Slave-making Ant Research Articles

Intracolonial conflict in the slave-making ant Protomognathus americanus : dominance hierarchies and individual reproductive success

Social group viability results from a trade-off between cooperation and conflict, driven respectively by group and individual interests. Workers of the slave-making ants are known to have a high egg-laying potential, leading to a potential conflict over male production. Queenright and queenless nests of the slave-making ant Protomognathus americanus show a near-linear dominance hierarchy, and dominance rank is correlated with reproductive activity. Genetic and behavioural analysis revealed that the queen, when present in the nest, is behaviourally dominant and monopolises reproduction. In queenless nests, the haploid (male) brood is produced primarily by a single worker. We suggest the dominance hierarchy regulates male production, between the queen and her workers as well as among workers. Comparison of our results to another study allows us to place our data in an ecological context. This slave-making ant species appears to fit the concession model of reproductive skew: where resources (i.e. host nests) are poor, there is strong skew and where resources are richer reproduction is more egalitarian.

Ecology of Leptothorax ants: impact of food, nest sites, and social parasites

In a long-term field manipulation, we demonstrate strong reactions of Leptothorax longispinosus ant colonies to food- and nest-site supplementation. Demographic and genetic responses varied over small geographic scales, and the two ecological factors interacted with the presence of the social parasite Protomognathus americanus. We conducted a 2×2 experiment in three blocks and found that the blocks, which were less than 100 m apart, reacted very differently to the treatments. Blocks differed in degree of polygyny, intranest relatedness, colony size, productivity, and sexual investment. Furthermore, these differences were associated with the presence of slave-making ants and the local availability of nest sites. Nest-site supplementation had a strong effect only in the site with the highest prevalence of social parasites, influencing there the density and investment patterns of colonies. L. longispinosus ants in the least parasitized area were strongly affected by both food- and nest-site supplementation. There, food supplementation led to a decrease in the number of queens per colony and consequently to an increase in intranest relatedness, while colonies in nest-site-supplemented areas invested fewer resources in males and produced a female-biased allocation ratio. By contrast, in a third block with a very low intracolonial relatedness, food supplementation induced an absolute and relative higher investment in males. We conclude that ecological factors influencing social organization in insect societies cannot be studied in isolation, because the interactions among factors produce far richer responses than any one variable.

THE ECOLOGY OF SLAVEMAKING ANTS AND THEIR HOSTS IN NORTH TEMPERATE FORESTS

Slavemaking ants are of great interest to biologists because of their highly specialized lifestyle. Slavemakers rely on the presence of heterospecific slaves to perform routine chores such as foraging and brood care. While we have considerable information on the behavior of these ants, mostly gleaned from laboratory studies, we know very little of their basic ecology. Here we report data collected over 20 yr in three geographic sites on the occurrence, spatial pattern, nest site use, and demography of two slavemaker species and three of the host species they enslave; all are small ants in the tribe Formicoxenini. We found geographic and temporal variation with respect to the interaction between social parasites and their hosts. The slavemaker Protomognathus americanuts occurred in each geographic site, and in each its most common host was Leptothorax longispinosus; the other known hosts of this slavemaker, L. curvispinosus and L. ambigunts were less abundant. In a West Virginia site, slavemaker nests were smaller than in New York and Vermont sites. Additional data from West Virginia showed that the slavemaker is strongly constrained by its hosts there, but we found little impact of the parasite on its hosts. By contrast, in the New York site, we found strong evidence that the majority host was affected by the slavemaker: host nests showed important life history shifts between neighborhoods con- taining slavemakers vs. those that were parasite-free. Furthermore, the slavemaker was able to subjugate large host nests there and had large slave pools. In a third site in Vermont, parasite and host demography reflected their interaction weakly. We discovered a second slavemaking species there, and both parasites were preferentially found in areas of high host density. However, we uncovered no demographic or spatial evidence that slavemakers affected their hosts in Vermont. Likewise, we found no evidence in any site of demographic responses by the minority hosts to the presence of slavemakers. Thus our results imply that host-parasite interactions varied among host species and among geographic locales. The slavernaker system therefore is amenable to analysis in terms of parasite-host coevolution.

The Ecology of Slavemaking Ants and Their Hosts in North Temperate Forests

The Ecology of Slavemaking Ants and Their Hosts in North Temperate Forests

Comparison of reproductive strategies and raiding behaviour in facultative and obligatory slave-making ants: the case of Formica sanguinea and Polyergus rufescens

A review of field and laboratory research concerning raiding behaviour, mating strategies and colony founding in Formica sanguinea and Polyergus rufescens (respectively facultative and obligatory parasites of the Serviformica species) is presented. The analysis and comparison of these crucial and peculiar moments in the life cycle of dulotic colonies may be a valid tool to clarify the evolutionary origins of slavery in ants.¶Concerning the reproductive behaviour, F. sanguinea females mate only in nuptial flights. P. rufescens females mate on the ground around their natal nest, or return to a dulotic colony after mating flights and wait for a raid, or mate directly during a raid. Moreover, field observations suggest that F. sanguinea adopts a strategy similar to the "male aggregation syndrome", whereas P. rufescens mating strategy can be considered similar to the "female calling syndrome". In the field, newly-mated queens of both slave-makers participate in raiding swarms: following a slave raid is an advantageous strategy to locate and invade host nests and to establish a new dulotic colony.¶For colony formation, F. sanguinea presents a great variety of possible strategies (independent foundation and dependent foundation including alliance, adoption, usurpation, and brood sack). This provides evidence of a behavioural plasticity that confirms its nature as a facultative parasite. On the contrary, P. rufescens depends only on usurpation, during which the Dufour's gland contents seem to play a crucial role in the appeasement of the residents of the target colony.¶Also the raiding behaviour of F. sanguinea is less specialized than that shown by P. rufescens. In fact, in the obligatory slave-maker the important role of scouts in the organization of slave-raids is confirmed, which are rapid and effective. By contrast, raids of F. sanguinea may be regarded as a continuation and expansion of common foraging and predatory activity, as predicted by Darwin's hypothesis for the origin and evolution of slavery in ants. Nevertheless, the intraspecific raids conducted by P. rufescens emphasize also the important role of territorial competition as evolutive cause of dulosis.

Prudent Protomognathus and despotic Leptothorax duloticus: differential costs of ant slavery.

The concept of ant slavery rests on the untested assumption that slave-making ants impose fitness costs on colonies of the species they raid. We tested that assumption by comparing the summertime seasonal productivity of Leptothorax spp. colonies in field exclosures without slavemakers, with a colony of the obligatory slave-making ant Protomognathus americanus, or with a colony of the obligatory slavemaker Leptothorax duloticus. Leptothorax longispinosus colonies placed in exclosures with P. americanus colonies did not differ significantly in any demographic attribute from colonies in exclosures without slavemakers. By contrast, Leptothorax curvispinosus colonies exposed to L. duloticus experienced significant reductions in dealate queens, workers, and larvae relative to control colonies exclosed without slavemakers. The pronounced difference in the impact of these slavemakers on their host-species populations correlates with differences in the behavior of the slavemakers observed in the laboratory and likely explains why P. americanus is more abundant than L. duloticus in nature. It seems that more advanced social parasites, like anatomical parasites, evolve to minimize their impact on their hosts, and thus can be regarded as "prudent social parasites."

Slave‐making ants get rough in New York

Science NewsVolume 159, Issue 21 p. 326-326 This Week Slave-making ants get rough in New York Susan Milius, Susan MiliusSearch for more papers by this author Susan Milius, Susan MiliusSearch for more papers by this author First published: 01 July 2009 https://doi.org/10.2307/3981695AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume159, Issue2126 May 2001Pages 326-326 RelatedInformation

Sociobiology of slave-making ants

Social parasitism is the coexistence in the same nest of two species of social insects, one of which is parasitically dependent on the other. Though parasitism in general is known to be of crucial importance in the evolution of host species, social parasites, though intriguing, are often considered as a phenomenon of marginal interest and are typically not taken into account in reviews on parasitism. Nevertheless, social parasites are rather common in social bees, wasps, and ants and therefore may offer unique model systems to study a number of fundamental problems in evolutionary biology. Here we review several aspects of the peculiar life history of slave-making ants, which is characterized by socially parasitic founding of colonies and the pillage of broods from neighboring host colonies during slave raids. In particular we focus on the evolution of slave-making habits (dulosis), communication mechanisms between slave makers and their hosts, sex-allocation ratios and reproductive conflict, and the effect of slave makers on host populations.

Chemical ecology and social parasitism in ants.

The chemical strategies by which parasites manage to break into the social fortresses of ants offer a fascinating theme in chemical ecology. Semiochemicals used for interindividual nestmate recognition are also involved in the mechanisms of tolerance and association between the species, and social parasites exploit these mechanisms. The obligate parasites are odorless ("chemical insignificance") at the time of usurpation, like all other callow ants, and this "invisibility" enables their entry into the host colony. By chemical mimicry (sensu lato), they later integrate the gestalt odor of this colony ("chemical integration"). We hypothesize that host and parasite are likely to be related chemically, thereby facilitating the necessary mimicry to permit bypassing the colony odor barrier. We also review the plethora of chemical weapons used by social parasites (propaganda, appeasement, and/or repellent substances), particularly during the usurpation period, when the young mated parasite queen synthesizes these chemicals before usurpation and ceases such biosynthesis afterwards. We discuss evolutionary trends that may have led to social parasitism, focusing on the question of whether slave-making ants and their host species are expected to engage in a coevolutionary arms race.

Slavemaker Ants: Misunderstood Farmers?

Slavemaker Ants: Misunderstood Farmers?

Patterns of reproduction in slave-making ants

Sex ratios in slave-making ants have been posed as important test cases for the hypothesis that eusociality evolved via kin selection in insects. Trivers and Hare proposed that sex ratios in slave-makers should reflect the queen's interests whereas sex ratios in free-living host ants should reflect the workers' interests. We analyse patterns of allocation to males versus females, as well as allocation to growth versus reproduction for slave-making ants in the tribe Formicoxenini. We find little support for the hypothesis of exclusive queen control; instead, our results implicate queen–worker conflict in slave-making ants, both over male allocation ratios and over allocation to growth versus reproduction.

Plasticity of the Cuticular Hydrocarbon Profile of the Slave-Making Ant Polyergus Rufescens Depending on the Social Environment

Analysis of cuticular hydrocarbon mixtures of the slave-making ant Polyergus rufescens and the Formica rufibarbis or F. cunicularia slaves with which it was living either naturally or after the slave species had been experimentally exchanged showed that cohabitation induced no qualitative homogenization of these species' cuticular signatures. The proportions of hydrocarbons common to both species tended however to be adjusted (in the case of the natural associations) or readjusted (in that of the experimental associations), especially in Polyergus towards those of their partners.On the other hand, differences were observed between the cuticular profiles of Polyergus and their Formica slaves which had been living separately from the original colony for several weeks in an experimental group, and those of the members of the original colony. The changes in the cuticular profiles occurred synchronously in all the individual members of the group.Comparisons between the cuticular versus postpharyngeal slave-maker and slave mixtures showed the existence of qualitative differences between the two mixtures. This indicates that the postpharyngeal glands are not directly involved in the production of the cuticular signatures. Some possible explanations for these results are discussed.

Selective acceptance of the brood of two formicine slave-making ants by host and non-host related species

In a laboratory choice-test, free-living ant workers ofFormica cunicularia andF. rufibarbis (subgenusServiformica), both potentially slave species of the obligatory slave-makerPolyergus rufescens, cared for cocoons of this parasite and for homocolonial cocoons at comparable rates. Both potential hosts did not differ in their capacity to rear the parasite brood. This fact is discussed in relation to host selection and specificity inP. rufescens. No such attraction and/or tolerance was found towards cocoons of the facultative slave-makerFormica sanguinea, which also enslaves both host species. Workers ofF. lugubris, a species which is never enslaved, destroyed cocoons from both slave-making species. The attractiveness of the brood ofP. rufescens for both potentially slave species could be due to an interspecific brood pheromone in addition to brood mimicry. An alternative hypothesis is a close phylogenetic distance between this slave-maker andServiformica species. The capacity to gain acceptance by adult slave workers might be one of the crucial evolutionary steps separating obligatory from facultative slave-making ants.

The reproductive potential of workers in slave-making ants

Colonies of slave-making ants have been used repeatedly to test sex allocation theory. It was suggested that workers of slave-making ants are more strongly selected to reproduce than workers of related, non-parasitic species, because they are incapable of manipulating sex allocation and the sexualization of larvae in their colonies. I show here that in slave-making Formicoxenini, worker ovaries on average consist of significantly more ovarioles than in non-parasiticLeptothorax species. Similarly, whereas in mostLeptothorax species, workers form reproductive hierarchies and lay eggs only in orphaned colonies, slave-maker workers show antagonistic interactions already in the presence of the queen and at least in some species have been observed ovipositing in queen-right colonies. The significance of these results is discussed.

Reproductive strategy of the slave antFormica podzolica relative to raiding efficiency of enslaver species

Formica podzolica serves as host to slave-making ants in North America. We propose thatF. podzolica may respond to slavery by two alternative colony-growth and reproductive strategies depending on the raiding ability of the slavemaker: (1) Rapid colony growth at the expense of producing sexuals to a stage where raiding by unspecialized, facultative slavemakers, capable of exploiting only small colonies, becomes unlikely owing to a strong work force and (2) Early production of sexual offspring at the cost of colony growth to secure some sexual production in an environment with specialized obligate enslavers, capable of raiding large colonies. We tested the strategies by excavating 30 small to moderately large mounds ofF. podzolica and measured reproductive parameters of colonies in relation to mound size, worker number, and worker size. Mound area predicted worker number satisfactorily. Worker number correlated significantly with worker head width and with number of worker and sexual offspring. With a growing work force, the proportion of sexual offspring increased in the total offspring. Two thirds of the colonies producing sexuals emitted single sex, sex being independent of colony size. Some of the large colonies produced both sexes with a strong bias toward either sex. The unweighted population-level sex ratio did not differ from even, being 0.52 (numerical) or 0.54 (biomass). Very large mounds (not excavated) had small workers and highly male-biased sex ratios, probably owing to energy constraints set by central-place foraging. Population-level colony ontogeny data did not fit either one of the suggested strategies, but imply a mixture of the two. We discuss an alternative, still untested raid-independent explanation to the ontogeny pattern.

Genetic relatedness among worker nestmates of three formicine slave-making ants

We estimated genetic relatedness among worker nestmates of the facultative slave-making antFormica subnuda (28 colonies), and the obligate slavemakers F. subintegra (19 colonies) andPolyergus breviceps (14 colonies) using horizontal starch gel electrophoresis. Relatedness among nestmates was 0.42 inF. subnuda, 0.70 inF. subintegra, and 0.49 inP. breviceps on average. Relatedness ofF. subintegra workers did not differ significantly from 0.75 indicating that this species is monogynous, though some females may mate multiply. The estimates ofF. subnuda andP. breviceps were significantly lower than 0.75 and, consequently, colonies were polygynous and/or poly-androus. The inbreeding coefficients were close to zero in all species suggesting random mating. We suggest that owing to practical monogyny and obligate nature of its slavemaking,F. subintegra is a good species for tests of sex allocation theory.

Selective adaptation of the cuticular hydrocarbon profiles of the slave-making ants Polyergus rufescens Latr. and their Formica rufibarbis Fab. and F. Cunicularia Latr. slaves

The results of comparisons between the cuticular hydrocarbon mixtures of the slave-making ants Polyergus rufescens, their Formica rufibarbis and F. cunicularia slaves and between slave and free-living workers (which were probably related to one another) from each Formica species showed the following. (1) Several products were common to all three species. (2) Each òf the two Formica species had its own particular products. (3) The Polyergus cuticular mixture did not contain any species-specific hydrocarbons but had some components in common with either rufibarbis or cunicularia. Because these products were present in Polyergus, whichever Formica species they enslaved, Polyergus must be able to synthesize their own cuticular hydrocarbons. (4) Cohabitation with another species as the result of slave making had no qualitative effects on the individual cuticular hydrocarbon mixtures: their composition was the same in the Polyergus whether living with F. rufibarbis or F. cunicularia and in the Formica of each species whether free living or enslaved. (5) The Polyergus resembled their Formica slaves, however, due to a tendency to adjust the proportions of some of the common hydrocarbons to those of their slaves; this tendency seems to have been reciprocal, although it was less marked in the case of the Formica. (6) The chemical signatures of mixed colonies inhabited by the same slave species depended mainly on the cuticular characteristics of the Formica slaves but also on those of the Polyergus, which differed from one colony to another. The finding that cuticular hydrocarbon mixtures of individuals of both species (slaves and slave makers) interacting within a mixed colony kept their species-specific hydrocarbons while the proportions of the common products showed a tendency to adapt to those of the other species suggests that there exists a selective mechanism probably involving the regulation of the synthesis of these products.

Facultative and obligate slavery in formicine ants: frequency of slavery, and proportion and size of slaves

Slave-making ants raid nests of other ant species, capture the developing offspring and rear them to slave workers. Here we compare slave-making of three formicine slave-making ants: the facultative Formica subnuda, the obligate Polyergus breviceps, and F. subintegra which previously has been considered facultative but appears to be an obligate slave-making ant. If F. subintegra is an obligate slavemaker, slave-making of F. subintegra should differ from that of F. subnuda but closely resemble slave-making of P. breviceps in the following aspects: (1) Obligate slavemakers are rarer than facultative slavemakers. (2) Slaveless colonies of facultative slavemakers are found, but obligate slavemakers always have slaves. (3) Because obligate slavemakers depend on their slaves, they should have a higher proportion of slaves than facultative slavemakers. (4) Owing to special adaptations obligate slavemakers are able to raid bigger colonies, and hence have bigger slaves than facultative slavemakers. (5) Dufour's gland of F. subintegra should be larger than that of F. subnuda. Per 100 free F. podzolica colonies, the number of P. breviceps and F. subintegra colonies with F. podzolica slaves were 1.3% and 3.9%, respectively, and the number of F. subnuda colonies with F. podzolica 3.7%, and without F. podzolica 7.5%. The proportion of slaves, when present, varied between 1–30% in the colonies of F. subnuda, and between 70–90% in the colonies of the other species. The slaves of F. subnuda were significantly smaller than those of F. subintegra and P. breviceps. The length of F. subnuda's Dufour's gland was one third of the length of F. subintegra's gland. The results show that slave-making of F. subintegra parallels that of P. breviceps, and contrary to the earlier notion, F. subintegra is an obligate slave-making ant. We suggest that F. subnuda and F. subintegra represent extreme modes of slave-making behaviour in the Formica sanguinea group.

Facultative and obligate slavery in formicine ants: frequency of slavery, and proportion and size of slaves

Abstract Slave-making ants raid nests of other ant species, capture the developing offspring and rear them to slave workers. Here we compare slave-making of three formicine slave-making ants: the facultative Formica subnuda , the obligate Polyergus breviceps , and F. subintegra which previously has been considered facultative but appears to be an obligate slave-making ant. If F. subintegra is an obligate slavemaker, slave-making of F. subintegra should differ from that of F. subnuda but closely resemble slave-making of P. breviceps in the following aspects: (1) Obligate slavemakers are rarer than facultative slavemakers. (2) Slaveless colonies of facultative slavemakers are found, but obligate slavemakers always have slaves. (3) Because obligate slavemakers depend on their slaves, they should have a higher proportion of slaves than facultative slavemakers. (4) Owing to special adaptations obligate slavemakers are able to raid bigger colonies, and hence have bigger slaves than facultative slavemakers. (5) Dufour's gland of F. subintegra should be larger than that of F. subnuda . Per 100 free F. podzolica colonies, the number of P. breviceps and F. subintegra colonies with F. podzolica slaves were 1·3% and 3·9%, respectively, and the number of F. subnuda colonies with F. podzolica 3·7%, and without F. podzolica 7·5%. The proportion of slaves, when present, varied between 1–30% in the colonies of F. subnuda , and between 70–90% in the colonies of the other species. The slaves of F. subnuda were significantly smaller than those of F. subintegra and P. breviceps . The length of F. subnuda 's Dufour's gland was one third of the length of F. subintegra 's gland. The results show that slave-making of F. subintegra parallels that of P. breviceps , and contrary to the earlier notion, F. subintegra is an obligate slave-making ant. We suggest that F. subnuda and F. subintegra represent extreme modes of slave-making behaviour in the Formica sanguinea group.

A comparative study of colony takeover between queens of facultative and obligatory slave-making ants (Hymenoptera: Formicidae)

A comparative study of colony takeover between queens of facultative and obligatory slave-making ants (Hymenoptera: Formicidae)