Polyergus Breviceps Research Articles

Sex Attractant Pheromone of the Japanese Slave-Making Ant, Polyergus samurai.

The objective of our project was to identify the sex attractant pheromone of queens of the slave-making ant Polyergus samurai, which was characterized as a blend of methyl 6-methylsalicylate and methyl 3-ethyl-4-methylpentanoate. Both compounds were identified in volatiles collected from squashed heads of queens, and in field trials, a blend of the two compounds was highly attractive to males. In contrast, males were not attracted to a blend of methyl 6-methylsalicylate with 3-ethyl-4-methylpentanol. Thus, the pheromone blend of this species is analogous to that of species in the Polyergus lucidus complex from eastern North America, rather than that of the Polyergus breviceps complex from western North America and the European species P. rufescens. These results are discussed in the context of speciation within the genus.

The Effect of Social Parasitism by Polyergus breviceps on the Nestmate Recognition System of Its Host, Formica altipetens.

Highly social ants, bees and wasps employ sophisticated recognition systems to identify colony members and deny foreign individuals access to their nest. For ants, cuticular hydrocarbons serve as the labels used to ascertain nest membership. Social parasites, however, are capable of breaking the recognition code so that they can thrive unopposed within the colonies of their hosts. Here we examine the influence of the socially parasitic slave-making ant, Polyergus breviceps on the nestmate recognition system of its slaves, Formica altipetens. We compared the chemical, genetic, and behavioral characteristics of colonies of enslaved and free-living F. altipetens. We found that enslaved Formica colonies were more genetically and chemically diverse than their free-living counterparts. These differences are likely caused by the hallmark of slave-making ant ecology: seasonal raids in which pupa are stolen from several adjacent host colonies. The different social environments of enslaved and free-living Formica appear to affect their recognition behaviors: enslaved Formica workers were less aggressive towards non-nestmates than were free-living Formica. Our findings indicate that parasitism by P. breviceps dramatically alters both the chemical and genetic context in which their kidnapped hosts develop, leading to changes in how they recognize nestmates.

Chemical communication in mating behaviour of the slave-making ant Polyergus rufescens (Hymenoptera, Formicidae): 3-ethyl-4-methylpentanol as a critical component of the queen sex pheromone

The aim of the research reported here was to determine whether 3-ethyl-4-methylpentanol, a minor but crucial component of the sex pheromone of the North American slave-making ant species Polyergus breviceps, was also a component of the sex pheromone of the European congener Polyergus rufescens. Thus, the contents of mandibular glands of P. rufescens virgin queen were extracted and analysed. The main component of the extracts was methyl 6-methylsalicylate and 3-ethyl-4-methylpentanol was identified as one of several minor components. Further analyses showed that the insects produce mainly the (R)-enantiomer of the alcohol. Males’ responses to various blends of methyl 6-methylsalicylate with the racemate or the pure enantiomers of 3-ethyl-4- methylpentanol were tested in field behavioural bioassays. The data showed that blends of methyl 6- methylsalicylate and 3-ethyl-4-methylpentanol were strongly synergistic, with the most active ratios being biased toward the first component. The addition of other minor components to the binary blend neither increased nor decreased responses by males. Only the (R)-enantiomer of the alcohol was biologically active; its antipode did not inhibit attraction. The results are discussed in terms of the evolution of signals, and are compared with the results previously obtained for the allopatric species Polyergus breviceps.

Pirate ants (Polyergus breviceps) and sympatric hosts (Formica occulta and Formica sp. cf. argentea): host specificity and coevolutionary dynamics

The pace and trajectory of coevolutionary arms races between parasites and their hosts are strongly influenced by the number of interacting species. In environments where a parasite has access to more than one host species, the parasite population may become divided in preference for a particular host. In the present study, we show that individual colonies of the pirate ant Polyergus breviceps differ in host preference during raiding, with each colony specializing on only one of two available Formica host species. Moreover, through genetic analyses, we show that the two hosts differ in their colony genetic structure. Formica occulta colonies were monogynous, whereas Formica sp. cf. argentea colonies were polygynous and polydomous (colonies occupy multiple nest sites). This difference has important implications for coevolutionary dynamics in this system because raids against individual nests of polydomous colonies have less impact on overall host colony fitness than do attacks on intact colonies. We also used primers that we designed for four microsatellite loci isolated from P. breviceps to verify that colonies of this species, like other pirate ants, are comprised of simple families headed by one singly mated queen.

Queen Sex Pheromone of the Slave-making Ant, Polyergus breviceps

Workers of the slave-making ant, Polyergus breviceps, raid nests of Formica ants and return with Formica pupae that mature into worker ants in the slave-makers' colony. These Formica workers then tend the Polyergus brood, workers, and reproductives. During raids in the mating season, winged virgin Polyergus queens accompany the workers in the raiding columns. During the raid, the virgin queens release a pheromone that attracts males that quickly mate with the queens. We report the identification, synthesis, and bioassay of the sex attractant pheromone of the queens as an approximately 1:6 ratio of (R)-3-ethyl-4-methylpentan-1-ol and methyl 6-methylsalicylate. The ants produce exclusively the (R)-enantiomer of the alcohol, and the (S)-enantiomer has no biological activity, neither inhibiting nor increasing attraction to blends of methyl 6-methylsalicylate with the (R)-enantiomer.

Raiding Activity of an Obligate (Polyergus breviceps) and Two Facultative (Formica puberula and F. gynocrates) Slave-Making Ants

Slave-making ants are social parasites that exploit the labor of workers from their host species by keeping them captive in the slave-maker nest. Slave-makers vary in their degree of specialization, ranging from obligate slave-makers that cannot survive without captives, to facultative slave-makers, which are often found living independently. Our study system included one obligate slave-maker, Polyergus breviceps, two facultative slave-makers, Formica puberula and F. gynocrates, and two hosts, F. occulta and F. sp. cf. argentea. We observed all raids conducted during two raiding seasons by seven P. breviceps colonies, two F. puberula colonies, and two F. gynocrates colonies. We report on raiding frequency, average raid distances, and then compare the probability of being raided multiple times in a single raiding season for the two host species. We also report on the spatial distribution of slave raids, which suggests that slave-makers avoid raiding in areas used by other slave-maker colonies. This is the first report of raiding activity for P. breviceps in this location, and the first report of raiding activity of any kind for F. puberula and F. gynocrates.

Do these eggs smell funny to you?: an experimental study of egg discrimination by hosts of the social parasite Polyergus breviceps (Hymenoptera: Formicidae)

Social parasites exploit the behaviours of other social species. Infiltration of host systems involves a variety of mechanisms depending on the conditions within the host society and the needs of the social parasite. For many species of socially parasitic ants, colony establishment entails the usurpation of colonies of other species. This frequently involves the eviction or death of the host colony queen and the subsequent adoption of the invading queen. The social parasite queen achieves host worker acceptance by either manipulating the nest-mate recognition processes of the host or undergoing chemical modification. Little is known, however, about how host workers respond to social parasite eggs or whether host species defend against brood parasitism during parasite invasions. Host species are believed to adopt social parasite offspring because the recent common ancestry between many social parasites and their hosts may grant the sharing of certain characteristics such as chemical cues. Use of multiple host species, however, suggests other processes are needed for the social bond between host and parasite young to form. This study reports the findings of adoption bioassays in which eggs from a slave-maker ant, Polyergus breviceps, were offered to workers of two of its host species from unparasitised or newly parasitised nests to determine whether P. breviceps eggs generally elicit rearing behaviours from multiple host species. Comparisons of parasite egg survival until adulthood with conspecific egg survival reveal that workers of both host species, free-living or newly enslaved, do not typically accept slave-maker eggs. Both host species thus have sufficient discriminatory power to reject social parasite eggs although our hydrocarbon analysis indicates parasite eggs may be adapted to their local host species. Combined these results suggest that host rearing of P. breviceps eggs may reflect an evolutionary equilibrium that is maintained by probability and cost of recognition errors.

Sex Pheromone of Queens of the Slave-Making Ant, Polyergus breviceps

The sex attractant pheromone produced in mandibular glands of queens of the slave-making ant Polyergus breviceps has been identified as a blend of methyl 6-methylsalicylate and 3-ethyl-4-methylpentanol. In field trials, each compound alone was completely unattractive to males, whereas blends of the two compounds attracted hundreds of males within a couple of hours.

Host queen killing by a slave-maker ant queen: when is a host queen worth attacking?

A new colony of the slave-making ant Polyergus breviceps is initiated when a newly mated gyne invades a host nest and kills the resident queen. This process seems to result in chemical camouflage of the invading gyne and allows her to usurp the position of colony reproductive. Young, recently mated Formica gynes, however, are not attacked. To determine whether worker and/or immature presence is the basis for aggression, we placed eggs, larvae, pupae and workers from mature F.gnava queens with newly mated F.gnava queens and observed the responses of introducedP.breviceps queens. Because no newly mated gyne was attacked, we tested newly mated F.gnava queens (1) once they had produced eggs, (2) when the offspring reached the larval, pupal and callow stages of development, and (3) every 2 weeks until aggression ensued. Eventually all F.gnava queens were attacked but only 29 weeks after having mated. Thus, although offspring are the ultimate benefit from attacking an established F.gnava queen,P.breviceps queens detect mature queens using another time-dependent feature that is reliably indicative of reproductive status. The similarity of host queen hydrocarbon profiles, often correlated with reproductive status in other ant species, suggests that other compounds reflect queen fecundity and produce a kairomonal effect, or that another cue signals host queen and colony suitability. Our findings indicate P.breviceps gynes have evolved to respond aggressively to a host gyne cue that appears long after mating, preventing attacks on gynes without the workers necessary for colony founding.Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.

Facultative and obligate slave making in Formica ants.

Here we show for the first time that the presumed facultative slave-making ant Formica subintegra does not activate outside its nest until July and August, when it raids slaves. A comparative behavioral study of seasonal and daily activities, retrieval of prey, and nest maintenance of F. subintegra, the obligate slavemaker Polyergus breviceps, and the facultative Formica subnuda, shows that the behavioral repertory of F. subintegra closely resembles that of P. breviceps and clearly differs from the repertory of F. subnuda. Unlike P. breviceps, F. subintegra has retained some nest-building activity which, owing to lack of competence, does not contribute to nest maintenance. We suggested earlier that F. subintegra is probably an obligate slavemaker, because it always has in its colonies a large proportion of slaves of the total workforce, whereas F. subnuda fares well even without slaves. This, coupled with no foraging in early summer and a raiding period later on, strongly suggests that F. subintegra is an obligate slave-making ant.

Changes in the cuticular hydrocarbon profile of the slave-maker ant queen, Polyergus breviceps emery, after killing a Formica host queen (Hymenoptera: Formicidae).

Queens of the slave-maker ant, Polyergus breviceps, take over nests of their Formica host species by fatally attacking the resident queen. As workers only begin grooming the P. breviceps queen once she has ceased her attack, we investigated whether a change in parasite queen chemistry may account for the change in worker behavior. Cuticular hydrocarbon profiles of newly mated P. breviceps queens and of queens of their two Formica host species were found to be species-specific. Profiles of newly mated P. breviceps queens that had attacked a Formica queen, however, were virtually identical to the queen profile of the species killed. Mass spectral analysis revealed that the hydrocarbons on the cuticles of newly mated P. breviceps changed from primarily normal alkanes to methyl and di-methyl branched alkanes after attacks. The results suggest that cuticular compounds from the host queen were transferred to the parasite queen during their aggressive interaction.

Responses of Two Potential Host Species (Formica gnava and Formica occulta) to Pupae of the Obligatory Slave-Making Ant, Polyergus breviceps (Hymenoptera: Formicidae)

Queens of the slave-making ant, Polyergus breviceps, take over nests of adult Formica workers when establishing new colonies. Although naive to slave-maker brood, the usurped Formica rear Polyergus offspring and nests containing both host and parasite species forms. Host worker acceptance of parasite brood has been attributed to the similarity of “brood tending signals” between these closely related taxa and/or the presence of an “attractive pheromone” in the slave-maker brood. By presenting single-species groups of Formica occulta and Formica gnava (two host species of P. breviceps) with a choice of Formica pupae of both species or with a choice of P. breviceps pupae from both types of mixed-species nests, it seems that neither close phylogenetic relatedness nor an attractive brood odor alone can account for the propensity of host workers to adopt slave-maker pupae. Significantly greater numbers of P. breviceps pupae were adopted by enslaved workers than by free-living workers, and within the enslaved groups and the free-living F. gnava group, greater numbers of P. breviceps pupae were adopted if they were from nests where the host species was conspecific to workers used in tests. When presented with F. gnava and F. occulta pupae, Formica workers adopted conspecific pupae almost exclusively and ignored or consumed pupae of the other host species. Taken together, these results imply that P. breviceps pupae have both a species-specific odor and a general brood-tending pheromone, upon which a host odor may be imposed. The disparate requirements of immatures at different stages of development for cue specificity or generality in maintaining nest exclusivity and maximizing inclusive fitness are discussed.

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.

The role of an attractive brood pheromone in the obligatory, slavemaking ant,Polyergus breviceps (hymenoptera: Formicidae)

Freeliving workers of Formica occulta, an ant species enslaved by the obligatory slavemaking ant Polyergus breviceps, retrieve and nurse Polyergus pupaejust as well as conspecific pupae in a choice test. No such attraction was found toward pupae of the facultative slavemaker; Formica wheeleri,which also enslaves F. occulta. Formica neogagates,a sympatric species which is not parasitized by either slavemaker, preferentially retrieves and tends conspecific brood over that of Polyergusand F. wheeleri.It is proposed that brood of obligatory slavemaking species must possess an attractive pheromone for slavemaker colony foundation to be successful, since slavemaker brood must be nursed by adult slave workers with no prior exposure to slavemaker brood. An attractive pheromone is not necessary in the brood of facultative slavemakers, since this brood is cared for by newly eclosed slave workers who imprint on the slavemaker brood.

Colony takeover by a socially parasitic ant, Polyergus breviceps: the role of chemicals obtained during host-queen killing

Abstract. The behavioural adaptations of parasitic ant queens are more complex than those of parasitic birds, in which the egg-laying female approaches the nest only when the host parents are absent, and leaves immediately after egg deposition. Queens of the socially parasitic ant Polyergus breviceps are incapable of rearing their own brood, and therefore require the assistance of host Formica workers soon after egg laying. Accordingly, a newly mated Polyergus queen must penetrate a nest of Formica, kill the host queen, and become permanently accepted by the slave species' workers. Laboratory tests show that a Polyergus queen will similarly attack and bite a dead (and therefore motionless) Formica queen. Immediately after attacking the dead host queen, the Polyergus queen will be accepted by workers from any colony of Formica belonging to the same species of the dead queen (but will be attacked by workers from other Formica species). Preliminary results also indicate that any adoption-facilitating chemicals obtained by the Polyergus queen are still effective 1 week after killing the host Formica queen. When Polyergus queens raised in colonies containing F. gnava were introduced into nests of F. occulta, most showed little interest in attacking the resident Formica queen. In four of 10 tests, however, the Polyergus queen killed the foreign queen and was accepted by the F. occulta workers. Such chemical transfer of foreign-queen odours may have played a key role in the evolution of social parasitism in Polyergus.

Slave raid by a diminutive colony of the socially parasitic ant,Polyergus breviceps (Hymenoptera: Formicidae)

Slave raid by a diminutive colony of the socially parasitic ant,Polyergus breviceps (Hymenoptera: Formicidae)

Behavioral adaptations for raiding in the slave-making ant,Polyergus breviceps

We studied recruitment behavior of the slavemaking ant Polyergus breviceps,which typically raids colonies of Formica gnava.The first test series demonstrated the importance of social context, by showing that recruitment was high during raiding, but virtually absent during preraid circling and during the return trip after a slave raid. The second test series showed that Formicapupae (alone or together with adults) must be present for workers of Polyegrusto recruit nestmates. The third test series demonstrated that panic alarm by raided Formicais caused by a pheromone, and we suggest that adults of Formicamay be the source of this secretion. Finally, the fourth test series showed that formic acid is lethal to adults of Formicabut has almost no adverse effect on Polyergus.This relative immunity by Polyergusmay enable them to remain organized while entering nests of Formicaduring slave raids.

Colony Founding by Queens of the Obligatory Slave‐making Ant, Polyergus breviceps: The Role of the Dufour's Gland1

AbstractWe conducted laboratory studies of the process by which newly‐mated queens of the slave‐making ant Polyergus breviceps invade colonies of their host species Formica gnava, kill the resident Formica queen, and appropriate the brood. The aggressive behavior of resident Formica workers towards the invading Polyergus queen subsides shortly after the Formica queen is killed. To elucidate the chemical basis for the reduction in aggression, we prepared extracts of Dufour's, pygidial, and poison glands from Polyergus queens. Workers of the harvester ant Pogonomyrmex occidentalis were daubed with these extracts, and introduced into dishes containing Formica workers. Only the Dufour's secretion protected the intruding ants from incessant aggression by Formica. Preliminary studies also show that the enlarged, bilobed Dufour's gland of the Polyergus queen decreases in size shortly after mating, when developing oocytes occupy a significant portion of the queen's gaster.

Mating Behavior of the Socially-Parasitic Ant Polyergus Breviceps: The Role of the Mandibular Glands

Mating Behavior of the Socially-Parasitic Ant Polyergus Breviceps: The Role of the Mandibular Glands