Extinct and extant termites reveal the fidelity of behavior fossilization in amber.

Fossils encompassing multiple individuals provide rare direct evidence of behavioral interactions among extinct organisms. However, the fossilization process can alter the spatial relationship between individuals and hinder behavioral reconstruction. Here, we report a Baltic amber inclusion preserving a female-male pair of the extinct termite species Electrotermes affinis. The head-to-abdomen contact in the fossilized pair resembles the tandem courtship behavior of extant termites, although their parallel body alignment differs from the linear alignment typical of tandem runs. To solve this inconsistency, we simulated the first stage of amber formation, the immobilization of captured organisms, by exposing living termite tandems to sticky surfaces. We found that the posture of the fossilized pair matches trapped tandems and differs from untrapped tandems. Thus, the fossilized pair likely is a tandem running pair, representing the direct evidence of the mating behavior of extinct termites. Furthermore, by comparing the postures of partners on a sticky surface and in the amber inclusion, we estimated that the male likely performed the leader role in the fossilized tandem. Our results demonstrate that past behavioral interactions can be reconstructed despite the spatial distortion of body poses during fossilization. Our taphonomic approach demonstrates how certain behaviors can be inferred from fossil occurrences.

Ancestral sex-role plasticity facilitates the evolution of same-sex sexual behavior.

Recent attempts to explain the evolutionary prevalence of same-sex sexual behavior (SSB) have focused on the role of indiscriminate mating. However, in many cases, SSB may be more complex than simple mistaken identity, instead involving mutual interactions and successful pairing between partners who can detect each other's sex. Behavioral plasticity is essential for the expression of SSB in such circumstances. To test behavioral plasticity's role in the evolution of SSB, we used termites to study how females and males modify their behavior in same-sex versus heterosexual pairs. Male termites follow females in paired "tandems" before mating, and movement patterns are sexually dimorphic. Previous studies observed that adaptive same-sex tandems also occur in both sexes. Here we found that stable same-sex tandems are achieved by behavioral plasticity when one partner adopts the other sex's movements, resulting in behavioral dimorphism. Simulations based on empirically obtained parameters indicated that this socially cued plasticity contributes to pair maintenance, because dimorphic movements improve reunion success upon accidental separation. A systematic literature survey and phylogenetic comparative analysis suggest that the ancestors of modern termites lack consistent sex roles during pairing, indicating that plasticity is inherited from the ancestor. Socioenvironmental induction of ancestral behavioral potential may be of widespread importance to the expression of SSB. Our findings challenge recent arguments for a prominent role of indiscriminate mating behavior in the evolutionary origin and maintenance of SSB across diverse taxa.

Enhanced heterozygosity from male meiotic chromosome chains is superseded by hybrid female asexuality in termites.

Although males are a ubiquitous feature of animals, they have been lost repeatedly in diverse lineages. The tendency for obligate asexuality to evolve is thought to be reduced in animals whose males play a critical role beyond the contribution of gametes, for example, via care of offspring or provision of nuptial gifts. To our knowledge, the evolution of obligate asexuality in such species is unknown. In some species that undergo frequent inbreeding, males are hypothesized to play a key role in maintaining genetic heterozygosity through the possession of neo-sex chromosomes, although empirical evidence for this is lacking. Because inbreeding is a key feature of the life cycle of termites, we investigated the potential role of males in promoting heterozygosity within populations through karyotyping and genome-wide single-nucleotide polymorphism analyses of the drywood termite Glyptotermes nakajimai We showed that males possess up to 15 out of 17 of their chromosomes as sex-linked (sex and neo-sex) chromosomes and that they maintain significantly higher levels of heterozygosity than do females. Furthermore, we showed that two obligately asexual lineages of this species-representing the only known all-female termite populations-arose independently via intraspecific hybridization between sexual lineages with differing diploid chromosome numbers. Importantly, these asexual females have markedly higher heterozygosity than their conspecific males and appear to have replaced the sexual lineages in some populations. Our results indicate that asexuality has enabled females to supplant a key role of males.

Molecular Phylogeny Reveals the Past Transoceanic Voyages of Drywood Termites (Isoptera, Kalotermitidae).

Termites are major decomposers in terrestrial ecosystems and the second most diverse lineage of social insects. The Kalotermitidae form the second-largest termite family and are distributed across tropical and subtropical ecosystems, where they typically live in small colonies confined to single wood items inhabited by individuals with no foraging abilities. How the Kalotermitidae have acquired their global distribution patterns remains unresolved. Similarly, it is unclear whether foraging is ancestral to Kalotermitidae or was secondarily acquired in a few species. These questions can be addressed in a phylogenetic framework. We inferred time-calibrated phylogenetic trees of Kalotermitidae using mitochondrial genomes of ∼120 species, about 27% of kalotermitid diversity, including representatives of 21 of the 23 kalotermitid genera. Our mitochondrial genome phylogenetic trees were corroborated by phylogenies inferred from nuclear ultraconserved elements derived from a subset of 28 species. We found that extant kalotermitids shared a common ancestor 84 Ma (75-93 Ma 95% highest posterior density), indicating that a few disjunctions among early-diverging kalotermitid lineages may predate Gondwana breakup. However, most of the ∼40 disjunctions among biogeographic realms were dated at <50 Ma, indicating that transoceanic dispersals, and more recently human-mediated dispersals, have been the major drivers of the global distribution of Kalotermitidae. Our phylogeny also revealed that the capacity to forage is often found in early-diverging kalotermitid lineages, implying the ancestors of Kalotermitidae were able to forage among multiple wood pieces. Our phylogenetic estimates provide a platform for critical taxonomic revision and future comparative analyses of Kalotermitidae.

The evolution of body size in termites.

Termites are social cockroaches. Because non-termite cockroaches are larger than basal termite lineages, which themselves include large termite species, it has been proposed that termites experienced a unidirectional body size reduction since they evolved eusociality. However, the validity of this hypothesis remains untested in a phylogenetic framework. Here, we reconstructed termite body size evolution using head width measurements of 1638 modern and fossil termite species. We found that the unidirectional body size reduction model was only supported by analyses excluding fossil species. Analyses including fossil species suggested that body size diversified along with speciation events and estimated that the size of the common ancestor of modern termites was comparable to that of modern species. Our analyses further revealed that body size variability among species, but not body size reduction, is associated with features attributed to advanced termite societies. Our results suggest that miniaturization took place at the origin of termites, while subsequent complexification of termite societies did not lead to further body size reduction.

Coordination of movement via complementary interactions of leaders and followers in termite mating pairs.

In collective animal motion, coordination is often achieved by feedback between leaders and followers. For stable coordination, a leader's signals and a follower's responses are hypothesized to be attuned to each other. However, their roles are difficult to disentangle in species with highly coordinated movements, hiding potential diversity of behavioural mechanisms for collective behaviour. Here, we show that two Coptotermes termite species achieve a similar level of coordination via distinct sets of complementary leader-follower interactions. Even though C. gestroi females produce less pheromone than C. formosanus, tandem runs of both species were stable. Heterospecific pairs with C. gestroi males were also stable, but not those with C. formosanus males. We attributed this to the males' adaptation to the conspecific females; C. gestroi males have a unique capacity to follow females with small amounts of pheromone, while C. formosanus males reject C. gestroi females as unsuitable but are competitive over females with large amounts of pheromone. An information-theoretic analysis supported this conclusion by detecting information flow from female to male only in stable tandems. Our study highlights cryptic interspecific variation in movement coordination, a source of novelty for the evolution of social interactions.

Complex Relationship between Tunneling Patterns and Individual Behaviors in Termites.

AbstractThe nests built by social insects are complex group-level structures that emerge from interactions among individuals following simple behavioral rules. Nest patterns vary among species, and the theory of complex systems predicts that there is no simple one-to-one relationship between variation in collective patterns and variation in individual behaviors. Therefore, a species-by-species comparison of the actual building process is essential to understand the mechanism producing diverse nest patterns. Here, we compare tunnel formation of three termite sp ecies and reveal two mechanisms producing interspecific variation: in one, a common behavioral rule yields distinct patterns via parameter tuning, and in the other, distinct rules produce similar patterns. We found that two related species transport sand in the same way using mandibles but build tunnels with different degrees of branching. The variation arises from different probabilities of choosing between two behavioral options at crowded tunnel faces: excavating the sidewall to make a new branch or waiting for clearance to extend the current tunnel. We further discovered that a third species independently evolved low-branched patterns using different building rules, namely, a bucket brigade that can excavate a crowded tunnel. Our findings emphasize the importance of direct comparative study of collective behaviors at both individual and group levels.

Molecular Phylogenetic Position of Hoplonympha natator (Trichonymphea, Parabasalia): Horizontal Symbiont Transfer or Differential Loss?

Hoplonympha natator is an obligate symbiont of Paraneotermes simplicicornis (Kalotermitidae), from southwestern North America. Another Hoplonympha species inhabits Hodotermopsis sjostedti (Archotermopsidae), from montane Southeast Asia. The large phylogenetic and geographical distance between the hosts makes the distribution of Hoplonympha puzzling. Here, we report the phylogenetic position of H. natator from P. simplicicornis through maximum likelihood and Bayesian analysis of 18S rRNA genes. The two Hoplonympha species form a clade with a deep node, making a recent symbiont transfer unlikely. The distribution of Hoplonympha may be due to an ancient transfer or strict vertical inheritance with differential loss from other hosts.

Termite males enhance mating encounters by changing speed according to density.

Search theory predicts that animals evolve efficient movement patterns to enhance encounter rates with specific targets. The optimal movements vary with the surrounding environments, which may explain the observation that animals often switch their movement patterns depending on conditions. However, the effectiveness of behavioural change during search is rarely evaluated because it is difficult to examine the actual encounter dynamics. Here we studied how partner-seeking termites update their search strategies depending on the local densities of potential mates. After a dispersal flight, termites drop their wings and walk to search for a mate; when a female and a male meet, they form a female-led tandem pair and search for a favourable nesting site. If a pair is separated, they have two search options-reunite with their stray partner, or seek a new partner. We hypothesized that the density of individuals affects separation-reunion dynamics and thus the optimal search strategy. We observed the searching process across different densities and found that termite pairs were often separated but obtained a new partner quickly at high mate density. After separation, while females consistently slowed down, males increased their speed according to the density. Under high mate density, separated males obtained a partner earlier than females, who do not change movement with density. Our data-based simulations confirmed that the observed behavioural change by males contributes to enhancing encounters. Males at very low mate densities did best to move slowly and thereby reduce the risk of missing their stray partner, who is the only available mate. On the other hand, males that experienced high mate densities did better in mating encounters by moving fast because the risk of isolation is low, and they must compete with other males to find a partner. These results demonstrate that termite males adaptively update their search strategy depending on conditions. Understanding the encounter dynamics experienced by animals is key to connecting the empirical work to the idealized search processes of theoretical studies.

Inferring collective behaviour from a fossilized fish shoal.

Collective motion by animal groups can emerge from simple rules that govern each individual's interactions with its neighbours. Studies of extant species have shown how such rules yield coordinated group behaviour, but little is known of their evolutionary origins or whether extinct group-living organisms used similar rules. Here, we report evidence consistent with coordinated collective motion in a fossilized group of the extinct fish Erismatopterus levatus, and we infer possible behavioural rules that underlie it. We found traces of two rules for social interaction similar to those used by extant fishes: repulsion from close individuals and attraction towards neighbours at a distance. Moreover, the fossilized fish showed group-level structures in the form of oblong shape and high polarization, both of which we successfully reproduced in simulations incorporating the inferred behavioural rules. Although it remains unclear how the fish shoal's structure was preserved in the fossil, these findings suggest that fishes have been forming shoals by combining sets of simple behavioural rules since at least the Eocene. Our study highlights the possibility of exploring the social communication of extinct animals, which has been thought to leave no fossil record.

Loss of males from mixed-sex societies in termites.

BACKGROUND: Sexual reproduction is the norm in almost all animal species, and in many advanced animal societies, both males and females participate in social activities. To date, the complete loss of males from advanced social animal lineages has been reported only in ants and honey bees (Hymenoptera), whose workers are always female and whose males display no helping behaviors even in normal sexual species. Asexuality has not previously been observed in colonies of another major group of social insects, the termites, where the ubiquitous presence of both male and female workers and soldiers indicate that males play a critical role beyond that of reproduction. RESULTS: Here, we report asexual societies in a lineage of the termite Glyptotermes nakajimai. We investigated the composition of mature colonies from ten distinct populations in Japan, finding six asexual populations characterized by a lack of any males in the reproductive, soldier, and worker castes of their colonies, an absence of sperm in the spermathecae of their queens, and the development of unfertilized eggs at a level comparable to that for the development of fertilized eggs in sexual populations of this species. Phylogenetic analyses indicated a single evolutionary origin of the asexual populations, with divergence from sampled sexual populations occurring about 14 million years ago. Asexual colonies differ from sexual colonies in having a more uniform head size in their all-female soldier caste, and fewer soldiers in proportion to other individuals, suggesting increased defensive efficiencies arising from uniform soldier morphology. Such efficiencies may have contributed to the persistence and spread of the asexual lineage. Cooperative colony foundation by multiple queens, the single-site nesting life history common to both the asexual and sexual lineages, and the occasional development of eggs without fertilization even in the sexual lineage are traits likely to have been present in the ancestors of the asexual lineage that may have facilitated the transition to asexuality. CONCLUSIONS: Our findings demonstrate that completely asexual social lineages can evolve from mixed-sex termite societies, providing evidence that males are dispensable for the maintenance of advanced animal societies in which they previously played an active social role.

A Genomic Imprinting Model of Termite Caste Determination: Not Genetic but Epigenetic Inheritance Influences Offspring Caste Fate.

Eusocial insects exhibit the most striking example of phenotypic plasticity. There has been a long controversy over the factors determining caste development of individuals in social insects. Here we demonstrate that parental phenotypes influence the social status of offspring not through genetic inheritance but through genomic imprinting in termites. Our extensive field survey and genetic analysis of the termite Reticulitermes speratus show that its breeding system is inconsistent with a genetic caste determination model. We therefore developed a genomic imprinting model, in which queen- and king-specific epigenetic marks antagonistically influence sexual development of offspring. The model accounts for all known empirical data on caste differentiation of R. speratus and other related species. By conducting colony-founding experiments and additively incorporating relevant socio-environmental factors into our genomic imprinting model, we show the relative importance of genomic imprinting and environmental factors in caste determination. The idea of epigenetic inheritance of sexual phenotypes solves the puzzle of why parthenogenetically produced daughters carrying only maternal chromosomes exclusively develop into queens and why parental phenotypes (nymph- or worker-derived reproductives) strongly influence caste differentiation of offspring. According to our model, the worker caste is seen as a "neuter" caste whose sexual development is suppressed due to counterbalanced maternal and paternal imprinting and opens new avenues for understanding the evolution of caste systems in social insects.

TManual: Assistant for manually measuring length development in structures built by animals.

Structures built by animals are extended phenotypes, and animal behavior can be better understood by recording the temporal development of structure construction. For most subterranean and wood-boring animals, these structures consist of gallery systems, such as burrows made by mice, tunnel foraging by termites, and nest excavation in ants. Measurement of the length development of such structures is often performed manually. However, it is time-consuming and cognitively costly to track length development in nested branching structures, hindering the quantitative determination of temporal development. Here, I introduce TManual, which aids the manual measurement of structure length development using a number of images. TManual provides a user interface to draw gallery structures and take over all other processes handling input datasets (e.g., zero-adjustment, scaling the units, measuring the length, assigning gallery identities, and extracting network structures). Thus, users can focus on the measuring process without interruptions. As examples, I provide the results of the analysis of a dataset of tunnel construction by three termite species after successfully processing 1125 images in ~3 h. The output datasets clearly visualized the interspecific variation in tunneling speed and branching structures. Furthermore, I applied TManual to a complex gallery system by another termite species and extracted network structures. Measuring the lengths of objects from images is an essential task in biological observation. TManual helps users handle many images in a realistic time scale, enabling a comparative analysis across a wide array of species. TManual does not require programming skills and outputs a tidy data frame in CSV format. Therefore, it is suitable for any user who wants to perform image analysis for length measurements.

Protocol to obtain long movement trajectories of leaders and followers in ant tandem runs.

Tandem running in ants is a sophisticated form of communication. Precise measurement of movement coordination by the tandem pair can shed light on social interactions. Here, we describe an integrative approach to obtain long movement trajectories of a specific tandem pair within a crowd of ants. We describe a maze-like arena, video recording and editing, and movement tracking. We integrate two pieces of image-based tracking software that have distinct individual assignment strategies. This protocol aids comparative studies of recruitment communication across species. For complete details on the use and execution of this protocol, please refer to Mizumoto et al. (2023)1 and Valentini et al. (2020).2.

Functional and mechanistic diversity in ant tandem communication.

Communication is fundamental to the organization of animal societies, often resulting in the convergent evolution of similar social behavior across lineages. However, this similarity may conceal underlying functional and mechanistic differences. Here we combined network and information-theoretic analysis to quantify how tandem recruitment is distinguishable between two ant genera, Temnothorax and Diacamma. We show that Temnothorax uses tandem running to recruit additional recruiters, while Diacamma uses it principally to move the passive majority of their colony, a task that Temnothorax accomplishes with a different behavior, social carrying. Accordingly, the network structure of Diacamma tandems was dissimilar to that of Temnothorax, instead resembling the social-carrying networks in Temnothorax. Furthermore, our information-theoretical analysis on movement trajectories revealed that Diacamma tandem runs lack bidirectional information transfer, the signature of route learning in Temnothorax. By quantifying the diversity of similar communication systems, this study increases the resolution of our understanding of animal societies.

Termite nest evolution fostered social parasitism by termitophilous rove beetles.

Colonies of social insects contain large amounts of resources often exploited by specialized social parasites. Although some termite species host numerous parasitic arthropod species, called termitophiles, others host none. The reason for this large variability remains unknown. Here, we report that the evolution of termitophily in rove beetles is linked to termite nesting strategies. We compared one-piece nesters, whose entire colony life is completed within a single wood piece, to foraging species, which exploit multiple physically separated food sources. Our epidemiological model predicts that characteristics related to foraging (e.g., extended colony longevity and frequent interactions with other colonies) increase the probability of parasitism by termitophiles. We tested our prediction using literature data. We found that foraging species are more likely to host termitophilous rove beetles than one-piece nesters: 99.6% of known termitophilous species were associated with foraging termites, whereas 0.4% were associated with one-piece nesters. Notably, the few one-piece nesting species hosting termitophiles were those having foraging potential and access to soil. Our phylogenetic analyses confirmed that termitophily primarily evolved with foraging termites. These results highlight that the evolution of complex termite societies fostered social parasitism, explaining why some species have more social parasites than others.

Age-based spatial distribution of workers is resilient to worker loss in a subterranean termite.

Elaborate task allocation is key to the ecological success of eusocial insects. Termite colonies are known for exhibiting age polyethism, with older instars more likely to depart the reproductive center to access food. However, it remains unknown how termites retain this spatial structure against external disturbances. Here we show that a subterranean termite Coptotermes formosanus Shiraki combines age polyethism and behavioral flexibility to maintain a constant worker proportion at the food area. Since this termite inhabits multiple wood pieces by connecting them through underground tunnels, disastrous colony splitting events can result in the loss of colony members. We simulated this via weekly removal of all individuals at the food area. Our results showed that termites maintained a worker proportion of ~ 20% at the food area regardless of changes in total colony size and demographic composition, where younger workers replaced food acquisition functions to maintain a constant worker proportion at the food area. Food consumption analysis revealed that the per-capita food consumption rate decreased with younger workers, but the colony did not compensate for the deficiency by increasing the proportion of workers at the feeding site. These results suggest that termite colonies prioritize risk management of colony fragmentation while maintaining suitable food acquisition efficiency with the next available workers in the colony, highlighting the importance of task allocation for colony resiliency under fluctuating environments.

Modern termites inherited the potential of collective construction from their common ancestor.

Animal collective behaviors give rise to various spatial patterns, such as the nests of social insects. These structures are built by individuals following a simple set of rules, slightly varying within and among species, to produce a large diversity of shapes. However, little is known about the origin and evolution of the behavioral mechanisms regulating nest structures. In this study, we discuss the perspective of inferring the evolution of collective behaviors behind pattern formations using a phylogenetic framework. We review the collective behaviors that can be described by a single set of behavioral rules, and for which variations of the environmental and behavioral parameter values produce diverse patterns. We propose that this mechanism could be at the origin of the pattern diversity observed among related species, and that, when they are placed in the proper conditions, species have the behavioral potential to form patterns observed in related species. The comparative analysis of shelter tube construction by lower termites is consistent with this hypothesis. Although the use of shelter tubes in natural conditions is variable among species, most modern species have the potential to build them, suggesting that the behavioral rules for shelter tube construction evolved once in the common ancestor of modern termites. Our study emphasizes that comparative studies of behavioral rules have the potential to shed light on the evolution of collective behaviors.

Chemical identification of an aggregation pheromone in the termite Reticulitermes speratus.

Social behaviours in termites are regulated by sophisticated chemical communication systems. The majority of subterranean termites continuously forage for new wood resources to expand their nesting areas; an aggregation pheromone is presumed to regulate this process. However, the chemical components of this pheromone have never been determined. We identified the chemical properties of the aggregation pheromone that signals nestmate presence and induces arrest in the termite Reticulitermes speratus. The results of gas chromatography-mass spectrometry analyses and bioassays indicated that R. speratus worker release the pheromone to their nesting site. The pheromone consists of an aromatic compound (2-phenylundecane), cuticular hydrocarbons (pentacosane and heptacosane), fatty acids (palmitic acid and trans-vaccenic acid), and cholesterol; the pheromone induces long-term aggregation at new nesting and feeding sites. Although 2-phenylundecane alone attracted workers, the combination of all six compounds showed greater arrestant activity than 2-phenylundecane alone. This suggests that 2-phenylundecane functions as an attractant, whereas the remaining five components function as arrestants. Our results indicate that foraging worker termites produce a multi-component aggregation pheromone by combining a volatile hydrocarbon and non-volatile lipids with cuticular hydrocarbons. This pheromone enables rapid, long-lasting aggregation of termite workers, which contributes to efficient feeding and colonisation of new wood. Our work furthers the understanding of chemical communication systems underlying social assembly in social insects.

Revealing the structure of information flows discriminates similar animal social behaviors.

Behavioral correlations stretching over time are an essential but often neglected aspect of interactions among animals. These correlations pose a challenge to current behavioral-analysis methods that lack effective means to analyze complex series of interactions. Here we show that non-invasive information-theoretic tools can be used to reveal communication protocols that guide complex social interactions by measuring simultaneous flows of different types of information between subjects. We demonstrate this approach by showing that the tandem-running behavior of the ant Temnothorax rugatulus and that of the termites Coptotermes formosanus and Reticulitermes speratus are governed by different communication protocols. Our discovery reconciles the diverse ultimate causes of tandem running across these two taxa with their apparently similar signaling mechanisms. We show that bidirectional flow of information is present only in ants and is consistent with the use of acknowledgement signals to regulate the flow of directional information.

Social animals continuously influence each other's behavior. Most of these interactions simply consist in an individual immediately responding to the behavior of another in a predictable way. Still, when the same individuals interact over long periods, complex social interactions can arise. These can be difficult for scientists to study, because how animals behave at a given moment depends on their shared history. Certain species of ants and termites use smell and touch to do 'tandem runs' and move in pairs through the environment. Only ants, however, can learn a new route from their running partner. Understanding how this difference arises means examining how the animals interact and communicate over longer time scales. This requires new approaches to capture how information flows between the insects. Here, Valentini et al. used a scientific methodology known as information theory to study tandem running in one species of ants and two species of termites. Information theory provides a framework to quantify how information is shared, processed and stored. The flow of information between individuals was measured separately for different aspects of tandem running. At small time scales, ant and termite behavior appeared identical, but over longer periods, it was possible to distinguish between the two types of insects. In termites, only one individual in a pair sent information to the other to instruct the second termite where to go. By contrast, in ants, both members of the tandem communicated with each other in a way that was consistent with how humans acknowledge information they receive from other individuals. The approach used by Valentini et al. will be useful to researchers who study how complex and often cryptic social interactions develop over extended periods in social animals. This framework could also be applied in other systems such as groups of cells, or economic networks.