Queens In Polygynous Colonies Research Articles

Social structure varies with elevation in an Alpine ant.

Insect societies vary greatly in social organization, yet the relative roles of ecological and genetic factors in driving this variation remain poorly understood. Identifying how social structure varies along environmental gradients can provide insights into the ecological conditions favouring alternative social organizations. Here, we investigate how queen number variation is distributed along elevation gradients within a socially polymorphic ant, the Alpine silver ant Formica selysi. We sampled low- and high-elevation populations in multiple Alpine valleys. We show that populations belonging to different drainage basins are genetically differentiated. In contrast, there is little genetic divergence between low- and high-elevation populations within the same drainage basin. Thus, elevation gradients in each of the drainage basins represent independent contrasts. Whatever the elevation, all well-sampled populations are socially polymorphic, containing both monogynous (= one queen) and polygynous (=multiple queen) colonies. However, the proportion of monogynous colonies per population increases at higher elevation, while the effective number of queens in polygynous colonies decreases, and this pattern is replicated in each drainage basin. The increased prevalence of colonies with a single queen at high elevation is correlated with summer and winter average temperature, but not with precipitation. The colder, unpredictable and patchy environment encountered at higher elevations may favour larger queens with the ability to disperse and establish incipient monogynous colonies independently, while the stable and continuous habitat in the lowlands may favour large, fast-growing polygynous colonies. By highlighting differences in the environmental conditions favouring monogynous or polygynous colonies, this study sheds light on the ecological factors influencing the distribution and maintenance of social polymorphism.

Nesting patterns, ecological correlates of polygyny and social organization in the neotropical arboreal ant Odontomachus hastatus (Formicidae, Ponerinae)

Queen number varies in the population of O. hastatus in SE Brazil. Here, we evaluate how nesting ecology and colony structure are associated in this species, and investigate how reproduction is shared among nestmate queens. Queen number per colony is positively correlated with nesting space (root cluster of epiphytic bromeliads), and larger nest sites host larger ant colonies. Plant samplings revealed that suitable nest sites are limited and that nesting space at ant-occupied bromeliads differs in size and height from the general bromeliad community. Dissections revealed that queens in polygynous colonies are inseminated, have developed ovaries, and produce eggs. Behavioral observations showed that reproduction in polygynous colonies is mediated by queen–queen agonistic interactions that include egg cannibalism. Dominant queens usually produced more eggs. Field observations indicate that colonies can be initiated through haplometrosis. Polygyny in O. hastatus may result either from groups of cofounding queens (pleometrosis) or from adoption of newly mated queens by established colonies (secondary polygyny). Clumping of bromeliads increases nest space and probably adds stability through a strong root system, which may promote microhabitat selection by queens and favor pleometrosis. Rainstorms that frequently knock down bromeliads can be a source of colony break-up and may promote polygyny. Bromeliads are limited nest sites and may represent a risk for young queens leaving a suitable nest, thus favoring secondary polygyny. Although proximate mechanisms mediating queen number are poorly understood, this study suggests that heterogeneous microhabitat conditions probably contribute to the coexistence of variable forms of social structure in O. hastatus.

Population genetics of the socially polymorphic ant Formica podzolica

We used microsatellite markers to analyze the hierarchical genetic structure of the North American mound building ant, Formica podzolica. About one-third of all colonies were headed by a single queen (monogynous) whose effective mating frequency was close to one (nestmate worker relatedness r = 0.70), while the remaining colonies were polygynous, with low average nestmate relatedness (r = 0.16). The low worker relatedness found in most polygynous colonies furthermore suggested that the numbers of queens in polygynous colonies of this ant are usually high. Contrary to what has been described from other ants with a queen number dichotomy, we did not find an effect of social form variation on the partitioning of genetic variation above the level of the colony. We found no significant differentiation between the sympatric social forms of F. podzolica, nor did differentiation among populations appear to be affected by colony social organization. These unexpected patterns of genetic structure may have resulted from differences either in the spatial distribution of the social forms or in their social flexibility.

Egg-laying in monogynous and polygynous colonies of the termite Macrotermes michaelseni (Isoptera, Macrotermitidae)

Our report provides quantitative information on egg production of termites in correlation with the weight of queens and the degree of polygyny of a colony. We suggest that in Macrotermes michaelseni king weight may be used as an independent surrogate for colony age. Queens of a given age (= king of the same weight) were heavier in monogynous colonies than in polygynous colonies. From isolated queens sampled in southern Kenya we found that egg-laying rates increased with queen weight but were independent of the degree of polygyny. Nevertheless, when comparing queens of the same age, the lower weight of queens in polygynous colonies resulted in an individual loss of egg-laying. In sum, however, all nestmate queens together laid more eggs and the colony as a whole had an advantage, at least in the short term.

Alternative reproductive tactics in the queen-size-dimorphic ant Leptothorax rugatulus (Emery) and their consequences for genetic population structure

We report the results of a comprehensive investigation of the queen size dimorphism in the North American ant Leptothorax rugatulus. Employing allozymes and microsatellites as genetic markers, we found no evidence that the gene pools of large (macrogynes) and small (microgynes) queens are distinct. Queens in polygynous colonies are related to each other, supporting the hypothesis that colonies with more than one queen commonly arise by the adoption of daughter queens into their natal colonies. The higher fat content of macrogynes, their predominance in monogynous societies and in small founding colonies, and their greater flight activity favor the view that macrogynes predominantly found colonies independently, while microgynes are specialized for dependent colony founding by readoption. When comparing the genetic structure of three different subpopulations, we found that the alternative life histories had no significant effect on population viscosity at the scale investigated.

Sociogenetic organization of the ants Myrmica ruginodis and Myrmica lobicornis: Number, relatedness and longevity of reproducing individuals

AbstractThe number and relationships of reproducing individuals create the observed genetic heterogeneity within a social insect colony. These are referred to as sociogenetic organization and were studied in the red ants M. ruginodis and M. lobicornis. Direct observations of the queen numbers were obtained by excavating colonies. The effective number of reproducing individuals was estimated from genetic relatedness based on genotype frequency data. Sociogenetic organization of colonies of both species is simple. The number of queens is low, single mating of queens is the rule and queen to queen variation in worker production is minor. The important variables of sociogenetic organization are the number and relatedness of coexisting queens in polygynous colonies. Queen nestmates are related on average by 0.405 in polygynous colonies of M. ruginodis, showing that colonies recruit their own daughters as new reproductives. The distribution of queen number in M. ruginodis indicates that the study population contains both microgyna and macrogyna types of the species. The large proportion of colonies where the resident queen(s) is not the mother of the workers shows that the average life span of a queen is short and colonies are serially polygynous.

The Assessment of Reproductive Success of Queens in Ants and Other Social Insects

Recently considerable research has focused on the causes of evolution of multiple-queen (polygynous) colonies. In order to better understand the factors which may have led to these polygynous associations it is vital to compare the reproductive success of queens in monogynous (one queen per colony) and polygynous colonies as well as the relative fitness of queens in polygynous colonies. This paper addresses the difficulties arising from such comparisons and their implications with regard to the methods commonly used to assess reproductive success in queens. The relative reproductive success or queens in monogynous and polygynous colonies is commonly assessed by comparing the relative number or reproductives they produce during a single reproductive season

Adoption of Newly-Mated Queens: A Mechanism for Proliferation and Perpetuation of Polygynous Red Imported Fire Ants, Solenopsis invicta Buren

The polygynous form of the red imported fire ant, Solenopsis invicta Buren was first reported from Mississippi in 1973; however, the source of the numerous fertile queens in polygynous colonies has remained an enigma. In 1987, 400 queens from a mating flight were marked with a durable paint and released in an area heavily populated with the polygynous form. None were recaptured after one week, but 9 months later, 4 clearly-marked queens were found in a nest 65 meters from their release point. This finding clearly points to adoption. About 5 weeks later, 37 of 107 fertile queens collected from 37 polygynous nests, were found to have partially histolyzed wing muscles and undeveloped ovaries. Mating flights had occurred a few days prior to the queen collections, thus it was apparent that these queens were newly adopted. This observation was verified following a second mating flight one week later. The results of our 3 studies clearly indicate that polygynous S. invicta can proliferate and perpetuate their colonies by queen adoption.