金毛弓背蚁行为谱与社会分工的研究

本研究在室内模拟自然蚁巢的结构和条件下,使用个体标记和直接观察法对一巢金毛弓背蚁Componotus tonkinus的行为类型和社会分工进行了研究。共34只来自同一巢穴的工蚁被标记。在持续一周的观察过程中对每只蚂蚁所执行的每种行为的频率进行了统计和聚类分析。结果表明：金毛弓背蚁可以区分出12种基本行为类型;该蚂蚁的成员大致可以分为5个功能组, 即繁殖（蚁后1个）、觅食（由10个工蚁组成,主要负责觅食）、巢穴内的维护及护育（由16个工蚁组成,主要负责巢穴的维修、清理及护育）、巢穴的防卫（包括3个工蚁,行巢穴防卫）及不活跃型（含5个工蚁）。     

Cuticular hydrocarbons correlated with reproductive status in a queenless ant

Reproductive division of labour is regulated behaviourally in social insects lacking morphologically specialized castes. The directional nature of dominance interactions shows that recognition occurs, but little is known about its basis. In the queenless ant Dinoponera quadriceps, the top worker in the hierarchy (''alpha'') mates and produces offspring in each colony, while other workers remain virgin. Dominant ants frequently rub one antenna of subordinates against their own cuticle, and alpha and infertile nest-mates consistently differ in their relative proportions of the cuticular hydrocarbon 9-hentriacontene (9-C₃₁). The second-ranking ''beta'' occasionally lays unfertilized eggs and we show that she has less 9-C₃₁ than the alpha but more than infertile workers. To investigate further the link between 9-C₃₁ and ovarian activity, we experimentally removed alpha workers (n=11 individuals) and used solid-phase microextraction (SPME) with gas chromatography to measure changes in 9-C₃₁ on live beta workers which attained alpha status. The proportion of 9-C₃₁ on the replacement alpha increased significantly after six weeks, in parallel with her gain in fecundity. We discuss whether 9-C₃₁ provides honest information about egg-laying ability, enabling ants to recognize the different classes of nest-mates involved in reproductive conflicts. Such fertility cues could reliably underpin the antagonistic interactions occurring in insect societies.     

Reproductive conflicts affect labor and immune defense in the queenless ant Diacamma sp. "nilgiri"

In many species of social Hymenoptera, totipotency of workers induces potential conflicts over reproduction. However, actual conflicts remain rare despite the existence of a high reproductive skew. One of the current hypotheses assumes that conflicts are costly and thus selected against. We studied the costs of conflicts in 20 colonies of the queenless ant Diacamma sp. "nilgiri" by testing the effects of conflicts on labor and worker immunocompetence, two parameters closely linked to the indirect fitness of workers. In this species, the dominant female is the only mated worker (gamergate) and monopolizes reproduction. We experimentally induced conflicts by splitting each colony into two groups, a control group containing the gamergate and an orphaned group displaying aggressions until a new dominant worker arises. Immunocompetence was assessed by the clearance of Escherichia coli bacteria that we injected into the ants. Time budget analysis revealed a lower rate of labor and especially brood care in orphaned groups, supporting the existence of a cost of conflicts on labor. Fifteen days after splitting, a lower immunocompetence was also found in orphaned groups, which concerned workers involved and not involved in conflicts. We propose that this immunosuppression induced by conflicts could stem from stress and not directly from aggression.     

Reproductive monopoly enforced by sterile police workers in a queenless ant

In societies of totipotent insects, dyadic dominance interactionsgenerate a hierarchy that often underlies an extreme reproductiveskew. Subordinates remain infertile but can maximize their indirectfitness benefits through collective power (worker policing):interference with challenging high-rankers can prevent an untimelyreplacement of the reproductive. However, police workers onlybenefit if they favor individuals with high fertility. In themonogynous queenless ant Streblognathus peetersi, we used behavioral,physiological, and chemical methods to show that police workershave the primary role in the selection of the reproductive,and that they probably use reliable information about fertilityencoded in the cuticular hydrocarbons to make their decision.We successfully decreased an alpha's fertility by using a hormonaltreatment (Pyriproxyfen, a juvenile hormone analogue), and shewas always removed from the hierarchy by police workers. Inthe preceding days, one of the high-rankers became aggressive,although her interactions were not directed at the treated alpha.All treated alphas (n = 10) remained aggressive but ended upimmobilized by low-ranking workers after a median time of 11.5days. By then, the challenging high ranker exhibited dominancebehaviors typical of the alpha rank. In parallel, the cuticularprofile of the treated alpha exhibited predictable and oppositemodifications to that of the challenger's. This is the firststudy that uncouples dominance and fertility in a social insect:it gives a better understanding of the crucial role of sterilehelpers in the control of reproductive skew in animal societies.     

Reproductive division of labor between hybrid and nonhybrid offspring in a fire ant hybrid zone

Abstract.— Interspecific hybridization can often impose a substantial fitness cost due to reduced hybrid viability or fecundity. In social insects, however, such costs disproportionately impact reproductive offspring, whereas hybrids who become sterile workers can be functional, and even beneficial, colony members. Genomic imprinting of the paternal genome in reproductive, but not worker female offspring has been proposed as a mechanism to avoid genomic incompatibilities in hybrid queens in a hybrid zone between two fire ant species, Solenopsis geminata and S. xyloni. A study of allozyme variation demonstrated differences between the worker caste displaying a hybrid phenotype, and the winged queen caste displaying only the mother's phenotype. In this study, we investigate whether these differences are caused by genomic imprinting or genetic differences between castes by comparing variability of proteins to that of microsatellite markers. Workers and winged queens differed genetically at both classes of marker, indicating that allozyme differences were caused by underlying genetic differences between castes rather than differences in gene expression due to imprinting. Workers were F1 S. geminata X S. xyloni hybrids, whereas nearly all winged queens were of pure S. xyloni ancestry. Thus, S. xyloni within the hybrid zone appears to have evolved social hybridogenesis, in which the loss of worker potential in pure-species offspring necessitates hybridization for worker production, but prevents hybrids from being represented in the reproductive caste.     

Dominance hierarchy and reproductive conflicts among subordinates in a monogynous queenless ant

In insect societies lacking morphologically specialized breedersand helpers, reproduction is often restricted to behaviorallydominant individuals. Such societies occur in about 100 speciesof ants that have secondarily lost the queen caste. All females,who are morphologically workers, can potentially mate and layeggs but only a few do so, and we demonstrate in Dinoponeraquadriceps that this is regulated by a dominance hierarchy.Six types of agonistic interactions allowed the ranking of 5-10workers in the hierarchy (n = 15 colonies). In particular, alphaand beta had characteristic behavioral profiles and were easily recognized.Only alpha mated, and workers ranking beta to delta sometimes producedunfertilized, male-destined eggs. Natural replacements (n = 19)and experimental removals (n = 15) of alpha demonstrated that betawas the individual most likely to replace alpha, although gammaand more rarely delta sometimes did, and we discuss the conflictthat occurs among high-ranking individuals over who should replacealpha. After such replacements, the new alpha behaved more aggressivelythan the overthrown alpha. Newly emerged workers tended to reachhigh ranks and displaced older high-ranking individuals downthe hierarchy. Low-ranking subordinates often prevented high-rankingindividuals from replacing alpha by biting and holding theirappendages (worker policing), which is consistent with the patternof relatedness associated with monogyny and monandry in D. quadriceps. Weinvestigated the relative importance of chemical communicationand dominance interactions to regulate reproduction. Alpha,beta, and sterile workers have different signatures of cuticularhydrocarbons, and these may provide honest information whichunderpins worker policing by low-ranking individuals.     

Lay eggs, live longer: division of labor and life span in a clonal ant species

Abstract Due to a trade-off between reproduction and life span, highly fertile individuals often live shorter lives than nonreproductive conspecifics. Perennial eusocial insects are exceptional in that reproductive queens live considerably longer than the nonreproductive workers. The two female castes may differ strongly in morphology, ontogeny, physiology, diet, behavior, and mating, and all these differences could be responsible for life span differences. In the ponerine ant Platythyrea punctata , morphological and ontogenetic caste differences do not exist. Instead, all workers are capable of producing diploid offspring through thelytokous parthenogenesis, and colonies are essentially clones. Here, we show that reproductives live significantly longer than nonreproductive workers. Reproductives stay in the nest during their whole life, whereas nonreproductives switch from intranidal tasks to foraging when they get older. Different work load and different hormone titers might proximately underlie the different life span of reproductives and nonreproductives in this ant.     

Regulation of reproduction in a queenless ant: aggression,pheromones and reduction in conflict

In the monogynous queenless ant Diacamma ceylonense, the future reproductive (future gamergate) is very aggressive towards infertile workers during the first days of her adult life. Overt aggression disappears at about three weeks, when the future gamergate begins to lay male-destined eggs and is ready to mate. Over the same period, her cuticular hydrocarbon profile alters, changing from a chemical signature similar to that of a sterile worker towards that of a gamergate. In nature, these behavioural and chemical changes will coincide with a reduction in conflict within the nest: faced with a virgin future gamergate, infertile workers have an interest in producing male-destined eggs; however, once the gamergate produces female eggs, they have an interest in rearing her offspring. This demonstration of a shift from physical inhibition to chemical signalling is interpreted in terms of sociogenetic theory, the role of cuticular hydrocarbons as an indicator of fertility in insects and the fact that the regulation of reproduction in Diacamma involves mechanisms redolent of both queenless and queenright ant species.     

Very low genetic variability in the Indian queenless ant Diacamma indicum

Abstract We developed microsatellite markers and combined them with mitochondrial markers to analyse the population genetic structure of the queenless ant Diacamma indicum. This species, lacking winged queens, is likely to have a restricted female dispersal but exhibits various life history traits suggesting higher dispersal abilities than the other Diacamma species. Only 4 of 11 microsatellites were polymorphic and only 1 had more than 4 alleles over 166 individuals originating from 7 populations from the south of India. Only one mitochondrial DNA (mtDNA) haplotype was detected throughout India (including one population in the north) and Sri Lanka. Such a level of polymorphism is particularly low compared with other Diacamma species having much smaller ranges in the south of India. A strong genetic differentiation was observed between populations separated by more than a few kilometres. We also analysed the genetic differentiation between the Indian populations and two populations from the Japanese island of Okinawa, which are morphologically similar and might belong to the same species. The genetic differentiation was high for both markers, suggesting an absence of ongoing gene flow between these populations.     

Nestmate discrimination in the queenless ponerine ant Diacamma sp. from Japan

We examined the nestmate discrimination ability of Diacamma sp., an ant that reproduces by colony budding. We also tested for a relationship between internest distance and hostility. Hostility toward non‐nestmates was significantly stronger than that toward nestmates, suggesting that Diacamma sp. discriminates between nestmates and non‐nestmates. There was no significant correlation between internest hostility and internest distance, which indicates the absence of a “dear enemy” phenomenon in this species.     

Sex-specific asymmetries in communication sound perception are not related to hand preference in an early primate

Background  

Left hemispheric dominance of language processing and handedness, previously thought to be unique to humans, is currently under debate. To gain an insight into the origin of lateralization in primates, we have studied gray mouse lemurs, suggested to represent the most ancestral primate condition. We explored potential functional asymmetries on the behavioral level by applying a combined handedness and auditory perception task. For testing handedness, we used a forced food-grasping task. For testing auditory perception, we adapted the head turn paradigm, originally established for exploring hemispheric specializations in conspecific sound processing in Old World monkeys, and exposed 38 subjects to control sounds and conspecific communication sounds of positive and negative emotional valence.     

Population genetic structure and male-biased dispersal in the queenless ant Diacamma cyaneiventre

In this study we investigated the population genetic structure of the queenless ant Diacamma cyaneiventre. This species, lacking winged queens, is likely to have a restricted female dispersal. We used both mitochondrial and microsatellite markers to assess the consequence of such restricted female dispersal at three geographical scales: within a given locality (< 1 km), between localities within a given region (< 10 km) and between regions (> 36 km). Within a locality, a strong population structure was observed for mitochondrial DNA (mtDNA) whereas weak or nonexistent population genetic structure was observed for the microsatellites (around 5% of the value for mtDNA). Male gene flow was estimated to be about 20-30 times higher than female gene flow at this scale. At a larger spatial scale, very strong genetic differentiation for both markers was observed between localities - even within a single region. Female dispersal is nonexistent at these scales and male dispersal is very restricted, especially between regions. The phylogeographical structure of the mtDNA haplotypes as well as the very low genetic diversity of mtDNA within localities indicate that new sites are colonized by a single migration event from adjacent localities, followed by successive colony fissions. These patterns of genetic variability and differentiation agree with what is theoretically expected when colonization events are kin-structured and when, following colonization, dispersion is mainly performed by males.     

Seasonality, division of labor, and dynamics of colony-level nutrient storage in the ant Pheidole morrisi

Nutritional provisioning is a critical component of life history strategies, and of particular interest in social insect colonies because of the role that division of labor plays in resource allocation. To explore the mechanisms that underlie colony nutritional strategies, I examined three populations of the ant Pheidole morrisi across a gradient of overwinter food scarcity over two seasons. P. morrisi colonies were found to employ amixed strategy of fat storage with regard to a longer overwinter period: members of both worker castes increase their percent-fat in a graded manner, while the proportion of a specialized subcaste of majors known as “repletes”, also increased within the colony. Geographic variation in other colony traits such as mean colony size, mean worker size, and minor/major caste ratio were also found, although not always in a manner clearly relating to fat storage. These results indicate that colony demography responds to seasonal fluctuations in food availability through behavioral alterations (increased fat stores and recruitment of replete workers) rather than physical alterations (changes in lean body sizes or caste ratio). The findings illustrate the dynamic role division of labor plays in the success of insect colonies confronting environmental variability. Received 9 May 2006; revised 19 July 2006; accepted 24 July 2006.     

Self-organized asymmetries in ant foraging: a functional response to food type and colony needs

The dominant paradigm to explain asymmetries in the spatialdistribution of foraging animals is that they track the spatialheterogeneity of their environment. However, in social insects,endogenous spatial asymmetries can emerge within a uniformenvironment as an outcome from the self-organizing processof trail recruitment. We studied how self-organized asymmetries contribute to the exploitation of different food sources (carbohydrateor proteins) in colonies of the aphid-tending ant Lasius nigervarying in their nutritional needs (presence or absence ofbrood). Colonies with brood fed on sucrose sources exhibita higher mobilization of foragers than the other experimentalgroups. Foraging patterns differ greatly according to food type: colonies strongly focus their activity on only one dropletof sucrose, whereas they show a rather homogeneous distributionof foragers between proteinaceous sources. In addition, thepresence of brood in the colony enhances the asymmetry of collectiveforaging for both types of food. These spatial differencesin self-organized foraging patterns allow efficient exploitationof natural resources and play a role in the competitive strategy of this widespread palearctic ant.     

Coupled adult-brood transport augments relocation in the Indian queenless ant Diacamma indicum

Colony relocation is an important aspect in the lives of social insects. In ants, the process of relocation is further complicated as brood, in addition to adults, have to be transported to the new nest. Here, we have investigated brood transport in the Indian ponerine ant Diacamma indicum, which uses tandem running—a primitive mode of recruitment—for the entire colony to relocate. We have found that there were no brood transport specialists and most of the brood was transported in the mandibles of followers that were being tandem run. Therefore, in a single tandem run, one adult and one brood item was effectively transported by tandem leaders augmenting the relocation process.