Manfred Kaib

Die Fleisch- und Blumenduftrezeptoren auf der Antenne der SchmeißfliegeCalliphora vicina

Summary1.Three morphologically different types of sensilla are found on the surface of the funiculus of the blowflyCalliphora vicina (=C. erythrocephala). In the large antennal pits there is an identical population of grooved hairs, and in the small antennal pits only sensilla basiconica are observed. It was proved that sensilla of the large pits have an olfactory function; likewise, those of the small pits probably perform an olfactory function.2.Different receptors responded to the odour of decaying meat and volatile compounds of flowers; we can thus classify them receptors for meat-odour and flower-odour. Their reaction spectra were determined using pure compounds.3.Six different types of meat-odour receptors have been identified. They respond with different states of excitation to the meat-odours, enabling the fly to detect to what degree the meat is decayed. Three types of flower-odour receptors are known, which respond to stimulation by different volatile flower compounds.4.The hexanol receptors (one type of meat-odour receptor) react well to compounds with a chain-length between 5 and 7 C-atoms (maximum 6 C-atoms) and either an alcohol, aldehyde, or keto group.5.The position of single functional groups is not important; however, the effectiveness of compounds with two functional groups (e.g. carbonyl group and double bond) increases with the distance between the functional groups.6.None of the odoriforous compounds tested that were effective on the hexanol receptors are identical with the effective fraction from the meat-odor.ZusammenfassungDrei morphologisch unterschiedliche Sensillentypen treten auf der Funiculusoberfläche der SchmeißfliegeCalliphora vicina (=C. erythrocephala) auf, in den großen Antennengruben ausschließlich identische Rillenhaare und in den kleinen Gruben ausschließlich Sensilla basiconica. Eine olfaktorische Funktion ist fÜr die Sensillen der großen Gruben nachgewiesen, fÜr die der kleinen Gruben wahrscheinlich gemacht.2.Mehrere Reaktionstypen reagieren auf den Geruch von faulem Fleisch oder auf flÜchtige Blumeninhaltsstoffe. Sie lassen sich zu zwei Rezeptorgruppen, den Fleischduftrezeptoren und den Blumenduftrezeptoren zusammenfassen. Ihre Geruchsspektren werden durch Reizung mit reinen Substanzen bestimmt.3.Sechs Typen von Fleischduftrezeptoren werden beschrieben, die den Duft verschieden alter Fleischproben mit unterschiedlicher Erregung beantworten und das Erkennen des Fäulnisgrades des Fleisches ermöglichen. Ferner können vorerst drei Typen von Blumenduftrezeptoren unterschieden werden, die eine Reizung mit flÜchtigen Blumeninhaltsstoffen mit Erregung beantworten.4.Der Hexanoltyp, einer der Fleischduftrezeptoren, wird von Verbindungen mit einer Kettenlänge von 5–7 Kohlenstoffatomen (Maximum bei C-6) erregt, die eine Alkohol-Aldehyd-oder Ketogruppe enthalten.5.Liegt nur eine funktioneile Gruppe vor, so ist deren Stellung nicht von Bedeutung. Bei zwei funktionellen Gruppen (z.B. Carbonylgruppe und Doppelbindung) wird die Verbindung umso wirksamer, je weiter sie voneinander entfernt stehen.6.Keine der erregenden Substanzen kommt fÜr den Hexanoltyp als wirksamste Fraktion des Fleischgeruches in Betracht.

Cuticular hydrocarbons and aggression in the termite Macrotermes subhyalinus.

Cuticular hydrocarbons are among the prime candidates for nestmate recognition in social insects. We analyzed the variation of cuticular hydrocarbons in the termite species M. subhyalinus in West Africa (Comoë National Park) on a small spatial scale (<1 km). We found considerable variation in the composition of cuticular hydrocarbons among colonies, with four distinct chemical phenotypes. Different phenotypes occurred within each of the four habitats. The difference between these phenotypes is primarily due to unsaturated compounds. A clear correlation between the difference of the hydrocarbon composition and the aggression between colonies was found. This correlation also holds in a multivariate analysis of genetic similarity (measured by AFLPs), morphometric distances (measured by Mahalanobis-distances), as well as geographic distances between colonies. In a more detailed analysis of the correlation between the composition of cuticular hydrocarbons and aggression, we found that no single compound is sufficient to explain variation in aggression between pairings of colonies. Thus, termites seem to use a bouquet of compounds. Multiple regression analysis suggested that many of these compounds are unsaturated hydrocarbons and, thus, may play a key role in colony recognition.

Variation between and within colonies in the termite: morphology, genomic DNA, and behaviour

We investigate the structure between and within colonies of Schedorhinotermes lamanianus (Isoptera: Rhinotermitidae) at a cluster of foraging galleries in Shimba Hills National Reserve, Kenya. Three independent methods (morphometrics of minor soldiers, multilocus fingerprinting from genomic DNA of workers, and aggression tests between workers) yielded concordant results concerning number and spatial extent of colonies as well as variation between and within colonies. At least three colonies exist in our study area. Genetic data reveal that the largest colony is genetically and spatially substructured in three subsidiary nests, which may form reproductive units. These subsidiary nests were not completely isolated as we were able to document exchange of workers. Subsidiary nests may facilitate foundation of colonies by budding which may generate isolation by distance (population viscosity).

Forest Fragmentation and Selective Logging Have Inconsistent Effects on Multiple Animal-Mediated Ecosystem Processes in a Tropical Forest

Forest fragmentation and selective logging are two main drivers of global environmental change and modify biodiversity and environmental conditions in many tropical forests. The consequences of these changes for the functioning of tropical forest ecosystems have rarely been explored in a comprehensive approach. In a Kenyan rainforest, we studied six animal-mediated ecosystem processes and recorded species richness and community composition of all animal taxa involved in these processes. We used linear models and a formal meta-analysis to test whether forest fragmentation and selective logging affected ecosystem processes and biodiversity and used structural equation models to disentangle direct from biodiversity-related indirect effects of human disturbance on multiple ecosystem processes. Fragmentation increased decomposition and reduced antbird predation, while selective logging consistently increased pollination, seed dispersal and army-ant raiding. Fragmentation modified species richness or community composition of five taxa, whereas selective logging did not affect any component of biodiversity. Changes in the abundance of functionally important species were related to lower predation by antbirds and higher decomposition rates in small forest fragments. The positive effects of selective logging on bee pollination, bird seed dispersal and army-ant raiding were direct, i.e. not related to changes in biodiversity, and were probably due to behavioural changes of these highly mobile animal taxa. We conclude that animal-mediated ecosystem processes respond in distinct ways to different types of human disturbance in Kakamega Forest. Our findings suggest that forest fragmentation affects ecosystem processes indirectly by changes in biodiversity, whereas selective logging influences processes directly by modifying local environmental conditions and resource distributions. The positive to neutral effects of selective logging on ecosystem processes show that the functionality of tropical forests can be maintained in moderately disturbed forest fragments. Conservation concepts for tropical forests should thus include not only remaining pristine forests but also functionally viable forest remnants.

Systematic search for food in the subterranean termite Reticulitermes santonensis De Feytaud (Isoptera, Rhinotermitidae)

Summary: The search for food in subterranean termites is investigated in the French species Reticulitermes santonensis De Feytaud (Isoptera, Rhinotermitidae). Not accompanied by soldiers, only few pioneer workers explore a new territory systematically in every direction by means of short exploratory trails (median: 1.3 cm). Following these trails, termites build subterranean tunnels and/or galleries in the open, hereby forming an extensive regularly branched net. Food is detected over distance by perceiving volatiles emanating from the wood. Then foragers appear more frequently and undertake longer exploratory runs (up to 15 cm), which are directed towards the odour source. Following contact with the wood, sucessful workers return to the nest precisely along their exploratory trail and hereby lay a recruitment trail. This recruitment trail is immediately followed by further workers as well as by single soldiers. Following the course of this trail, termites build a non‐branched subterranean tunnel or a gallery above ground leading straight to the wood. This direct access requires less investment and provides workers with a shelter ensuring a rapid and safe exploitation of the food source.

Cuticular Hydrocarbon Profiles in the Slave-Making Ant Harpagoxenus sublaevis and Its Hosts

Although the sex pheromone of the former was estimated to be 100% (+)dispalure, the gypsy moth possesses cells specialized to (+)and (-)-dispalure (a pheromone inhibitor), whereas in the nun moth, which was estimated to utilize 90% (-)-, and 10% (+)-dispalure, both cells responded to (+)-dispalure and no (-)-dispalure-sensitive cell was found. We are grateful to K. Asaoka, Dr. A. Sen, and Dr. J. Inouchi for advice regarding the preparations of samples for SEM and TEM as well as for their critical review of the manuscript. We thank Nitto Electric Co. for providing the synthetic S-enantiomer.

A new family of tricyclic alkaloids from Myrmicaria ants

Abstract The poison gland secretion of the African ant, Myrmicaria opaciventris , contains three families of new alkaloids. These alkaloids are represented by a “monomeric” type with 15 carbon atoms in a row forming derivatives of indolizines, while the two other families are “dimers” and “trimers” with 30 and 45 carbon atoms, respectively. The major constituents of the low molecular weight alkaloids are identified to be pyrrolo[2,1,5-cd]indolizines, highly dominated by l-ethyl-3,4,41,5,6,7-hexahydro-2-((1 Z )-1-propenyl)-pyrrolo[2,1,5-cd]indolizine, myrmicarin 215A . The higher molecular weight components show complex oligocyclic structures, which are closely related to the pyrroloindolizines. The alkaloid pattern shows a high degree of intraspecific variation.

Within-colony relatedness in a termite species : Genetic roads to eusociality?

Hamiltons theory predicts that relatedness asymmetries, with higher relatedness between alloparents and brood than between parents and brood, favour the evolution of eusociality. The haplodiploid reproductive system of the social Hymenoptera does indeed produce relatedness asymmetries, but the diplodiploid system of the eusocial Isoptera does not automatically do so. Three mechanisms that might favour relatedness asymmetries, and therefore eusociality, in termites have been extensively debated: First, substantial inbreeding generates the background for effective kin-selection. Second, inbreeding-outbreeding cycles within and between colonies cause a higher relatedness between individuals of the same generation than between them and their potential offspring. This would be analogous to the haplodiploid system. Third, translocation complexes of sex-linked chromosomes may generate higher relatedness within sexes than between sexes, again analogous to the haplodiploid system. We tested these three hypotheses for the African termite Schedorhinotermes lamanianus (Isoptera, Rhinotermitidae) using estimates of within-colony relatedness derived by multilocus DNA fingerprinting with a synthetic oligonucleotide probe. We found little support for any of the three hypotheses. We observed inbreeding to occur only during one or a few generations within colonies, which is unlikely to be an operational basis for ongoing kin-selection. Overall, we conclude that ecological factors and constraints must be considered a major selective force.

Unrelated queens coexist in colonies of the termite Macrotermes michaelseni

Relatedness increases the likelihood of cooperation within colonies of social insects. Polygyny, the coexistence of numerous reproductive females (queens) in a colony, is common in mature colonies of the termite Macrotermes michaelseni. In this species, polygyny results from pleometrosis and from several female alates that jointly found a new colony. To explain this phenomenon, it was suggested that only related females cooperate and survive during maturation of colonies. Using multilocus fingerprints as well as microsatellites, we showed that nestmate queens in mature colonies are unrelated. Furthermore, we found that all nestmate queens contributed to the production of steriles. Even in mature colonies, several matrilines of steriles coexist within a colony. Although genetic diversity within colonies may increase the likelihood of conflicts, high genetic diversity may be important for foraging, colony growth, and resistance to disease and parasites.

Hydroquinone: A general phagostimulating pheromone in termites

The organization of termite societies depends predominantly on intraspecific chemical signals (pheromones) produced by exocrine glands, which induce and modulate individual behavioral responses. Here, the saliva-producing labial glands of termites were investigated with respect to their pheromonal role in communal food exploitation of termite colonies. From these glands, we identified for the first time hydroquinone (1,4-dihydroxybenzene) as a phagostimulating pheromone in the Australian termite species Mastotermes darwiniensis. Hydroquinone is released from the labial glands of termite workers and applied onto the food. It stimulates nestmates to feed at the spot of application and is, thus, employed to mark feeding sites. No synergistic effect with other identified labial gland compounds, such as glucose, inositol, and arbutin, was evident. Significantly, we show that termite species from all over the world, irrespective of taxonomic position and biological traits, produce and employ hydroquinone as phagostimulating signal. The use of the same chemical signal throughout an order is a unique phenomenon, not reported before in animals. Its possible biosynthetic pathway, ecological significance, and evolution are discussed.