Developmental pathways of Psammotermes hybostoma (Isoptera: Rhinotermitidae): old pseudergates make up a new sterile caste

Cryptic subterranean diversity: regional phylogeography of the sand termite Psammotermes allocerus Silvestri, 1908 in the wider Namib region

Psammotermes allocerus Silvestri, 1908 is the only described species representing the genus Psammotermes Desneux, 1902 in Southern Africa. The large geographical range of this subterranean termite covers both summer and winter rainfall regimes. Deadwood is the preferred food when available, but in more arid habitats, both live and dead grasses form the major dietary component. Along the Namib Desert margins, the species’ localised herbivory creates circular bare patches known as fairy circles. For a regional phylogeographic study of this species, we sampled 65 sand termite populations within drier parts of Namibia, South Africa, and Angola. Based on combined molecular and ecological data, we found considerable genetic diversification within P. allocerus. Analyses of two mitochondrial markers (COI, COII), including a Bayesian inference tree, haplotype analysis and genetic distances suggest a delineation into seven highly differentiated genetic groups. The ‘Succulent Karoo’ group is additionally characterised by unique features of the royal chamber, nest and tunnel system. In conclusion, our data suggest that P. allocerus should be not regarded as one species but as a species complex. Termites of each analysed group ‘Northern Namib’, ‘Western Kalahari Basin’, ‘Nama’, ‘Southwestern Kalahari’, ‘East Gariep’, ‘Southern Namib’ and ‘Succulent Karoo’ should be considered as distinct species. The species name P. allocerus should be used for termites of the ‘Succulent Karoo’.

Termite evolution: mutualistic associations, key innovations, and the rise of Termitidae

Termites are a clade of eusocial wood-feeding roaches with > 3000 described species. Eusociality emerged ~ 150 million years ago in the ancestor of modern termites, which, since then, have acquired and sometimes lost a series of adaptive traits defining of their evolution. Termites primarily feed on wood, and digest cellulose in association with their obligatory nutritional mutualistic gut microbes. Recent advances in our understanding of termite phylogenetic relationships have served to provide a tentative timeline for the emergence of innovative traits and their consequences on the ecological success of termites. While all "lower" termites rely on cellulolytic protists to digest wood, "higher" termites (Termitidae), which comprise ~ 70% of termite species, do not rely on protists for digestion. The loss of protists in Termitidae was a critical evolutionary step that fostered the emergence of novel traits, resulting in a diversification of morphology, diets, and niches to an extent unattained by "lower" termites. However, the mechanisms that led to the initial loss of protists and the succession of events that took place in the termite gut remain speculative. In this review, we provide an overview of the key innovative traits acquired by termites during their evolution, which ultimately set the stage for the emergence of "higher" termites. We then discuss two hypotheses concerning the loss of protists in Termitidae, either through an externalization of the digestion or a dietary transition. Finally, we argue that many aspects of termite evolution remain speculative, as most termite biological diversity and evolutionary trajectories have yet to be explored.

Silencing Orco Impaired the Ability to Perceive Trail Pheromones and Affected Locomotion Behavior in Two Termite Species

Sophisticated social behaviors in termite colonies are mainly regulated via chemical communication of a wide range of pheromones. Trail pheromones play important roles in foraging behavior and building tunnels and nests in termites. However, it is almost unclear how termites perceive trail pheromones. Here, we cloned and sequenced of olfactory co-receptor (Orco) genes from the two termites Reticulitermes chinensis Snyder (Isoptera: Rhinotermitidae) and Odontotermes formosanus (Shiraki) (Isoptera: Termitidae), and then examined their responses to trail pheromones after silencing Orco through RNA interference (RNAi). We found that Orco knockdown impaired their ability to perceive trail pheromones and resulted in the disability of following pheromone trails in the two termite species. Our locomotion behavior assays further showed that Orco knockdown significantly decreased the distance and velocity in the two termite species, but significantly increased the angular velocity and turn angle in the termite R. chinensis. These findings strongly demonstrated that Orco is essential for termites to perceive their trail pheromones, which provides a potential way to control termite pests by damaging olfactory system.

Ant-termite interactions: an important but under-explored ecological linkage

Animal interactions play an important role in understanding ecological processes. The nature and intensity of these interactions can shape the impacts of organisms on their environment. Because ants and termites, with their high biomass and range of ecological functions, have considerable effects on their environment, the interaction between them is important for ecosystem processes. Although the manner in which ants and termites interact is becoming increasingly well studied, there has been no synthesis to date of the available literature. Here we review and synthesise all existing literature on ant-termite interactions. We infer that ant predation on termites is the most important, most widespread, and most studied type of interaction. Predatory ant species can regulate termite populations and subsequently slow down the decomposition of wood, litter and soil organic matter. As a consequence they also affect plant growth and distribution, nutrient cycling and nutrient availability. Although some ant species are specialised termite predators, there is probably a high level of opportunistic predation by generalist ant species, and hence their impact on ecosystem processes that termites are known to provide varies at the species level. The most fruitful future research direction will be to evaluate the impact of ant-termite predation on broader ecosystem processes. To do this it will be necessary to quantify the efficacy both of particular ant species and of ant communities as a whole in regulating termite populations in different biomes. We envisage that this work will require a combination of methods, including DNA barcoding of ant gut contents along with field observations and exclusion experiments. Such a combined approach is necessary for assessing how this interaction influences entire ecosystems.

Drywood Pest Termite Cryptotermes brevis (Blattaria: Isoptera: Kalotermitidae): a Detailed Morphological Study of Pseudergates

The Kalotermitidae Cryptotermes brevis (Walker) presents colonies that lack a true worker caste. They have totipotent worker-like individuals named pseudergates. Few studies have characterized the morphology of immature instars, including pseudergates. In order to identify these instars and characterize the pseudergates, we conducted a comparison between morphometric and morphological variations among immature individuals of C. brevis colonies. Juvenile hormone analog (JHA) was used in the first instar nymphs to induce regressive molts and compare morphological differences between nymphs and pseudergates. Results showed the existence of three larval instars and four nymphal instars. These immatures were morphologically characterized. Individuals classified as third instar larvae presented white body, 10 to 12 antennal articles, absent or small non-pigmented compound eyes, and absence of wing buds. Pseudergates presented pigmented abdomen and sclerotized cuticle, 10 to 12 antennal articles, and absent or small compound eyes, and few specimens had large pigmented compound eyes and absence of wing buds. First instar nymphs had pigmented abdomen and sclerotized cuticle, 10 to 12 antennal articles, both large non-pigmented and pigmented compound eyes, the presence of wing buds. Bioassays using JHA on first instar nymphs resulted in a large percentage of nymph-soldier intercastes. We concluded that abdomen pigmentation and sclerotized cuticle are good characters to differentiate pseudergates from larvae and the absence of wing buds is a good character to differentiate pseudergates from nymphs. Our findings not only contribute to the basic biological and morphological information of this species but also help to identify correctly pseudergates in further studies that involve applied bioassays.

The evolution of sociality in termites from cockroaches: A taxonomic and phylogenetic perspective

Despite multiple studies and advances, sociality still puzzles evolutionary biologists in numerous ways, which might be partly addressed with the advent of sociogenomics. In insects, the majority of sociogenomic studies deal with Hymenoptera, one of the two groups that evolved eusociality with termites. But, to fully grasp the evolution of sociality, studies must obviously not restrict to eusocial lineages. Multiple kinds of social system transitions have been recorded and they all bring complementary insights. For instance, cockroaches, the closest relatives to termites, display a wide range of social interactions and evolved convergently subsocial behaviors (i.e., brood care). In this context, we emphasize the need for natural history, taxonomic, and phylogenetic studies. Natural history studies provide the foundations on which building hypotheses, whereas taxonomy provides the taxa to sample to test these hypotheses, and phylogenetics brings the historical framework necessary to test evolutionary scenarios of sociality evolution.

Phylogenetic position of the enigmatic termite family Stylotermitidae (Insecta : Blattodea)

Termites are eusocial insects currently classified into nine families, of which only Stylotermitidae has never been subjected to any molecular phylogenetic analysis. Stylotermitids present remarkable morphology and have the unique habit of feeding on living trees. We sequenced mitogenomes of five stylotermitid samples from China and Taiwan to reconstruct the phylogenetic position of Stylotermitidae. Our analyses placed Stylotermitidae as the sister group of all remaining Neoisoptera. The systematic position of Stylotermitidae calls for additional studies of their biology, including their developmental pathways and pheromone communication, which have the potential to change our understanding of termite evolution.

The evolutionary history of termites as inferred from 66 mitochondrial genomes

Termites have colonized many habitats and are among the most abundant animals in tropical ecosystems, which they modify considerably through their actions. The timing of their rise in abundance and of the dispersal events that gave rise to modern termite lineages is not well understood. To shed light on termite origins and diversification, we sequenced the mitochondrial genome of 48 termite species and combined them with 18 previously sequenced termite mitochondrial genomes for phylogenetic and molecular clock analyses using multiple fossil calibrations. The 66 genomes represent most major clades of termites. Unlike previous phylogenetic studies based on fewer molecular data, our phylogenetic tree is fully resolved for the lower termites. The phylogenetic positions of Macrotermitinae and Apicotermitinae are also resolved as the basal groups in the higher termites, but in the crown termitid groups, including Termitinae + Syntermitinae + Nasutitermitinae + Cubitermitinae, the position of some nodes remains uncertain. Our molecular clock tree indicates that the lineages leading to termites and Cryptocercus roaches diverged 170 Ma (153-196 Ma 95% confidence interval [CI]), that modern Termitidae arose 54 Ma (46-66 Ma 95% CI), and that the crown termitid group arose 40 Ma (35-49 Ma 95% CI). This indicates that the distribution of basal termite clades was influenced by the final stages of the breakup of Pangaea. Our inference of ancestral geographic ranges shows that the Termitidae, which includes more than 75% of extant termite species, most likely originated in Africa or Asia, and acquired their pantropical distribution after a series of dispersal and subsequent diversification events.

Chemical alarm in the termite Termitogeton planus (Rhinotermitidae)

Effective defense is a common characteristic of insect societies. Indeed, the occurrence of specialized defenders, soldiers, has been the first step toward eusociality in several independent lineages, including termites. Among the multitude of defensive strategies used by termite soldiers, defense by chemicals plays a crucial role. It has evolved with complexity in advanced isopteran lineages, whose soldiers are equipped with a unique defensive organ, the frontal gland. Besides direct defense against predators, competitors, and pathogens, the chemicals emitted by soldiers from the frontal gland are used as signals of alarm. In this study, we investigated the chemical composition of the defensive secretion produced by soldiers of the termite Termitogeton planus (Isoptera: Rhinotermitidae), from West Papua, and the effects of this secretion on the behavior of termite groups. Detailed two-dimensional gas chromatography/mass spectrometry analyses of the soldier defensive secretion revealed the presence of four linear and nine monoterpene hydrocarbons. Soldier head extracts, as well as synthetic mixtures of the monoterpenes found in these extracts, elicited alarm behavior in both soldiers and pseudergates. Our results suggest that the alarm is not triggered by a single monoterpene from the defensive blend, but by a multi-component signal combining quantitatively major and minor compounds.