The architecture of termite mounds: a result of a trade-off between thermoregulation and gas exchange?

We examined the influence of gas exchange on the architectureof termite mounds. In Comoé National Park (Côted'Ivoire), Macrotermes bellicosus builds, as an adaptation toambient temperature conditions, differently shaped mounds inthe shrub savanna and the gallery forest. Previous studies suggestedthat there might be a constraint that limits the degree of thermalinsulation of the interior (i.e., nest) of the mounds in environmentswith relatively low ambient temperatures. This factor causes,in proximate terms, suboptimal low nest temperatures and ultimatelyleads to reduced reproductive success in the gallery forest.In this study, we examined whether the necessity for gas exchangemight constrain mound architecture. We measured CO₂ concentrationsin the air channels of mounds in different habitats and undermanipulated temperature regimes. During both the dry and therainy season we found higher CO₂ concentrations in mounds ofthe gallery forest than in mounds of the savanna. Additional measurementsin forest mounds, architecturally resembling those of the savanna dueto an experimental increase in ambient temperatures, revealedlower CO₂ concentrations than unmanipulated mounds in this habitat. Generally,concentrations were higher during the rainy season comparedto the dry season and lower during day than during night. Summarizingthese results we present a model that illustrates this trade-offbetween thermoregulation and gas exchange under different temperatureregimes. Both factors together result in different mound architecturesunder different environmental temperatures and may finally limitthe distribution of this species.     

‘Magnetic’ termite mounds: is their unique shape an adaptation to facilitate gas exchange and improve food storage?

Social insects can build impressive nest mounds but the functional significance of their architecture is rarely studied in experiments. The ‘magnetic’ termite mounds of monsoonal northern Australia built by Amitermes meridionalis are notable for their elongated wedge shape and north–south axial orientation. We tested whether the shape is an adaptation to facilitate gas exchange and the preservation of food stores by two experimental manipulations of mounds in situ covering all seasons. First, mounds were shaded to limit drying after rain and second, mound shape was amended from wedge to (approximate) sphere. Food storage, fungal contamination, and internal CO₂ concentration were unaffected by manipulation, but showed a distinct seasonal dynamic, with storage peaking towards the onset of rains and fungal load towards the end of the rainy season. Internal CO₂ concentrations were subject to a diurnal cycle, but also showed elevation during rains. We propose that one advantage of the wedge shape is the efficient use of building effort to achieve good passive ventilation for the food storage areas.     

Isolation and characterization of six microsatellite loci in the drywood termite Cryptotermes secundus (Kalotermitidae)

The Kalotermitidae is a family of lower termites and its species are ideal to study the evolution and maintenance of eusociality within the Isoptera. Co‐dominant genetic markers are an essential tool to elucidate the putatively complex colony and population structure. Six polymorphic microsatellite loci were identified in the drywood termite Cryptotermes secundus (Kalotermitidae). To test the variability of the markers, 18 colonies (n = 18) from Darwin (Australia) were assayed. We found two to eight alleles per locus with the level of observed heterozygosity at each locus ranging from 0.00 to 0.53. The significantly positive F_IT value suggests that some kind of inbreeding does occur in this population.     

Effect of food restriction on survival and reproduction of a termite

Food availability affects the trade-off between maintenance and reproduction in a wide range of organisms, but its effects on social insects remain poorly understood. In social insects, the maintenance-reproduction trade-off seems to be absent in individuals but may appear at the colony level, although this is rarely investigated. In this study, we restricted food availability in a termite species to test how it affects survival and reproduction, both at the individual and colony level. Using Bayesian multivariate response models, we found very minor effects of food restriction on the survival of queens, individual workers or on the colonies. In contrast, queen fecundity was significantly reduced, whereas colony-level fecundity (i.e., the number of dispersing alates, future reproductives) increased under food restriction as workers gave up cooperation within the colony and became alates that dispersed. Our study shows that life-history trade-offs can be mitigated by individuals' social behaviours in social organisms.     

Mathematical analysis of the oncornavirus maturation process (virion RNA conversion and morphological condensation)

The rate of the maturation process of avian myeloblastosis virus experimentally estimated on the basis of genomic viral RNA conversion and morphological transition of virions was mathematically analysed. Three mathematical models were suggested and fitted to experimental data. It was found that: (a) model of simple kinetics (Model 1) does not agree with experimental data. Therefore, two hypotheses were considered in further mathematical modelling: (b) virions are identical in time of budding: maturation is dependent on the presence of a virion component which is degraded with time (Model 2). This model agrees with experimental data in all stages of the maturation process. (c) Virions are released from cells at different stages of assembly (Model 3). This model differs from experimental data especially in early stages of maturation. The hypothesis used for the construction of Model 2 seems to be the most plausible to explain the maturation process and is in agreement with data of murine leukemia virus maturation which was found to be accomplished by cleavage of p70 precursor protein.