ejaculate. It is shown, at least in this limited sample, that the effective number of matings is lower in A. florea than in A. mellifera.     

The evolution of polyandry by queens in social Hymenoptera: the significance of the timing of removal of diploid males

Summary Multiple mating by queens in social Hymenoptera with single locus sex determination may be an adaptation to reduce the effect of genetic load caused by the production of diploid males, if there is a concave relationship between queen fitness and the proportion of diploid male offspring in the colony. In this situation queens should be selected to reduce the variance in the production of diploid male offspring by multiple mating. It has been suggested that this concave relationship occurs in species such as the honey bee, Apis mellifera, in which reproduction occurs near the peak of colony population. This paper suggests that the timing of diploid male removal may influence mating frequency, with early removal of diploid males favoring multiple mating and late removal of diploid males favoring single mating. This idea is explored in two ways. A mathematical model shows that cell use in the brood area of species that rear young in cells will be more efficient with multiple mating. This would favor multiple mating in species, such as the honey bee, in which brood rearing is constrained by the usable area of the brood chamber. Secondly, comparison of polyandrous honey bees (early removal of diploid males as young larvae) with monandrous fire ants, Solenopsis invicta, and Melipona bees (non-removal of immature diploid males) suggests that in the species without diploid male removal, variance reduction may reduce queen fitness. Suggestions are made for testing this hypothesis.     

Recognition of caste and mating status maintains monogyny in the ant Aphaenogaster senilis

In ants dispersing through colony fission, queens mate near their natal nest and found a new society with the help of workers. This allows potential future queens to challenge the mother queen’s reproductive monopoly. Conflicts might be resolved if the mated queen signals her presence and the workers control the developmental fate of the diploid larvae (whether they develop to worker or queen). In this study we sought to determine whether, in the fission-performing ant Aphaenogaster senilis, conflicts between queens for control of the colony are resolved by the resident queen signalling her mating status. Virgin queens were less effective than newly mated queens in inhibiting queen rearing. Moreover, potential challenger queens were recognized and heavily aggressed independent of mating status. Chemical analyses showed that mating status was associated with changes in cuticular hydrocarbon and poison gland composition, but not in Dufour’s gland composition. Cuticular dimethylalkanes were identified as potential constituents that signal both caste (present in queens only) and mating status (mated queens have higher amounts). We hypothesised that pheromone emission by virgin queens did not reach the threshold needed to fully inhibit larval development into queens but was sufficiently high to stimulate overt aggression by mated queens. These findings provide evidence for the complexity of chemical communication in social insects, in which a small number of signals may have a variety of effects, depending on the context.