Timekeeping through social contacts: social synchronization of circadian locomotor activity rhythm in the carpenter ant Camponotus paria

In ant colonies a large proportion of individuals remain inside nests for most of their lives and come out only when necessary. It is not clear how, in a nest of several thousand individuals, information about local time is communicated among members of the colony. Central to this seem to be circadian clocks, which have an intrinsic ability to keep track of local time by entraining to environmental light-dark, temperature, and social cycles. Here, the authors report the results of their study aimed at understanding the role of cyclic social interactions in circadian timekeeping of a day-active species of carpenter ant Camponotus paria. The authors found that daily social interactions with visitors (worker ants) was able to synchronize the circadian locomotor activity rhythm of host worker ants and queens, in one-on-one (pair-wise) and multi-individual (group-wise) interactions. Interestingly, the outcome of cyclic social interactions was context specific; when visitor workers socially interacted with host workers one-on-one, host workers considered the time of interaction as subjective day, but when visitor workers interacted with a group of workers and queens, the hosts considered the time of interaction as subjective night. These results can be taken to suggest that members of the ant species C. paria keep track of local time by socially interacting with workers (foragers) who shuttle in and out of the colony in search of food. (Author correspondence: vsharma@jncasr.ac.in ).     

Nutrient allocation for somatic maintenance and worker production by the queen of the Japanese black carpenter ant, <Emphasis Type="Italic">Camponotus japonicus</Emphasis> (Hymenoptera: Formicidae)

Because queens of claustral colony-founding ants raise their first workers without foraging outside the nest, the number of first workers produced depends on the nutrient reserves of the queen when she begins to establish the colony. Although a low mortality rate of queens may be expected because they seal themselves off in the nest chambers, they do face a risk of starvation. Therefore, the queens must allocate nutrients for somatic maintenance and worker production, including the feeding of larvae. However, there are few reports on the nutrient consumption of queens. To clarify the nutrient resource utilization of claustral colony-founding queens, newly mated queens of the Japanese black carpenter ant, Camponotus japonicus (Mayr), were collected just after the nuptial flight and reared in an incubator at 25 °C in the dark. The non-lipid mass and lipid mass of the queens were measured at 0, 10, 20, 30, 40, and 52 days after the nuptial flight. A significant decline in the non-lipid mass was found in the queens after hatching of larvae. In contrast, the lipid mass of the queen decreased soon after the nuptial flight. The results indicate that the somatic maintenance of the founding queens relies exclusively on lipids, while other nutrients, such as protein, may be used for feeding the larvae.     

Short- and long-day responses in the pre-adult developmental duration of two species of Camponotus ants

We assessed the effect of different day/night lengths on the pre-adult developmental time of two species of Camponotus ants that normally develop in dark underground nests. We assayed larval (egg-to-pupal formation), pupal (pupal formation-to-adult emergence), and pre-adult (egg-to-adult emergence) durations in these ants under three different light/dark (LD) cycles of 12:12 h, 10:14 h, and 14:10 h. We observed that the pre-adult development time of ants under these day lengths was significantly different. Although both species developed fastest under 12:12 h LD, when asymmetric LD cycles were compared, night-active species (Camponotus compressus) developed faster under short days (10:14 h) and day-active species (C. paria) developed faster under long days (14:10 h). This day/night-length-mediated difference in pre-adult developmental duration was mostly due to modulation of larval duration; however, in day-active species it was also via altered pupal duration. These results thus indicate that the two species of Camponotus ants respond differently to short and long days, suggesting that seasonal timers regulate pre-adult development time in tropical ant species living in dark underground nests.     

婚飞行为影响中华蜜蜂性成熟处女蜂王的基因表达

婚飞是性成熟处女蜂王与雄蜂交配过程中的一个重要前奏, 在该过程中蜂王体内伴随着一系列重要的生理变化。为了探究中华蜜蜂Apis cerana cerana处女蜂王婚飞过程中基因表达变化, 本研究利用数字基因表达谱(digital gene expression, DGE) 技术分析了中华蜜蜂性成熟处女蜂王飞行与未飞行之间的基因表达差异。经DGE测序, 分别从两个样品中获得5.98和6.01 百万条Clean标签。通过分析检测到250个基因有差异表达, 其中133个基因在飞行蜂王中上调表达, 117个基因在飞行蜂王中下调表达。这些差异基因可以归类到348个功能性类别和142个生化途径。结果表明中华蜜蜂性成熟处女蜂王在婚飞过程中大量基因的表达发生了变化。这些结果为进一步研究中华蜜蜂蜂王婚飞过程中生理变化的分子机制提供了重要的基因表达信息。     

Colony genetic structure in the mono- and polygynous sibling species of the antsCamponotus nawai andCamponotus yamaokai: DNA fingerprint analysis

Using the ant-derived probe (pMY7), we performed DNA fingerprinting in monogynous and polygynous sibling ant speciesCamponotus nawai andCamponotus yamaokai. In monogynousC. nawai, band-sharing probabilities were low between unrelated individuals (mean 0.09), but those and relatedness estimates were consistently high between workers of the same nest (mean 0.85 and 0.74–0.83, respectively), suggesting that the queen mated once and nestmate workers are super-sisters. It also suggested monoandry: that is, that all nestmate workers shared most of the bands which were considered to have derived from a male. In polygynousC. yamaokai, band-sharing probabilities were low between queens of different populations (mean 0.13), moderate between queens of different nests in the same population (mean 0.25), but very high between queens of the same nest (within-nest means were 0.84–0.96). These results suggest that nestmate queens are genetically closely related with each other. Relatedness estimates between colony members sometimes reached 1. This might result from successive intranidal mating (inbreeding or large Wahlund effect) and adoption of new queens into the natal nests.     

Monogyny and regulation of worker mating in the queenless antDinoponera quadriceps

The morphologically specialized queen caste has been lost in various ponerine ants, and mated workers (‘gamergates’) reproduce instead of queens. Unlike previous reports in the literature, we found only one gamergate in each colony ofDinoponera quadriceps. We documented monogyny by dissecting ovaries and spermathecae in 914 workers from 15 colonies, and by observing mating in the laboratory. In colonies without a gamergate, aggressive interactions among some of the unmated nestmates led to the behavioural differentiation of a top-ranking worker (‘alpha’), which laid almost all the eggs. Only the alpha went outside the nest at night, and mated if foreign males were present (N=11 tests), thus becoming a gamergate. The alpha was sexually attractive even when her ovaries were not yet active. After intromission, the male remained linked to the alpha while she severed the end of his abdomen. Pieces of the male genitalia remained attached to her genital tract, and she removed them after 30±18 min (X±sdN=9). We interpret this to be a mating plug, preventing other males from fathering her offspring. None of these newly inseminated gamergates continued to go outside the nest, and, when tested, they never re-mated (N=4). Thus, gamergates ofD. quadricepsprobably mate only once. In queenless ant species, comparative evidence indicates that worker mating is often regulated in monogynous species, while unrestricted mating of young individuals is typical of polygynous species (oviposition is regulated subsequently). Furthermore, the occurrence of either monogyny or polygyny influences the mating strategies of males, and mating plugs have been reported only in some monogynous species.     

Reproduction by virgin queen fire ants in queenless colonies: Comparative study of three taxa (Solenopsis richteri,hybridS. invicta/richteri,S. geminata) (Hymenoptera: Formicidae)

Summary In the fire ant,Solenopsis invicta, some winged virgin queens are known to shed their wings (dealate) upon removal of the mated mother queen. These virgin queens then develop their ovaries and begin to lay eggs, thereby foregoing the option of leaving on mating flights and attempting to found their own colonies. Such a response of virgin queens to queenlessness has not been reported for other ants. In order to determine if virgin queens of some other fire ants (subgenusSolenopsis) would respond in the same way, experiments were conducted onS. richteri, hybridS. invicta/richteri andS. geminata, a member of a species complex different from that of the other taxa. Just as inS. invicta, virgin queens ofS. richteri and the hybrid dealated and began to lay eggs within days of the removal of the queen. In addition, workers executed many of the reproductively active virgin queens, a phenomenon also found inS. invicta. In contrast, virgin queens ofS. geminata did not dealate or quickly begin to lay eggs upon separation from the queen. Reasons for the variability in the response of virgin queens of the different species may be 1) higher probability of reproductive success for unmated dealated queens compared to normal claustral founding inS. invicta andS. richteri linked to relatively frequent loss of the mother queen; or 2) phylogenetic constraint.     

Polygyny and Monoandry in the Ant Formica japonica (Hymenoptera: Formicidae)

Queen number, mating frequency and nest kin-structure of the ant Formica japonica were studied in the field and the laboratory. Nest excavation in the study site, the east slope of Mt. Fuji, Gotenba, Japan, revealed that F. japonica is weakly polygynous all year round and the queen number increases after the nuptial flight season, suggesting the adoption of newly mated queens by established nests. Dissection and laboratory rearing demonstrated that nearly all queens in polygynous nests had mated and were fertile with mature oocytes in their ovaries. Multilocus DNA fingerprinting was used to examine kin relationships among ants found in the same nests. The fingerprint band patterns were apparently governed by a simple genetic rule and suggested monoandry (single mating per queen). The mean band sharing score of DNA fingerprints among full sisters was 0.90, and the mean value between queens and their daughters was 0.75. Comparison of DNA fingerprints of adult and pupal workers with pupal gynes suggested that multiple queens in a nest may contribute unequally to gyne (new queen) production.     

Mate number,kin selection and social conflicts in stingless bees and honeybees

Microsatellite genotyping of workers from 13 species (ten genera) of stingless bees shows that genetic relatedness is very high. Workers are usually daughters of a single, singly mated queen. This observation, coupled with the multiple mating of honeybee queens, permits kin selection theory to account for many differences in the social biology of the two taxa. First, in contrast to honeybees, where workers are predicted to and do police each other''s male production, stingless bee workers are predicted to compete directly with the queen for rights to produce males. This leads to behavioural and reproductive conflict during oviposition. Second, the risk that a daughter queen will attack the mother queen is higher in honeybees, as is the cost of such an attack to workers. This explains why stingless bees commonly have virgin queens in the nest, but honeybees do not. It also explains why in honeybees the mother queen leaves to found a new nest, while in stingless bees it is the daughter queen who leaves.     

Developmental plasticity in the queen-polymorphic ant Temnothorax longispinosus

Females of social Hymenoptera show developmental plasticity in response to varying social and environmental conditions, though some species have strong genetic influences on the form of the female reproductives. In ants, a queen polymorphism can occur in which large queens initiate new colonies on their own, while small queens enter established nests. Most queen polymorphisms studied to date originate due to genetic differences between individuals of differing form. Here, we report on the development of female form in response to social factors within the nest in the queen-polymorphic ant Temnothorax longispinosus. Three queen size morphs occur: a rare large queen with higher fat stores that can found new colonies independently, a large queen that has low fat stores and is behaviorally flexible, and a small queen that rejoins the natal nest. Both in nesting units collected from the field and those reared in the lab, queen presence during larval development led to fewer larvae developing as gynes (virgin, winged queens), and most of those gynes were the small morph. This queen effect is transferred to developing gyne larvae by close, physical interaction between queens and workers, and causes slower larval development. We conclude that gyne size, and therefore reproductive behavior, in T. longispinosus is developmentally plastic in response to queen presence. Plasticity in reproductive behavior may be an adaptive response to the nest sites utilized by this species. T. longispinosus nests predominantly in acorns and hickory nuts, which can vary dramatically from 1 year to the next. Since queens are more likely to be present in each nesting unit when fewer nest sites are available, the queen effect that results in more small gynes produced links the expression of colony-founding traits to ecological conditions across habitat patches.     

The behaviour of queen honeybees and their attendants

Abstract. The behaviour of queen and worker honeybees (Apis mellifera L.) was observed using small colonies in observation hives. Workers paid more attention to queens which had been mated for 2 months or more than to those which were newly mated; virgin queens received least attention. Queens received most attention when they were stationary and least when they were walking over the comb; virgin queens were most active. Queen cells had as many attendants as virgin queens and queen larvae were inspected almost continuously. The queen pheromone component 9–oxo-trans-2–decenoic acid stimulated 'court' behaviour when presented on small polyethylene blocks, but workers responded aggressively to complete extracts of queens' heads. Both the heads and abdomens of mated queens received much attention from court workers but the abdomens were palpated by more workers for longer and were licked much more. The queens' thoraces were least attended. Abdominal tergites posterior to tergite glands were licked for longer than those anterior to the glands. Only worker bees very near to the queen reacted to her and joined her 'court'.
No evidence was found of a diel periodicity in the behaviour of a queen or her 'court'. During the winter the queen's court was smaller than in summer and she walked less and laid fewer eggs. When colonies were fed with sucrose syrup in winter, their queens laid more eggs and workers reared more brood but there was no change in the attention received by the queens.
The implications of these findings for the secretion and distribution of queen pheromones are discussed.     

Habitat structure,dispersal strategies and queen number in two boreal Leptothorax ants

In two nearctic ants, Leptothorax canadensis and Leptothorax sp. A, young queens may either found their own nest solitarily after mating or seek adoption into an established colony. Whether a queen disperses or not is associated with genetically determined queen morphology in Leptothorax sp. A. Whereas a majority of winged queens attempt solitary colony founding after mating, most wingless, intermorphic queens return to their maternal nests and new colonies are founded by budding after hibernation. The latter strategy appears to be correlated with patchy, isolated habitats, whereas in extended boreal forests dispersal on the wing is probably more common. Alternative dispersal strategies strongly affect the average number of queens per colony and seasonal fluctuations of colony structure.     

Mating‐Associated Changes in the Behaviour of Leptothorax gredleri Ant Queens

Throughout their lives, animals adapt their behaviour to environmental fluctuations and to their own requirements. In social insects, behavioural changes are often particularly conspicuous. For example, in many ant species, reproductive sexuals leave their maternal nests and engage in risky mating and dispersal activities. Female sexuals experience, during a short period of time, dramatic changes in terms of behaviour and environmental conditions. But because sexual activities of ants are not easily observed, few studies have quantified in detail how behaviour alters with maturation and mating. We studied how various behavioural traits of Leptothorax gredleri female sexuals, a species in which female sexuals attract males by ‘female calling’, change before and after mating. We tested the hypothesis that behavioural variation reflects the altered requirements of queens to adapt to a particular situation. To this end, we compared geotactic, phototactic and locomotor behaviour across a wide range of life stages from lightly coloured, unmated female sexuals to old, mated queens. The results showed that female sexuals of L. gredleri change conspicuously their geotactic, phototactic and locomotor behavioural traits over their life stages. Three different behavioural states were evident (1) from light to dark female sexuals, individuals have negative phototaxis and reduced locomotor activity; (2) mature female sexuals during the daily period of sexual activity have strong phototaxis, negative geotaxis and an important locomotor activity; and (3) freshly mated and old mated queens avoid light and decrease their locomotor activity. These sharp differences in behaviour between stages match the transition from the relative safety of the nest chamber to the adversary world outside the nest , and back.     

Decision-making conditions for intra- or inter-nest mating of winged males in the male-dimorphic ant <Emphasis Type="Italic">Cardiocondyla minutior</Emphasis>

Only winged male and female ants generally mate through nuptial flight during the reproductive season. In the ants of Cardiocondyla, the males show wing dimorphism and their reproductive strategies differ depending on the differences in wing morphology. It has been suggested that wingless “ergatoid” males bearing very similar external morphologies to workers mate within natal nests, whereas winged males bearing typical ant male morphology disperse from their nests to mate. However, some behavioral observations suggest that the winged males of some Cardiocondyla ants such as C. obscurior and C. minutior may mate within natal nests before dispersion. We evaluated the factors affecting the mating behaviors of the winged males of C. minutior under laboratory conditions. We found that (1) the winged males remained and mated with virgin females in natal nests when either virgin winged females or the relatively mature pupae of winged females (i.e., at least 10 days) were present in the nest, (2) the winged males dispersed to adjacent nests with virgin winged females when only mated queens and the relatively young pupae of winged females (i.e., <9 days) were present in the nest, and (3) all winged males were accepted by the workers of non-natal nests irrespective of the distance from the natal nests in the field. Although most ergatoid males were accepted by the workers of close non-natal nests, they were all attacked and killed by the workers of distant non-natal nests. These results suggest that intra-nest mating and the dispersion of the winged males of C. minutior are facultatively determined by the condition of winged females (virginity and relative pupal age) in natal nests. Furthermore, our results suggest that winged males are likely to seek mating partners chemically and to mate with virgin winged females.     

Cuticular lipid profiles of fertile and non-fertile Cardiocondyla ant queens

Both mating and reproduction strongly affect the physiology of insect females. In the ant Cardiocondyla obscurior, a comparison among virgin queens, mated queens, and queens mated with sterilized males ("sham-mated") allows to separate the different effects of mating and egg laying. Here, we investigate whether and how different mating status is reflected in the cuticular lipid profiles of queens, i.e., the blend of chemicals that is thought to signal a queen's fertility. Surprisingly, discriminant analyses failed to reliably distinguish among virgin, mated, and sham-mated queens. A generalized linear model on individual substances showed only very subtle differences. While mating appeared to be positively associated with the proportions of 3-MeC(25,) 11-/13-MeC(27), 5-MeC(27), 3-MeC(27), and 12-/14-MeC(28) and negatively with C(27:1), fecundity was negatively associated with C(29:1), C(31:1), and a sterol derivative. We discuss these results in the light of the special life history of C. obscurior, with completely sterile workers and low egg laying rates in queens.     

Queen reproductive state modulates pheromone production and queen-worker interactions in honeybees

The mandibular glands of queen honeybees produce a pheromone that modulates many aspects of worker honeybee physiology and behavior and is critical for colony social organization. The exact chemical blend produced by the queen differs between virgin and mated, laying queens. Here, we investigate the role of mating and reproductive state on queen pheromone production and worker responses. Virgin queens, naturally mated queens, and queens instrumentally inseminated with either semen or saline were collected 2 days after mating or insemination. Naturally mated queens had the most activated ovaries and the most distinct chemical profile in their mandibular glands. Instrumentally inseminated queens were intermediate between virgins and naturally mated queens for both ovary activation and chemical profiles. There were no significant differences between semen- and saline-inseminated queens. Workers were preferentially attracted to the mandibular gland extracts from queens with significantly more activated ovaries. These studies suggest that the queen pheromone blend is modulated by the reproductive status of the queens, and workers can detect these subtle differences and are more responsive to queens with higher reproductive potential. Furthermore, it appears as if insemination substance does not strongly affect physiological characteristics of honeybee queens 2 days after insemination, suggesting that the insemination process or volume is responsible for stimulating these early postmating changes in honeybee queens.     

Stay or drift? Queen acceptance in the ant <Emphasis Type="Italic">Formica paralugubris</Emphasis>

The acceptance of new queens in ant colonies has profound effects on colony kin structure and inclusive fitness of workers. Therefore, it is important to study the recognition and discrimination behaviour of workers towards reproductive individuals entering established colonies. We examined the acceptance rate of queens in populations of the highly polygynous ant F. paralugubris, where the genetic differentiation among nests and discrimination ability among workers suggest that workers might reject foreign queens. We experimentally introduced young queens in their natal nest and in foreign nests. Surprisingly, the survival rate of mated queens did not differ significantly when introduced in a foreign male-producing nest, a foreign female-producing nest, or the natal nest. Moreover, the survival of virgin queens in their natal nest was twice the one of mated queens, suggesting that mating status plays an important role for acceptance. The results indicate that other factors than queen discrimination by workers are implicated in the limited longdistance gene flow between nests in these populations. Received 8 April 2008; revised 16 June 2008; accepted 1 July 2008.     

Breeding system, colony and population structure in the weaver ant Oecophylla smaragdina

Weaver ants ( Oecophylla smaragdina ) are dominant ants in open forests from India, Australia, China and Southeast Asia, whose leaf nests are held together with larval silk. The species, together with its sole congener O. longinoda , has been important in research on biological control, communication, territoriality and colony integration. Over most of the range, only one queen has been found per colony, but the occurrence of several queens per nest has been reported for the Australian Northern Territory. The number of males mating with each queen is little known. Here we report on the colony structure of O. smaragdina using published and new microsatellite markers. Worker genotype arrays reflect the occurrence of habitual polygyny (more than one queen per colony) in 18 colonies from Darwin, Northern Australia, with up to five queens inferred per colony. Monogyny (one queen per colony) with occasional polygyny was inferred for 14 colonies from Queensland, Australia, and 20 colonies from Java, Indonesia. Direct genotyping of the sperm carried by 77 Queensland queens and worker genotypic arrays of established colonies yielded similar results, indicating that less than half of the queens mate only once and some mate up to five times. Worker genotype arrays indicated that queens from Java and the Northern Territory also often mate with more than one male, but less often than those from Queensland. A strong isolation-by-distance effect was found for Queensland samples. The variation uncovered means that O. smaragdina is a more versatile study system than previously supposed.     

Polygynous supercolonies of the acacia‐ant Pseudomyrmex peperi,an inferior colony founder

In ant–plant protection mutualisms, plants provide nesting space and nutrition to defending ants. Several plant–ants are polygynous. Possessing more than one queen per colony can reduce nestmate relatedness and consequently the inclusive fitness of workers. Here, we investigated the colony structure of the obligate acacia‐ant Pseudomyrmex peperi, which competes for nesting space with several congeneric and sympatric species. Pseudomyrmex peperi had a lower colony founding success than its congeners and thus, appears to be competitively inferior during the early stages of colony development. Aggression assays showed that P. peperi establishes distinct, but highly polygynous supercolonies, which can inhabit large clusters of host trees. Analysing queens, workers, males and virgin queens from two supercolonies with eight polymorphic microsatellite markers revealed a maximum of three alleles per locus within a colony and, thus, high relatedness among nestmates. Colonies had probably been founded by one singly mated queen and supercolonies resulted from intranidal mating among colony‐derived males and daughter queens. This strategy allows colonies to grow by budding and to occupy individual plant clusters for time spans that are longer than an individual queen’s life. Ancestral states reconstruction indicated that polygyny represents the derived state within obligate acacia‐ants. We suggest that the extreme polygyny of Pseudomyrmex peperi, which is achieved by intranidal mating and thereby maintains high nestmate relatedness, might play an important role for species coexistence in a dynamic and competitive habitat.