Divergence times in the termite genus Macrotermes (Isoptera: Termitidae).

The evolution of fungus-growing termites is supposed to have started in the African rain forests with multiple invasions of semi-arid habitats as well as multiple invasions of the Oriental region. We used sequences of the mitochondrial COII gene and Bayesian dating to investigate the time frame of the evolution of Macrotermes, an important genus of fungus-growing termites. We found that the genus Macrotermes consists of at least 6 distantly related clades. Furthermore, the COII sequences suggested some cryptic diversity within the analysed African Macrotermes species. The dates calculated with the COII data using a fossilized termite mound to calibrate the clock were in good agreement with dates calculated with COI sequences using the split between Locusta and Chortippus as calibration point which supports the consistency of the calibration points. The clades from the Oriental region dated back to the early Tertiary. These estimates of divergence times suggested that Macrotermes invaded Asia during periods with humid climates. For Africa, many speciation events predated the Pleistocene and fall in range of 6-23 million years ago. These estimates suggest that savannah-adapted African clades radiated with the spread of the semi-arid ecosystems during the Miocene. Apparently, events during the Pleistocene were of little importance for speciation within the genus Macrotermes. However, further investigations are necessary to increase the number of taxa for phylogenetic analysis.

Juvenile hormone III influences task-specific cuticular hydrocarbon profile changes in the ant Myrmicaria eumenoides.

We investigated the influence of juvenile hormones (JH) on the composition of cuticular hydrocarbons (CHCs) and the division of labor in colonies of the African ant Myrmicaria eumenoides. CHCs have long been implicated in nestmate recognition in social insect colonies. In M. eumenoides, the CHC profiles also vary with the task performed from brood-tender-type to forager type. The endocrine factors regulating the task allocation as well as the intracolonial recognition cues are not well understood, but JHs are prime candidates. Only JH III was identified in the hemolymph of M. eumenoides workers. Foragers had significantly higher JH III titers than brood tenders. The application of exogenous JH III and a JH analogue (methoprene) to M. eumenoides workers did not result in an observable acceleration of task change in our study. However, longevity of the focus workers, and thus the observational period, was reduced by the applications. Changes from a brood-tender-type to a forager-type CHC profile were accelerated by the application of JH III and methoprene, resulting in brood-tending workers that displayed forager-type CHC profiles. We present the first data supporting that recognition cues of an eusocial Hymenopteran are influenced by JH III, which could thus play a major role in the regulation of the dynamic nature of social insect colonies. JH III is connected to at least two key processes: the acceleration of CHC changes and the more long-term modulation of task shifting. Moreover, this indicates that changes in CHC recognition cues do not trigger task allocation in social insect colonies.

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.

Food exploitation in termites: indication for a general feeding-stimulating signal in labial gland secretion of isoptera.

The paired labial glands are located in all termite species in the thorax. During food exploitation workers of the French termite Reticulitermes santonensis and the African termite Schedorhinotermes lamanianus release the secretion of their labial glands directly onto the food. The secretion carries a water-soluble, heat-resistant, nonvolatile signal that stimulates gnawing and feeding and leads to aggregations of feeding workers. In a feeding bioassay, extracts of the labial glands of 11 termite species from five families all proved to have this feeding-stimulating effect both on R. santonensis and S. lamanianus. The heat resistance of the feeding-stimulating signal also could be shown for selected species from all termite families tested. A combined thin layer chromatography-feeding bioassay on cellulose TLC plates showed that after chromatography of labial gland secretion, the feeding-stimulating signal is located in all 11 species in the same area from Rf 0.46 to 0.88. An extract of labial glands of cockroaches stimulated feeding in R. santonensis and S. lamanianus as well, but was not active after heat treatment and after TLC. This points towards a general feeding-stimulating signal having evolved only in the labial gland secretion of termites.

Thin-layer chromatography assessing feeding stimulation by labial gland secretion compared to synthetic chemicals in the subterranean termite Reticulitermes santonensis.

The labial gland of the French subterranean termite Reticulitermes santonensis De Feytaud contains a polar, heat-resistent, and persistent chemical signal that is released onto the food during food exploitation and stimulates feeding in nestmates. Separation of the labial gland secretion by thin-layer chromatography on cellulose plates revealed that the secretion contains components with reducing and amino groups. In feeding bioassays conducted on the cellulose plate after TLC, termites preferred the area between Rf 0.46 and 0.88 (biologically active zone) for feeding, indicating the location of the feeding-stimulating signal. Thirty-five synthetic chemicals with similar chemical properties as the feeding-stimulating signal were analyzed with TLC. None of them covered the biologically active zone. Therefore, all chemical classes tested, such as sugars, amino acids, and salts, are unlikely as possible sources for the signal structure. In feeding choice tests with synthetic chemicals, termites showed clear feeding preference only for sugarlike components with physiologically excessive concentrations of 10 mmol and 100 mmol. Amino acids induced only light feeding preference. The intensity of feeding stimulation by the natural signal from the labial gland as compared to synthetic phagostimulants is discussed.

Task-related variation of postpharyngeal and cuticular hydrocarbon compositions in the ant Myrmicaria eumenoides.

In the ant Myrmicaria eumenoides we investigated postpharyngeal and cuticular hydrocarbons. At eclosion the glands contained almost no hydrocarbons and there were no lipid inclusions in the glandular epithelium. During the first 3 weeks of adult life the amount of hydrocarbons in the gland increased until day 5, and then remained constant while the lipid content in the epithelium increased steadily. Intracolonial hydrocarbon compositions were not uniform. Compositions of post-pharyngeal and cuticular hydrocarbons in individual ants varied simultaneously, but in different manner depending on the tasks of the ant (brood-tenders, foragers, scouts). Variations on the cuticle were greater than in the gland, but they were strongly correlated. Independent of ants' age and task, cuticular hydrocarbon compositions were dominated by alkenes and alkadienes. Task-specific differences in cuticular compositions were mainly in the amount of alkenes (high in foragers) and alkadienes (high in brood-tenders). Variation of hydrocarbons was low in ants up to 10 weeks old. Thereafter, ants fell into two groups: (1) ants that did not change their hydrocarbons and remained in the nest, and (2) ants that changed their hydrocarbon compositions and became foragers. These results contribute to an ongoing discussion of the dynamic relationship between post-pharyngeal and cuticular hydrocarbons.

Trail-following in termites: Evidence for a multicomponent system.

Several African termite species from different subfamilies and different habitats are sensitive to trail-active extracts or to naturally laid trails from other species. Using single-extract bioassays, it is shown that the response threshold for trail-following is nearly identical for all tested species (except forHodotermes mossambicus). However, when termite workers have a choice between trails from their own species and from other species, conspecific trail-following is exclusively observed. This phenomenon can be counteracted by dilution (1∶10) of the conspecific trail-pheromone extract. Tests of the trail activity of various synthetic alcohols show that among these, the highest sensitivity of termite workers is to (Z)-3-dodecen-1-ol. Based on our experimental data, we postulate that, in addition to a generally active trail-pheromone constituent (an unsaturated primary C12 alcohol) or a pool of chemically closely related alcohols, other species-specific components are present in termite trails.