Evidence for a conserved queen-worker genetic toolkit across slave-making ants and their ant hosts

The ecological success of social Hymenoptera (ants, bees, wasps) depends on the division of labour between the queen and workers. Each caste is highly specialized in their respective function in morphology, behaviour and life history traits, such as lifespan and fecundity. Despite strong defences against alien intruders, insect societies are vulnerable to social parasites, such as workerless inquilines or slave-making (dulotic) ants. Here, we investigate whether gene expression varies in parallel ways between slave-making ants and their host ants across five independent origins of ant slavery in the Formicoxenus-group of the ant tribe Crematogastrini. As caste differences are often less pronounced in slave-making ants than non-parasitic ants, we also compare the transcriptomes of queens and workers in these species. We demonstrate a substantial overlap in expression differences between queens and workers across taxa, irrespective of lifestyle. Caste affects the transcriptomes much more profoundly than lifestyle, as indicated by 37 times more genes being linked to caste than to lifestyle and by multiple caste-associated gene modules with strong connectivity. However, several genes and one gene module are linked to the slave-making lifestyle across the independent origins, pointing to some evolutionary convergence. Finally, we do not find evidence for an interaction between caste and lifestyle, indicating that caste differences remain consistent even when species switch to a parasitic lifestyle. Our findings are a strong indication for the existence of a core set of genes whose expression is linked to the queen and worker caste in this ant taxon, supporting the genetic-toolkit hypothesis.

The first queen-worker association for Cretaceous Formicidae: the winged caste of Haidomyrmex cerberus

Two queen ant specimens, one alate and one dealate, from mid-Cretaceous (Late Albian–Early Cenomanian) Burmese amber are herein reported as belonging Haidomyrmex cerberus Dlussky, 1996. This is the first discovery and documentation of an alate queen in Haidomyrmex. Compared with workers of Haidomyrmex cerberus, alate and dealate queens are larger in body size, have smaller compound eyes, a longer antennal scape, more complex mandibles, and a relatively large-sized metasoma. It is hypothesized that these differences are due to caste differences.

Shared Devotion, Shared Food

This book is about a deceptively simple question: when Hindu devotional or bhakti traditions welcomed marginalized people—women, low castes, and Dalits—were they promoting social equality? This is the modern formulation of the bhakti-caste question. It is what Dalit leader B. R. Ambedkar had in mind when he concluded that the saints promoted spiritual equality but did not transform society. While taking Ambedkar’s judgment seriously, when viewed in the context of intellectual history and social practice, the bhakti-caste question is more complex. This book dives deeply into Marathi sources to explore how one tradition in western India worked out the relationship between bhakti and caste on its own terms. Food and eating together were central to this. As stories about saints and food changed while moving across manuscripts, theatrical plays, and films, the bhakti-caste relationship went from being a strategically ambiguous riddle to a question that expected—and received—answers. Shared Devotion, Shared Food demonstrates the value of critical commensality to understand how people carefully negotiate their ethical ideals with social practices. Food’s capacity to symbolize many things made it made an ideal site for debating bhakti’s implications about caste differences. In the Vārkarī tradition, strategically deployed ambiguity and the resonating of stories across media over time developed an ideology of inclusive difference—not social equality in the modern sense, but an alternative holistic view of society.

The Scent of Ant Brood: Caste Differences in Surface Hydrocarbons of Formica exsecta Pupae

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.

Bumble bee queens activate dopamine production and gene expression in nutritional signaling pathways in the brain

To explore the neuroendocrine mechanisms underlying caste-specific behavior and its evolution from primitive to advanced eusocial bees, the monoamine levels and expression of genes involved in monoamine production and signaling in the brain were compared between the castes of Bombus ignitus. Higher levels of dopamine and its related substances were found in the brains of newly emerged queens than in the brains of emerged workers. The degree of caste differences in B. ignitus was smaller than that reported in Apis mellifera, indicating a link to different social stages in the two species. There was no differential expression in genes involved in dopamine biosynthesis between castes, suggesting that the high dopamine production in queens was not largely influenced by the expression of these genes at emergence, rather it might be influenced by tyrosine supply. Genome-wide analyses of gene expression by RNA-sequencing indicated that a greater number of genes involved in nutrition were actively expressed in the brains of newly emerged queens in comparison to the emerged workers. Some of the expression was confirmed by real-time quantitative PCR. The signaling pathways driven by the expression of these genes may be associated with dopamine signaling or the parallel activation of dopamine production.

Cuticular hydrocarbon profiles differ between ant body parts: implications for communication and our understanding of CHC diffusion

Insect cuticular hydrocarbons (CHCs) serve as communication signals and protect against desiccation. They form complex blends of up to 150 different compounds. Due to differences in molecular packing, CHC classes differ in melting point. Communication is especially important in social insects like ants, which use CHCs to communicate within the colony and to recognize nestmates. Nestmate recognition models often assume a homogenous colony odour, where CHCs are collected, mixed and re-distributed in the postpharyngeal gland (PPG). Via diffusion, recognition cues should evenly spread over the body surface. Hence, CHC composition should be similar across body parts and in the PPG. To test this, we compared CHC composition among whole-body extracts, PPG, legs, thorax and gaster, across 17 ant species from three genera. Quantitative CHC composition differed between body parts, with consistent patterns across species and CHC classes. Early-melting CHC classes were most abundant in the PPG. In contrast, whole body, gaster, thorax and legs had increasing proportions of CHC classes with higher melting points. Intra-individual CHC variation was highest for rather solid, late-melting CHC classes, suggesting that CHCs differ in their diffusion rates across the body surface. Our results show that body parts strongly differ in CHC composition, either being rich in rather solid, late-melting or rather liquid, early-melting CHCs. This implies that recognition cues are not homogenously present across the insect body. However, the unequal diffusion of different CHCs represents a biophysical mechanism that enables caste differences despite continuous CHC exchange among colony members.

Alcohol intoxication resistance and alcohol dehydrogenase levels differ between the honeybee castes

Various animal models are used in the study of alcoholism, with the honeybee (Apis mellifera L.) among them. Here, we tested the hypothesis that foragers show higher intoxication resistance to alcohol than nurses, an issue thus far not investigated. To this end, we measured the latency to full sedation when exposed to alcohol in foragers, nurses and reverted nurses. In addition, we measured alcohol dehydrogenase (ADH) levels in these worker castes. Caste status was confirmed by comparison of the size of their hypopharyngeal glands. We detected high intoxication resistance to alcohol and presence of ADH in foragers. In nurses, we detected significantly lower intoxication resistance to alcohol and no ADH. These between-caste differences cannot be explained by the age difference between castes as in reverted nurses, characterized by similar age to foragers, we detected an intermediate intoxication resistance to alcohol and no ADH. Our results suggest possible natural exposure to alcohol in different castes of workers. As such, we further develop the honeybee as a model in alcoholism-related research and open new research avenues.

Living on the Edge: Interrogating Migrant Labourer Lives of Bengaluru/Bangalore

This paper proposes to create a discourse of migrant labourers in the city of Bengaluru/Bangalore, especially during the current period of crisis ensued by COVID-19 pandemic. Despite being an essential part of the informal sector economy these workers are often rendered invisible from the urban social, cultural and political spaces of this global city. The United Nations Conference on Housing and Sustainable Development (Habitat III), held in Quito, Ecuador in October 2016 declared the New Urban Agenda (NUA) — that was adopted as the guideline for urban development for the next twenty years — with the vision of ‘cities for all’. But in reality, for their regional, linguistic, cultural, class and caste differences, the migrant labourers in the city are marginalized from the mainstream urban scene. The paper investigates the historiography of the migrant labourers in the city to interrogate the space they occupy in Bengaluru/Bangalore. Some of the important questions the paper attempts to grapple with are also about their fight for survival amidst the outbreak of COVID-19 pandemic and the relief measure responses from the state. Evidences show, the immigrant labourers are perceived as the city’s necessary ‘Other’ who are needed to build the city but barely finds any representation in the planning grids of urban architects. Their direct experiences and negotiations with ‘the lived city’, available from news archives and other secondary sources, will be interrogated through the lens of ‘the Right to the City’, a concept introduced by Henri Lefebvre. The paper attempts to explore if they have any agency to assert their rights to the city and become a meaningful stakeholder in the democratic control over Bengaluru/Bangalore.

Gauging Class and Caste differences in Mortality: The Indian Experience

This study is an exposition of class-caste based differences in mortality experience based on an indicator called household prevalence of death. It involves 75,432 death cases collected in National Family Health Survey-4, analysed using Relative Deprivation Index (RDI). We found, the prevalence of death found to be 11.8% in India, which varies across states and social and economic groups. The RDI values depict that the poorer households along with social group identities like schedule tribe and schedule caste households displayed a uniform disadvantage as regarding mortality across many states. The analysis offers evidence on differential experience of mortality across socio-economic identities. The evidence suggests poorer states having a marked disadvantage along with social and economic classes.

Antennal Proteome of the Solenopsis invicta (Hymenoptera: Formicidae): Caste Differences in Olfactory Receptors and Chemosensory Support Proteins

Little is known about the expression pattern of odorant and pheromone transporters, receptors, and deactivation enzymes in the antennae of ants carrying out different tasks. In order to begin filling in this information gap, we compared the proteomes of the antennae of workers and males of the red fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae). Male ants do not perform any colony work, and their only activity is to leave the nest on a mating flight. Previous studies showed that male ants express fewer types of odorant receptors than workers. Thus, we expected to find large differences between male and worker antennae for expression of receptors, transporters, and deactivators of signaling chemicals. We found that the abundance of receptors was consistent with the expected caste-specific signaling complexity, but the numbers of different antenna-specific transporters and deactivating enzymes in males and workers were similar. It is possible that some of these proteins have antenna-specific functions that are unrelated to chemosensory reception. Alternatively, the similar complexity could be a vestige of ant progenitors that had more behaviorally active males. As the reduced behavior of male ants evolved, the selection process may have favored a complex repertoire of transporters and deactivating enzymes alongside a limited repertoire of odorant receptors.