@article{MaihoffBohlkeBrockmannetal.2022,
  author    = {Maihoff, Fabienne and Bohlke, Kyte and Brockmann, Axel and Schmitt, Thomas},
  title     = {Increased complexity of worker CHC profiles in Apis dorsata correlates with nesting ecology},
  series = {PLoS ONE},
  volume    = {17},
  journal   = {PLoS ONE},
  number    = {7},
  doi       = {10.1371/journal.pone.0271745},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-301353},
  year      = {2022},
  abstract  = {Cuticular hydrocarbons (CHC) are known to serve as discrimination cues and will trigger defence behaviour in a plethora of eusocial insects. However, little is known how about nestmate recognition ability selects for CHC diversification. In this study we investigate differences in CHC composition of four major honey bee species with respect to the differences in their nesting behavior. In contrast to A. mellifera, A. cerana and A. florea, the giant honey bee A. dorsata prefers to build their nests in aggregations with very small spatial distances between nests, which increases the probability of intrusions. Thus, A. dorsata exhibits a particularly challenging nesting behavior which we hypothesize should be accompanied with an improved nestmate recognition system. Comparative analyses of the worker CHC profiles indicate that A. dorsata workers exhibit a unique and more complex CHC profile than the other three honey bee species. This increased complexity is likely based on a developmental process that retains the capability to synthesize methyl-branched hydrocarbons as adults. Furthermore, two sets of behavioral experiments provide evidence that A. dorsata shows an improved nestmate discrimination ability compared to the phylogenetically ancestral A. florea, which is also open-nesting but does not form nest aggregations. The results of our study suggest that ecological traits like nesting in aggregation might be able to drive CHC profile diversification even in closely related insect species.},
  language  = {en}
}
@article{CastilloWurdackPaulietal.2022,
  author    = {Castillo, Ruth and Wurdack, Mareike and Pauli, Thomas and Keller, Alexander and Feldhaar, Heike and Polidori, Carlo and Niehuis, Oliver and Schmitt, Thomas},
  title     = {Evidence for a chemical arms race between cuckoo wasps of the genus Hedychrum and their distantly related host apoid wasps},
  series = {BMC Ecology and Evolution},
  volume    = {22},
  journal   = {BMC Ecology and Evolution},
  number    = {1},
  doi       = {10.1186/s12862-022-02093-8},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-301289},
  year      = {2022},
  abstract  = {Background Brood parasites can exert strong selection pressure on their hosts. Many brood parasites escape their detection by mimicking sensory cues of their hosts. However, there is little evidence whether or not the hosts are able to escape the parasites' mimicry by changing these cues. We addressed this question by analyzing cuticular hydrocarbon (CHC) profiles of Cerceris and Philanthus wasps and their brood parasites, cuckoo wasps mimicking the CHC profiles of their hosts. Some of these hosts use hydrocarbons to preserve their prey against fungal infestation and thus, they cannot significantly change their CHC composition in response to chemical mimicry by Hedychrum brood parasites. Results We found that the CHC overlap between brood parasites and their hosts was lower in case of host wasps not preserving their prey than in case of prey-preserving host wasps, whose CHC evolution is constrained. Furthermore, the CHC profiles in non-preserving host wasps is more strongly diversified in females than in males, thus in the sex that is chemically mimicked by brood parasites. Conclusion Our results provide evidence for a chemical arms race between those hosts that are liberated from stabilizing selection on their chemical template and their parasites.},
  language  = {en}
}
@article{MorisChristmannWirtgenetal.2021,
  author    = {Moris, Victoria C. and Christmann, Katharina and Wirtgen, Aline and Belokobylskij, Sergey A. and Berg, Alexander and Liebig, Wolf-Harald and Soon, Villu and Baur, Hannes and Schmitt, Thomas and Niehuis, Oliver},
  title     = {Cuticular hydrocarbons on old museum specimens of the spiny mason wasp, Odynerus spinipes (Hymenoptera: Vespidae: Eumeninae), shed light on the distribution and on regional frequencies of distinct chemotypes},
  series = {Chemoecology},
  volume    = {31},
  journal   = {Chemoecology},
  number    = {5},
  issn      = {0937-7409},
  doi       = {10.1007/s00049-021-00350-8},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-306999},
  pages     = {311-322},
  year      = {2021},
  abstract  = {The mason wasp Odynerus spinipes shows an exceptional case of intrasexual cuticular hydrocarbon (CHC) profile dimorphism. Females of this species display one of two CHC profiles (chemotypes) that differ qualitatively and quantitatively from each other. The ratio of the two chemotypes was previously shown to be close to 1:1 at three sites in Southern Germany, which might not be representative given the Palearctic distribution of the species. To infer the frequency of the two chemotypes across the entire distributional range of the species, we analyzed with GC-MS the CHC profile of 1042 dry-mounted specimens stored in private and museum collections. We complemented our sampling by including 324 samples collected and preserved specifically for studying their CHCs. We were capable of reliably identifying the chemotypes in 91\% of dry-mounted samples, some of which collected almost 200 years ago. We found both chemotypes to occur in the Far East, the presumed glacial refuge of the species, and their frequency to differ considerably between sites and geographic regions. The geographic structure in the chemotype frequencies could be the result of differential selection regimes and/or different dispersal routes during the colonization of the Western Palearctic. The presented data pave the route for disentangling these factors by providing information where to geographically sample O. spinipes for population genetic analyses. They also form the much-needed basis for future studies aiming to understand the evolutionary and geographic origin as well as the genetics of the astounding CHC profile dimorphism that O. spinipes females exhibit.},
  language  = {en}
}
@article{PolidoriBallesterosWurdacketal.2020,
  author    = {Polidori, Carlo and Ballesteros, Yolanda and Wurdack, Mareike and As{\´i}s, Josep Daniel and Tormos, Jos{\´e} and Ba{\~n}os-Pic{\´o}n, Laura and Schmitt, Thomas},
  title     = {Low host specialization in the cuckoo wasp, Parnopes grandior, weakens chemical mimicry but does not lead to local adaption},
  series = {Insects},
  volume    = {11},
  journal   = {Insects},
  number    = {2},
  issn      = {2075-4450},
  doi       = {10.3390/insects11020136},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-200651},
  year      = {2020},
  abstract  = {Insect brood parasites have evolved a variety of strategies to avoid being detected by their hosts. Few previous studies on cuckoo wasps (Hymenoptera: Chrysididae), which are natural enemies of solitary wasps and bees, have shown that chemical mimicry, i.e., the biosynthesis of cuticular hydrocarbons (CHC) that match the host profile, evolved in several species. However, mimicry was not detected in all investigated host-parasite pairs. The effect of host range as a second factor that may play a role in evolution of mimicry has been neglected, since all previous studies were carried out on host specialists and at nesting sites where only one host species occurred. Here we studied the cuckoo wasp Parnopes grandior, which attacks many digger wasp species of the genus Bembix (Hymenoptera: Crabronidae). Given its weak host specialization, P. grandior may either locally adapt by increasing mimicry precision to only one of the sympatric hosts or it may evolve chemical insignificance by reducing the CHC profile complexity and/or CHCs amounts. At a study site harbouring three host species, we found evidence for a weak but appreciable chemical deception strategy in P. grandior. Indeed, the CHC profile of P. grandior was more similar to all sympatric Bembix species than to a non-host wasp species belonging to the same tribe as Bembix. Furthermore, P. grandior CHC profile was equally distant to all the hosts' CHC profiles, thus not pointing towards local adaptation of the CHC profile to one of the hosts' profile. We conducted behavioural assays suggesting that such weak mimicry is sufficient to reduce host aggression, even in absence of an insignificance strategy, which was not detected. Hence, we finally concluded that host range may indeed play a role in shaping the level of chemical mimicry in cuckoo wasps.},
  language  = {en}
}
@article{MenzelBluethgenTolaschetal.2013,
  author    = {Menzel, Florian and Bl{\"u}thgen, Nico and Tolasch, Till and Conrad, J{\"u}rgen and Beifuss, Uwe and Beuerle, Till and Schmitt, Thomas},
  title     = {Crematoenones - a novel substance class exhibited by ants functions as appeasement signal},
  series = {Frontiers in Zoology},
  volume    = {10},
  journal   = {Frontiers in Zoology},
  number    = {32},
  issn      = {1742-9994},
  doi       = {10.1186/1742-9994-10-32},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-122595},
  year      = {2013},
  abstract  = {Background: Parasitic, commensalistic, and mutualistic guests in social insect colonies often circumvent their hosts' nestmate recognition system to be accepted. These tolerance strategies include chemical mimicry and chemical insignificance. While tolerance strategies have been studied intensively in social parasites, little is known about these mechanisms in non-parasitic interactions. Here, we describe a strategy used in a parabiotic association, i.e. two mutualistic ant species that regularly share a common nest although they have overlapping food niches. One of them, Crematogaster modiglianii, produces an array of cuticular compounds which represent a substance class undescribed in nature so far. They occur in high abundances, which suggests an important function in the ant's association with its partner Camponotus rufifemur. Results: We elucidated the structure of one of the main compounds from cuticular extracts using gas chromatography, mass spectrometry, chemical derivatizations and nuclear magnetic resonance spectroscopy (NMR). The compound consists of two fused six-membered rings with two alkyl groups, one of which carries a keto functionality. To our knowledge, this is the first report on the identification of this substance class in nature. We suggest naming the compound crematoenone. In behavioural assays, crematoenones reduced interspecific aggression. Camponotus showed less aggression to allospecific cuticular hydrocarbons when combined with crematoenones. Thus, they function as appeasement substances. However, although the crematoenone composition was highly colony-specific, interspecific recognition was mediated by cuticular hydrocarbons, and not by crematoenones. Conclusions: Crematenones enable Crematogaster to evade Camponotus aggression, and thus reduce potential costs from competition with Camponotus. Hence, they seem to be a key factor in the parabiosis, and help Crematogaster to gain a net benefit from the association and thus maintain a mutualistic association over evolutionary time. To our knowledge, putative appeasement substances have been reported only once so far, and never between non-parasitic species. Since most organisms associated with social insects need to overcome their nestmate recognition system, we hypothesize that appeasement substances might play an important role in the evolution and maintenance of other mutualistic associations as well, by allowing organisms to reduce costs from antagonistic behaviour of other species.},
  language  = {en}
}
@phdthesis{Schmitt2004,
  author    = {Schmitt, Thomas},
  title     = {Communication in the hymenoptera : chemistry, ecology and evolution},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-11267},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2004},
  abstract  = {Insects exhibit complex systems of communication with chemical signalling being the most important mode. Although there are many studies on chemical communication in insects, the evolution of chemical signals is not well understood. Due to the conflict of interests between individuals, different selective pressures might act on sender and receiver. In this thesis I investigate different types of communication where either the sender, the receiver or both parties yield benefits. These studies were conducted with one digger wasp species, honeybees, one chrysidid wasp, and three ant species. Senders might benefit by exploiting existing preferences of receivers. Such sensory exploitation might influence the evolution of male signals that are designed to attract females. The sex pheromone of male European beewolves Philanthus triangulum (Hymenoptera, Crabronidae) might have evolved according to the sensory exploitation hypothesis. A three-step scenario is supported by our studies. First, a major component of the honeybee alarm pheromone, (Z)-11-eicosen-1-ol, is also found on the cuticles and in the air surrounding foraging honeybees. Second, it could be shown, that (Z)-11- eicosen-1-ol plays a crucial role as kairomone for prey identification of honeybees by beewolf females. Third, a reanalysis of the beewolf male sex pheromone shows a remarkable similarity of compounds between the pheromone and the honeybee cuticle, besides the co-occurrence of (Z)-11-eisosen-ol. The majority of the cuticular hydrocarbons of honeybees occur also in the headspace of foraging workers. These results strongly support the hypothesis that beewolf males evolved a pheromone that exploits the females' pre-existing sensory sensitivity. In addition, the male sex pheromone shows a significantly higher similarity among brothers than among non-related individuals, which might enable beewolf females to discriminate against brothers and avoid detrimental effects of breeding. Together with the studies on the possible sensory exploitation this result shows that both, male and female beewolves probably gain more benefits than costs from the pheromone communication and, thus, the communication system as a whole can be regarded as cooperative. To maintain the reproductive division of labour in eusocial colonies, queens have to signal their presence and fecundity. In the ant Camponotus floridanus (Hymenoptera, Formicidae) queens mark their own eggs with a distinctive pattern of cuticular hydrocarbons. Two different hypotheses have been developed. One suggests a form of worker manipulation by the queen. The alternative hypothesis assumes a cooperative signal that provides information on the condition of the queen. The results of our investigation clearly favour the latter hypothesis. Chemical mimicry is a form of non-cooperative communication that benefits predominantly the sender. We provided conclusive evidence that the cockoo wasp, Hedychrum rutilans (Hymenoptera, Chrysididae), the primary brood parasitoid of Philanthus triangulum, evades recognition by beewolf females most probably by chemical mimicry of the odour of its host. Furthermore, the adaptation of the chemical signature in the social ant parasite Protomognathus americanus (Hymenoptera, Formicidae) to its Leptothorax (Hymenoptera, Formicidae) hosts was investigated. Although this parasite is principally adapted to its hosts' cuticular hydrocarbon profile, there are still pronounced differences between the profiles of parasites and hosts. This might be explained by the trade-off, which the parasites faces when confronted locally with two host species with different cuticular hydrocarbon profiles. Non-cooperative communication in the sense that only receivers benefit was discovered in the exploitation of honeybees volatile cuticular hydrocarbons by beewolf females. By using emitted (Z)-11-eicosen-1-ol as a kairomone, the receiver, the beewolf female, yields the benefits and the sender, the honeybee prey, bears all the costs. The results of these studies contribute to the understanding of the evolution of cooperative and non-cooperative communication with chemical signals taking into account differential benefits for sender and/or receiver.},
  subject      = {Hautfl{\"u}gler},
  language  = {en}
}