Polygynous Colonies Research Articles

No major difference in growth and productivity between monogynous and polygynous colonies in the ant Myrmecina graminicola

No major difference in growth and productivity between monogynous and polygynous colonies in the ant Myrmecina graminicola

Gut Microbiome Composition of the Fire Ant Solenopsis invicta: an Integrated Analysis of Host Genotype and Geographical Distribution.

Gut symbiotic bacteria are known to be closely related to insect development, nutrient metabolism, and disease resistance traits, but the most important factors leading to changes in these communities have not been well clarified. To address this, we examined the associations between the gut symbiotic bacteria and the host genotype and geographical distribution of Solenopsis invicta in China, where it is invasive and has spread primarily by human-mediated dispersal. Thirty-two phyla were detected in the gut symbiotic bacteria of S. invicta. Proteobacteria were the most dominant group among the gut symbiotic bacteria. Furthermore, the Bray-Curtis dissimilarity matrices of the gut symbiotic bacteria were significantly positively correlated with the geographical distance between the host ant colonies, but this relationship was affected by the social form. The distance between monogyne colonies had a significant effect on the Bray-Curtis dissimilarity matrices of gut symbiotic bacteria, but the distance between polygyne colonies did not. Moreover, the Bray-Curtis dissimilarity matrices were positively correlated with Nei's genetic distance of the host but were not correlated with the COI-based genetic distance. This study provides a scientific basis for further understanding the ecological adaptability of red imported fire ants during invasion and dispersal. IMPORTANCE We demonstrated that gut microbiota composition and diversity varied among populations. These among-population differences were associated with host genotype and geographical distribution. Our results suggested that population-level differences in S. invicta gut microbiota may depend more on environmental factors than on host genotype.

Unequal Reproduction Early in a Social Transition: Insights from Invasive Wasps.

AbstractIn eusocial insects, nestmate queens can differ in their reproductive output, causing asymmetries in the distribution of mutual benefits. However, little is known about how reproductive success is partitioned in incipiently polygynous species, which would provide clues about the evolutionary forces shaping the emergence of polygyny. Here, we leverage a recent transition from predominantly single-queen (monogyne) to multiple-queen (polygyne) colonies in an invasive yellowjacket species to investigate whether queens in incipiently polygyne colonies invest equally in reproductive effort or vary in their relative investment in each caste. We excavated nine polygyne Vespula pensylvanica colonies in Hawaii and used restriction site-associated DNA sequencing to infer the parentage of worker, male, and gyne (daughter queen) pupae from each nest comb. In four colonies with at least eight gyne pupae, a single queen produced most or all gynes. These queens had no male offspring and few worker offspring, suggesting that a subset of nestmate queens might exploit the collective benefits of newly polygyne societies. In contrast to most queens, gyne producers had offspring distributed nonrandomly across nest combs. Nestmate queens generally exhibited low relatedness levels. Our results suggest that rapid, ecologically driven transitions to polygyny among unrelated queens may, at their onset, be vulnerable to reproductive asymmetries that are likely evolutionarily unstable. More broadly, this study contributes to the understanding of social evolution by uncovering asymmetric partitioning of reproduction in a population with newly evolved polygyny and raises questions about the future trajectories of introduced populations.

A novel distribution of supergene genotypes is present in the socially polymorphic ant Formica neoclara

BackgroundSupergenes are chromosomal regions with tightly linked clusters of alleles that control compound phenotypic traits. Supergenes have been demonstrated to contribute to the maintenance of polymorphisms within populations in traits as diverse as mimetic wing coloration in butterflies, mating strategies in birds, and malarial susceptibility in mosquitoes. A large supergene also underlies variation in social organization in Formica ants. Alternative supergene haplotypes are associated with the presence of either a single queen (monogyny) or multiple queens (polygyny) within colonies. Here, we assess the social structure and supergene status of the North American species Formica neoclara.ResultsWe sequenced a subset of the genome in 280 individuals sampled in populations from California to northern British Columbia using ddRADseq. We determined that F. neoclara is socially polymorphic in queen number, and we show that the social polymorphism is associated with alternative haplotypes at the social supergene. Intriguingly, polygyne colonies can harbor workers that are homozygous for both haplotypes as well as heterozygotes.ConclusionsThis colony genetic composition contrasts with other Formica species, in which almost all individuals in polygyne colonies have the polygyne-associated haplotype. The social polymorphism is present in widely distributed and genetically subdivided populations of F. neoclara. In studying this system in F. neoclara, we expand our understanding of the functional evolution of supergene haplotypes as they diverge in different lineages.

Early queen joining and long-term queen associations in polygyne colonies of an invasive wasp revealed by longitudinal genetic analysis.

Invasive social insects rank among the most damaging of terrestrial species. They are responsible for extensive damage and severely threaten the biodiversity of environments where they are introduced. Variation in colony social form commonly occurs in introduced populations of yellowjacket wasps (genus Vespula). In particular, invasive colonies may contain multiple queens (i.e., polygyne) and persist several years, while in the native range, the colonies are usually annual and harbor a single queen (i.e., monogyne). In this study, we used genome‐wide loci obtained by double digest restriction site‐associated DNA sequencing (RADseq) to investigate the genetic structure and queen turnover in colonies of the western yellowjacket, Vespula pensylvanica, in their introduced range in Hawaii. Of the 27 colonies monitored over four months (October–January), 19 were polygyne and already contained multiple queens on the first day of sampling. Contrary to previous speculation, this finding suggests that polygyny often arises early in the annual colony cycle, before the production of new queens in the fall. Furthermore, polygyne colonies exhibited a prolonged average lifespan relative to those headed by a single queen. As a result, there is no clear window during which colony eradication efforts would be more effective than upon first discovery. The relatedness among nestmate queens was slightly above zero, indicating that these colonies are generally composed of nonrelatives. The queen turnover within each colony was low, and we detected some full‐sibling workers sampled up to four months apart. Finally, we did not detect any population structure among colonies, suggesting that queens disperse up to several kilometers. Taken together, our results provide the first insights into the requeening dynamics in this invasive and incipiently polygyne population and illuminate the early establishment of multiple long‐lasting queens in these damaging colonies.

Cooperation by ant queens during colony-founding perpetuates alternative forms of social organization

Key social traits, like queen number in eusocial insect colonies, have long been considered plastic, but the recent finding that colony social organization is under strict genetic control in multiple ant lineages challenges this view. This begs the question of which hardwired behavioral mechanism(s) generate alternative forms of social organization during colony development. We addressed this question in the Alpine silver ant, Formica selysi, a species with two social forms determined by a supergene. Queens that carry exclusively the M haplotype are produced by and live in monogyne (= single-queen) colonies, whereas queens that carry at least one copy of the P haplotype are produced by and live in polygyne (= multiple-queen) colonies. With extensive field samplings and laboratory experiments, we show that both types of queens successfully establish colonies independently, without being accompanied by workers, but that they do so in contrasting ways. Monogyne queens were generally intolerant of other queens and founded colonies solitarily, whereas polygyne queens were mutually attracted to each other and mainly founded colonies cooperatively. These associations persisted for months after worker emergence, suggesting that cooperative colony-founding leads to permanent multiple queening. Overall, our study shows that queens of each social form found colonies independently in the field but that P-carrying queens are more likely to cooperate, thereby contributing to perpetuate alternative forms of social organization.Significance statementUnderstanding the genetic and behavioral underpinnings of social organization is a major goal in evolutionary biology. Recent studies have shown that colony social organization is controlled by supergenes in multiple ant lineages. But the behavioral processes linking the genotype of a queen to the type of colony she will form remain largely unknown. Here, we show that in Alpine silver ants, alternative supergene genotypes are associated with different levels of social attraction and tolerance in young queens. These hardwired differences in social traits make queens carrying the P supergene haplotype more prone to cooperate and form durable associations during independent colony-founding. These findings help explain how genetic variants induce alternative forms of social organization during the ontogeny of a colony. They also illustrate how simple phenotypic differences at the individual level can result in large differences at higher levels of organization.

Distinct colony boundaries and larval discrimination in polygyne red imported fire ants (Solenopsis invicta).

Evaluating the factors that promote invasive ant abundance is critical to assess their ecological impact and inform their management. Many invasive ant species show reduced nestmate recognition and an absence of boundaries between unrelated nests, which allow populations to achieve greater densities due to reduced intraspecific competition. We examined nestmate discrimination and colony boundaries in introduced populations of the red imported fire ant (Solenopsis invicta; hereafter, fire ant). Fire ants occur in two social forms: monogyne (colonies with a single egg-laying queen) and polygyne (colonies with multiple egg-laying queens). In contrast with monogyne nests, polygyne nests are thought to be interconnected due to the reduced antagonism between non-nestmate polygyne workers, perhaps because polygyne workers habituate the colony to an odour unique to Gp-9b -carrying adults. However, colony boundaries and nestmate discrimination are poorly documented, particularly for worker-brood interactions. To delimit boundaries between field colonies, we correlated the exchange of a 15 N-glycine tracer dissolved in a sucrose solution with social form. We also evaluated nestmate discrimination between polygyne workers and larvae in the laboratory. Counter to our expectations, polygyne colonies behaved identically to monogyne colonies, suggesting both social forms maintain strict colony boundaries. Polygyne workers also preferentially fed larval nestmates and may have selectively cannibalized non-nestmates. The levels of relatedness among workers in polygyne colonies was higher than those previously reported in North America (mean±standard error: 0.269±0.037). Our study highlights the importance of combining genetic analyses with direct quantification of resource exchange to better understand the factors influencing ant invasions.

Disentangling the mechanisms linking dispersal and sociality in supergene-mediated ant social forms.

The coevolution between dispersal and sociality can lead to linked polymorphisms in both traits, which may favour the emergence of supergenes. Supergenes have recently been found to control social organization in several ant lineages. Whether and how these ‘social supergenes’ also control traits related to dispersal is yet unknown. Our goal here was to get a comprehensive view of the dispersal mechanisms associated with supergene-controlled alternative social forms in the ant Formica selysi. We measured the production and emission of young females and males by single-queen (monogyne) and multiple-queen (polygyne) colonies, the composition of mating aggregations, and the frequency of crosses within and between social forms in the wild. We found that males and females from alternative social forms did not display strong differences in their propensity to leave the nest and disperse, nor in their mating behaviour. Instead, the social forms differed substantially in sex allocation. Monogyne colonies produced 90% of the females flying to swarms, whereas 57% of the males in swarms originated from polygyne colonies. Most crosses were assortative with respect to social form. However, 20% of the monogyne females did mate with polygyne males, which is surprising as this cross has never been found in mature monogyne colonies. We suggest that the polygyny-determining haplotype free rides on monogyne females, who establish independent colonies that later become polygyne. By identifying the steps in dispersal where the social forms differ, this study sheds light on the behavioural and colony-level traits linking dispersal and sociality through supergenes.

Social organization and the evolution of life-history traits in two queen morphs of the ant Temnothorax rugatulus.

During the evolution of social insects, not only did life-history traits diverge, with queens becoming highly fecund and long lived compared with their sterile workers, but also individual traits lost their importance compared with colony-level traits. In solitary animals, fecundity is largely influenced by female size, whereas in eusocial insects, colony size and queen number can affect the egg-laying rate. Here, we focused on the ant Temnothorax rugatulus, which exhibits two queen morphs varying in size and reproductive strategy, correlating with their colony's social organization. We experimentally tested the influence of social structure, colony and body size on queen fecundity and investigated links between body size, metabolic rate and survival under paraquat-induced oxidative stress. To gain insight into the molecular physiology underlying the alternative reproductive strategies, we analysed fat body transcriptomes. Per-queen egg production was lower in polygynous colonies when fecundity was limited by worker care. Colony size was a determinant of fecundity rather than body size or queen number, highlighting the super-organismal properties of these societies. The smaller microgynes were more frequently fed by workers and exhibited an increase in metabolic activity, yet they were similarly resistant to oxidative stress. Small queens differentially expressed metabolic genes in the fat body, indicating that shifts in molecular physiology and resource availability allow microgyne queens to compensate for their small size with a more active metabolism without paying increased mortality costs. We provide novel insights into how life-history traits and their associations were modified during social evolution and adapted to queen reproductive strategies.

Fine-scale habitat heterogeneity favours the coexistence of supergene-controlled social forms in Formica selysi

BackgroundSocial insects vary widely in social organization, yet the genetical and ecological factors influencing this variation remain poorly known. In particular, whether spatially varying selection influences the maintenance of social polymorphisms in ants has been rarely investigated. To fill this gap, we examined whether fine-scale habitat heterogeneity contributes to the co-existence of alternative forms of social organization within populations. Single-queen colonies (monogyne social form) are generally associated with better colonization abilities, whereas multiple-queen colonies (polygyne social form) are predicted to be better competitors and monopolize saturated habitats. We hypothesize that each social form colonizes and thrives in distinct local habitats, as a result of their alternative dispersal and colony founding strategies. Here, we test this hypothesis in the Alpine silver ant, in which a supergene controls polymorphic social organization.ResultsMonogyne and polygyne colonies predominate in distinct habitats of the same population. The analysis of 59 sampling plots distributed across six habitats revealed that single-queen colonies mostly occupy unconnected habitats that were most likely reached by flight. This includes young habitats isolated by water and old habitats isolated by vegetation. In contrast, multiple-queen colonies were abundant in young, continuous and saturated habitats. Hence, alternative social forms colonize and monopolize distinct niches at a very local scale.ConclusionsAlternative social forms colonized and monopolized different local habitats, in accordance with differences in colonization and competition abilities. The monogyne social form displays a colonizer phenotype, by efficiently occupying empty habitats, while the polygyne social form exhibits a competitor phenotype, thriving in saturated habitats. The combination of the two phenotypes, coupled with fine-scale habitat heterogeneity, may allow the coexistence of alternative social forms within populations. Overall, these results suggest that spatially varying selection may be one of the mechanisms contributing to the maintenance of genetic polymorphisms in social organization.

Development of polygynous colonies of <i>Messor muticus</i> ants in laboratory conditions

The process of growing a family of reaper ants Messor muticus (Nylander, 1849) in a test tube incubator according to the method proposed by G.M. Dlussky and M.P. Bukin (1986) considers its structure and principle of operation. The queens were captured during the flight and identified in accordance with the phylogenetic analysis of F. Steiner. The test ant colonies were divided into 3 experimental and one control groups. The main factors influencing the polygyny development of ant colonies, such as nest size and temperature are considered. The features of the destructive behavior of worker ants and their participation in the regulation of oviparous queens number in the family, as well as the influence of pheromone activity on the relationship between workers and reproductive individuals are described. The main goal of the experiment was to confirm the theory of the effect of nest size and temperature on the development of dimatological colonies of a species with a monogyny family structure. The experiment was carried out for 71 days, observations were recorded every week, the results were summed up on the 8th and 10th weeks of the experiment. The conclusion confirms the theoretical assumptions about the influence of temperature and the size of the primary nest on the development of polygynous colonies of reaper ants Messor muticus. The data obtained can serve as a basis for further study of polygyny in ant colonies, ants behavior in an unnatural habitat and the existence of ants under controlled conditions.

Breeding systems and genetic diversity in tropical carpenter ant colonies: different strategies for similar outcomes in Brazilian Cerrado savanna

Abstract Eusocial insects tend to present low genetic diversity (GD) within colonies, which can increase with the co-occurrence of multiple queens (polygyny) or with multiple mating by a single queen (polyandry). Therefore, it is important to elucidate how these strategies influence GD, which in turn mediate population ecology and how organisms respond to their environment. We studied two carpenter ant species from the Brazilian savanna, Camponotus renggeri and C. rufipes. Using microsatellites, we evaluated the number of breeders, the genetic relatedness and the contribution of polygyny and polyandry to GD within colonies. Both species exhibited facultative polygyny. In C. renggeri, low related queens formed colonies jointly and present low mating frequency. In this species, colony GD increased with the number of queens. Contrastingly, closely related queens of C. rufipes formed polygynous colonies, exhibiting high mating frequency. In C. rufipes, both queens and males contributed to colony GD. Despite the differences, the two species have similar GD at the colony scale. Under low mating frequency, our data support that polygyny has evolutionary importance for increasing GD in ant colonies, a mechanism mainly conferred to polyandry. Although the impact of GD in variable ecological and adaptive contexts remains uncertain, this study highlights how distinct reproductive strategies may generate similar patterns of GD in ants.

Prevalence and management of Solenopsis invicta in China

Red imported fire ant, Solenopsis invicta, was first found in Taiwan province of China in 2003. To prevent transboundary expansion, the Chinese government has formulated various control strategies in the last 15 years to slow down the spread of S. invicta. Despite all efforts, S. invicta invasion has reached more than 390 counties of 13 provinces and two special administrative regions in China; at present, S. invicta remains at the stage of rapid expansion. The transnational entry of S. invicta is linked to imported logs and wastepaper coming mostly from the United States. In domestic settings, long-distance expansion of S. invicta relied on potted plant and turf transportation. Both monogyne and polygyne social forms of S. invicta were present in China with polygyne colonies as the dominant one. Data on population and breeding dynamics of S. invicta reveal the presence of two peaks annually with nuptial flights occurring throughout the year. Arthropods, plant seeds, and honeydew are important food sources of S. invicta, thereby causing negative impacts on the abundance, diversity, and richness of native arthropod communities. Fire ants are threats not only to agriculture and power facilities, but also to human health, with more than 30% of people having suffered from the sting and 10% having experienced an allergic reaction. To address the expansion of S. invicta, the National Fire Ant Detection and Management Union was established and the formulation and implementation of management policies were drawn. Plant quarantine becomes an essential step in fire ant management, whereas the two-step method of combing toxic baits and contact dust emerges as the forefront method crucial in managing S. invicta. The experience and lessons learned from fire ant management in China could benefit other countries when facing similar challenges.

Colony fitness and garden growth in the asexual fungus-growing ant Mycocepurus smithii (Attini, Formicidae)

Nest-founding in the fungus-growing ant Mycocepurus smithii is typically by single queens (monogyny) and colonies transition to multiple queens (polygyny) as they grow larger. Here, we study the transition from monogyny to polygyny of M. smithii under lab conditions. We hypothesize that the worker-to-queen ratio affects colony growth, fungus-garden growth, and colony survival. Monogyne colonies with small gardens (0.1 g) had greater garden growth than polygyne colonies, suggesting that monogyny may be the superior strategy for small colonies after initial nest establishment. In monogyne colonies with small gardens and either 30, 60, or 90 workers, colonies with 60 workers produced the largest gardens, suggesting that an intermediate worker-to-queen ratio is optimal for monogyne colonies with small gardens. For monogyne colonies with larger gardens (0.45 g) and with either 6, 18, 60, or 90 workers, colonies with 60 or 90 workers had significantly greater garden growth than those with 6 or 18 workers. New daughter queens were produced only by colonies with a worker-to-queen ratio of 60 or 90, suggesting that only colonies with sufficient worker numbers and garden growth are stimulated to produce new queens. A single queen lays only 1.12 ± 0.06 (SE) eggs within 24 h, therefore, limiting growth of monogyne colonies. The transition from monogyny to polygyny through the addition of supernumary queens, as well as a worker-to-queen ratio of around 60, are, therefore, critical for colony growth and reproduction in M. smithii.

Population and colony structure of an ant with territorial males, Cardiocondyla venustula

BackgroundMany species of social insects have large-scale mating and dispersal flights and their populations are therefore often relatively homogenous. In contrast, dispersal on the wing appears to be uncommon in most species of the ant genus Cardiocondyla, because its males are wingless and the winged queens mate in their natal nests before dispersing on foot. Here we examine the population structure of C. venustula from South Africa. This species is of particular interest for the analysis of life history evolution in Cardiocondyla, as it occupies a phylogenetic position between tropical species with multi-queen (polygynous) colonies and fighting males and a Palearctic clade with single-queen colonies and mutually peaceful males. Males of C. venustula exhibit an intermediate strategy between lethal fighting and complete tolerance – they mostly engage in non-lethal fights and defend small territories inside their natal nests. We investigated how this reproductive behavior influences colony and population structure by analyzing samples on two geographic scales in South Africa: a small 40 × 40m2 plot and a larger area with distances up to 5 km between sampling sites in Rietvlei Nature Reserve near Pretoria.ResultsColonies were found to be facultatively polygynous and queens appear to mate only with a single male. The extraordinarily high inbreeding coefficient suggests regular sib-mating. Budding by workers and young queens is the predominant mode of colony-founding and leads to high population viscosity. In addition, some queens appear to found colonies independently or through adoption into foreign nests.ConclusionWhile C. venustula resembles tropical Cardiocondyla in queen number and mating frequency, it differs by the absence of winged disperser males. Dispersal by solitary, mated queens on foot or by short flights and their adoption by alien colonies might promote gene flow between colonies and counteract prolonged inbreeding. The abundance of suitable habitat and the high density of nests facilitate the spread of this species by budding and together with the apparent resistance against inbreeding make it a highly successful pioneer species and invader of degraded and man-made habitats.

Joint Evolution of Asexuality and Queen Number in an Ant

Ants exhibit a striking diversity of reproductive systems, varying in traits such as the number of reproductives per colony [1], the mode of daughter production(sexual or asexual) [2], and the mode of caste determination (genetic or environmental) [3]. Species employing mixed reproductive systemspresent a unique opportunity to explore the causesand consequences of alternative breeding strategies. Mixed reproductive systems in ants include social polymorphism in colony queen number, whereby single-queen (monogyne) and multiple-queen (polygyne) colonies co-occur within species[4-7], and facultative asexuality, in which female offspring may be produced sexually or asexually within colonies [8-13]. Here, we document a remarkable confluence of multiple mixed reproductive systems in the tropical fire ant, Solenopsis geminata, in a population with three important features: (1) polygyne colonies produce workers sexually but queens asexually, whereas monogyne colonies produce both castes sexually; (2) polygyne queens mate with monogyne males to produce workers, but monogyne queens do not mate with polygyne males; and (3) different asexual/polygyne lineages evidently were founded separately by genetically distinct founder queens, which appear to have originatedfrom the same neighboring monogyne population.Multiple asexual/polygyne genomes are transmitted undiluted in this system, but sterile workers produced with sperm from a sexually-reproducing/monogynepopulation are necessary for the persistence of these lineages. The intersection of social polymorphism, facultative asexuality, and genetic caste determination marks this population of S.geminata as an embodiment of the diversityof ant reproductive systems and suggests previously unknown connections between these phenomena.

Asymmetric assortative mating and queen polyandry are linked to a supergene controlling ant social organization.

Nonrecombining genomic variants underlie spectacular social polymorphisms, from bird mating systems to ant social organization. Because these "social supergenes" affect multiple phenotypic traits linked to survival and reproduction, explaining their persistence remains a substantial challenge. Here, we investigate how large nonrecombining genomic variants relate to colony social organization, mating system and dispersal in the Alpine silver ant, Formica selysi. The species has colonies headed by a single queen (monogynous) and colonies headed by multiple queens (polygynous). We confirmed that a supergene with alternate haplotypes-Sm and Sp-underlies this polymorphism in social structure: Females from mature monogynous colonies had the Sm/Sm genotype, while those from polygynous colonies were Sm/Sp and Sp/Sp. Queens heading monogynous colonies were exclusively mated with Sm males. In contrast, queens heading polygynous colonies were mated with Sp males and Sm males. Sm males, which are only produced by monogynous colonies, accounted for 22.9% of the matings with queens from mature polygynous colonies. This asymmetry between social forms in the degree of assortative mating generates unidirectional male-mediated gene flow from the monogynous to the polygynous social form. Biased gene flow was confirmed by a significantly higher number of private alleles in the polygynous social form. Moreover, heterozygous queens were three times as likely as homozygous queens to be multiply mated. This study reveals that the supergene variants jointly affect social organization and multiple components of the mating system that alter the transmission of the variants and thus influence the dynamics of the system.

An Alpine ant’s behavioural polymorphism: monogyny with and without internest aggression in Tetramorium alpestre

Social structure influences animal societies on various levels (e.g., relatedness, behaviour). In ants, both the number of matings per queen and the number of queens per colony can vary strongly. While workers from both monogynous and polygynous colonies often fight fiercely, in supercolonies (an extreme form of polygyny comprising thousands of queens in spatially separated but interconnected nests), non-nestmates interact peacefully. Studies on social and behavioural polymorphism within ant species can help elucidate their influence on genetic diversity and behaviour and the factors triggering variation in social structure and behaviour. Here, we reveal a behavioural and social polymorphism comprising monogyny with and without internest aggression in Tetramorium alpestre sampled in Tyrol, Austria. The social polymorphism is based on genetic and behavioural evidence and contrasts with the supercolonial organisation known from another location in Austria (Carinthia), 150 km away. Microsatellite genotyping using eight polymorphic loci revealed monogyny-monandry and high intranest pairwise relatedness. Interestingly, various experimental one-on-one worker encounters revealed only occasional aggressive behaviour between monogynous colonies, and thus a behavioural polymorphism. Mantel tests revealed a significant negative correlation between spatial distance and relatedness, while worker behaviour was not correlated with relatedness or spatial distance. These results indicate that behaviour might be influenced by other factors – for example, the experience of workers, ecological, chemical, and/or genetic factors not characterised in this study. However, workers distinguished nestmates from non-nestmates also when aggression was lacking. We hypothesise an adaptive value of reduced aggression. We speculate that the non-aggressive and partly aggressive encounters observed represent different options in the social structure of T. alpestre, the non-aggressiveness possibly also promoting supercolony development. The social and behavioural polymorphisms observed offer opportunities to identify the factors triggering these changes and thus further explore the behavioural and social polymorphism of this ant species.

Social structure of the polygynous ant, Crematogaster osakensis

The colony structures of social insects vary greatly among species. In ant societies, the number of queens within a colony is variable during colony maturation. We investigated the social structure of a polygynous ant Crematogaster osakensis in a series of field and laboratory experiments. First, the initial colonies headed by multiple queens were found in the field. In laboratory experiments, queens that were artificially cohabited after their nuptial flight harmoniously co-existed even in the presence of newly emerged workers, suggesting that mated queens of this species can establish their colony cooperatively as primary polygynous colonies. In addition, the mating frequency of a queen was typically more than one, estimated from the sperm number stored in field-collected males and queens, and from genetic relatedness among daughters of lab-reared monogynous colonies. Second, our assessment of genetic relatedness in a mature field colony of this species revealed that dealated queens, as well as workers and alates, were relatives. The number of developed oocytes identified reproductive skew in two of five field-collected nests. Moreover, under laboratory conditions, the most fertile egg layer altered over 3 months of observation. Based on these lines of evidence, we propose that in C. osakensis, polygynous foundresses might either be unrelated and subsequently be replaced by daughter queens of particular foundresses, or be related in the first place.

Extreme polygyny in the previously unstudied subtropical ant Temnothorax tuscaloosae with implications for the biogeographic study of the evolution of polygyny

Evolutionary ecologists often seek to explain life history variation at geographical scales. Progress in this regard has been slower in social insects than in unitary organisms, due in part to limited information about species distributions and the complexity of studying colony-level traits. Temnothorax ants have proven useful for investigating associations between ecology and life history traits in ants, because they have small colonies ( 400 species that range from temperate to tropical biomes. Here, we generate the first global map of Temnothorax diversity and demonstrate that previous ecological hypotheses for colony life history variation in the genus are based on data and studies confined to a small part of the overall genus-level distribution. For example, studies of northern-latitude species have suggested that overwintering success is a prominent selective force favoring polygyny but little is known about polygyny in Temnothorax species from other regions. We report the highest observed queen numbers known in the genus in the subtropical species T. tuscaloosae and confirm that all queens in these polygynous colonies are mated and actively laying eggs. Behavioral laboratory experiments further indicate that this species has a fluid nest structure and lacks intraspecific aggression at the whole-forest scale. These results extend the biogeographical extent of life history studies for this genus and point to evolutionary discoveries awaiting comparative research of the global Temnothorax fauna.