Major changes in domain arrangements are associated with the evolution of termites

Domains as functional protein units and their rearrangements along the phylogeny can shed light on the functional changes of proteomes associated with the evolution of complex traits like eusociality. This complex trait is associated with sterile soldiers and workers, and long-lived, highly fecund reproductives. Unlike in Hymenoptera (ants, bees, and wasps), the evolution of eusociality within Blattodea, where termites evolved from within cockroaches, was accompanied by a reduction in proteome size, raising the question of whether functional novelty was achieved with existing rather than novel proteins. To address this, we investigated the role of domain rearrangements during the evolution of termite eusociality. Analysing domain rearrangements in the proteomes of three solitary cockroaches and five eusocial termites, we inferred more than 5,000 rearrangements over the phylogeny of Blattodea. The 90 novel domain arrangements that emerged at the origin of termites were enriched for several functions related to longevity, such as protein homeostasis, DNA repair, mitochondrial activity, and nutrient sensing. Many domain rearrangements were related to changes in developmental pathways, important for the emergence of novel castes. Along with the elaboration of social complexity, including permanently sterile workers and larger, foraging colonies, we found 110 further domain arrangements with functions related to protein glycosylation and ion transport. We found an enrichment of caste-biased expression and splicing within rearranged genes, highlighting their importance for the evolution of castes. Furthermore, we found increased levels of DNA methylation among rearranged compared to non-rearranged genes suggesting fundamental differences in their regulation. Our findings indicate the importance of domain rearrangements in the generation of functional novelty necessary for termite eusociality to evolve.

Higher levels of the lipophilic antioxidants coenzyme Q10 and vitamin E in long-lived termite queens than in short-lived workers

Termite queens and kings live longer than nonreproductive workers. Several molecular mechanisms contributing to their long lifespan have been investigated; however, the underlying biochemical explanation remains unclear. Coenzyme Q (CoQ), a component of the mitochondrial electron transport chain, plays an essential role in the lipophilic antioxidant defense system. Its beneficial effects on health and longevity have been well studied in several organisms. Herein, we demonstrated that long-lived termite queens have significantly higher levels of the lipophilic antioxidant CoQ10 than workers. Liquid chromatography analysis revealed that the levels of the reduced form of CoQ10 were 4 fold higher in the queen's body than in the worker's body. In addition, queens showed 7 fold higher levels of vitamin E, which plays a role in antilipid peroxidation along with CoQ, than workers. Furthermore, the oral administration of CoQ10 to termites increased the CoQ10 redox state in the body and their survival rate under oxidative stress. These findings suggest that CoQ10 acts as an efficient lipophilic antioxidant along with vitamin E in long-lived termite queens. This study provides essential biochemical and evolutionary insights into the relationship between CoQ10 concentrations and termite lifespan extension.

Experience-expectant brain plasticity corresponds to caste-specific abiotic challenges in dampwood termites (Zootermopsis angusticollis and Z. nevadensis)

Hypotheses for adaptive brain investment predict associations between the relative sizes of functionally distinct brain regions and the sensory/cognitive demands animals confront. We measured developmental differences in the relative sizes of visual processing brain regions (optic lobes) among dampwood termite castes to test whether optic lobe investment matches caste differences in exposure to visually complex environments. The winged primary reproductives (Kings/Queens) on mating flights are the only caste to leave the dark nest cavities and as predicted, Kings/Queens showed greater relative investment in optic lobe tissue than nestbound (neotenic) reproductives and soldiers in two dampwood termite species (Zootermopsis angusticollis and Z. nevadensis). Relative optic lobe size spanned more than an order of magnitude among the castes we studied, suggesting the growth of the optic lobes incurs substantial tissue costs. Optic lobe growth was experience-expectant: the optic lobes of Z. angusticollis brachypterous nymphs, which typically develop into Kings/Queens, were relatively larger than the optic lobes of apterous nymphs, which precede neotenics and soldiers, and relative optic lobe size of nestbound brachypterous nymphs was statistically similar to that of Kings/Queens. Experience-expectant brain tissue growth is rarely documented in insects, likely because it entails high potential costs of tissue production and maintenance and relatively low immediate sensory/cognitive benefits. We develop hypotheses for the conditions under which experience-expectant growth in brain regions could be favored by natural selection.

Disentangling the aging gene expression network of termite queens

Background

Most insects are relatively short-lived, with a maximum lifespan of a few weeks, like the aging model organism, the fruit-fly Drosophila melanogaster. By contrast, the queens of many social insects (termites, ants and some bees) can live from a few years to decades. This makes social insects promising models in aging research providing insights into how a long reproductive life can be achieved. Yet, aging studies on social insect reproductives are hampered by a lack of quantitative data on age-dependent survival and time series analyses that cover the whole lifespan of such long-lived individuals. We studied aging in queens of the drywood termite Cryptotermes secundus by determining survival probabilities over a period of 15 years and performed transcriptome analyses for queens of known age that covered their whole lifespan.

Results

The maximum lifespan of C. secundus queens was 13 years, with a median maximum longevity of 11.0 years. Time course and co-expression network analyses of gene expression patterns over time indicated a non-gradual aging pattern. It was characterized by networks of genes that became differentially expressed only late in life, namely after ten years, which associates well with the median maximum lifespan for queens. These old-age gene networks reflect processes of physiological upheaval. We detected strong signs of stress, decline, defense and repair at the transcriptional level of epigenetic control as well as at the post-transcriptional level with changes in transposable element activity and the proteostasis network. The latter depicts an upregulation of protein degradation, together with protein synthesis and protein folding, processes which are often down-regulated in old animals. The simultaneous upregulation of protein synthesis and autophagy is indicative of a stress-response mediated by the transcription factor cnc, a homolog of human nrf genes.

Conclusions

Our results show non-linear senescence with a rather sudden physiological upheaval at old-age. Most importantly, they point to a re-wiring in the proteostasis network and stress as part of the aging process of social insect queens, shortly before queens die.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07649-4.

Why and how do termite kings and queens live so long?

Lifespan varies greatly across the tree of life. Of the various explanations for this phenomenon, those that involve trade-offs between reproduction and longevity have gained considerable support. There is an important exception: social insect reproductives (queens and in termites, also kings) exhibit both high reproductive outputs and extraordinarily long lives. As both the ultimate and proximate mechanisms underlying the absence of the fecundity/longevity trade-off could shed light on the unexpected dynamics and molecular mechanisms of extended longevity, reproductives of social insects have attracted much attention in the field of ageing research. Here, we highlight current ecological and physiological studies on ageing and discuss the various possible evolutionary and molecular explanations of the extended lifespans of termite reproductives. We integrate these findings into a coherent framework revealing the evolution of longevity in these reproductives. Studies on termites may explain why and how ageing is shaped by natural selection. This article is part of the theme issue 'Ageing and sociality: why, when and how does sociality change ageing patterns?'

Eusociality Shapes Convergent Patterns of Molecular Evolution across Mitochondrial Genomes of Snapping Shrimps

Eusociality is a highly conspicuous and ecologically impactful behavioral syndrome that has evolved independently across multiple animal lineages. So far, comparative genomic analyses of advanced sociality have been mostly limited to insects. Here, we study the only clade of animals known to exhibit eusociality in the marine realm-lineages of socially diverse snapping shrimps in the genus Synalpheus. To investigate the molecular impact of sociality, we assembled the mitochondrial genomes of eight Synalpheus species that represent three independent origins of eusociality and analyzed patterns of molecular evolution in protein-coding genes. Synonymous substitution rates are lower and potential signals of relaxed purifying selection are higher in eusocial relative to noneusocial taxa. Our results suggest that mitochondrial genome evolution was shaped by eusociality-linked traits-extended generation times and reduced effective population sizes that are hallmarks of advanced animal societies. This is the first direct evidence of eusociality impacting genome evolution in marine taxa. Our results also strongly support the idea that eusociality can shape genome evolution through profound changes in life history and demography.

The complete mitochondrial genome of the eusocial sponge-dwelling snapping shrimp Synalpheus microneptunus

In the marine realm, eusociality is only known to have evolved within a clade of sponge-dwelling snapping shrimps in the genus Synalpheus. Deciphering the genomic underpinnings of eusociality in these marine shrimps has been limited by the sparse genomic resources in this genus. Here, we report, for a eusocial shrimp Synalpheus microneptunus, a complete mitochondrial genome (22X coverage) assembled from short Illumina 150 bp paired-end reads. The 15,603 bp long mitochondrial genome of S. microneptunus is AT-rich and includes 13 protein-coding genes (PCGs), 2 ribosomal RNA genes, 22 transfer RNA genes and an 834 bp intergenic region assumed to be the D-loop. The gene order is identical to that reported for most caridean shrimps and corresponds to the presumed Pancrustacean ground pattern. All PCGs showed signs of purifying selection, with K_A/K_S <<1 across the whole PCGs and most sliding windows within PCGs. Maximum-likelihood and Bayesian inference phylogenetic analyses of 13 PCGs and 68 terminals supports the monophyly of the Caridea and the family Alpheidae. The complete mitochondrial genome of the eusocial shrimp Synalpheus microneptunus will contribute to a better understanding of the selective pressures and rates of molecular evolution in marine eusocial animals.

Reproduction deep inside wood: a low O2 and high CO2 environment promotes egg production by termite queens

Extreme conditions are normal for animals living in harsh environments. These animals adapt to their habitats and can use difficult conditions by default. Organisms living in enclosed spaces, notably termites in decaying wood, experience low O₂ and high CO₂ gas conditions due to limited gas exchange and high insect density. Termite queens, in particular, reproduce in royal chambers deep inside the wood, wherein tens of thousands of individuals engage in social labour. Here, we demonstrate that royal chambers in termite nests have low O₂ and high CO₂ gas concentrations, which enhance egg production by queens. We identified a unique gas condition of royal chambers in the nest of the subterranean termite Reticulitermes speratus, which is characterized by low O₂ (15.75%) and high CO₂ (4.99%) concentrations. Queens showed significantly greater fecundity under the low O₂ and high CO₂ gas conditions in the royal chambers than under ambient gas conditions. Quantitative PCR analysis revealed that the royal chamber gas conditions significantly promoted the expression levels of the vitellogenin genes RsVg1, RsVg2 and RsVg3 in queens compared with ambient gas conditions. This study highlights the adaptation of animals that live in closed habitats, which are hypoxic and hypercapnic as the result of their own metabolism, so as to have a high fitness in such environmental conditions.

Interspecific Hybridization between the Two Sympatric Termite Reticulitermes Species under Laboratory Conditions

Closely related species have similar reproductive behaviors and recognition systems, which contribute to interspecific interactions. However, few studies have explored interspecific reproduction choice and mating in termites. We investigated whether hybridization between two sympatric termites, Reticulitermes flaviceps and R. chinensis, occurs under laboratory conditions. We found that frequencies of acceptance were significantly higher than those of agonism between interspecific partners. There were no significant differences in frequencies of tandem and mating behaviors between intraspecific and interspecific partners. However, the allogrooming frequencies of interspecific partners were significantly higher than intraspecific partners. There were no significant differences in the duration of tandem, allogrooming, or mating behavior at each time between conspecific partners and heterospecfic partners. Genotyping analyses further showed that both intraspecific and interspecific mating were able to produce offspring. We conclude that interspecific hybridization does occur between two termite Reticulitermes species under laboratory conditions.

Evolutionary relationship of fat body endoreduplication and queen fecundity in termites

Endoreduplication or nuclear genome replication without cell division is widely observed in the metabolically active tissues of plants and animals. The fat body cells of adult female insects produce abundant yolk proteins and become polyploid, which is assumed to accelerate egg production. Recently, it was reported that in termites, endopolyploidy in the fat body occurs only in queens but not in the other females; however, the relationship between the fecundity and ploidy level in the fat body remains unclear. Termite queens exhibit a huge variation in their egg-producing capacity among different species; queens in the species with a foraging lifestyle, in which workers leave the nest to forage outside, are much more fecund than those in the species living in a single piece of wood. In this study, we conducted ploidy analyses on three foragings and three wood-dwelling termites via flow cytometry. In all the species, the fat body of queens contained significantly more polyploid cells than that of other nonreproductive females, considering their body size effect. However, the male fat body, which is not involved in yolk production, did not show consistency in polyploid cell numbers among the species studied. Moreover, highly fecund queens in foraging termites exhibit higher levels of endopolyploidy in their fat body than those with less fecundity in wood-dwelling termites. These results suggest that endopolyploidy in the fat body of termite queens can boost their egg production, and the level of endopolyploidy in their fat body is linked to their fecundity. Our study provides a novel insight into the evolutionary relationship between endoreduplication and caste specialization in social insects.

Diversity of Termite Breeding Systems

Termites are social insects that live in colonies headed by reproductive castes. The breeding system is defined by the number of reproductive individuals in a colony and the castes to which they belong. There is tremendous variation in the breeding system of termites both within and among species. The current state of our understanding of termite breeding systems is reviewed. Most termite colonies are founded by a primary (alate-derived) king and queen who mate and produce the other colony members. In some species, colonies continue throughout their life span as simple families headed by the original king and queen. In others, the primary king and queen are replaced by numerous neotenic (nymph- or worker-derived) reproductives, or less commonly primary reproductives, that are descendants of the original founding pair leading to inbreeding in the colony. In still others, colonies can have multiple unrelated reproductives due to either founding the colonies as groups or through colony fusion. More recently, parthenogenetic reproduction has shown to be important in some termite species and may be widespread. A major challenge in termite biology is to understand the ecological and evolutionary factors driving the variation in termite breeding systems.

Hypoxia adaptation in termites: hypoxic conditions enhance survival and reproductive activity in royals

Termite royals (queen and king) exhibit extraordinary longevity without sacrificing reproductive performance, unlike most animals, in whom lifespan is generally negatively associated with reproduction. Therefore, the regulatory mechanisms underlying longevity have attracted much attention. Although the ageing process is influenced by environmental factors in many insects during their life cycle, it remains unclear whether any factors have an effect on the extended survival and high reproductive capacity of termite royals. Here, we show that hypoxia, possibly an important environmental factor in the nests, enhances survival and reproductive activity in incipient royals of the subterranean termite Reticulitermes speratus compared with those in control conditions. Quantitative real-time PCR analysis revealed that the expression levels of the vitellogenin gene in queens are maintained to a greater extent under hypoxic conditions than under control conditions. The expression levels of the antioxidant enzyme genes RsCAT1 and RsPHGPX are also significantly promoted by hypoxia in queens and kings respectively. These results suggest that hypoxic exposure can contribute in part to achieving high reproductive output by altering gene expression after founding of colonies in the royals. Our study provides novel insights into the effect of a nest environment on the reproductive characteristics in termite royals.

A lipocalin protein, Neural Lazarillo, is key to social interactions that promote termite soldier differentiation

Social communication among castes is a crucial component of insect societies. However, the genes involved in soldier determination through the regulation of inter-individual interactions are largely unknown. In an incipient colony of the damp-wood termite Zootermopsis nevadensis, the first larva to develop into a third instar always differentiates into a soldier via frequent trophallactic feeding from the reproductives. Here, by performing RNA-seq analysis of third instar larvae, a homologue of Neural Lazarillo (named ZnNLaz1) was found to be the most differentially expressed gene in these soldier-destined larvae, compared with worker-destined larvae. This gene encodes a lipocalin protein related to the transport of small hydrophobic molecules. RNAi-induced knockdown of ZnNLaz1 significantly inhibited trophallactic interactions with the queen and decreased the soldier differentiation rates. This protein is localized in the gut, particularly in the internal wall, of soldier-destined larvae, suggesting that it is involved in the integration of social signals from the queen through frequent trophallactic behaviours. Based on molecular phylogenetic analysis, we suggest that a novel function of termite NLaz1 has contributed to social evolution from the cockroach ancestors of termites. These results indicated that a high larval NLaz1 expression is crucial for soldier determination through social communication in termites.

Asexual queen succession in the higher termite Embiratermes neotenicus

Asexual queen succession (AQS), in which workers, soldiers and dispersing reproductives are produced sexually while numerous non-dispersing queens arise through thelytokous parthenogenesis, has recently been described in three species of lower termites of the genus Reticulitermes. Here, we show that AQS is not an oddity restricted to a single genus of lower termites, but a more widespread strategy occurring also in the most advanced termite group, the higher termites (Termitidae). We analysed the genetic structure in 10 colonies of the Neotropical higher termite Embiratermes neotenicus (Syntermitinae) using five newly developed polymorphic microsatellite loci. The colonies contained one primary king accompanied either by a single primary queen or by up to almost 200 neotenic queens. While the workers, the soldiers and most future dispersing reproductives were produced sexually, the non-dispersing neotenic queens originated through thelytokous parthenogenesis of the founding primary queen. Surprisingly, the mode of thelytoky observed in E. neotenicus is most probably automixis with central fusion, contrasting with the automixis with terminal fusion documented in Reticulitermes. The occurrence of AQS based on different mechanisms of ploidy restoration raises the hypothesis of an independent evolutionary origin of this unique reproductive strategy in individual lineages of lower and higher termites.

Major Hurdles for the Evolution of Sociality

Why do most animals live solitarily, while complex social life is restricted to a few cooperatively breeding vertebrates and social insects? Here, we synthesize concepts and theories in social evolution and discuss its underlying ecological causes. Social evolution can be partitioned into (a) formation of stable social groups, (b) evolution of helping, and (c) transition to a new evolutionary level. Stable social groups rarely evolve due to competition over food and/or reproduction. Food competition is overcome in social insects with central-place foraging or bonanza-type food resources, whereas competition over reproduction commonly occurs because staying individuals are rarely sterile. Hence, the evolution of helping is shaped by direct and indirect fitness options and helping is only altruism if it reduces the helper's direct fitness. The helper's capability to gain direct fitness also creates within-colony conflict. This prevents transition to a new evolutionary level.

Extended longevity of reproductives appears to be common in Fukomys mole-rats (Rodentia, Bathyergidae)

African mole-rats (Bathyergidae, Rodentia) contain several social, cooperatively breeding species with low extrinsic mortality and unusually high longevity. All social bathyergids live in multigenerational families where reproduction is skewed towards a few breeding individuals. Most of their offspring remain as reproductively inactive “helpers” in their natal families, often for several years. This “reproductive subdivision” of mole-rat societies might be of interest for ageing research, as in at least one social bathyergid (Ansell's mole-rats Fukomys anselli), breeders have been shown to age significantly slower than non-breeders. These animals thus provide excellent conditions for studying the epigenetics of senescence by comparing divergent longevities within the same genotypes without the inescapable short-comings of inter-species comparisons. It has been claimed that many if not all social mole-rat species may have evolved similar ageing patterns, too. However, this remains unclear on account of the scarcity of reliable datasets on the subject. We therefore analyzed a 20-year breeding record of Giant mole-rats Fukomys mechowii, another social bathyergid species. We found that breeders indeed lived significantly longer than helpers (ca. 1.5–2.2fold depending on the sex), irrespective of social rank or other potentially confounding factors. Considering the phylogenetic positions of F. mechowii and F. anselli and unpublished data on a third Fukomys-species (F. damarensis) showing essentially the same pattern, it seems probable that the reversal of the classic trade-off between somatic maintenance and sexual reproduction is characteristic of the whole genus and hence of the vast majority of social mole-rats.

Nonrelatives inherit colony resources in a primitive termite

The evolution of eusociality, especially how selection would favor sterility or subfertility of most individuals within a highly social colony, is an unresolved paradox. Eusociality evolved independently in diverse taxa, including insects (all ants and termites; some bees, wasps, thrips, and beetles), snapping shrimp, and naked mole rats. Termites have received comparatively less focus than the haplodiploid Hymenoptera (ants, bees, and wasps); however, they are the only diploid group with highly complex colonies and an extraordinary diversity of castes. In this study we staged encounters between unrelated colonies of primitive dampwood termites, Zootermopsis nevadensis, mimicking natural meetings that occur under bark. During encounters, kings and/or queens were killed and surviving members merged into one colony. After encounters, members of both unrelated colonies cooperated as a single social unit. We determined the colony of origin of replacement reproductives that emerged after death of kings and/or queens. Here, we document that replacement reproductives developed from workers in either or both original colonies, inherited the merged resources of the colony, and sometimes interbred. Because this species shares many characteristics with ancestral termites, these findings demonstrate how ecological factors could have promoted the evolution of eusociality by accelerating and enhancing direct fitness opportunities of helper offspring, rendering relatedness favoring kin selection less critical.

Lifetime reproductive success and longevity of queens in an annual social insect

Although central to understanding life-history evolution, the relationship between lifetime reproductive success and longevity remains uncertain in many organisms. In social insects, no studies have reported estimates of queens' lifetime reproductive success and longevity within populations, despite the importance of understanding how sociality and associated within-group conflict affect life-history traits. To address this issue, we studied two samples of colonies of the annual bumblebee, Bombus terrestris audax, reared from wild-caught queens from a single population. In both samples, queens' lifetime reproductive success, measured as either queens' inclusive fitness or as total biomass of queen-produced sexuals (new queens and males), was significantly positively associated with queen longevity, measured from the day the first worker was produced. We suggest that a positive relationship between reproductive success and longevity was inherited from nonsocial ancestors showing parental care and maintained, at least in part, because the presence of workers buffers queens against extrinsic mortality.

Benefits and costs of secondary polygyny in the dampwood termite Zootermopsis angusticollis

Newly molted female neotenic reproductives of the dampwood termite Zootermopsis angusticollis Hagen were allowed to mature in the presence of a neotenic male, a fixed number of larval helpers, and varying numbers of sibling neotenic queens to assess the impact of secondary polygyny to the individual and colony. Under monogyne conditions, neotenics developed more ovarioles per ovary and had higher individual fecundities after 60 d compared with females under polygyne conditions. Queens in groups of three females were able to gain more body mass than those in groups of five. Although the division of resources provided by helpers reduced individual female development and fecundity under polygyne conditions, it resulted in an overall increase in colony fecundity. In addition, neotenic females in polygynous colonies did not differ significantly in reproductive competence. There was no evidence that neotenics were attacked or injured by other reproductives or larval helpers, suggesting little if any reproductive competition among sibling queens. The physiological responses of neotenics to the increasing queen/worker ratio may have the benefit of enhancing the colony growth at the cost of the fecundity of individual queens.

Inducible immune proteins in the dampwood termite Zootermopsis angusticollis

Dampwood termites, Zootermopsis angusticollis (Isoptera: Termopsidae), mount an immune response to resist microbial infection. Here we report on results of a novel analysis that allowed us to electrophoretically assess changes in hemolymph proteins in the same individual before and after exposure to a pathogen. We demonstrate that contact with a sublethal concentration of the entomopathogenic fungus Metarhizium anisopliae (Deuteromycotina:Hypomycetes) induces the production of protective proteins in nymphs, pseudergates (false workers), and soldiers. Termites exposed to an immunizing dosage of fungal conidia consistently showed an enhancement of constitutive proteins (62-85 kDa) in the hemolymph as well as an induction of novel proteins (28-48 kDa) relative to preimmunization levels. No significant differences in protein banding patterns relative to baseline levels in control and naïve termites were observed. Incubating excised and eluted induced proteins produced by immunized pseudergates or immunized soldiers with conidia significantly reduced the germination of the fungus. The fungistatic effect of eluted proteins differed significantly among five colonies examined. Our results show that the upregulation of protective proteins in the hemolymph underscores the in vivo immune response we previously recorded in Z. angusticollis.

The evolution of male traits in social insects

Pair formation in social insects mostly happens early in adult life and away from the social colony context, which precludes promiscuity in the usual sense. Termite males have continuous sperm production, but males of social Hymenoptera have fixed complements of sperm, except for a few species that mate before female dispersal and show male-fighting and lifelong sperm production. We develop an evolutionary framework for testing sexual selection and sperm competition theory across the advanced eusocial insects (ants, wasps, bees, termites) and highlight two areas related to premating sexual selection (sexual dimorphism and male mate number) that have remained understudied and in which considerable progress can be achieved with relatively simple approaches. We also infer that mating plugs may be relatively common, and we review further possibilities for postmating sexual selection, which gradually become less likely in termite evolution, but for which eusocial Hymenoptera provide unusual opportunities because they have clonal ejaculates and store viable sperm for up to several decades.

Evolution of eusociality and the soldier caste in termites: a validation of the intrinsic benefit hypothesis

In termites the evolution of reproductive altruism is not based on a particularly high relatedness between nestmates. For the evolution and maintenance of the ancestral sterile soldier caste, the benefits generated by the soldiers' presence must compensate the loss of the soldiers' reproductive potential. To study the impact of soldiers on colony's fitness, we manipulated the proportion of soldiers to nonsoldiers in colonies of the dry-wood termite Cryptotermes secundus.'Soldier-less' colonies were obtained by removing soldiers and inhibiting their development with an extract of soldier heads. The colonies were set up for 1 year in experimental nests in the field. 'Soldier-less' colonies produced fewer soldiers. The reduction of soldiers neither affected colony survival nor helper growth, but fewer dispersing sexuals were produced in 'soldier-less' than in control colonies. This confirms what was only supposed so far, that in termites soldiers are maintained for their intrinsic benefit to cost ratio.

From genes to societies

Research on model organisms has substantially advanced our understanding of aging. However, these studies collectively lack any examination of the element of sociality, an important feature of human biology. Social insects present a number of unique possibilities for investigating social influences on aging and potentially detecting new mechanisms for extremely prolonged, healthy life spans that have evolved naturally. Social evolution has led to life spans in reproductive females that are much longer (up to over 100-fold) than those of males or of nonreproductive worker castes. These differences are particularly dramatic because they are due to environmental influences, as all individuals develop from the same genomes. Social insect colonies consist of semi-autonomous individuals, and the relationship between the colony and the individual creates many interesting predictions in the light of the common theories of aging. Furthermore, the variety of lifestyles of social insects creates the potential for crucial comparative analyses across distinct social systems.

Evolution of eusociality and the soldier caste in termites: influence of intraspecific competition and accelerated inheritance

We present new hypotheses and report experimental evidence for powerful selective forces impelling the evolution of both eusociality and the soldier caste in termites. Termite ancestors likely had a nesting and developmental life history similar to that of the living family Termopsidae, in which foraging does not occur outside the host wood, and nonsoldier helpers retain lifelong options for differentiation into reproductives. A local neighborhood of families that live exclusively within a limited resource results in interactions between conspecific colonies, high mortality of founding reproductives, and opportunities for accelerated inheritance of the nest and population by offspring that differentiate into nondispersing neotenic reproductives. In addition, fertile reproductive soldiers, a type of neotenic previously considered rare and docile, frequently develop in this intraspecific competitive context. They can be highly aggressive in subsequent interactions, supporting the hypothesis that intercolonial battles influenced the evolution of modern sterile termite soldier weaponry and behaviors.