Ant colonies may have a single or several reproductive queens (monogyny and polygyny, respectively). In polygynous colonies, colony reproduction may occur by budding, forming multinest, polydomous ...colonies. In most cases, budding leads to strong genetic structuring within populations, and positive relatedness among nestmates. However, in a few cases, polydomous populations may be unicolonial, with no structuring and intra-nest relatedness approaching zero. We investigated the spatial organisation and genetic structure of a polygynous, polydomous population of Formica truncorum in Finland. F. truncorum shifts nest sites between hibernation and the reproductive season, which raises the following question: are colonies maintained as genetic entities throughout the seasons, or is the population unicolonial throughout the season? Using nest-specific marking and five microsatellite loci, we found a high degree of mixing between individuals of the population, and no evidence for a biologically significant genetic structuring. The nestmate relatedness was also indistinguishable from zero. Taken together, the results show that the population is unicolonial. In addition, we found that the population has undergone a recent bottleneck, suggesting that the entire population may have been founded by a very limited number of females. The precise causes for unicoloniality in this species remain open, but we discuss the potential influence of intra-specific competition, disintegration of recognition cues and the particular hibernation habits of this species.
Spatial recognition cues used in site fidelity in the ant Formica uralensis Ruzsky were studied using outdoor and laboratory arenas. Ant workers visiting symmetrically spaced feeders were ...colour‐marked corresponding to the initial feeder visited during sampling. The effect of manipulating environmental cues on the mean ‘spatial specialization’ of the population was measured. Site recognition appears to be based on visual landmark/canopy cues. However, ants maintained some fidelity when shielded from these cues, suggesting the involvement of additional cues. When ridding our experimental device of olfactory deposits and shielding visual cues, site fidelity was lost. Idiothetic and/or geomagnetic cues are thought to provide spatial references to visual or olfactory landmarks. Altering nest position relative to the arena and changing the geomagnetic field within the arena in our study, however, did nothing to the site fidelity of visually deprived and non‐deprived foragers.
We conclude that site fidelity is developed in a visually structured environment but supplemented by an olfactory backup system that is probably based on discrete home range markings rather than radial odour trails. We demonstrate furthermore that the visual component involved in site location can be stored in the memory of individual F. uralensis foragers during a 6‐month hibernation period.
Genetic organization of colonies and populations of the ant Formica aquilonia were studied at the edge of the urban area of the city of Helsinki within an area of about 400 km2. Over six thousand old ...queens and workers were sampled from a total of 288 nest mounds from 14 populations (patches of forest) for an allozyme study, and workers from 13—15 nests in each of three populations were also characterized by microsatellite genotyping. Genetic relatedness among nest mates within populations was close to zero for both queens (estimates ranging from 0.02 to 0.13) and workers (from 0.01 to 0.22), with some of the estimates being significantly greater than zero. These results supported the view of a high level of polygyny within the nests. The populations showed significant genetic differences both at the allozyme loci (overall FST = 0.17) and at the microsatellites (FST = 0.24). The estimates of FST between pairs of populations varied from 0.01 to 0.61, the largest values being associated to reduced genetic variation and an apparent bottleneck within one population. The results showed that the local populations of this highly polygynous (multiple queens in a nest) and polydomous (multiple nests in a colony) ant can be differentiated genetically within potential dispersal distances, suggesting restricted dispersal and possible bottlenecks when colonizing new patches of forest.
This work examines behavioural relationships between young females (potential queens) and workers, in a multi-nest population (supercolony), of Formica lugubris. Each nest contains hundreds of ...functional queens but the colony is initiated by a single foundress (secondary polygyny). Thus, recruitment of new queens into the nests is part of the population dynamics. Substantial variation in worker response towards introduced female sexuals, ranging from execution to complete acceptance, is demonstrated. The mating status of the introduced females has a clear effect on the worker response: virgin females are accepted with about twice the probability of inseminated females. When native alates are present in a nest, all introduced females are accepted with higher probability than when the native alates are absent, later in the season. No effect of distance (between donor and recipient nests) on the worker reaction was found, within the supercolony borders. Proximate mechanisms and selective forces regulating the recruitment process are discussed in light of these findings.
Workers of social insects may enhance their inclusive fitness by laying unfertilized eggs that develop into males. In particular, workers may gain from rearing worker-produced males if their average ...relatedness to them exceeds their relatedness to queen-produced males. These relatedness values depend both on the queen mating frequency and on the number and relatedness of nestmate queens. We examined the occurrence of worker reproduction in field colonies of four ant species of the genera Formica and Myrmica. Based on relatedness arguments alone, worker reproduction was expected in all species because of low queen mating frequency, or low effective queen numbers. Nevertheless, genotype matching of workers and males showed that worker reproduction was absent or rare in two of the three Formica species studied here. In M. ruginodis, queens may have been the sisters of the workers in many cases, which means that workers of this species may regularly rear nephews. In the three species in which worker reproduction was not found, workers bias colony sex ratios to enhance their inclusive fitness. We therefore hypothesize that sex ratio biasing and male production may be mutually exclusive strategies for workers.
Colony and population sex ratios were studied in 13 species of Formica ants in southern Finland. The data are based on material collected from nests mainly as pupae. Stability of both colony and ...population sex ratios, and the similarity of sex ratios in conspecific populations living in similar environments, suggest that the sex ratios can be considered as adaptive strategies produced by genetic evolution. From the 23 population samples examined, 12 disagreed with the assumption of equal parental investment in the two sexes, there being departures in some in favour of males and in others of females. The most obvious explanation for these deviations is polydomy (multinest associations) leading to strongly male-biased ratios in three species. We further examine the correlations between sex ratios and the degree of polygyny and levels of intranest genetic relatedness between the offspring and workers caring for them, and the patterns of variance of colony sex ratios. The data indicate that in the mound-building red wood ants of the Formica rufa group, which produce sexuals as the first offspring in early spring and whose gynes affect the caste determination by laying eggs predisposed to develop as sexuals, the gynes probably control the sex ratios. In the other species which produce sexuals and new workers in mid-summer, the results fit the hypothesis that the sex ratio is controlled, or at least greatly influenced, by workers. Evidence from our genetic studies suggests that workers do not normally have offspring, but may produce males in orphaned nests. /// Соотношение полов в колонии и популяции исследовали у 13 видов муравъев рода Formica в южной финляндии. Данные основаны на материале, собранном из муравейников, преимущественно в виде куколок. Стабилъностъ соотношения полов в колонии и популяции и сходство в соотношении полов у популяций одного вида, обитающих в сходных условиях, говорит о том, что соотношение полов может рассматриватъся как адаптивная стратегия, представляющая резулътат генетической эволюции. Из исследованных проб 23 популяций 12 не соотвествовали представлению о равном соотношении полов в родителъском поколении; так, были найдены отклонения в сторону преобладания самцов, а в некоторых случаяхсамок. Наиболее вероятное объяснение этих отклонений - наличие полидомии (многогнездных ассоциаций), ведущее к силъному преобладанию самцов в соотношении полов у трех видов. Далее мы исследовали корреляции между соотношением полов и степенъю политинии и уровнем внутригнездной генетической связи между молодым поколением и ухаживающими за ними рабочими особами и характером изменчивости соотношения полов в колонии. Резулътаты показали, что у рыжих лесных муравъев группы Formica rufa, строящих земляной купол и дающих половые сооби в первом поколении ранней весной и чъи размножающиеся самки влияют на формирование каст откладыванием яиц, предиспозированных для развития половых особей, самки, очевидно, определяют соотношение полов. у других видов, дающих половые особи молодых рабочих муравъев в середине лета, резулътаты исследования подтверждают гипотезу о том, что соотношение полов регулируется или, по крайней мере, находится под влиянием рабочих особей. Резулътаты наших генетических исследований показали, что рабочие особи обычно не размножаются, но могут даватъ самцов в разоренных гнездах.
The inner nest temperature in field colonies of ants of the F. rufa group was studied with thermograph recordings and spot sampling. The observations indicate that in colonies with a worker ...complement exceeding 1 million, nest-warming after winter could start as an autocatalytic process and hence may not require triggering by sunning behaviour. In the colony studied with the thermograph the intranest temperature remained at a stable level, near 30°C in late spring and summer, even when the outside temperature temporarily dropped below freezing point. A slight "overshoot" or increase in inner nest temperature, was evident, however, when the outside temperature dropped below the threshold for ant activity in spring. It was found that nests later producing sexuals maintain a significantly higher inner temperature in spring than nests later producing only worker broods. The nest-warming effect of insolation is considered more important in small or weak colonies, whereas endogenous nest heating, based on the metabolism of the ants and their clustering behaviour, is more compatible with the observations in the case of vigorous colonies. The recordings suggest that a capacity for social thermoregulation is a cause of thermal stability in red wood ant nests.
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