Techniques for studying the execution of foreign queens by temporal subcastes in fire ants (Solenopsis invicta)

Using monogynous and polygynous colonies of the fire ant, Solenopsis invicta Buren, we developed methodology to determine which behavioural subcaste of workers was responsible for executing unfamiliar queens that were introduced to them. Separation of subcastes and introduction of queens to each of these separately was partly effective, but more accurate results were obtained by removing workers that were in the act of executing queens, marking them individually, and returning them to the colony. Their subsequent behaviour was then recorded to determine whether they behaved like nurses, reserves, or foragers. The results showed that foragers are dominant in execution behaviour and that all morphological subcastes (minors, medias, and majors) are involved. This methodology may be applied to other social insect species.

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Résumé A l'aide de colonies monogynes de S. invicta Buren, nous avons testé la sensibilité de deux méthodes: Premièrement, nous avons isolé les trois sous-castes temporelles des ouvrières (nurses, réserves et fourrageuses) auxquelles nous avons introduit des reines étrangères. Nous avons trouvé que les fourrageuses étaient le groupe le plus agressif, exécutant un pourcentage élevé des reines qui leur étaient présentées. Le degré de physogastrie de la reine étrangère, sa colonie d'origine et la présence de couvain n'avaient pas d'effet visible sur sa destinée. La sensibilité de cette méthode était limitée par la difficulté d'une séparation complète des souscastes temporelles.Deuxièmement, nous avons capturé des ouvrières exécutant activement des reines étrangères, après marquage nous les avons remises dans leur colonie pour observations ultérieures. Nous avons remarqué que leur localisation dans le nid et leur comportement correspondaient aux séquences trouvées pour les fourrageuses bien plus qu'à celles des ouvrières réserves ou nurses. Cette méthode est plus sensible. Des mesures de la largeur de la capsule céphalique de ces ouvrières ont montré qu'aucune des sous-caste morphologiques (mineurs, moyennes et majeurs) étaient dominantes dans le comportement d'exécution. Nos résultats indiquent que la sensibilité des ouvrières à certaines phéromones de la reine et odeur de la colonie augmente avec leur âge.

     

SIMPLE GENETIC BASIS FOR IMPORTANT SOCIAL TRAITS IN THE FIRE ANT SOLENOPSIS INVICTA

Variation in queen phenotype and reproductive role in the fire ant Solenopsis invicta has been shown to have a simple genetic basis in a single introduced population in the United States. The evidence consists of an association between this variation and queen genotype at Pgm-3, a phosphoglucomutase-encoding gene. In the present study, we surveyed Pgm-3 allele and genotype frequencies in diverse populations from the native and introduced ranges of this ant to learn whether this simple genetic basis for reproductive traits is a general feature of the species or a genetic anomaly in introduced ants stemming from a recent bottleneck or the invasion of novel habitats. No egg-laying queens living in polygyne (multiple-queen) nests possessed the homozygous genotype Pgm-3^a/a in any of the study populations, yet nonreproductive females from such nests (workers as well as queens that had not yet initiated oogenesis) possessed this genotype at moderate frequencies. Remarkably, Pgm-3^a/a was the most common genotype among all classes of females, including egg-laying queens, in monogyne (single-queen) nests from all populations studied. Genotype proportions at Pgm-3 in polygyne populations typically departed strongly from the proportions expected under Hardy-Weinberg equilibrium, whereas those in monogyne populations did not. These patterns establish that a single mendelian gene influences queen reproductive role in S. invicta and that this gene uniformly is under strong directional selection in the polygyne social form only. Moreover, the perfect association of Pgm-3 genotype and reproductive role in all populations, combined with the known function of phosphoglucomutase in insect metabolism, suggest that this gene may directly influence queen phenotypes rather than merely serving as a marker for a linked gene that causes the effects.     

Behavioral strategies of aphid hyperparasitoids to escape aggression by honeydew-collecting ants

We analyzed the behavioral interactions between two species of honeydew-collecting ants (Lasius niger, Myrmica laevinodis) and foraging females of four species of aphid hyperparasitoids (Aphidencyrtus aphidivorus, Dendrocerus carpenteri, Pachyneuron aphidis, Asaphes vulgaris) usingAphis fabae ssp.cirsiiacanthoidis andLysiphlebus cardui on thistles as aphid and primary parasitoid, respectively. The observed interaction patterns and foraging parameters varied within hyperparasitoid species and revealed different strategies based upon behavioral and morphological constraints.D. carpenteri generally tried to avoid ant encounters. This avoidance strategy was successful in interactions withM. laevinodis but failed when encountering the more aggressiveL. niger, which caused about 26% adult mortality. In contrast,A. aphidivorus, P. aphidis, andA. vulgaris possess jumping ability and were hardly exposed to mortality risks. The escape reaction jump off was used as soon as ants made physical contact with foraging females. While the flight strategy ofP. aphidis is connected with cryptic movement patterns without avoidance behavior,A. aphidivorus first avoided ants and jumped off only as a last resort. Similar patterns, but less expressive, are displayed byA. vulgaris. We suggest that these different strategies are responsible for different foraging success in ant-attended resources in field.     

Ants remove virtually all western myall (Acacia papyrocarpa Benth.) seeds at Middleback,South Australia

Abstract Ants can have a profound effect on the numbers of seeds present in the seed-bank. We investigated the removal of seeds of an important arid zone tree species, the western myall (Acacia papyrocarpa Benth.). The species has seed characteristics typical of other Acacia species: a hard seed-coat and a small, white aril or elaiosome; the latter is reported to be attractive to ants. An experiment was conducted to see how rapidly and completely the seeds would be removed under various caging treatments. Observations were also made to discover the major seed removers and the fate of the seeds. Seed removal was rapid (< 12h) and was almost entirely by ants, and while our observations were not conclusive, we speculate that much of the seed supply is effectively destroyed by seed harvester ants which thus act as true granivores, not seed dispersers. Whether this matters for western myall in the long term is problematic because the species is so long-lived; rare but successful recruitment events may well be sufficient for its long-term survival.     

Respective contributions of leader and trail during recruitment to food inTetramorium bicarinatum (Hymenoptera: Formicidae)

Summary This paper describes the food recruitment strategy of the antTetramorium bicarinatum, at both the individual and collective levels. The general organisation of recruitment used by this species during the exploitation of sucrose solutions shows similarities with group recruitment described for other species. However, our experiments demonstrate that inT. bicarinatum, the first trail laid by a recruiter during its return trip to the nest is more efficient than in other species using group recruitment, for exampleTetramorium impurum. Moreover, the efficiency of the first trail of aT. bicarinatum recruiter is comparable with that ofTapinoma erraticum, a species that uses mass recruitment. Despite the efficiency of the trail, choice experiments show that the recruited workers prefer to follow the leader rather than the first trail, suggesting the emission of a more attractive signal by the leader on its way back to the food. The function of the leader in this strategy is discussed in terms of collective decisions.     

Comparison of the ant communities of annually inundated and terra firme forests at Trombetas in the Brazilian Amazon

Summary The composition of the ant community was assessed along standardized 100 m transects in annually flooded Varzea forest and in terra firme forests on sandy soil (Flanco forest) and on claytopped mesas (Planalto forest). Standardized samples were taken by unit-time hand collecting (day and night times), sweeping, beating, baiting and by Winkler sacks. A total of 156 species, representing 49 genera were found, of which 98, 88 and 55 were respectively found in the Planalto, Flanco and Varzea forests. Species lists are presented and the ant community composition and species richness are compared between the three forests. By considering the nesting and foraging habits of the various species, the differences in overall community composition are related to the forest type and susceptibility to inundation of the three forests which were surveyed.The data confirm the view that tropical rain forests support an extremely diverse ant fauna and comparisons with other forested areas suggest that ant species richness declines in subtropical and temperate rain forests. Although alpha diversity is high, species turnover between forests is lower than expected, suggesting that ant species richness in this forested region is not as great as is implied in some published estimates of global arthropod diversity.     

Endophytic fungi alter foraging and dispersal by desert seed-harvesting ants

Endophytic fungi are thought to interact mutualistically with host plants by producing alkaloid metabolites that deter herbivory. Since such fungi are transmitted via seed in some grasses, the presence of endophytes may also protect plants from seed predators. We conducted seed choice experiments for two dominant seed harvesting ants, Pogonomyrmex rugosus in the Sonoran desert and Pogonomyrmex occidentalis at a higher elevation, riparian zone in Arizona, USA. Non-infected fescue (Festuca arundinacea) seeds and seeds infected with the endophytic fungus, Acremonium coenophialum, were presented to ant colonies in three different populations. Infected seeds were harvested less frequently than non-infected seed for the two populations of Pogonomyrmex rugosus but not for the population of Pogonomyrmex occidentalis. We also a conducted seed dispersal experiment for one population of Pogonomyrmex rugosus. Of the seeds that were harvested, most of the colonies discarded more infected seeds into refuse piles than expected by chance. Seeds discarded into refuse piles have greater germination success than surrounding areas. The most important interaction of endophytes and grasses may be deterrence of seed predation and enhancing the probability of germinating in favorable sites, since these processes directly increase plant fitness.     

Flower nectar of an autogamous perennialRorippa indica as an indirect defense mechanism against herbivorous insects

This report shows that one of the most important roles of the flower nectar of an autogamous perennialRorippa indica (L.) Hieron is as an attractant for employing some ant species as a defense against herbivorous insects. The plant has flowers from spring to early winter. Its flower nectar is frequently stolen by some ant species (hereafter cited as ants) which also feed on small herbivorous insects on the plant. Internations among the tritrophic levels (R. indica, herbivores, ants) were experimentally examined and the followings became clear. (1) Ants were attracted toR. indica in search of its flower nectar. (2) The gradual secretion of flower nectar seemed to detain ants on the plant. (3)Pieris butterfly lavae were the major herbivores onR. indica and were potentially harmful to the plant. (4) The presence of ants reduced the survival rate ofP. rapae larvae onR. indica. (5) The presence of ants reduced the feeding damage toR. indica. (6) The disadvantage of nectar use by ants seemed to be minimal for the plant since the ants did not disturb the other flower visitors. These facts suggest a mutualistic relationship betweenR. indica and ants. That is, the flower nectar serves as an indirect defense against herbivorous insects.     

The diversity and evolution of recruitment behaviour in ants,with a discussion of the usefulness of parsimony criteria in the reconstruction of evolutionary histories

Summary Three alternative hypotheses about the evolution of recruitment behaviour in ants, based on accounts in the literature, are compared by means of a cladistic analysis. The three hypotheses are the following:Hypothesis 1. Increasingly efficient recruitment behaviours exhibited by different ant species have been shaped by or are correlated with ant phylogeny.Hypothesis 2. Increasingly efficient recruitment behaviours represent necessary evolutionary steps independently followed during the evolution of different ant clades.Hypothesis 3. Differently efficient recruitment behaviours have been selected in a convergent way among different species by similar population/environmental constraints.In a first stage of the analysis, these hypotheses have been compared in terms of parsimony (i.e. in terms of tree length = TL) of alternative cladograms based on recruitment behaviour only. The analysis gave the following results: Hypothesis 1, TL = 4; Hypothesis 2, TL = 18; Hypothesis 3, TL = 11. At least in terms of parsimony, hence, Hypothesis 1 appears to be the best. This hypothesis, however, cannot be retained for its total lack of congruence with current views on ant phylogeny. Among the remaining two hypotheses, Hypothesis 3 is again much (ca. 40%) more parsimonious than Hypothesis 2, but the retention index for recruitment behaviour on the relative cladogram is 0.2 as compared with 0.7 for Hypothesis 2. Practically, this implies biologically very implausible behavioural evolution indicated by very improbable ancestors for the species included in the analysis. In the case of recruitment evolution the biological credibility of each hypothesis is inversely proportional to its parsimony.The three hypotheses on the evolution of recruitment behaviour are compared again taking into account the morphological and behavioural correlates of recruitment. The results confirm those obtained by simple cladistic analysis of behaviour alone, namely that an obligatory (i. e. neither reversible nor random) increase in recruitment efficiency has been repeatedly selected within different ant clades. Inclusion of the recruitment correlates allows, in addition, a more precise formulation of the implications of each hypothesis and a tentative test of two other alternatives deduced from the literature. Most papers dealing with recruitment assume this behaviour to be controlled by a single gland, while at least two experimental analyses show that more than one gland is likely to be involved as behavioural releaser. A cladistic approach allowed testing of the following two adaptational hypotheses: A) Synergic behavioural control by several glands, allowing shift of the dominant role from one gland to another. B) Single gland control, making improbable the replacement of one gland by another that performs the same function. The results of the analysis appear to favour alternative A slightly, though neither alternative results in implausible evolutionary paths.It is stressed that parsimony remains the sole decisional criterion when no other criteria are available but it can by no way be preferred to the slightest trace of biological common sense.     

Collective behavior in relation with changing environments: Dynamics,modularity, and agency

Collective behavior operates without central control, using local interactions among participants to adjust to changing conditions. Many natural systems operate collectively, and by specifying what objectives are met by the system, the idea of agency helps to describe how collective behavior is embedded in the conditions it deals with. Ant colonies function collectively, and the enormous diversity of more than 15K species of ants, in different habitats, provides opportunities to look for general ecological patterns in how collective behavior operates. The foraging behavior of harvester ants in the desert regulates activity to manage water loss, while the trail networks of turtle ants in the canopy tropical forest respond to rapidly changing resources and vegetation. These examples illustrate some broad correspondences in natural systems between the dynamics of collective behavior and the dynamics of the surroundings. To outline how interactions among participants, acting in relation with changing surroundings, achieve collective outcomes, I focus on three aspects of collective behavior: the rate at which interactions adjust to conditions, the feedback regime that stimulates and inhibits activity, and the modularity of the network of interactions. To characterize the dynamics of the surroundings, I consider gradients in stability, energy flow, and the distribution of resources and demands. I then propose some hypotheses that link how collective behavior operates with changing environments.