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.     

Diploid male production — a significant colony mortality factor in the fire ant Solenopsis invicta (Hymenoptera: Formicidae)

Summary Two forms of the fire ant, Solenopsis invicta, occur in North America; the monogyne form has colonies with a single functional queen while the polygyne form has colonies containing many functional queens. Field surveys indicate that diploid males are common in natural populations of the polygyne form but absent from monogyne populations, in contrast to laboratory data showing that similar frequencies of queens producing such males occur in the two types of populations. Our results show that mature monogyne colonies with adopted queens rear diploid males in the laboratory, so it is unlikely that the absence of these males from monogyne colonies in the field is due to discrimination against them by monogyne workers. On the other hand, incipient monogyne colonies that produce diploid males exhibit significantly higher mortality and significantly slower rates of growth (Figs. 1–3) than colonies producing workers only. These results suggest that the observed distribution of male diploidy in S. invicta can be explained by differential mortality of diploid male producing colonies of the two forms, with such colonies of the monogyne form experiencing 100% mortality early in development. The mortality differences due to this factor are shown to be related to the different social structures and modes of colony founding characterizing the two forms.     

Experimental conversion of colony social organization by manipulation of worker genotype composition in fire ants (<Emphasis Type="Italic">Solenopsis invicta</Emphasis>)

Previous studies have shown that colony social organization in Solenopsis invicta is under strong genetic control. Colonies containing some proportion of workers with the Bb or bb genotypes at the gene Gp-9 display polygyne social organization (multiple reproductive queens per colony), whereas colonies with only BB workers express monogyne organization (single reproductive queen per colony). The hypothesis that the presence of workers bearing the b allele confers the polygyne social phenotype on a colony leads to the prediction that social organization can be manipulated by experimentally altering frequencies of adult workers bearing this allele. We did this by replacing queens in colonies of each social form with single queens of the alternate form, which differ in Gp-9 genotype. As worker Gp-9 genotype compositions changed, experimental colonies switched to the alternate social organization. These switches occurred when frequencies of workers with the b allele passed an identifiable threshold, such that colonies with fewer than 5% such workers behaved like monogyne colonies and those with more than 10% behaved like polygyne colonies. Our data thus confirm the prediction that colony social organization in this ant can be altered by manipulating adult worker genotype compositions, and thereby support the hypothesis that the expression of polygyny requires the presence of adult workers bearing the b allele at Gp-9.     

Lack of detectable nepotism in multiple-queen colonies of the fire ant Solenopsis invicta (Hymenoptera: Formicidae)

Multiple-queen (polygyne) colonies of the introduced fire ant Solenopsis invicta present a paradox for kin selection theory. Egg-laying queens within these societies are, on average, unrelated to one another, and the numbers of queens per colony are high, so that workers appear to raise new sexuals that are no more closely related to them than are random individuals in the population. This paradox could be resolved if workers discriminate between related and unrelated nestmate sexuals in important fitness-related contexts. This study examines the possibility of such nepotism using methods that combine the following features: (1) multiple relevant behavioral assays, (2) colonies with an unmanipulated family structure, (3) multiple genetic markers with no known phenotypic effects, and (4) a statistical technique for distinguishing between nepotism and potentially confounding phenomena. We estimated relatedness between interactants in polygyne S. invicta colonies in two situations, workers tending egg-laying queens and workers feeding maturing winged queens. In neither case did we detect a significant positive value of relatedness that would implicate nepotism. We argue that the non-nepotistic strategies displayed by these ants reflect historical selection pressures experienced by native populations, in which nestmate queens are highly related to one another. The markedly different genetic structure in native populations may favor the operation of stronger higher-level selection that effectively opposes weaker individual-level selection for nepotistic interactions within nests. Received: 28 June 1996 / Accepted after revision: 6 October 1996     

Differential reproduction in multiple-queen colonies of the fire ant Solenopsis invicta (Hymenoptera: Formicidae)

Summary The contribution to maternity of workers and female sexuals over time by queens in six multiple-queen laboratory colonies of Solenopsis invicta was directly assessed by use of enzyme genetic markers. Queens contributed more equally to the worker pool than to the pool of sexuals in virtually all samples (Fig. 1), and individuals producing a substantial proportion of the workers often had low or no representation of their daughters in the pool of sexuals. Signficant disparity among queens in their relative production of sexual daughters was often evident, with dominance in production of sexuals by a given queen commonly occurring in association with a pronounced loss of weight followed shortly by her death. The results suggest that significant variability in short-as well as long-term reproductive success may occur among the distantly related queens associating in natural polygyne S. invicta nests. Variance in apportionment of maternity of sexuals did not appear to be simply related to varying levels of fecundity, suggesting that the common presumption that reproductive success can be equated with fecundity in polygyne social Hymenoptera may not be well founded. The observed variance also did not appear to result from a simple mechanism of kin recognition and discrimination by workers in the process of brood rearing. Rather, this variance may have largely resulted from either, 1) recognition of certain queens and their progeny coupled with preferential sexualization of these immatures by nurse workers, or, 2) queen biasing of eggs toward development as sexuals. The frequent association of weight loss and death of mother queens with high levels of sexual daughter production may be best explained by the latter mechanism.     

Queen number and the production of sexuals in the fire ant,Solenopsis invicta (Hymenoptera: Formicidae)

Summary To investigate the possibility of queen control over the production of sexuals in polygyne colonies of the fire ant, Solenopsis invicta, large colonies were divided into polygyne (P) and monogyne (M) or queenless (Q-) halves. Sexual larvae were evident in the M and Q- halves 3 to 4 days after colony division, whereas sexual forms failed to develop in all but one of the 32 P halves examined. Both male and female sexuals were produced in abundance in all M (n=25) and Q- (n=7) halves. Evidently, individuals capable of sexualization are present in colonies with many functional queens but are normally prevented from developing. Electrophoretic and morphometric analyses indicated that both haploid and diploid males were produced in the Q- halves, although diploids far outnumbered haploids. It thus appears that queens exert control over all potential and genetically determined sexuals regardless of sex or ploidy. The timing of the appearance of sexual forms following colony division suggests that queen control may be pheromonally mediated and inhibits the growth of sexuals late in larval development. An experiment in which the queens from M and P halves of colonies were exchanged demonstrated the reversible nature of this inhibition within colonies, but also suggested that once individual larvae develop beyond a critical point they are no longer subject to queen control. Despite seasonal variation in the production of sexuals in the field, no substantial differences between colonies collected in the summer and fall were found in their response to colony manipulations. The interaction of colony weight and number of queens present prior to colony division was associated with the number of males produced in the Q- halves, but no factors examined were associated with the number of females produced in these halves, or with the number of males or females produced in the M halves.     

Mutual pheromonal inhibition among queens in polygyne colonies of the fire ant Solenopsis invicta

Summary Decrease in individual reproductive output with increasing numbers of reproductives is a general feature of social insect colonies. The previously described negative relationship between the fecundity of individual queens and number of resident queens in polygyne (multiple-queen) colonies of the fire ant Solenopsis invicta appears to result from mutual pheromonal inhibition. In an experimental test for the presence of fecundity reducing pheromones, corpses of functional (egg-laying) queens were found to effectively inhibit the fecundity of functional queens, suggesting that queen-produced pheromones suppress egg production in such queens. Evidence concerning a possible mechanism mediating this inhibition was also obtained. Treatment of queens with methoprene, a juvenile hormone (JH) analog, increased ovary development, suggesting that fecundity in functional queens may be mediated by the level of endogenous JH. These findings are consistent with the occurrence of mutual pheromonal inhibition among queens achieved by suppression of endogenous JH titers.     

High genetic relatedness among nestmate queens in the polygynous ponerine ant Gnamptogenys striatula in Brazil

Gnamptogenys striatula is a polygynous ant species, in which all workers are potentially able to mate. The reproductive status, relatedness and pedigree relationships among nestmate queens and winged females in a Brazilian population were investigated. We collected all the sexual females of 12 colonies (2–44 queens per colony, plus 2–18 winged females in 3 colonies). Dissections revealed that 98% of the queens were inseminated and that the queens in the most polygynous colonies did not lay equal numbers of eggs. The sexual females and a sample of the population were genotyped using eight microsatellite markers. Relatedness among nestmate queens was among the highest recorded to date (0.65±0.25), and tests of pedigree relationship showed that they were likely to be full-sisters, and sometimes cousins. Mated winged females were always full-sisters, the estimated genetically effective queen numbers were low and tests of pedigree relationship showed that only a few queens in the colony could be the mothers. These results suggest that the high queen-queen relatedness in polygynous colonies of G. striatula is maintained by an unusual mechanism: winged females are mostly produced by only one or a few queens, and these groups of full-sisters are recruited back into their original nest after mating. Received: 26 November 1999 / Revised: 7 September 2000 / Accepted: 7 September 2000     

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.     

Extended family structure in the ant Formica paralugubris: the role of the breeding system

In populations of various ant species, many queens reproduce in the same nest (polygyny), and colony boundaries appear to be absent with individuals able to move freely between nests (unicoloniality). Such societies depart strongly from a simple family structure and pose a potential challenge to kin selection theory, because high queen number coupled with unrestricted gene flow among nests should result in levels of relatedness among nestmates close to zero. This study investigated the breeding system and genetic structure of a highly polygynous and largely unicolonial population of the wood ant Formica paralugubris. A microsatellite analysis revealed that nestmate workers, reproductive queens and reproductive males (the queens' mates) are all equally related to each other, with relatedness estimates centring around 0.14. This suggests that most of the queens and males reproducing in the study population had mated within or close to their natal nest, and that the queens did not disperse far after mating. We developed a theoretical model to investigate how the breeding system affects the relatedness structure of polygynous colonies. By combining the model and our empirical data, it was estimated that about 99.8% of the reproducing queens and males originated from within the nest, or from a nearby nest. This high rate of local mating and the rarity of long-distance dispersal maintain significant relatedness among nestmates, and contrast with the common view that unicoloniality is coupled with unrestricted gene flow among nests. Received: 8 February 1999 / Received in revised form: 15 June 1999 / Accepted: 19 June 1999     

Genetic population structure and sociogenetic organisation in Formica truncorum (Hymenoptera; Formicidae)

Summary The genetic population structure and the sociogenetic organization of the red wood ant Formica truncorum were compared in two populations with monogynous colonies and two populations with polygynous colonies. The genetic population structure was analysed by measuring allele frequency differences among local subsets of the main study populations. The analysis of sociogenetic organisation included estimates of nestmate queen and nestmate worker relatedness, effective number of queens, effective number of matings per queen, relatedness among male mates of nestmate queens and relatedness between queens and their male mates. The monogynous populations showed no differentiation between subpopulations, whereas there were significant allele frequency differences among the subpopulations in the polygynous population. Workers, queens and males showed the same genetical population structure. The relatedness among nestmate workers and among nestmate queens was identical in the polygynous societies. In three of the four populations there was a significant heterozygote excess among queens. The queens were related to their male mates in the polygynous population analysed, but not in the monogynous ones. The data suggest limited dispersal and partial intranidal mating in the populations with polygynous colonies and outbreeding in the populations having monogynous colonies. Polyandry was common in both population types; about 50% of the females had mated at least twice. The males contributed unequally to the progeny, one male fathering on average 75% of the offspring with double mating and 45–80% with three or more matings. Correspondence to: L. Sundström     

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     

Worker discrimination among queens in newly founded colonies of the fire ant Solenopsis invicta

Although colonies of the fire ant Solenopsis invicta are often founded by small groups of queens, all but one of the queens are soon eliminated due to worker attacks and queen fighting. The elimination of supernumerary queens provides an important context for tests of discrimination by the workers, since the outcome of these interactions strongly affects the workers' inclusive fitness. To test whether workers in newly founded colonies discriminate among nestmate queens, paired cofoundresses were narrowly separated by metal screens that prevented direct fighting, but through which the workers could easily pass. Soon after the first workers completed development, they often attacked one of the queens; these attacks were strongly associated with queen mortality. When one queen's brood was discarded, so that the adult workers were all the daughters of just one queen, the workers were significantly less likely to bite their mother than the unrelated queen; however, this tendency was comparatively weak. Queens kept temporarily at a higher temperature to increase their rate of investment in brood-rearing lost weight more rapidly than paired queens and were subsequently more likely to be attacked and killed by workers. Workers were more likely to bite queens that had been temporarily isolated than queens that remained close to brood and workers. When queens were not separated by screens, the presence of workers stimulated queen fights. These results show that workers discriminate strongly among equally familiar queens and that discrimination is based more on the queens' condition and recent social environment than on kinship. Received: 9 June 1998 / Accepted after revision: 10 October 1998     

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

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

Inbreeding and local mate competition in the ant Cardiocondyla batesii

The ant species Cardiocondyla batesii is unique in that, in contrast to all other ant species, both sexes are flightless. Female sexuals and wingless, ergatoid males mate in the nest in autumn and young queens disperse on foot to found their own colonies in spring. The close genetic relatedness between queens and their mates (r_qm=0.76±SE 0.12) and the high inbreeding coefficient (F=0.55; 95%CI 0.45–0.65) suggest that 83% of all matings are between brothers and sisters. As expected from local mate competition theory, sex ratios were extremely female biased, with more than 85% of all sexuals produced being young queens. Despite the common occurrence of inbreeding, we could not detect any adult diploid males. Though the probability of not detecting multiple mating was relatively high, at least one-third of all queens in our sample had mated more than once. Multiple mating to some extent counteracts the effects of inbreeding on worker relatedness (r_ww=0.68±SE 0.05) and would also be beneficial through decreasing diploid male load, if sex was determined by a single locus complementary system.Communicated by L. Sundström     

Effects of foundress number on brood raids and queen survival in the fire ant Solenopsis invicta

In several ant species, colonies are founded by small groups of queens (pleometrosis), which coexist until the first workers eclose, after which all but one queen is killed. It has been hypothesized that, by producing a larger cohort of workers, cooperating queens may increase colony success during brood raids, a form of competition in which brood and workers from losing nests are absorbed into winning colonies. To test whether this benefit is sufficient to favor pleometrosis, newly mated queens of the fire ant Solenopsis invicta were assembled in groups of one, two, three, or four, reared in the laboratory until the first workers eclosed, then planted in the field in replicated assemblages. The proportion of colonies engaging in brood raids increased with average foundress number per nest and with colony density but was unaffected by variance in foundress number among interacting colonies. Within mixed assemblages of single-queen and multiple-queen colonies, queen number had no effect on the likelihood of engaging in raids or the probability of nest survival through the brood raiding period. However, following nearly 30% of raids, queens moved to new nests and displaced the resident queens. When queen relocation and subsequent mortality were accounted for, it was found that the survival of queens from four-queen groups was substantially higher than that of solitary queens. By contrast, the survival of queens from two-queen colonies was no greater than that of solitary queens. These results show that the competitive advantages of multiple-queen colonies are sufficient to counterbalance the increased mortality of queens within groups only when the number of foundresses is greater than two and when colonies are founded at high density. When colonies lose brood raids, the workers appear to abandon their mothers to join surviving colonies. However, in laboratory experiments, queens attempting to enter foreign nests were significantly more likely to displace the resident queen if their own daughters were present within the invaded nest. Thus, workers may be able to bias the probability that their mother rejoins them and displaces competing queens.     

Control of food influx by temporal subcastes in the fire ant,Solenopsis invicta

Summary Temporal subcastes in the fire ant, Solenopsis invicta Buren were selectively starved to determine if foragers could assess the nutritional status of their nestmates and respond accordingly. We found that starved foragers increase the honey entering the colony (Fig. 1). When nurses are starved more oil and liquid egg yolk enters the colony (Figs. 2, 3) and when both reserves and nurses are starved, more egg yolk powder is brought in by the foragers (Fig. 4). When queens are starved, more liquid egg yolk and oil enters the colony (Figs. 2, 3). Starved larvae increase the oil in the colony (Fig. 2) and when held with nurses for 24h before feeding, increase the egg yolk powder brought in and receive significantly more of it than other subcaste members (Fig. 5). We conclude that foragers can respond to the nutritional needs of their nestmates. Based on our behavioural observations, the quantity of food brought in by the foragers is regulated via discriminatory solicitation by reserves in response to the nutritional needs of the nurses.     

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     

Reproductive conflicts and egg discrimination in a socially polymorphic ant

The ability to discriminate against competitors shapes cooperation and conflicts in all forms of social life. In insect societies, workers may detect and destroy eggs laid by other workers or by foreign queens, which can contribute to regulate reproductive conflicts among workers and queens. Variation in colony kin structure affects the magnitude of these conflicts and the diversity of cues used for discrimination, but the impact of the number of queens per colony on the ability of workers to discriminate between eggs of diverse origin has so far not been investigated. Here, we examined whether workers from the socially polymorphic ant Formica selysi distinguished eggs laid by nestmate workers from eggs laid by nestmate queens, as well as eggs laid by foreign queens from eggs laid by nestmate queens. Workers from single- and multiple-queen colonies discriminated worker-laid from queen-laid eggs, and eliminated the former. This suggests that workers collectively police each other in order to limit the colony-level costs of worker reproduction and not because of relatedness differences towards queens’ and workers’ sons. Workers from single-queen colonies discriminated eggs laid by foreign queens of the same social structure from eggs laid by nestmate queens. In contrast, workers from multiple-queen colonies did not make this distinction, possibly because cues on workers or eggs are more diverse. Overall, these data indicate that the ability of F. selysi workers to discriminate eggs is sufficient to restrain worker reproduction but does not permit discrimination between matrilines in multiple-queen colonies.     

Colony fission affects kinship in a social insect

Establishment of new groups is an important step in the life history of a social species. Fissioning is a common mode not only in group proliferation, for instance, as a regular part of the life cycle in the honey bee, but also when multiple females reproduce in the same group, as in multiple-queen ant societies. We studied the genetic consequences of fissioning in the ant Proformica longiseta, based on DNA microsatellites. In P. longiseta, new nests arise by fissioning from the old ones when they grow large, and the daughter nests consist of workers and queens or queen pupae but never both. Our results show that fissioning is not entirely random with respect to kinship. Workers tend to segregate along kin lines, but only when the initial relatedness in the parental nests is low. Workers in a daughter nest also tend to be associated with closely related adult queens, whereas such an association is not detected between workers and queen pupae. Most queens and workers are carried to the daughter nest by a specialized group of transporting workers, suggesting active kin discrimination by them. Fissioning pattern in P. longiseta is different from that found in other social insects with regular fission (e.g., the honey bee, swarm-founding wasps), where no fissioning along kin lines has been found. It does, however, resemble fissioning in another group of social animals: primates.