Workers and queens of the European hornetVespa crabro L. have colony-specific cuticular hydrocarbon profiles (Hymenoptera: Vespidae)

Summary Cuticular hydrocarbons were extracted from sixty individual workers from six colonies ofVespa crabro L. and analyzed by combined gas-chromatography/mass spectrometry. Discriminant analysis of the cuticular hydrocarbon profiles of workers and queens showed that the wasps could be grouped by colony and by caste. Stepwise discriminant analysis selected the components which were weighted most heavily in these analyses. Different combinations of cuticular hydrocarbons were important in grouping workers by colony, queens and workers by colony, and workers and queens by caste.     

Aggression,cooperation, and relatedness among colonies of the invasive ant, <Emphasis Type="Italic">Monomorium pharaonis</Emphasis>, originating from different areas of the world

The cooperation and aggression between five laboratory colonies of Monomorium pharaonis were compared using an aggressiveness test and pupa-carrying test in laboratory arenas. The colonies were derived from field collections in different parts of Europe and USA. Generally, inter-colony aggressiveness was low and acceptance of pupae from other colonies was high. Workers from one colony (Lužiny, CZ), however, frequently displayed aggressive behavior when paired with workers from other colonies, and the Lužiny pupae were avoided by workers of other colonies in pupa-carrying tests. Behavioral tests were only partly consistent with the phylogenetic relatedness of ants because the Wisconsin colony (USA) grouped with the Lužiny colony (and not with the other three colonies) in the phylogenetic analysis but grouped with the other three colonies in the behavioral tests.     

Colony‐age‐dependent variation in cuticular hydrocarbon profiles in subterranean termite colonies

Cuticular hydrocarbons (CHCs) have, in insects, important physiological and ecological functions, such as protection against desiccation and as semiochemicals in social taxa, including termites. CHCs are, in termites, known to vary qualitatively and/or quantitatively among species, populations, castes, or seasons. Changes to hydrocarbon profile composition have been linked to varying degrees of aggression between termite colonies, although the variability of results among studies suggests that additional factors might have been involved. One source of such variability may be colony age, as termite colony demographics significantly change over time, with different caste and instar compositions throughout the life of the colony. We here hypothesize that the intracolonial chemical profile heterogeneity would be high in incipient termite colonies but would homogenize over time as a colony ages and accumulates older workers in improved homeostatic conditions. We studied caste‐specific patterns of CHC profiles in Coptotermes gestroi colonies of four different age classes (6, 18, 30, and 42 months). The CHC profiles were variable among castes in the youngest colonies, but progressively converged toward a colony‐wide homogenized chemical profile. Young colonies had a less‐defined CHC identity, which implies a potentially high acceptance threshold for non‐nestmates conspecifics in young colonies. Our results also suggest that there was no selective pressure for an early‐defined colony CHC profile to evolve in termites, potentially allowing an incipient colony to merge nonagonistically with another conspecific incipient colony, with both colonies indirectly and passively avoiding mutual destruction as a result.     

Nest volatiles as modulators of nestmate recognition in the ant Camponotus fellah

When ants from alien colonies encounter each other the stereotypic reaction is usually one of aggressive behavior. It has been shown that factors such as queen-derived cues or nest-odors modulate this reaction. Here we examined whether nest volatiles affect nestmate recognition by observing the reaction of nestmates towards individual workers under one of four regimes: completely isolated; isolated but receiving a constant airflow from the mother colony; as previous but with the passage of nest volatiles towards the isolated ants blocked by adsorption on a SuperQ column; or reversed airflow direction-from the isolated ants to the nest interior. Ants that had been completely isolated for three weeks were subjected to aggressive behavior, but not those that had continued to receive airflow from the mother colony. Adsorbing the nest volatiles from the airflow by SuperQ abolished this difference, with these ants now also being subjected to aggression, indicating that nest volatiles can modulate nestmate recognition. Reverse airflow also reduced the level of aggression but to a lesser extent than airflow directed from the mother colony. In queenless colonies the overall aggression was reduced under all regimes, and there was no effect of flow, suggesting that the volatiles involved are queen-borne. The SuperQ adsorbed volatiles originated from Dufour's gland secretions of both workers and queen, implicating them in the process. Cuticular hydrocarbon profiles were not affected by exposure to nest volatiles, suggesting that the latter either constitute part of the recognition cues or affect worker behavior via a different, as yet elusive mechanism.     

Intraspecific aggression and the colony structure of the invasive ant Myrmica rubra

1. Patterns of aggression between ants from different nests influence colony and population structure. Several species of invasive ants lack colony boundaries over large expanses, forming ‘supercolonies’ with many nests among which workers can move without encountering aggression. 2. Bioassays of aggression were used to determine the colony structure of the invasive ant Myrmica rubra (L.) at eight sites in Massachusetts, the state where the species was first discovered in North America. To improve the ability to distinguish systematic patterns from background variability in aggressiveness, a repeated‐measures design was used and replicate assays for each pair of nests were conducted. 3. Aggressive responses showed that populations at all sites consisted of multiple distinct colonies. Patterns of aggression were repeatable and transitive, with few exceptions. Colonies were identified as clusters of nests whose workers showed little to no aggression towards one another but were aggressive towards conspecifics from more distant nests. 4. The degree of aggression varied considerably among different colony pairs but did not depend in any consistent way on the distance of separation or on whether colonies were neighbours. 5. Territories of neighbouring colonies abutted, indicating that they were restricted by intraspecific competition. Mapped territories ranged in size from 0.03 to 1.2 ha, but colonies at the study sites have not undergone the enormous expansions seen in introduced populations of some other species of invasive ants, and neighbouring colonies compete locally.     

Agonistic behavior correlated with hydrocarbon phenotypes in dampwood termites,Zootermopsis (Isoptera: Termopsidae)

The dampwood termite genus ZootermopsisEmerson contains three recognized species with four distinct and consistent hydrocarbon phenotypes. Agonistic behaviors among nonreproductive insects from colonies of the same and different hydrocarbon phenotypes were observed in the laboratory. Various combinations of soldier versus nymphs, pseudergate versus pseudergate, and soldier versus soldier encounters were used in experimental trials. Soldiers or pseudergates seldom attack individuals of the same hydrocarbon phenotype. Z. angusticollis(Hagen) (phenotype II) is typically aggressive toward phenotype III of Z. nevadensis(Hagen) but not always aggressive against phenotype I of Z. nevadensis.The variation in response is dependent on which castes are placed in the bioassay arena: soldier versus soldier bouts result in consistent aggression, while pseudergate versus pseudergate or soldier versus nymphs contacts do not. Both pseudergates and soldiers of Z. laticeps(Banks) (phenotype IV) respond agonistically toward the other three phenotypes: Z. angusticollis (II) and Z. nevadensis(I and III). Although hydrocarbon phenotypes I and III, both Z. nevadensis,are morphologically indistinguishable, agonistic behavioral responses between phenotype I and phenotype III are not equivalent to I versus I or III versus III behavioral responses. The I versus III engagements, regardless of the castes involved, display a greater proportion of avoidance and aggressive responses than I or III intraphenotype encounters. We interpret the lack of avoidance or aggressive behavior within each of the two phenotypes of Z. nevadensisand the significant avoidance and aggressive behavior between phenotypes as definite evidence of discrimination between disparate hydrocarbon phenotypes. These agonistic bioassays along with data on distinct hydrocarbon patterns and geographic distributions serve as the basis for creating two subspecies of Z. nevadensis: Z. n. nevadensis(Hagen) and Z. n. nuttingiHaverty and Thorne, ssp. nov.     

Colony-structure variation and interspecific competitive ability in the invasive Argentine ant

The success of some invasive species may depend on phenotypic changes that occur following introduction. In Argentine ants ( Linepithema humile) introduced populations typically lack intraspecific aggression, but native populations display such behavior commonly. We employ three approaches to examine how this behavioral shift might influence interspecific competitive ability. In a laboratory experiment, we reared colonies of Forelius mccooki with pairs of Argentine ant colonies that either did or did not exhibit intraspecific aggression. F. mccooki reared with intraspecifically non-aggressive pairs of Argentine ants produced fewer eggs, foraged less actively, and supported fewer living workers than those reared with intraspecifically aggressive pairs. At natural contact zones between competing colonies of L. humile and F. mccooki, the introduction of experimental Argentine ant colonies that fought with conspecific field colonies caused L. humile to abandon baits in the presence of F. mccooki, whereas the introduction of colonies that did not fight with field colonies of Argentine ants resulted in L. humile retaining possession of baits. Additional evidence for the potential importance of colony- structure variation comes from the Argentine ants native range. At a site along the Rio de la Plata in Argentina, we found an inverse relationship between ant richness and density of L. humile (apparently a function of local differences in colony structure) in two different years of sampling.     

Manipulation of colony environment modulates honey bee aggression and brain gene expression

The social environment plays an essential role in shaping behavior for most animals. Social effects on behavior are often linked to changes in brain gene expression. In the honey bee (Apis mellifera L.), social modulation of individual aggression allows colonies to adjust the intensity with which they defend their hive in response to predation threat. Previous research has showed social effects on both aggression and aggression‐related brain gene expression in honey bees, caused by alarm pheromone and unknown factors related to colony genotype. For example, some bees from less aggressive genetic stock reared in colonies with genetic predispositions toward increased aggression show both increased aggression and more aggressive‐like brain gene expression profiles. We tested the hypothesis that exposure to a colony environment influenced by high levels of predation threat results in increased aggression and aggressive‐like gene expression patterns in individual bees. We assessed gene expression using four marker genes. Experimentally induced predation threats modified behavior, but the effect was opposite of our predictions: disturbed colonies showed decreased aggression. Disturbed colonies also decreased foraging activity, suggesting that they did not habituate to threats; other explanations for this finding are discussed. Bees in disturbed colonies also showed changes in brain gene expression, some of which paralleled behavioral findings. These results show that bee aggression and associated molecular processes are subject to complex social influences .     

Brood reduction in temperate and sub-tropical ospreys

Summary In an effort to understand patterns and causes of nestling loss in Ospreys (Pandion haliaetus), I studied brood reduction in three eastern U.S. Osprey colonies during 1978 and 1979. The colonies, located in Florida Bay (1) and on coastal Long Island, N.Y. (2), differed in the average daily amount of food delivered to nestlings; Florida nests received 43% and 11% less fish per day than nests in the two N.Y. colonies, largely because latitude and season restricted day length and thus foraging time for the winter-breeding Florida Ospreys. Increased distance from stable food sources accounted for the lower rate of feeding at one of the N.Y. colonies. Variation in clutch size in the three colonies reflected differences in latitude more than in food availability; average clutch sizes in Long Island were larger than Florida clutches by 0.5 of an egg, but were similar to each other and to those in other northeastern U.S. Osprey populations.Increased nestling loss coincided with reduced food delivery rates and, in food stressed colonies, this loss was 2–3 times greater than any recorded for Ospreys. Starvation was the primary cause of nestling death, with mortality concentrated on third chicks, which hatched on average 3.9 d later and from eggs 5.6% smaller than chicks hatching first. Sibling aggression accounted for the preferential feeding of older nestmates,but only in colonies or nests where food was limited. Aggressive chicks nearly always stopped fighting after being fed. This behavior provided a reversible mechanism for controling brood reduction that was based on nutrition. Growth rates of young measured during the first half of the growth period were more variable between colonies than within nests. This is interpreted as reflecting both the differences in colony food delivery rates as well as the evolutionary pressures of sibling competition to equalize the growth of nestmates.     

Evaluation of DNA Fingerprinting, Aggression Tests, and Morphometry as Tools for Colony Delineation of the Formosan Subterranean Termite

Multilocus DNA fingerprinting, aggression tests, and morphometry were compared to evaluate their potential for the delineation of colonies of Coptotermes formosanus Shiraki (Isoptera; Rhinotermitidae) in Hawaii. DNA fingerprinting segregates the termites from all collection sites and allows the assignment of all individuals to their original collection site. The genetic similarity of termites from different collection sites approaches the population's genetic background similarity, consequently collection sites represent independent colonies. Aggression between colonies is comparatively low and does not provide reliable colony delineation. Morphometry allows a 79% classification rate of termites to their colony of origin. No correlation among genetic similarities, aggression levels, and morphometric distances is found. Of the three investigated methods, we conclude that the genetic approach is the most useful tool for colony delineation in C. formosanus.     

Intraspecific nestmate recognition in two parabiotic ant species: acquired recognition cues and low inter-colony discrimination

Parabiotic ants—ants that share their nest with another ant species—need to tolerate not only conspecific nestmates, but also nestmates of a foreign species. The parabiotic ants Camponotus rufifemur and Crematogaster modiglianii display high interspecific tolerance, which exceeds their respective partner colony and extends to alien colonies of the partner species. The tolerance appears to be related to unusual cuticular substances in both species. Both species possess hydrocarbons of unusually high chain lengths. In addition, Cr. modiglianii carries high quantities of hereto unknown compounds on its cuticle. These unusual features of the cuticular profiles may affect nestmate recognition within both respective species as well. In the present study, we therefore examined inter-colony discrimination within the two parabiotic species in relation to chemical differentiation. Cr. modiglianii was highly aggressive against workers from alien conspecific colonies in experimental confrontations. In spite of high inter-colony variation in the unknown compounds, however, Cr. modiglianii failed to differentiate between intracolonial and allocolonial unknown compounds. Instead, the cuticular hydrocarbons functioned as recognition cues despite low variation across colonies. Moreover, inter-colony aggression within Cr. modiglianii was significantly influenced by the presence of two methylbranched alkenes acquired from its Ca. rufifemur partner. Ca. rufifemur occurs in two varieties (‘red’ and ‘black’) with almost no overlap in their cuticular hydrocarbons. Workers of this species showed low aggression against conspecifics from foreign colonies of the same variety, but attacked workers from the respective other variety. The low inter-colony discrimination within a variety may be related to low chemical differentiation between the colonies. Ca. rufifemur majors elicited significantly more inter-colony aggression than medium-sized workers. This may be explained by the density of recognition cues: majors carried significantly higher quantities of cuticular hydrocarbons per body surface.     

The role of cuticular hydrocarbons as chemical cues for nestmate recognition in the invasive Argentine ant (<Emphasis Type="Italic">Linepithema humile</Emphasis>)

Argentine ants (Linepithema humile) in their native South American range, like most other ant species, form spatially restricted colonies that display high levels of aggression toward other such colonies. In their introduced range, Argentine ants are unicolonial and form massive supercolonies composed of numerous nests among which territorial boundaries are absent. Here we examine the role of cuticular hydrocarbons (CHCs) in nestmate recognition of this highly damaging invasive ant using three supercolonies from its introduced range. We conducted behavioral assays to test the response of Argentine ants to workers treated with colonymate or non-colonymate CHCs. Additionally, we quantified the amount of hydrocarbons transferred to individual ants and performed gas chromatography-mass spectrometry (GC/MS) to qualitatively characterize our manipulation of CHC profiles. The GC/MS data revealed marked differences in the hydrocarbon profiles across supercolonies and indicated that our treatment effectively masked the original chemical profile of the treated ants with the profile belonging to the foreign individuals. We found that individual workers treated with foreign CHCs were aggressively rejected by their colonymates and this behavior appears to be concentration-dependent: larger quantities of foreign CHCs triggered higher levels of aggression. Moreover, this response was not simply due to an increase in the amount of CHCs applied to the cuticle since treatment with high concentrations of nestmate CHCs did not trigger aggression.The results of this study bolster the findings of previous studies on social insects that have implicated CHCs as nestmate recognition cues and provide insight into the mechanisms of nestmate recognition in the invasive Argentine ant. Received 6 February 2007; revised 31 May and 27 July 2007; accepted 16 August 2007.     

Apparent Dear-enemy Phenomenon and Environment-based Recognition Cues in the Ant Leptothorax nylanderi

Inter- and intraspecific competition was investigated in ants of the myrmicine genus leptothorax in a deciduous woodland near Würzburg, Germany. The most common species, A. (Myrafant) nylanderi, lives in rotting pine, oak, and elder sticks and may locally reach densities of 10 nests per m². In the studied sites, only a small fraction of colonies were polydomous, i.e. single colonies typically did not inhabit several nest sites. The home ranges of nylanderi colonies overlap the ranges of other conspecific colonies and colonies of other species, especially L. (s.str.) gredleri. Foragers from different colonies encountering one another in the field back off without exhibiting strong aggression, suggesting that colonies do not defend absolute foraging territories. In laboratory experiments, the frequency and severity of agonistic interactions among workers from different colonies, all living in pine sticks, increased significantly with the distance between their nests. Workers from colonies nesting in different types of wood exhibited significantly more aggression. Experiments in which we transferred colonies from pine sticks into artificial pine or oak nests corroborate the hypothesis that nesting material strongly influences colony odour in L. nylanderi. The evolutionary significance of this apparent dear-enemy phenomenon is discussed.     

Per-capita productivity in a social wasp: no evidence for a negative effect of colony size

Optimal colony size in eusocial insects likely reflects a balance between ecological factors and factors intrinsic to the social group. In a seminal paper Michener (1964) showed for some species of social Hymenoptera that colony production of immature stages (productivity), when transformed to a per-female basis, was inversely related to colony size. He concluded that social patterns exist in the social insects that cause smaller groups to be more efficient than larger groups. This result has come to be known as “Michener’s paradox” because it suggests that selection on efficiency would oppose the evolution of the large and complex societies that are common in the social insects. Michener suggested that large colony size has other advantages, such as improved defense and homeostasis, that are favored by selection. For his analysis of swarm-founding wasps, Michener combined data from colonies of different species and different developmental stages in order to obtain adequate sample sizes; therefore, his study did not make a strong case that efficiency decreases with increasing colony size (across colonies) in these wasps. We tested Michener’s hypothesis on the Neotropical swarm-founding wasp Parachartergus fraternus, while controlling for stage of colony development. We found that small colonies were more variable in percapita productivity relative to larger colonies, but found no evidence for a negative relationship between efficiency and size across colonies. Received 1 February 2006; revised 5 May 2006; accepted 11 May 2006.     

The Effects of Water,Season, and Colony Composition on Foraging Preferences of <Emphasis Type="Italic">Pheidole ceres</Emphasis> [Hymenoptera: Formicidae]

Field colonies of the ant Pheidole ceres were presented with a choice between a protein source and a carbohydrate source, under wet and dry conditions, at three different times in the year. These time periods corresponded with different reproductive (the production of sexuals) and growth (the production of workers) stages of the colony. Moisture had no effect on the forging behavior of P. ceres but the colonies did change their foraging preferences during different times of the year. This behavior correlated with the amount of larvae in the colony. However, lab experiments demonstrated that larvae did not directly influence the foraging decisions of the workers but that adult reproductives did.     

Soldier diterpene patterns in relation with aggressive behaviour,spatial distribution and reproduction of colonies in Nasutitermes princeps

The territorial organization of the colonies of N. princeps (Desneux) (Isoptera: Temitidae) was studied by four methods: maps of nest systems, tests of aggressiveness, comparison of soldier diterpene patterns, and determination of the reproductive status of the nests. The diterpene patterns are rather variable among sympatric colonies, and allow the tracing of soldiers from their respective colonies throughout their foraging range. Soldiers from neighbouring nests display in some instances closely resembling diterpene patterns, suggesting close genetic relatedness and polycalic colonies, i.e. composed of several linked nests spread over large territories. Most likely, N, princeps colonies reproduce by budding. The number and type of reproductives found in the nests are consistent with this hypothesis. Tests of aggressiveness supported the above conclusions, but absence of aggression did not always indicate that the termites belonged to the same colony.     

Cuticular hydrocarbons in workers of the slave-making ant Polyergus samurai and its slave, Formica japonica (Hymenoptera: Formicidae)

Comparisons of cuticular hydrocarbons between workers of the dulotic ant Polyergus samurai and its slave, Formica japonica, were carried out. Gas chromatography–mass spectrometry showed that the slave‐maker and its slave shared the major cuticular hydrocarbon compounds, but possessed several minor products unique to each species. No difference in hydrocarbon composition was detected between enslaved and free‐living F. japonica workers, suggesting that association with P. samurai has no qualitative effect on hydrocarbon composition in these ants. Principal component analyses of the cuticular hydrocarbon profiles (CHP) revealed that (i) CHP was species specific in a given mixed colony; and (ii) among mixed colonies, P. samurai workers had species‐colony specific CHP, while the same feature was not always found in enslaved and free‐living F. japonica workers. Therefore, a ‘uniform colony odor’ in terms of CHP is not achieved in naturally mixed colonies of P. samurai nor those of its slaves, F. japonica.     

Testing the role of cuticular hydrocarbons on intercolonial agonism in two subterranean termite species (Coptotermes) and their hybrids

Recognition of nestmates is an important function in many social insects, as it maintains colony integrity by preventing outsiders from entering the colony. Agonism usually results from the interaction of con-specific non-nestmate individuals in termite colonies. Previous studies hypothesized that the cuticular hydrocarbon (CHC) profile of individuals had a role in nestmate recognition. However, contradictory results from previous studies in some subterranean termites raise questions on the validity of the cuticular hydrocarbon hypothesis. In the current study, Coptotermes gestroi (Wasmann), Coptotermes formosanus Shiraki and their hybrids were reared in identical conditions from colony foundation. This approach eliminates sources of variability in their cuticular hydrocarbon profiles aside from a genetic component. The parental species displayed dissimilar profiles of predominant alkanes and methyl alkanes, but both hybrid types displayed an overlapping, intermediate profile of these CHC. The mixture of the most abundant CHCs alone did not determine kin recognition; while the two hybrid types’ CHC profiles converged, the hybrids still showed strong agonism. One of the hybrid mating types easily merged with C. formosanus, despite only partial genetic similarity and dissimilar cuticular profiles for the common alkanes and methyl alkanes. This study suggests that in Coptotermes termites, the variable abundance of the major alkanes and methyl alkanes commonly found in most Coptotermes species does not explain agonistic patterns, and that other factors such as possibly more complex but less abundant CHC are likely to be involved in colonial recognition.

     

Tissue compatibility between colonies and between newly settled larvae of Pocillopora damicornis

Grafting experiments with newly settled larvae and with adult colonies of Pocillopora damicornis were performed. When pairs of newly settled larvae released from different colonies were kept in contact, they fused to form an aggregated colony. Even newly settled larvae derived from colonies belonging to different color morphs fused with each other and no sign of allogeneic rejection was observed. However, when branches of adult colonies belonging to different color morphs were kept in contact, they did not fuse. Fusion was observed only when branches derived from the same colony were paired. The present results suggest that juvenile corals lack the functional histocompatibility system as shown by adult colonies.     

Colony structure in introduced and native populations of the invasive Argentine ant, <Emphasis Type="Italic">Linepithema humile</Emphasis>

Summary. The Argentine ant, Linepithema humile, severely decreases the abundance and diversity of native ant fauna in areas where it invades, but coexists with a more diverse assemblage of ants in its native range. The greater ecological dominance of L. humile in the introduced range may be associated with differences in colony structure and population density in the introduced range relative to the native range. In this study, I compared aspects of L. humiles colony structure, including density, the spatial pattern of nests and trails, and patterns of intraspecific aggression in parts of the introduced and native ranges. I also compared the number of ant species coexisting with L. humile. Introduced and native populations did not differ significantly in nest density, ant density, nest size, and nearest-neighbor distances. In three of the four study populations in the native range and all of the study populations in the introduced range, colonies were organized into supercolonies: they consisted of multiple, interconnected nests that were dense and spatially clumped, and aggression among conspecifics was rare. In one population in the native range, colonies were organized differently: they occupied single nest sites, nests were sparse and randomly dispersed, and ants from neighboring nests were aggressive toward each other. Species richness was significantly higher in the native range than in the introduced range, even in areas where L. humile formed dense supercolonies. The results suggest that differences in species coexistence between ranges may due to factors other than L. humiles colony structure. One likely factor is the superior competitive ability of other ant species in the native range.Received 23 January 2004; revised 30 March 2004; accepted 20 April 2004.