Termites evolved eusociality independently from social Hymenoptera. As a common trait, reproductive monopoly is maintained through chemical communication. The queen (and in termites also a king) ...prevents workers from reproduction by conveying their reproductive status. In termites all soldiers are sterile, but workers’ potential to reproduce differs between species. It ranges from totipotency in wood-dwelling lower termites where workers are a transient stage from which all other castes develop, to sterile workers in some higher termites. Intermediate are species in which workers can develop into replacement sexuals within the nest but not into winged sexuals. I summarize the patchy picture about fertility signaling that we currently have for termites, pointing also to potential conflicts over reproduction that differ from those in social Hymenoptera. Recent findings imply that, similar to many social Hymenoptera, wood-dwelling termites that live in confined nests use long-chain cuticular hydrocarbons (CHCs) as fertility signals. Yet other compounds are important as well, comprising proteinaceous secretions and especially volatiles. For a subterranean termite, two volatiles have been identified as primer pheromones that prevent reproductive differentiation of workers. It requires more data to test whether wood-dwelling termites use CHCs, while species with larger colonies and less confined nests use volatiles, or whether all species rely on multicomponent signals. Ultimately, we need more effort to model and test potential conflicts over reproduction between queens, kings and workers. Here results from social Hymenoptera cannot be transferred to termites as the latter are diploid and commonly inbred. This review illustrates promising future research avenues.
Many ants have independently evolved castes with novel morphology as well as function, such as soldiers and permanently wingless (ergatoid) queens. We present a conceptual model, based on modularity ...in morphology and development, in which evolutionary innovation is facilitated by the ancestral ant polyphenism of winged queens and wingless workers. We suggest that novel castes evolved from rare intercastes, anomalous mosaics of winged queens and workers, erratically produced by colonies through environmental or genetic perturbations. The colonial environment is highly accommodating and buffers viable intercastes from individual selection. Their cost is limited because they are diluted by the large number of nestmates, yet some can bring disproportionate benefits to their colonies in the context of defense or reproduction (e.g., wingless intercastes able to mate). Useful intercastes will increase in frequency as their morphology is stabilized through genetic accommodation. We show that both soldiers and ergatoid queens are mosaics of winged queens and workers, and they are strikingly similar to some intercastes. Modularity and developmental plasticity together with winged/wingless polyphenism thus allow for the production of highly variable mosaic intercastes, and colonies incubate the advantageous mosaics.
A colony of
Protanilla
sp. was collected from the floor of a selectively logged forest in Ulu Gombak, Peninsular Malaysia, in March 2011. The colony contained 17 ergatoid queens and 25 workers. The ...ergatoid queens had 6–10 ovarioles per individual with a sperm-filled spermatheca while workers had two ovarioles and a vestigial spermatheca. In the laboratory, foraging workers responded to
Occasjapyx
sp. (Japygidae) only; larvae, workers, and ergatoid queens fed on this prey. Ergatoid queens frequently showed larval and egg care, and transported larvae when the nest was disturbed. Compared to
Leptanilla
, morphological and behavioral specialization of both castes in
Protanilla
sp. does not seem developed.
Strongly polyphenic social insects provide excellent models to examine the neurobiological basis of division of labor. Turtle ants, Cephalotes varians, have distinct minor worker, soldier, and ...reproductive (gyne/queen) morphologies associated with their behavioral profiles: small-bodied task-generalist minors lack the phragmotic shield-shaped heads of soldiers, which are specialized to block and guard the nest entrance. Gynes found new colonies and during early stages of colony growth overlap behaviorally with soldiers. Here we describe patterns of brain structure and synaptic organization associated with division of labor in C. varians minor workers, soldiers, and gynes. We quantified brain volumes, determined scaling relationships among brain regions, and quantified the density and size of microglomeruli, synaptic complexes in the mushroom body calyxes important to higher-order processing abilities that may underpin behavioral performance. We found that brain volume was significantly larger in gynes; minor workers and soldiers had similar brain sizes. Consistent with their larger behavioral repertoire, minors had disproportionately larger mushroom bodies than soldiers and gynes. Soldiers and gynes had larger optic lobes, which may be important for flight and navigation in gynes, but serve different functions in soldiers. Microglomeruli were larger and less dense in minor workers; soldiers and gynes did not differ. Correspondence in brain structure despite differences in soldiers and gyne behavior may reflect developmental integration, suggesting that neurobiological metrics not only advance our understanding of brain evolution in social insects, but may also help resolve questions of the origin of novel castes.
Current global challenges call for a rigorously predictive ecology. Our understanding of ecological strategies, imputed through suites of measurable functional traits, comes from decades of work that ...largely focussed on plants. However, a key question is whether plant ecological strategies resemble those of other organisms.
Among animals, ants have long been recognised to possess similarities with plants: as (largely) central place foragers. For example, individual ant workers play similar foraging roles to plant leaves and roots and are similarly expendable. Frameworks that aim to understand plant ecological strategies through key functional traits, such as the ‘leaf economics spectrum’, offer the potential for significant parallels with ant ecological strategies.
Here, we explore these parallels across several proposed ecological strategy dimensions, including an ‘economic spectrum’, propagule size‐number trade‐offs, apparency‐defence trade‐offs, resource acquisition trade‐offs and stress‐tolerance trade‐offs. We also highlight where ecological strategies may differ between plants and ants. Furthermore, we consider how these strategies play out among the different modules of eusocial organisms, where selective forces act on the worker and reproductive castes, as well as the colony.
Finally, we suggest future directions for ecological strategy research, including highlighting the availability of data and traits that may be more difficult to measure, but should receive more attention in future to better understand the ecological strategies of ants. The unique biology of eusocial organisms provides an unrivalled opportunity to bridge the gap in our understanding of ecological strategies in plants and animals and we hope that this perspective will ignite further interest.
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Read the free Plain Language Summary for this article on the Journal blog.
Chemical communication is common across all organisms. Insects in particular use predominantly chemical stimuli in assessing their environment and recognizing their social counterparts. One of the ...chemical stimuli used for recognition in social insects, such as ants, is the suite of long-chain, cuticular hydrocarbons. In addition to providing waterproofing, these surface hydrocarbons serve as a signature mixture, which ants can perceive, and use to distinguish between strangers and colony mates, and to determine caste, sex, and reproductive status of another individual. They can be both environmentally and endogenously acquired. The surface chemistry of adult workers has been studied extensively in ants, yet the pupal stage has rarely been considered. Here we characterized the surface chemistry of pupae of
Formica exsecta
, and examine differences among sexes, castes (reproductive vs. worker), and types of sample (developing individual vs. cocoon envelope). We found quantitative and qualitative differences among both castes and types of sample, but male and female reproductives did not differ in their surface chemistry. We also found that the pupal surface chemistry was more complex than that of adult workers in this species. These results improve our understanding of the information on which ants base recognition, and highlights the diversity of surface chemistry in social insects across developmental stages.
Termites (Blattodea, Termitoidea, or Isoptera) constitute one of the major lineages of eusocial insects. In termite societies, multiple types of functional individuals, that is, castes, perform ...divisions of labors to coordinate social behaviors. Among other castes, the soldier caste is distinctive since it is sterile and exclusively specialized into defensive behavior with largely modified morphological features. Therefore, many of the previous studies have been focused on soldiers, in terms of ecology, behavior, and evolution as well as developmental and physiological mechanisms. This article overviews the accumulation of studies especially focusing on the developmental and physiological mechanisms underlying the soldier differentiation in termites. Furthermore, the evolutionary trajectories that have led the acquisition of soldier caste and have diversified the soldier characteristics in association with the social evolution are discussed.
Termites possess soldiers in their colonies. This article overviews the recent advances of studies on physiological and developmental mechanisms underlying the soldier differentiation in termites, together with the evolutionary implications.
Ants use various communication channels to regulate their social organisation. The main channel that drives almost all the ants' activities and behaviours is the chemical one, but it is long ...acknowledged that the acoustic channel also plays an important role. However, very little is known regarding exploitation of the acoustical channel by myrmecophile parasites to infiltrate the ant society. Among social parasites, the ant nest beetles (Paussus) are obligate myrmecophiles able to move throughout the colony at will and prey on the ants, surprisingly never eliciting aggression from the colonies. It has been recently postulated that stridulatory organs in Paussus might be evolved as an acoustic mechanism to interact with ants. Here, we survey the role of acoustic signals employed in the Paussus beetle-Pheidole ant system. Ants parasitised by Paussus beetles produce caste-specific stridulations. We found that Paussus can "speak" three different "languages", each similar to sounds produced by different ant castes (workers, soldiers, queen). Playback experiments were used to test how host ants respond to the sounds emitted by Paussus. Our data suggest that, by mimicking the stridulations of the queen, Paussus is able to dupe the workers of its host and to be treated as royalty. This is the first report of acoustic mimicry in a beetle parasite of ants.
Effective coordination of group actions underlies the success of group‐living organisms. Making decisions collectively is a crucial step in executing behaviours affecting the whole group. In social ...insects, decision‐making is typically achieved in a self‐organised manner and incorporates a quorum process, which can improve decision accuracy and be tailored to different conditions. Studies of the nest‐selection process in different social insect species have revealed remarkable consistency in the mode of decision‐making despite marked differences in life history and colony size. However, an often‐overlooked aspect of this decision process is how it might be influenced by diversity in behavioural propensity among colony members. Higher diversity can improve collective processes, but could also represent a cost if certain classes of individual do not contribute to the cooperative activity. Many ant species exhibit caste polymorphism, with different worker castes specialised to different functions. These castes could thus enhance or erode the collective decision process depending on whether they contribute to this process or not. In this study, we explore the process of colony emigration and nest‐site choice in the small carpenter ant Camponotus yamaokai, a species with two distinct worker castes. We show that this species is likely to use a quorum decision process facilitated by navigation with chemical trails. Both major and minor castes contributed to the collective decision and emigration process. However, although major workers comprised 24% of the colony on average, they were 5.5 times less likely than expected to be involved in assessing new nests and 4.6 times less likely than expected to contribute to brood transport. This may represent a previously unrecognised cost to the colony in the emigration process. In addition, we document the first observations of sequential brood transfer during emigration behaviour and speculate upon the function of this behaviour.
In this study, we explore how different castes contribute to collective decision‐making during nest emigration in an ant with major and minor workers. We find that majors of Camponotus yamaokai make a lower‐than‐expected contribution to colony emigration, though no evidence this impaired the emigration process. We show that this species likely uses a quorum‐decision process facilitated by chemical trails and document the novel behaviour of sequential brood transport.
Poverty is multifaceted. The global poverty profile shows 41% of multidimensionally poor people living in South Asian countries. Though castes and tribes are a more prevalent line of social ...stratification in India, and their socio-economic characteristics also vary remarkably, hardly any study has explored these dimensions while analysing multidimensional poverty in India. Hence, this study attempts to assess the multidimensional status of poverty among the social groups in India. National Family Health Survey, 2015-16 (NFHS-4) is a source of rich information on 579,698 households' well-being for this analysis. Alkire- Foster technique was applied to decompose the Multidimensional Poverty Index (M.sub.0) across its dimensions and indicators for all the social groups. Three broad dimensions of deprivation-Health, Education and Standard of Living-include 12 indicators, guided by the poverty literature, data availability and the country's sustainable Development Goals (SDGs). There were three main findings in this study: (1) Scheduled Tribes (STs) are the most disadvantaged subgroup in India with remarkably high values of headcount (H = 0.444;), intensity (A = 0.486), and M.sub.0 (0.216), followed by Scheduled Castes (SCs) (H = 0.292; A = 0.473; M.sub.0 = 0.138), and Other Backward Classes (OBCs) (H = 0.245; A = 0.465; M.sub.0 = 0.114); and Others category is the most privileged with very low values of H = 0.149, A = 0.463, and M.sub.0 = 0.069; (2) STs contribute nearly twice their population share for both H and M.sub.0, and the SCs contribution is also noticeably higher than their population share; (3) States located in the central and eastern regions of India have the higher H, A and M.sub.0 for all the social groups. This suggests that there is a need for a thorough assessment of poverty at specific levels to uncover the poverty situation in society, improve the effectiveness of evidence-based planning and effective policymaking.
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