Juvenile hormone titers and caste differentiation in the damp-wood termite Hodotermopsis sjostedti (Isoptera, Termopsidae)

Termites are social insects, presenting morphologically distinct castes, performing specific tasks in the colony. The developmental processes underlying caste differentiation are mainly controlled by juvenile hormone (JH). Although many fragmentary data support this fact, there was no comparative work on JH titers during the caste differentiation processes. In this study, JH titer variation was investigated using a liquid chromatography-mass spectrometry (LC-MS) quantification method in all castes of the Japanese damp-wood termite Hodotermopsis sjostedti, especially focusing on the soldier caste differentiation pathway, which was induced by treatment with a JH analog. Hemolymph JH titers fluctuated between 20 and 720pg/microl. A peak of JH was observed during molting events for the pseudergate stationary molt and presoldier differentiation, but this peak was absent prior to the imaginal molt. Soldier caste differentiation was generally associated with high JH titers and nymph to alate differentiation with low JH titers. However, JH titer rose in females during alate maturation, probably in relation to vitellogenesis. In comparison, JH titer was surprisingly low in neotenics. On the basis of these results in both natural and artificial conditions, the current model for JH action on termite caste differentiation is discussed and re-appraised.     

Surface irregularity induced-tunneling behavior of the formosan subterranean termite

Subterranean termites forage from place to place by tunneling through soil. In order to examine termite-tunneling responses to external factors, we designed a square arena that contains five introduction chambers connected with narrow paths, which was filled with sand. Triangle-shaped indentation with width W and height H was provided as surface irregularity on the sand facing the introduction chambers by using templates. After termites were introduced into the chambers, we measured elapsed time, τ, for a tunnel to reach the point at 3 mm away from the apex of the irregularity. We found that for W = 0 mm (the absence of irregularity), termites (Coptotermes formosanus Shiraki) did not tunnel for 7 h, whereas, for W = 1, 2, 3, and 4 mm, they exhibited the tunneling behavior within 20 min. The result indicated that the presence of surface irregularity is essential to induce termite tunneling. In addition, we found that W was correlated with τ, whereas H did not influence τ. This was briefly discussed in the context of individual movement behavior.     

Rounding a corner of a bent termite tunnel and tunnel traffic efficiency

Subterranean termites construct underground tunnels, tens to hundreds of feet, to reach feeding sites and to transport food items to their nest. To ensure a high rate food return to the nest, an optimized tunnel should be constructed. We found that termites (Coptotermes formosanus Shiraki) fill the corner of a bent tunnel with soil particles excavated from tunnel tip where their digging behavior is activated. The corner-filling behavior, eventually, made a sharp corner smooth-rounded. In the present study, we showed that the corner-filling behavior could play an important role in improving the tunnel traffic efficiency. To do this, we compared the termites' time spent for passing corners between with a right-angled flat tip (RA-corner), corresponding to the sharp corner, and with a rounded tip (R-corner) corresponding to the smooth-rounded corner. As a result, the passing time in the R-corner was significantly shorter than in the RA-corner. In addition, tunnel width effect was discussed in terms of individual movement.     

A simulation study of territory size distribution of mangrove termites on Atlantic coast of Panama

The territory size distribution of the termites Nasutitermes nigriceps and Nasutitermes corniger (Isoptera: Termitidae) in a mangrove forest on the Atlantic coast of Panama showed a rapidly decline region in the rear part and was strongly affected by the degree of connection between the prop roots of mangrove trees [Adams, E.S., Levings, S., 1987. Territory size and population limits in mangrove termites. J. Anim. Ecol. 56, 1069–1081]. To account for these empirical facts, we introduced a lattice model to simulate territorial competition under seasonal cycle, dry and wet season. The simulated territory grew during the wet season while it shrunk during the dry season. The model simulation showed that the shrinkage and expansion process resulted in winner and loser territories in the territorial competition, which consequently led to generate the declining regions.     

Phylogenetic relationships of symbiotic spirochetes in the gut of diverse termites

Phylogenetic relationships of symbiotic spirochetes in the gut of diverse termites were analyzed without cultivation of these microorganisms. A portion of the 16S rDNA (ca. 850 bp) was amplified directly from DNA of the mixed population in the gut by PCR and cloned. A total of 30 spirochetal phylotypes affiliated with the treponemes were identified from four termite species and they were compared with those already reported from other termites. They represented separate lines of descent from any known species of Treponema, and they were divided into two discrete clusters; one was related to Spirochaeta stenostrepta and S. caldaria, and the other was grouped together with members of the Treponema bryantii subgroup. Although some sequences from evolutionarily related termites showed close similarity, most of the sequences of spirochetes were dissimilar among different termite species, and spirochetal sequences from a single termite species occurred in several distinct phylogenetic positions. These findings suggest that termites constitute a rich reservoir of novel spirochetal diversity and that evolution of the symbiosis is not simple.     

Symbiotic spirochetes in the termite hindgut: phylogenetic identification of ectosymbiotic spirochetes of oxymonad protists

Some species of protists inhabiting the hindgut of lower-termites have a large number of ectosymbiotic spirochetes on the cell surface. The phylogenetic positions of the ectosymbiotic spirochetes of three oxymonad protists, Dinenympha porteri in the gut of Reticulitermes speratus, and Pyrsonympha sp. and Dinenympha sp. in Hodotermopsis sjoestedti, were investigated without cultivation of these organisms. Protist fractions carefully collected with a micromanipulator were used as templates for the amplification of small subunit ribosomal RNA genes (SSU rDNA). The phylogenetic tree inferred from the nucleotide sequences of the SSU rDNA showed that they were affiliated with the Treponema cluster of spirochetes and they were divided into two clusters. One was grouped together with the spirochetal sequences reported previously from the gut of termites and the other was related to the Treponema bryantii subgroup of treponemes (denoted as termite Treponema clusters I and II, respectively). Whole-cell in situ hybridization using a fluorescent-labeled oligonucleotide probe specific for the group of sequences in cluster II identified most of the ectosymbiotic spirochetes of the oxymonad protists in the gut of R. speratus and H. sjoestedti. However, not all of the ectosymbiotic spirochetes could be detected by means of this cluster II group-specific probe and the population of ectosymbiotic spirochetes of cluster II was different among the oxymonad species. In the case of D. porteri, an oligonucleotide probe specific for one member of cluster II recognized a portion of the ectosymbiotic spirochetes of cluster II, and their population was also different depending on the cell-type of D. porteri in terms of the attachment of ectosymbiotic spirochetes. The results indicate that the spirochetes of cluster II and probably those of a part of cluster I can be assigned to ectosymbiotic species of oxymonad protists and that the population of ectosymbiotic spirochetes associated with a single protist consists of at least three species of phylogenetically distinct spirochetes.