Polygyny,relatedness and nest founding in the polygynous myrmicine ant Leptothorax acervorum (Hymenoptera; Formicidae)

Summary There is high within-nest relatedness for functional queens (with corpora lutea), nonfunctional queens (without corpora lutea), and workers in polygynous nests of Leptothorax acervorum. The high functional queen relatedness suggests that young mated queens are adopted back to their mother nest. Functional queen relatedness does not change with the number of queens present in the nest, suggesting that the number of generations of queens, on average two to three, is rather stable. Worker relatedness decreases with increasing number of functional queens per nest (Tables 5, 6). The number of queens contributing offspring to the nest (mothers), estimated from worker and functional queen relatedness, is lower than the number of functional queens, particularly in highly polygynous nests. Estimates of number of mothers in monogynous nests indicate that these nests previously were polygynous (Table 7). There is no correlation between nest relatedness and distance between nests, and budding-off, if present, thus appears to be a rare mode of nest founding (Table 8). There are no indications of inbreeding in the two populations studied since the frequency of heterozygotes is as high as expected from random mating (Table 4). Most likely, polygyny is the rule in L. acervorum and serves to secure the presence of queens in the nest.     

Annual cycles in worker size of the seed-harvester antVeromessor pergandei (Hymenoptera: Formicidae)

Summary The seed-harvester antVeromessor pergandei Mayr is primitively polymorphic; workers are monophasically allometric. There is a distinct annual cycle in mean worker body size that replicates across colonies and habitats (Fig. 1); this cycle occurs through alteration of the worker size distribution (Fig. 2). There is little, if any, morphspecific task specialization by workers suggesting worker size variance is a colony-level adaptation permitting maintenance of a large and constant worker force during periods of resource fluctuation. Smaller workers appear in the foraging force following the triple crunch of reduced seed availability, reduced favorable times to forage, and alate production during winter months. Adult and startingV. pergandei colonies exhibit strong intraspecific territoriality, suggesting the selective advantage for maintenance of a large and constant worker force. Such selective pressures may have provided the initial variance in worker size distributions that led subsequently to specialized castespecific task performance in more distinctly polymorphic ant species.     

Genetic relatedness of worker nestmates in Myrmica ruginodis (Hymenoptera : Formicidae) populations

Summary Genetic relatedness and mating structure of the red ant, Myrmica ruginodis, were studied from a large data set in several natural populations, one of which was a substructured archipelago population. Within-colony relatedness of worker nestmates was measured as genotypic correlation and mating structure as deviation from random mating; both were calculated from the genotype frequency data. The average relatedness of worker nestmates was rather high across populations (0.43–0.73), and random mating was the rule within populations. The data were used to deduce the social structure of populations. With one possible exception, populations turned out to be weakly polygynous, implying that they consisted of the macrogyne form of the species. The exceptional population was relatively more polygynous and inbred, suggesting that it might include the microgyne form. This exceptional population lived in a habitat not noticeably different from that of the other populations, challenging previous suggestions of the habitat specialization of the two forms. The colonies were facultatively polygynous, and a comparison with earlier studies shows that polygyny is functional. Relatedness of worker nestmates varied slightly among populations, indicating that the social structure of Myrmica colonies is flexible.     

Differential reproduction in multiple-queen colonies of the fire ant Solenopsis invicta (Hymenoptera: Formicidae)

Summary The contribution to maternity of workers and female sexuals over time by queens in six multiple-queen laboratory colonies of Solenopsis invicta was directly assessed by use of enzyme genetic markers. Queens contributed more equally to the worker pool than to the pool of sexuals in virtually all samples (Fig. 1), and individuals producing a substantial proportion of the workers often had low or no representation of their daughters in the pool of sexuals. Signficant disparity among queens in their relative production of sexual daughters was often evident, with dominance in production of sexuals by a given queen commonly occurring in association with a pronounced loss of weight followed shortly by her death. The results suggest that significant variability in short-as well as long-term reproductive success may occur among the distantly related queens associating in natural polygyne S. invicta nests. Variance in apportionment of maternity of sexuals did not appear to be simply related to varying levels of fecundity, suggesting that the common presumption that reproductive success can be equated with fecundity in polygyne social Hymenoptera may not be well founded. The observed variance also did not appear to result from a simple mechanism of kin recognition and discrimination by workers in the process of brood rearing. Rather, this variance may have largely resulted from either, 1) recognition of certain queens and their progeny coupled with preferential sexualization of these immatures by nurse workers, or, 2) queen biasing of eggs toward development as sexuals. The frequent association of weight loss and death of mother queens with high levels of sexual daughter production may be best explained by the latter mechanism.     

Predatory behavior and chemical communication in two Metapone species (Hymenoptera:Formicidae)

Summary. Colonies of two species of Metapone (M. madagascarica, M. new species.) were collected in Madagascar and established in laboratory nests. It could be demonstrated that both species are specialist predators of termites (Cryptotermes kirbyi). During hunting the ants sting the termites and thereby paralyze and preserve the prey alive. In this way prey can be stored in the ant nest for extended periods. During foraging and colony emigrations the ants lay chemical trails with poison gland secretions. Among the seven compounds identified in the venom only methyl pyrrole-2-carboxylate elicits trail following behavior in both Metapone species. Received 11 February 2002, accepted 23 February 2002.     

Teams in social insects: group retrieval of prey by army ants (Eciton burchelli,Hymenoptera: Formicidae)

Summary Eciton burchelli workers frequently form groups to retrieve large prey items. Such groups have a definite structure. There is a constant relationship between total ant dry weight and prey item dry weight for both individual porters and groups, and this relation is such that a larger weight of ant or ants can carry disproportionately heavy items. Furthermore, all prey items are carried at a standard retrieval speed. This means that groups are superefficient; they can carry items that are so large that if they were fragmented the original members of the group would be unable to carry all the fragments. Groups also have a distinct caste distribution. There is a significant tendency for each group to have a single submajor, the specialist porter caste in Eciton burchelli. These findings which were verified by experiments suggest that groups fulfill the criteria of efficient teams. The biomechanics are proposed to explain the superefficiency of groups. The organization of co-operation is considered as is the role of teams in the economy of these societies. Colony caste profiles can only be understood by examining the role of teams which form a plastic supercaste.     

Trail discrimination signal of Lasius japonicus (Hymenoptera: Formicidae)

Summary. Trail-following behavior of Lasius japonicus was colony-specific in the field, while trail pheromone activity was not. We found that the footprint substance caused colony-specific trail-following behavior only when working in conjunction with the trail pheromone. The footprint substance alone did not lead the workers to follow trails. The substance consisted mainly of hydrocarbons with composition almost identical to that of cuticular hydrocarbons, except for the absence of n-alkanes. Nestmate workers shared footprint hydrocarbon profiles as well as cuticular hydrocarbons, but the profiles differed among colonies. We therefore consider that the footprint hydrocarbon profiles serve as the trail discrimination signal in L. japonicus.     

Effects of parasites on foraging and defense behavior of a termitophagous ant,Pheidole titanis Wheeler (Hymenoptera: Formicidae)

Summary Pheidole titanis Wheeler, an ant that occurs in desert and deciduous thorn forest in the southwestern United States and western Mexico, is a predator on termites. In the dry season well-coordinated raids against termite foraging parties occur early in the morning or late in the afternoon, whereas in the wet season most raids occur at night. This seasonal shift in the timing of raids is due to the increased activity of a fly (Diptera: Phoridae) that is a specialist parasitoid on P. titanis workers and soldiers. When parasitic flies discover P. titanis nest entrances or raiding columns, workers stop foraging and defend themselves against oviposition attacks. Flies are only active during the day and never interfere with foraging at night. However, P. titanis does not increase the frequency of raids at night and, as a result, colonies collect less food in the wet season compared to the dry season. Presence of parasitic flies also interferes with normal defense behavior of P. titanis against conspecific and heterospecific enemy ants. Dissections of P. titanis workers and soldiers suggest that the parasitism rate by flies is less than 2% and observations indicate that parasitic flies are much rarer than their host workers and soldiers. Nonetheless, these parasites exert a strong ecological impact on their host.     

Trail and recruitment pheromones in Camponotus socius (Hymenoptera: Formicidae)

Summary. Worker ants of Camponotus socius employ multicomponent signals during group recruitment to food sources and nest emigrations. The chemical signals consist of trail orientation pheromones that originate from the hindgut. Two components that elicit trail orientation behavior were identified: (2S,4R,5S)-2,4-dimethyl-5-hexanolide and 2,3-dihydro-3,5-dihydroxy-6-methylpyran-4-one. Although both compounds release trail following behavior, in choice tests the former compound is preferred significantly. The major recruitment signal appears to be formic acid discharged from the poison gland. Compounds identified in the Dufour gland secretions do not seem to be involved in the recruitment process.     

Comparative study of genetic and social structure in two forms of the fire ant Solenopsis invicta (Hymenoptera: Formicidae)

Summary The genetic and social structures of polygyne and monogyne forms of the fire ant, Solenopsis invicta, are investigated in a comparative manner using allozyme data from two polymorphic loci. Foundress queens of the monogyne form are signly inseminated and appear to produce all males present in the colony during the major summer mating flights. The average regression coefficient of relatedness (b) among female nestmates of the monogyne form is 0.714 (Fig. 2), statistically indistinguishable from the pedigree coefficient of relatedness (G) of 0.75. We suggest that the evolution of obligate worker sterility in Solenopsis is associated with this high relatedness between workers and the queens they rear. Functional queens in polygyne nests also are singly inseminated and are no more closely related to nestmate queens than to other queens (within-nest b=0). Within-nest relatedness of workers in the polygyne population is similarly low (Fig. 2). Both the monogyne and polygyne populations from northcentral Georgia are in Hardy-Weinberg equilibrium at both allozyme loci and we found no evidence of significant population subdividion or inbreeding in the polygyne population. These results do not support the view that kin selection has promoted the evolution of polygyny in North American S. invicta. Rather, mutualism appears to be the most likely selective factor mediating queen associations inthis ant.     

Dominance orders in the ponerine ant Pachycondyla apicalis (Hymenoptera,Formicidae)

Summary Intracolony aggression among workers of the neotropical ponerine ant species Pachycondyla apicalis leads to dominance orders. Antagonistic interactions can entail either overt physical attacks with the subordinate individual often exhibiting a submissive posture or the robbing and destruction of eggs laid by nestmates. The single queen, however, was never observed either attacking or being attacked by any colony member. The hierarchical structure among workers consists of one dominant individual and several subordinates; the relationships among subordinate workers are unclear, however. We report for the first time a natural (nonmanipulated) change in the social status of individuals within an ant dominance order. Dominant workers usually had better developed ovaries, laid more eggs and were more frequently observed attending the egg pile than subordinate individuals. This pattern became even more striking when the queen was excluded from the colony. These results indicate that workers of P. apicalis lay eggs even in the presence of the queen. It is possible that some of these haploid eggs may develop into males.Offprint requests to: B. Holldobler     

The chemical basis for trail recognition in Lasius nipponensis (Hymenoptera: Formicidae)

Summary. In this paper we report on the chemical basis for trail recognition in Lasius nipponensis. On and near trails in the field, workers became aggressive against conspecific intruders and succeeded in protective contests, while intruders usually avoided confrontation. Such asymmetric interactions were also observed in the laboratory when two non-nestmate workers were sequentially placed in a clean glass dish, while mutual aggression was observed when they were placed simultaneously. Asymmetric aggression was also observed when the workers were placed in a dish previously conditioned by other workers, or when the dish was treated with the hexane rinse of the conditioned dish. The rinse contained a series of hydrocarbons, in which components and proportion were almost identical to those of the cuticular hydrocarbons of the workers, except for a lack of n-alkanes. Amounts of the hydrocarbons that remained on the dish were very small when all the tarsi of the workers were incapacitated. We therefore consider that the hydrocarbons are not adhesion of the cuticular hydrocarbons but secretion from the tarsi of workers, and serve as a key signal for trail recognition in this ant.