Queen Mating Frequency Research Articles

Genetic diversity, worker size polymorphism and division of labour in the polyandrous ant Cataglyphis cursor

Understanding the adaptive significance of multiple mating (polyandry) by females has long been a challenge in evolutionary biology. Several genetic and nongenetic benefits have been proposed to explain the evolution and maintenance of polyandry. In eusocial Hymenoptera, a prominent hypothesis is that increased genetic diversity within colonies results in more polymorphic workers and facilitates division of labour. We analysed the genetic basis of worker size (i.e. worker head width) and task preference in Cataglyphis cursor, an ant showing natural variations in queen-mating frequency. Our data show that increased genetic diversity within colonies does not result in more polymorphic workers. Moreover, worker head width is not different between patrilines within colonies. Consistent with these findings, worker size has a low heritable component. Moreover, task performance is not correlated with patriline. By contrast, it is significantly associated with worker size: the first foragers leaving the nest at sunrise are significantly larger than workers remaining in the nest. Overall, these results do not support the hypothesis that multiple mating is favoured because increased genetic diversity within colonies translates into more polymorphic workers and facilitates genetic polyethism. We discuss other hypotheses to account for the evolution of polyandry in C. cursor.

Mating structure and male production inVespa analisandVespa simillima(Hymenoptera: Vespidae)

AbstractWe estimated queen mating frequency, genetic relatedness between workers and worker reproduction in the hornetsVespa analisandVespa simillimausing microsatellite DNA genotyping. The 20V. analiscolonies studied each contained a queen inseminated by a single male. Of the 15V. simillimacolonies studied, nine had a queen inseminated by a single male, four had a queen inseminated by two males, and two had a queen inseminated by three males. The estimated effective number of matings was 1.33 ± 0.74 (mean ± SD), with 75–85% of the offspring of the six multiply mated queens sired by single males. The values for genetic relatedness between the workers ofV. analisandV. simillimawere 0.739 ± 0.004 and 0.698 ± 0.013 (mean ± SD), respectively. We conclude thatV. analisandV. simillimacolonies are genetically monogynous and monandrous. When high relatedness between the workers occurs within colonies, kin selection theory predicts a potential conflict between queens and workers over male production. To determine whether males were derived from queens or workers, males fromV. analisandV. simillimacolonies were genotyped at four microsatellite loci and the level of ovary activation in workers was determined. None of the 787V. analisworkers and only 15 of 3520V. simillimaworkers had developed ovaries. Furthermore, the genotyping identified no worker‐produced males in any colony. The presence of reproductive workers correlated positively with the number of workers within the colony. These results suggest that eusocial colonies with an annual life cycle tend to break down socially when they become large and are close to dying.

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.

Polygyny and polyandry in small ant societies

Social insects, ants in particular, show considerable variation in queen number and mating frequency resulting in a wide range of social structures. The dynamics of reproductive conflicts in insect societies are directly connected to the colony kin structure, thus, the study of relatedness patterns is essential in order to understand the evolutionary resolution of these conflicts. We studied colony kin structure and mating frequencies in two closely related Neotropical ant species Pachycondyla inversa and Pachycondyla villosa. These represent interesting model systems because queens found new colonies cooperatively but, unlike many other ant species, they may still co-exist when the colony becomes mature (primary polygyny). By using five specific and highly variable microsatellite markers, we show that in both species queens usually mate with two or more males and that cofounding queens are always unrelated. Polygynous and polyandrous colonies are characterized by a high genetic diversity, with a mean relatedness coefficient among worker nestmates of 0.27 (+/- 0.03 SE) for P. inversa and 0.31 (+/- 0.05 SE) for P. villosa. However, relatedness among workers of the same matriline is high (0.60 +/- 0.03 in P. inversa, 0.62 +/- 0.08 in P. villosa) since males that mated with the same queen are on average closely related. Hence, we have found a new taxon in social Hymenoptera with high queen-mating frequencies and with intriguing mating and dispersal patterns of the sexuals.

THE EVOLUTION OF MULTIPLE MATING IN ARMY ANTS

The evolution of mating systems in eusocial Hymenoptera is constrained because females mate only during a brief period early in life, whereas inseminated queens and their stored sperm may live for decades. Considerable research effort during recent years has firmly established that obligate multiple mating has evolved only a few times: in Apis honeybees, Vespula wasps, Pogonomyrmex harvester ants, Atta and Acromyrmex leaf-cutting ants, the ant Cataglyphis cursor, and in at least some army ants. Here we provide estimates of queen-mating frequency for New World Neivamyrmex and Old World Aenictus species, which, compared to other army ants, have relatively small colonies and little size polymorphism among workers. To provide the first overall comparative analysis of the evolution of army ant mating systems, we combine these new results with previous estimates for African Dorylus and New World Eciton army ants, which have very large colonies and considerable worker polymorphism. We show that queens of Neivamyrmex and Aenictus mate with the same high numbers of males (usually ca. 10-20) as do queens of army ant species with very large colony sizes. We infer that multiple queen mating is ancestral in army ants and has evolved over 100 million years ago as part of the army ant adaptive syndrome. A comparison of army ants and honeybees suggests that mating systems in these two distantly related groups may have been convergently shaped by strikingly similar selective pressures.

Do army ant queens re-mate later in life?

Queens of eusocial Hymenoptera are inseminated only during a brief period before they start to lay eggs. This has probably been kin-selected because repeated insemination of old queens would normally be against the inclusive fitness interest of their daughter workers. Army ants have been considered to be the only possible exception to this rule due to their idiosyncratic life-history. We studied two distantly related species of army ants, the African Dorylus (Anomma) molestus and the Neotropical Eciton burchellii and present data from microsatellite genotyping, behavioural observations and sperm counts.We also describe the copulation behaviour of African army ants for the first time. Our results strongly suggest that, contradictory to earlier contentions, army ant queens do not mate repeatedly throughout their life and thus do not constitute an exception among the eusocial Hymenoptera in this respect. Sperm counts for males and queens of both species show that army ant queens have to mate with several males to become fully inseminated. However, sperm limitation by queens is unlikely to have been the prime reason for the evolution of high queen-mating frequencies in this group.

Are mistakes inevitable? Sex allocation specialization by workers can reduce the genetic information needed to assess queen mating frequency

Insect workers can increase their inclusive fitness by biasing colony sex allocation towards males when their mother queen is mated to multiple males and females when she is singly mated. Workers need heritable variation in odour diversity to assess queen mating frequency. Here we present a simple one-locus two-allele model, which shows that the sex ratio specialization itself will often select against rare alleles that would provide additional information for the assessment of queen mating frequency. However, under certain rather restricted conditions, such as when sex ratios are highly female biased, and when worker reproduction is rare, sex ratio specialization can select for rare alleles. This suggests that sex allocation biasing by workers will usually reduce the very information that workers need to assess queen mating frequency. Our model is an example where an explicit treatment of underlying genetics and mechanisms of behaviour, such as information use, is necessary to fully understand the evolution of an adaptive behavioural strategy.

A reassessment of the mating system characteristics of the army ant Eciton burchellii

In a recent study, Denny et al. (2004a) showed that queens of the army ant, Eciton burchellii, mate with multiple males and presented estimates suggesting that they mate with more males than queens of any other ant species so far investigated. They also inferred that data were consistent with queens being inseminated repeatedly throughout their life, which would be exceptional among the social Hymenoptera and contradictory to predictions from kin selection theory. In the present study, we reanalyze these data using new software and supplement them with similar microsatellite data from other colonies of the same species. Mating frequencies in E. burchellii are indeed very high (mean observed and effective queen-mating frequencies of 12.9 each) but considerably lower than the previous estimates. We show that the number of patrilines represented in the first worker offspring of a young queen is lower than in older queens but suggest that this may be due to initial sperm clumping in the queen's sperm storage organ, rather than to repeated inseminations. Moreover, we found no evidence for repeated mating by genotyping sequential worker generations produced by a single old queen, showing that she did not obtain new inseminations despite ample opportunities for mating.

Quantifying honey bee mating range and isolation in semi-isolated valleys by DNA microsatellite paternity analysis

Honey bee males and queens mate in mid air and can fly many kilometres on their nuptial flights. The conservation of native honey bees, such as the European black bee (Apis mellifera mellifera), therefore, requires large isolated areas to prevent hybridisation with other subspecies, such as A. m. ligustica or A. m. carnica, which may have been introduced by beekeepers. This study used DNA microsatellite markers to determine the mating range of A. m. mellifera in two adjacent semi-isolated valleys (Edale and Hope Valley) in the Peak District National Park, England, in order to assess their suitability for native honey bee conservation and as isolated mating locations. Three apiaries were set up in each valley, each containing 12 colonies headed by a virgin queen and 2 queenright drone producing hives. The virgin queens were allowed to mate naturally with drones from the hives we had set up and with drones from hives owned by local beekeepers. After mating, samples of worker larvae were taken from the 41 queens that mated successfully and genotyped at 11 DNA microsatellite loci. Paternity analyses were then carried out to determine mating distances and isolation. An average of 10.2 fathers were detected among the 16 worker progeny. After correction for non-detection and non-sampling errors, the mean effective mating frequency of the test queens was estimated to be 17.2, which is a normal figure for honey bees. Ninety percent of the matings occurred within a distance of 7.5 km, and fifty percent within 2.5 km. The maximal mating distance recorded was 15 km. Queens and drones did occasionally mate across the borders between the two valleys, showing that the dividing mountain ridge Losehill does not provide complete isolation. Nevertheless, in the most isolated part of Edale sixty percent of all matings were to drones from Edale hives. The large majority of observed mating distances fell within the range of Hope Valley, making this site a suitable location for the long term conservation of a breeding population of black bees.

Genetic variance of mating frequency in the honeybee (Apis mellifera L.)

The genetic variance of queen mating frequency was studied in honeybees (Apis mellifera carnica). Worker offspring (N = 966) of 28 naturally mated half sister-queens (r = 0.25) from seven unrelated breeding lines were genotyped at four DNA microsatellites. The mating frequencies of the queens were derived from the offspring genotypes. The number of observed matings per queen ranged from 10 to 28 with an average of 17.32 ± 1.10 (number of estimated matings: 24.94 ± 2.51; number of effective matings: 20.09 ± 1.73). Half-sib analyses of the breeding lines were used to estimate heritability. Heritability was h2 = 0.449 ± 0.135 for the estimated number of matings and h2 = 0.262 ± 0.103 for the number of effective males, which are both significantly different from zero. We conclude that a high genetic variance for polyandry in honeybees can be favored by balanced selection between individual queen and colony level.

Mating frequency, within‐colony relatedness and male production in a yellow jacket wasp, Dolichovespula arenaria

We examined the mating frequencies of queens in a social wasp, Dolichovespula arenaria (Vespinae) using DNA microsatellites. Five of the seven colonies supported the hypothesis of single mating by queens. The other two colonies supported two and three matings, with effective paternity of 1.48 and 1.91. Mean worker relatedness was 0.77 +/- 0.09. In two of the four male-containing colonies, all were likely progeny of the queen. In the other two colonies workers produced 8 and 14% of the male wasps. Overall, 94.3% of the male wasps were likely progeny of the queen. These patterns are consistent with published studies of vespine wasps.

Extremely high mating frequency in the Florida harvester ant (Pogonomyrmex badius)

High effective multiple queen mating is a rare but taxonomically widespread phenomenon in eusocial Hymenoptera that has arisen convergently in several taxa. In ants, high effective mating frequencies have been confirmed in only two clades: the higher leaf-cutters (Atta, Acromyrmex) and the Pogonomyrmex seed harvesters. We analysed polyandry in Pogonomyrmex badius, which has a life-history unique within the genus, and report the highest numerical mating frequencies thus far recorded in ants. We also show that P. badius is characterized by one of the highest effective mating frequencies hitherto found in ants. It is now clear that all major sub-clades of Pogonomyrmex sensu stricto exhibit high levels of polyandry. Therefore, multiple mating must have arisen early in the evolution of the genus, and may have constituted a mechanism to increase offspring variability for queens that were confronted with increasingly complex levels of organization. Too few congeners have been investigated by the same method to be certain that polyandry in P. badius is really higher than in the rest of the genus. If so, research should concentrate on a possible link between high queen mating frequency and the distinct caste system found in P. badius.

Male reproductive investment and queen mating-frequency in fungus-growing ants

Sperm number and male accessory gland compounds are often important determinants of male mating success but have been little studied in social insects. This is because mating in social insects is often difficult to manipulate experimentally, and first evidence for an explicit influence of accessory gland secretions on male mating success in social insects was obtained only recently. Here we perform a comparative analysis of male sexual organs across 11 species of attine fungus-growing ants, representing both genera with single- and multiple-queen mating. We found that the general morphology of the male sexual organs was very similar across all species, but the relative sizes of the accessory glands and the sperm-containing accessory testes vary significantly across species. Small testes and large accessory glands characterize species with singly mated queens, whereas the opposite is found in species with multiply mated queens. However, in the social parasite Acromyrmex insinuator, in which queens have secondarily reverted to single mating, males have accessory gland characteristics reminiscent of the lower attine ants, but without having significantly reduced their investment in sperm production. We hypothesize that the main function of accessory gland compounds in attine ants is to monopolize male paternity in similar ways as known from other social insects. This would imply that the evolution of polyandry in the terminal clade of the fungus-growing ants (the leafcutter ants) has resulted in selection for decreased investment by males in accessory gland secretions and increased investment in sperm number, in response to sperm competition for sperm storage.

Mating structure and male production in the giant hornet Vespa mandarinia (Hymenoptera: Vespidae)

Queen mating frequency, genetic relatedness between workers and worker reproduction were estimated in Vespa mandarinia by microsatellite DNA markers. Of 20 colonies examined, eighteen contained queens inseminated by a single male and two colonies contained queens inseminated by two males. The estimated effective number of matings was 1.03±0.023 (mean±SE) with 85% of the offspring of the two multiply-mated queens being sired by one of the two males. The genetic relatedness between workers was 0.738±0.008, which was almost identical to the predicted value of 0.75 under monogyny and monandry. For this low paternity, kin selection theory predicts a potential conflict between queens and workers over male production. To learn whether males are derived from queens or workers, 400 males from 20 colonies were genotyped at four microsatellite loci. We found that queens produced all males. This finding was confirmed by the observation that 4,317 dissected workers had not developed ovaries. There was no relationship between queen mating frequency and the frequency of worker reproduction, and workers did not produce any male offspring. These results strongly suggest that male production dominated by queens in V. mandarinia is possibly due to worker policing.

Kin structure and colony male reproduction in the hornet Vespa crabro (Hymenoptera: Vespidae)

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

Power over reproduction in social hymenoptera.

Inclusive fitness theory has been very successful in predicting and explaining much of the observed variation in the reproductive characteristics of insect societies. For example, the theory correctly predicts sex-ratio biasing by workers in relation to the queen's mating frequency. However, within an insect society there are typically multiple reproductive optima, each corresponding to the interest of different individual(s) or parties of interest. When multiple optima occur, which party's interests prevail? Presumably, the interests of the party with the greatest 'power'; the ability to do or act. This article focuses on factors that influence power over colony reproduction. In particular, we seek to identify the principles that may cause different parties of interest to have greater or lesser power. In doing this, we discuss power from two different angles. On the one hand, we discuss general factors based upon non-idiosyncratic biological features (e.g. information, access to and ability to process food) that are likely to be important to all social Hymenoptera. On the other hand, we discuss idiosyncratic factors that depend upon the biology of a taxon at any hierarchical level. We propose that a better understanding of the diversity of reproductive characteristics of insect societies will come from combining inclusive fitness theory with a wide range of other factors that affect relative power in a conflict situation.

Within-colony relatedness asymmetry and social conflicts in ants

The haplodiploïd sex-determining system of Hymenoptera, whereby males usually develop from unfertilized eggs and females from fertilised eggs, results in relatedness coefficients that are not uniform among colony members. These asymmetries in relatedness are directly affected by the genetic architecture of the colony, which in turn depends on various factors such as queen number or queen mating frequency. Relatedness asymmetries induce different fitness returns per unit investment and, as a result, conflicts over brood composition may arise among colony members. Conflicts between the queen(s) and the workers over sex ratio represent one of the most frequent conflicts in eusocial Hymenoptera. Arrhenotoky allows queens great flexibility to control the sex of their progeny, by fertilizing or not the eggs; however because workers take care of the brood, they may influence the sex ratio by preferentially rearing one sex. Another salient conflict concerns the females over reproduction. In species where workers can mate and reproduce, physical aggressions or chemical communication may lead to dominance hierarchies for access to reproduction.

A scientific note on levels of polyandry of 2 queens of the Himalayan giant honeybee, Apis laboriosa

Honeybee queens mate with more males and have the lowest coefficient of genetic relatedness among workers among all eusocial Hymenoptera (Tarpy and Nielsen, 2002). In particular, the recently discovered Asian cavity-nesting honeybee Apis nigrocincta F. Smith exhibits the highest degree of polyandry in the genus Apis L. (Palmer et al., 2001). The evolution of multiple mating by honeybee queens is central to the issue of kin selection and social evolution in the Hymenoptera. Therefore, much attention has been paid to the evolution and maintenance of multiple mating in the genus Apis in concentration with kin selection or gene diversity, for which several hypotheses have been proposed (Palmer and Oldroyd, 2000). The Himalayan giant honeybee A. laboriosa F. Smith is found in the mountainous regions of Vietnam, Bhutan, China India and Nepal. The first specimen of A. laboriosa was reported in Yunnan, China. More recently, Sakagami et al. (1980) reported that A. laboriosa shows many morphological differences from A. dorsata Fabricius. Furthermore, Underwood (1986) was the first to report on certain behaviors of A. laboriosa. Specifically, he reports that this species constructs a large single comb in an open space in high cliffs at altitudes ranging from 1200 to 3600 m, makes a seasonal migration depending on the availability of nectar and pollen resources, and tends to colonize one site in a reproductive season. However, the comparative levels of polyandry in giant honeybee colonies are unknown within the genus Apis. In the present study, we used microsatellite DNA analysis to estimate queen mating frequency and the genetic relatedness among workers of two colonies of the Himalayan giant honeybee A. laboriosa. In June of 1999, two colonies of A. laboriosa were collected by local honey hunters of Rai tribe in Sadhi Village, Nepal. These colonies had nested in the same cliff site. We were unable to obtain the queen of either colony, but we collected from 45 to 53 worker pupae from each, and these were stored at 99% ethanol until DNA extraction. We chose to sample pupae in order to avoid the problem of drifted individuals which may contaminate the result. Microsatellite DNA analysis was conducted using 4 primers designed by Estoup et al. (1994), A14, A88, A107 and B124. The levels of polyandry were calculated according to Oldroyd et al. (1996). Genotype frequency was observed at the selected four microsatellite loci with 4, 5, 3 and 5 alleles at loci A14, A88, A107 and B124, respectively. The results are given in Table I. The queen of Colony 1 was found to have mated with 23 drones and the queen of Colony 2 with 21. The number of effective matings revealed 22.12 in the Colony 1, and 17.01 in Colony 2. The genetic relatedness of nestmate workers were 0.272 in Colony 1 and 0.278 in Colony 2. Our study demonstrates that queens of two A. laboriosa colonies mate 20 times, a similar level of polyandry to that found in A. dorsata (Moritz et al., 1995; Oldroyd et al., 1996). However, the level of polyandry of A. mellifera carnica queens ranged from 6 to 24 patrilines within species (Neumann et al., 1999; Tarpy and Nielsen, 2002). It is possible that the mating frequency of A. laboriosa queens has an equally large range, but more colonies need to be analyzed to estimate more precisely the levels of polyandry in A. laboriosa.

Low mating frequency of queens in the stingless bee Scaptotrigona postica 1 and worker maternity of males

Kin selection models of intracolonial conflict over the maternity of males predict that social hymenopteran workers should favour the production of sons and nephews over brothers when the effective mating frequency (me) of the queen is low (me 2. Stingless bees have been used to support these models in that me within the group is considered low and workers are thought often to monopolise the parentage of males. We genetically analysed 20 worker and 20 male pupae from each of 10 colonies of the stingless bee Scaptotrigona postica (= Scaptotrigona aff. depilis) using six microsatellite loci and demonstrate queen monandry in eight nests and apparent low me in the other two. However, four colonies contained an additional matriline, possibly due to queen supersedure (serial polygyny), which complicated their genetic structure. Across colonies, workers were responsible for the maternity of 13% of all males. These data are broadly in agreement with predictions from kin selection theory, though the question remains open as to why workers do not secure a greater share of male maternity in this and other stingless bee species in which workers are more closely related to nephews than brothers.

Bumblebee workers from different sire groups vary in susceptibility to parasite infection

Abstract Female multiple mating with different males (polyandry) can be advantageous because the resulting genetic heterogeneity among offspring reduces the effects of parasitism. However, the underlying assumption that offspring fathered by different males vary in their susceptibility to parasites is so far only supported indirectly. Here we tested this crucial assumption using data from a study on the bumblebee Bombus terrestris L. with queens inseminated with sperm of either one or several males that originated from different sire groups (i.e. groups of brothers). We found that, under field conditions, workers from different sire groups, forming a patriline within a given colony, indeed differ in their susceptibility to the common intestinal parasite, Crithidia bombi, and do so independently of queen mating frequency.