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 km(2). 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 F-ST = 0.17) and at the microsatellites (F-ST = 0.24). The estimates of F-ST 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.

It is suggested that the evolution of polyandry by social hymenopteran queens is caused by colony-level selection, either because polyandry affects the distribution of non-functional diploid males in colonies (the load hypothesis) or because it increases the genetic diversity of the worker force (the diversity hypothesis).Diploid males that arise from fertilized eggs that are homozygous at the sex-determining locus (or loci) are inviable or infertile. Models of the load hypothesis analysed in this study suggest that slow growth and high mortality of colonies with diploid males favour single mating by queens. The longer the period of colony growth (the period with selective differences) and the heavier the mortality, the stronger is the selection for monandry. The load hypothesis also predicts an association between monogyny and monandry. In contrast, the diversity hypothesis predicts an association between monogyny and polyandry, as multiple mating offers a way by which a monogynous colony could increase its genetic heterogeneity.Up to 10% of all males are diploid in species and populations of Formica ants with highly polygynous colonies (F. aquilonia, F. polyctena, F. truncorum). No diploid males were found in two mainly monogynous species (F. exsecta, F. pratensis) which also have a high level of monandry. This agrees with the prediction of the load hypothesis. A surprisingly high frequency of nests in three other species (F. rufa, F. lugubris, F. truncorum) with monogynous/weakly polygynous colonies produce diploid males, although the frequency varies among their populations. In extreme cases half of the diploid sexuals within a colony develop into males. Diploid males have been observed only at the time of normal sexual production. It seems that at other times they are eliminated at early developmental stages, so as to minimize the load on the colony.

Sexuals ofFormica lugubris fly to mating places, where females attract males by using a sex pheromone. Females collected on the nest surface before departing on a mating flight are much less attractive than those collected on the mating place after the mating flight, suggesting that the mating flight triggers the release of the sex pheromone. Olfactory cues are essential for males to locate females while they patrol. Males probably use visual cues to locate females once they have alighted nearby them. Males are also attracted by aggregations of other males on the ground, probably because one or several females are likely to be close to male aggregations.

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.

1. We studied how colonies of the red wood ant, Formica polyctena , adjust the numbers of foragers allocated to different foraging trails. In a series of field experiments, foragers were marked and transferred from one nest to another, related nest, where they joined the foraging force. Transferred workers acted as a reserve of uncommitted, available foragers. 2. Previous work shows that each individual forager habitually uses one trail. We found that for an uncommitted forager, the influence of recruitment initially is stronger than that of directional fidelity. Transferred workers were likely to use trails leading to new food sources. When transferred to a new nest, foragers were not likely to use a trail in the same direction as their original trail in the donor nest. 3. After a week, transferred foragers tended to develop route fidelity. Even after bait was no longer present, they continued to use the trail that had formerly led to a bait source. 4. We examined how colonies adjust numbers on a trail by experimentally depleting some trails. Colonies usually did not compensate for depletion: foragers were not recruited to depleted trails. 5. In general, the dynamics of foraging in this species facilitate a consistent foraging effort rather than rapid adjustments of forager allocation.

A long term study on the reproductive strategies of Formica lugubris (Formica rufa group) has revealed many new important facts. Within a supercolony the sex-ratio is strongly female biased. Some of the sexuals mate on the nest surface, whereas others fly from the nest. Those sexuals participating in flights aggregate in particular meadow sites (mating places). On these places females attract males by releasing a sex pheromone.

Abstract A major conceptual problem in ant-plant protection mutualisms is the variability of costs and benefits in space and time (Beattie 1985; Janzen 1985; Addicott 1986). The classical debate about the ‘usefulness’ of red wood ants (Cotti 1963) provides an illustration of that point. A problem with this old debate, however, is that it tends to confuse benefits in terms of human forestry with benefits in terms of tree fitness.

Identification des substrats utilises par les sexues au cours du vol nuptial. Suivi de l'accumulation et de l'utilisation de ces substrats entre l'emergence de l'image et la fin du vol nuptial

Nuptial flight in Formica lugubris was studied within a super-colony located in the Swiss Jura. Sexuals (imago) were present in the nests during one month (June). The flight season was ea. 2-3 weeks. The presence of sexuals at nest surface as well as take-off were temperature-dependant, occuring above l0°C and l8°C, respectively. Length of daily flights, number of sexuals leaving the nest as well as number of sexuals produced were estimated. There was no proof of any circadian rhythm and no marked differences between males and females except in mixed nests where females did not fly and copulated at nest surface.

Laboratory experiments confirm that protein-starved red wood ants of the Formica rufa group and Formica truncorum Fabr. react to the presence of protein baits in the for aging area with alerting and orienting signals resulting in directional recruitment. Evi dence is presented that the cause of directional recruitment in F. rufa group ants is a scent trail laid from the bait toward the nest, while centripetal recruitment, due to orienting signals provided by scouts returning to the bait from the nest, is of negligible importance. An interesting complication was detected in F. truncorum, which showed adequate communication of direction to a food source in the light, but not in the dark. Alternative explanations for the latter phenomenon are discussed. The laboratory results are related to field observations of red wood ant colonies, which indicate a rather limited use of directional recruitment, because of the stable distribution of resources. It is pointed out, however, that temporary shortages of resources, especially in spring, may have favoured evolution of mechanisms for directional recruitment.

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 be haviour. 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 main tain 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 thermoregula tion is a cause of thermal stability in red wood ant nests.

Formica exsecta Nyl. populations in southern Finland exhibit two distinct male size classes. This phenomenon, which also occurs in Formica sanguinea Latr., is seen both within single nests and at the population level. Small males (micraners) appear to mature later, to have sharper diurnal activity peaks and to disperse more widely than do large males (macraners). Micraners appear to predominate in crowded polydomous colonies characterized by strongly male biased sex ratios, while macraners are charac teristic of monodomous populations with a sex ratio close to 1:1. We suggest that macraners represent a mating tactic based on limited dispersal, including inbreeding, and that they may be most common during the early stage of the colony cycle preceding polygyny, while micraners represent an outbreeding strategy associated with a decline in resource availability.

Route fidelity and site allegiance (Ortstreue) ofFormica rufa group ants are analysed with repect to orienting cues and preservation through periods of isolation or winter dormancy. Colour-marked workers showed certain site allegiance to different parts of a moundnest, but the phenomenon was too weak to explain the retention of extranidal Ortstreue measurad in nature. The same applies to kinesthetic and other cues based on intranest architecture. Evidence is presented that extranidal Ortstreue is based on long-lasting individual memory of spatially organized visual cues. The engram stored through several months of winter dormancy can be indirectly identified with a representation of landmark/canopy patterns. The experiments carried out in large openair arenas show, however, that olfactory cues, probably identical with scent markings of the home range, are a cause of idiosyncratic Ortstreue during the dark period. The latter orienting cues, which in the main are switched off in the presence of visual cues, may also be stored in the memory, but preservation through winter dormancy could not be confirmed. The possibility that the ants may use geomagnetic cues was tested, but the result was negative. The ecological implications of the findings are discussed.

Genetic population structure was studied in two types of populations in the ants Formica exsecta and F. pressilabris: populations consisting of single-nest colonies (monodomy) and populations consisting of multi-nest colonies (polydomy). These characteristics seem to be associated with the number of egg-laying females (gynes) in a nest, mating structure of the population, sex ratio and male size variation. The monodomous populations are characterized by single-gyne nests, the population sex ratio is either I:1 or female-biased, males are mainly large-sized, and there is slight inbreeding in the population. The polydomous populations have multi-gyne nests with gynes related to each other, sex ratio is strongly male-biased, most males are small-sized, and there is slight genetic microdifferentiation within the populations. Diploid males found in a polydomous F. pressilabris population suggest that the population is inbred and isolated. Habitat localization is presented as a plausible explanation for the evolution of the polygynous and polydomous population structure.

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

The chromosome numbers of the species Formica aquilonia Yarr., Formica uralensis Ruzsk. and Formica pressilabris Nyl. were all found to be n=26. The chromosome number of F. uralensis thus does not accord with the view that this species belongs to be subgenus Serviformica. Chromosomal polymorphism was found in Formica truncorum Fabr., one population having the haploid number n=28, instead of n=26. The chromosome numbers obtained for South Finnish populations of Formica polyctena Foerst., Formica pratensis Retz., Formica lugubris Zett., Formica rufibarbis Fabr. and Formica transkaucasica Nas. were the same as those reported from Central Europe.