Is the postpharyngeal gland of a solitary digger wasp homologous to ants? Evidence from chemistry and physiology

The postpharyngeal gland (PPG) was thought to be restricted to ants where it serves a crucial function in the generation of the colony odour. Recently, head glands that closely resemble the PPG of ants were discovered in females of a solitary digger wasp, the European beewolf. The function of this gland necessarily differs from ants: beewolf females apply the secretion of their PPG onto the bodies of paralysed honeybees that serve as larval provisions in order to delay fungus growth. Since ants and digger wasps are not closely related, the occurrence of this gland in these two taxa might either be due to convergent evolution or it is a homologous organ inherited from a common ancestor. Here we test the hypothesis that the PPGs of both taxa are homologous by comparing characteristics of chemical composition and physiology of the PPG of beewolves and ants. Based on reported characteristics of the PPG content of ants, we tested three predictions that were all met. First, the PPG of beewolves contained mainly long-chain hydrocarbons and very few compounds with functional groups. Second, the composition of hydrocarbons in the beewolf PPG was similar to that of the hemolymph. Taking the structure of the gland epithelium and the huge requirements of beewolf females for gland secretion into account this result suggests that the content of the PPG is also sequestered from the hemolymph in beewolves. Third, the chemical composition of the PPG and the cuticle was similar in beewolves since cuticular hydrocarbons derive either from the hemolymph or the PPG. Taking the considerable morphological similarities into account, our results support the hypothesis of a homologous origin of the PPG in beewolves and ants

Recognition in Ants: Social Origin Matters

The ability of group members to discriminate against foreigners is a keystone in the evolution of sociality. In social insects, colony social structure (number of queens) is generally thought to influence abilities of resident workers to discriminate between nestmates and non-nestmates. However, whether social origin of introduced individuals has an effect on their acceptance in conspecific colonies remains poorly explored. Using egg-acceptance bioassays, we tested the influence of social origin of queen-laid eggs on their acceptance by foreign workers in the ant Formica selysi. We showed that workers from both single- and multiple-queen colonies discriminated against foreign eggs from single-queen colonies, whereas they surprisingly accepted foreign eggs from multiple-queen colonies. Chemical analyses then demonstrated that social origins of eggs and workers could be discriminated on the basis of their chemical profiles, a signal generally involved in nestmate discrimination. These findings provide the first evidence in social insects that social origins of eggs interfere with nestmate discrimination and are encoded by chemical signatures

Unicoloniality in Reticulitermes urbis: a novel feature in a potentially invasive termite species.

International audienceSocial insects are among the world's most successful species at invading of new habitats. A good example of this invasive ability is Reticulitermes (Rhinotermitidae), a prominent group of subterranean termites. As a result of human intervention, i.e. transportation and creation of urban heat islands, Reticulitermes have been able to invade and thrive in cities located in areas where the natural habitat is normally too cold for colonization. They commonly infest man-made structures where they can cause extensive damage.This study was designed to evaluate the invasiveness of Reticulitermes urbis that was probably introduced in France from the Balkans. Invasive potential was assessed on the basis of features typical to invasive social insects, i.e. unicoloniality, low intraspecific aggression, high level of polygyny and colony reproduction by budding. The opportunity to study establishment and spreading processes arose after extensive sampling of an imported Reticulitermes urbis population was performed over the entire city of Dom?, France (Rh?Alpes region).For the first time, genetic analysis showed that the termites belonged to a single 'genetic entity' forming a vast colony covering about seven hectares. The colony was structured as an extended family with separate reproductive centres. We speculate that termites were introduced in a single location from which they gradually budded throughout the old town. Based on the absence of aggression among different nests within the colony, we defined this 'genetic entity' as a supercolony

Facultative social parasites mark host nests with branched hydrocarbons

International audienceThe chemical integration strategies of facultative social parasites of social insects have not received thescientific attention they deserve, even though there is considerable research being done on the strategiesof obligate social parasites. We simulated intraspecific nest usurpations in the social paper wasp, Polistesbiglumis, by dividing each nest into two parts and putting one half in the care of the original foundressand the other half in the care of a usurper. After 8 days, we removed and killed foundresses and usurpers,and later tested the responses of naïve, sister-offspring to them. In each half-colony, the offspring weremore tolerant to the female that was last on the nest, regardless of whether she was the foundress ora usurper. This suggested that usurpers had the chemical means to be tolerated by the host offspring.Comparisons between the epicuticular hydrocarbon profiles of foundresses and usurpers showed thatusurpers were neither chemically insignificant nor transparent, nor were they mimetic, as obligateparasites often are. Instead, usurpers had chemical profiles richer in methyl-branched hydrocarbons thanthose of the foundresses. Analyses of the hydrocarbon profiles of nest paper revealed that usurperssupplemented host nests with their own hydrocarbons, a sort of nest marking. As a result, the chemicalprofiles of the host nests became qualitatively more similar to those of the usurpers. These chemicalstrategies illustrate that branched hydrocarbons play a role as semiochemicals and that facultativeparasites may not all be on the main pathway to obligate parasitism. 2011 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.Parasites exploit any resources that free-living organisms offer:from molecular engines to whole cells, from whole organisms tothe structures they make. In their struggle to exploit hosts, parasitesprovide some of the best evidence of adaptation by naturalselection. Brood parasites are species that do not target organismsbut rather the resources that free-living organisms build orproduce: their nests, their parental care and/or their social structures(Wilson 1971; Rothstein 1990). Brood parasites exhibit traitsthat give them an advantage in fooling and exploiting their hostsand these traits are the results of reciprocal hosteparasite interactionsacross evolutionary time (Brooke & Davies 1988). Therecognition system

High occurrence of colony fusion in a European population of the American termite Reticulitermes flavipes

International audienceThe coexistence of multiple unrelated reproductives within social insect colonies decreases the relatedness among colony members and therefore challenges kin selection theory. This study investigated the colony genetic structure of a French introduced population of the American subterranean termite Reticulitermes flavipes by analyzing genotypes at eight microsatellite loci and at one mtDNA region. Results revealed that all colonies contained numerous related secondary reproductives, and that 31% of colonies possessed more than two unrelated reproductives. The presence of several unrelated reproductives within colonies of this species is commonly assumed to result from colony fusion. Although such a high occurrence of colony fusion is the highest ever observed in a termite population, it is probable that the available methodology underestimated the detection of colony fusion in French populations. Overall, these results suggest that French colonies might differ strongly from the great majority of American colonies in their capacity to produce secondary reproductives as well as in their ability to merge. The nature and evolutionary origin of these population differences are discussed

Synchronized evolution of the chemical signature of Reticulitermes Endogenous synchronization of the chemical signature of Reticulitermes (Isoptera, Rhinotermitidae) worker termites

National audienceTermites of the genus Reticulitermes are characteristic of temperate regions. Their colonies comprise various castes, the most numerous being that of workers which can develop into soldiers or secondary reproductives (neotenics). Each caste has a mixture of hydrocarbons (HCs) on the cuticle forming a chemical signature. The primary aim of this study was to compare the changes in the chemical signature of a population of worker termites fed on paper with juvenile hormone to differentiate them into soldiers with a control population of termites fed only on paper or wood for one month. Gas chromatography was used to analyze the cuticular profi les of Reticulitermes fl avipestermites to determine whether they changed, and, if so, when and how. The data collected over one month showed that the workers fed with JH did not differentiate into soldiers but that there were progressive changes in the hydrocarbon profi le independent of the treatment. These results indicate that the differentiation of the chemical signature of the worker caste is a dynamic process, depending only on time and not on colony membership, confi rming that, for these termites, this signature has a lesser role in colony membership than caste membership, unlike the chemical signatures of other social insects. The temporal process of this cuticular change is also associated with a change in the alkene / methyl-branched alkane rati

Chemical Heterogeneity in Inbred European Population of the Invasive Hornet Vespa velutina nigrithorax

International audienceInvasive social insect populations that have been introduced to a new environment through a limited number of introduction events generally exhibit reduced variability in their chemical signatures (cuticular hydrocarbons) compared to native populations of the same species. The reduced variability in these major recognition cues could be caused by a reduction of genetic diversity due to a genetic bottleneck. This hypothesis was tested in an inbred European population of the in-vasive hornet Vespa velutina nigrithorax. Our results show that, in spite of the limited amount of genetic diversity present in the European population, the chemical signatures of individuals were highly heterogeneous according to their caste, sex, and colony origin. In queens, some specific saturated and unsaturated hydrocarbons were identified. These results suggest that epi-genetic and/or environmental factors could play a role in modifying cuticular hydrocarbon profiles in this introduced hornet population despite the observed reduction of genetic diversity