Reproductive Division Of Labor Research Articles

Cell type specific polyploidization in the royal fat body of termite queens

Tissue-specific endopolyploidy is widespread among plants and animals and its role in organ development and function has long been investigated. In insects, the fat body cells of sexually mature females produce substantial amounts of egg yolk precursor proteins (vitellogenins) and exhibit high polyploid levels, which is considered crucial for boosting egg production. Termites are social insects with a reproductive division of labor, and the fat bodies of mature termite queens exhibit higher ploidy levels than those of other females. The fat bodies of mature termite queens are known to be histologically and cytologically specialized in protein synthesis. However, the relationship between such modifications and polyploidization remains unknown. In this study, we investigated the relationship among cell type, queen maturation, and ploidy levels in the fat body of the termite Reticulitermes speratus. We first confirmed that the termite fat body consists of two types of cells, that is, adipocytes, metabolically active cells, and urocytes, urate-storing cells. Our ploidy analysis using flow cytometry has shown that the fat bodies of actively reproducing queens had more polyploid cells than those of newly emerged and pre-reproductive queens, regardless of the queen phenotype (adult or neotenic type). Using image-based analysis, we found that not urocytes, but adipocytes became polyploid during queen differentiation and subsequent sexual maturation. These results suggest that polyploidization in the termite queen fat body is associated with sexual maturation and is regulated in a cell type-specific manner. Our study findings have provided novel insights into the development of insect fat bodies and provide a basis for future studies to understand the functional importance of polyploidy in the fat bodies of termite queens.

Plastic brain structure changes associated with the division of labour and ageing in termites.

Division of labour is a prominent feature of social insect societies, where different castes engage in different specialised tasks. As brain differences are associated with behavioural differences, brain anatomy may be linked to caste polymorphism. Here, we show that termite brain morphology changes markedly with caste differentiation and age in the termite, Reticulitermes speratus. Brain morphology was shown to be associated with reproductive division of labour, with reproductive individuals (alates and neotenic reproductives) having larger brains than non-reproductives (workers and soldiers). Micro-computed tomography (CT) imaging and dissection observations showed that the king's brain morphology changed markedly with shrinkage of the optic lobes during their long life in the dark. Behavioural experiments showed that mature primary kings lose visual function as a result of optic lobe shrinkage. These results suggested that termites restructure their nervous systems to perform necessary tasks as they undergo caste differentiation, and that they also show flexible changes in brain morphology even after the final moult. This study showed that brain morphology in social insects is linked to caste and ageing, and that the evolution of the division of labour is underpinned by the development of diverse neural systems for specialised tasks. This article is protected by copyright. All rights reserved.

The Evolution of Eusociality: Insights From Comparing Two Indian Paper Wasp Species

Eusocial species live in colonies with a reproductive division of labour into fertile reproductive castes and sterile non-reproductive castes, an overlap of generations and cooperative brood care. A further distinction can be usefully made between primitively eusocial species which do not have morphological caste differentiation and highly eusocial species which do. Ropalidia marginata is a tropical primitively eusocial wasp that has been extensively studied, especially compared to other tropical social wasps. R. marginata has several distinct traits, such as a docile queen, well-developed age polyethism, and decentralized work regulation, which makes it different from other primitively eusocial wasps and reminiscent of highly eusocial species. since tropical wasps, especially those belonging to the genus Ropalidia have been poorly studied, we cannot be sure whether R. marginata is unique or its traits are more common among tropical Ropalidia species. to begin to overcome this problem, we have extended our research to the congeneric and sympatric Ropalidia cyathiformis. Here, we compare and contrast what we now know about these two species, especially concerning their reproductive and non-reproductive division of labour. We find that R. cyathiformis, unlike R. marginata, has a behaviourally dominant queen, weak and rigid age polyethism, likely uses behavioural dominance to regulate worker reproduction and individual workers self-regulate their own non-reproductive activities. We, therefore, conclude that R. marginata is indeed unique and argue that R. marginata is intermediate between primitively and highly eusocial wasps.

Honeybee queen mandibular pheromone induces a starvation response in Drosophila melanogaster

Eusocial insect societies are defined by the reproductive division of labour, a social structure that is generally enforced by the reproductive dominant(s) or ‘queen(s)’. Reproductive dominance is maintained through behavioural dominance or production of queen pheromones, or a mixture of both.Queen mandibular pheromone (QMP) is a queen pheromone produced by queen honeybees (Apis mellifera) which represses reproduction in worker honeybees. How QMP acts to repress worker reproduction, the mechanisms by which this repression is induced, and how it has evolved this activity, remain poorly understood. Surprisingly, QMP is capable of repressing reproduction in non-target arthropods.Here we show that in Drosophila melanogaster QMP treatment mimics the starvation response, disrupting reproduction. QMP exposure induces an increase in food consumption and activation of checkpoints in the ovary that reduce fecundity and depresses insulin signalling. The magnitude of these effects is indistinguishable between QMP-treated and starved individuals. As QMP triggers a starvation response in an insect diverged from honeybees, we propose that QMP originally evolved by co-opting nutrition signalling pathways to regulate reproduction.

DNA methylation and expression of the egfr gene are associated with worker size in monomorphic ants.

The reproductive division of labour is a hallmark of eusocial Hymenoptera. Females are either reproductive queens or non-reproductive workers. In ants, workers often display further task specialisation that is associated with variation in size and/or morphology. Because female polyphenism is typically under environmental control, it is thought epigenetic mechanisms (such as DNA methylation) play a central role since they mediate gene-by-environment interactions. Methylation of the growth-promoting gene epidermal growth factor receptor (egfr) was indeed shown to control worker size in a highly polymorphic ant. However, it remains unknown if egfr methylation could also regulate worker size in monomorphic species. By combining experimental pharmacology and molecular biology, we show that worker size is associated with egfr methylation in two monomorphic ants. Furthermore, we functionally demonstrate that EGFR signalling affects worker size. These results indicate that worker size regulation by egfr methylation has been mechanistically conserved in ants but remains unexploited in monomorphic species.

Environmentally responsive reproduction: neuroendocrine signalling and the evolution of eusociality.

Eusociality is a rare but successful life-history strategy that is defined by the reproductive division of labour. In eusocial species, most females forgo their own reproduction to support that of a dominant female or queen. In many eusocial insects, worker reproduction is inhibited via dominance hierarchies or by pheromones produced by the queen and her brood. Here, we consider whether these cues may act as generic ‘environmental signals’, similar to temperature or nutrition stress, which induce a state of reproductive dormancy in some solitary insects. We review the recent findings regarding the mechanisms of reproductive dormancy in insects and highlight key gaps in our understanding of how environmental cues inhibit reproduction.

Deterministic Response Threshold Models of Reproductive Division of Labor Are More Robust Than Probabilistic Models in Artificial Ants.

We implement an agent-based simulation of the response threshold model of reproductive division of labor. Ants in our simulation must perform two tasks in their environment: forage and reproduce. The colony is capable of allocating ant resources to these roles using different division of labor strategies via genetic architectures and plasticity mechanisms. We find that the deterministic allocation strategy of the response threshold model is more robust than the probabilistic allocation strategy. The deterministic allocation strategy is also capable of evolving complex solutions to colony problems like niche construction and recovery from the loss of the breeding caste. In addition, plasticity mechanisms had both positive and negative influence on the emergence of reproductive division of labor. The combination of plasticity mechanisms has an additive and sometimes emergent impact.

Self-Domestication Underground? Testing for Social and Morphological Correlates of Animal Personality in Cooperatively-Breeding Ansell’s Mole-Rats (Fukomys anselli)

Ansell’s mole-rats (Fukomys anselli) are sexually dimorphic subterranean rodents that live in families consisting of a single breeding pair and their late-dispersing non-breeding offspring. Most individuals exhibit a conspicuous white head patch, which results from integumental depigmentation. Alongside other morphological, physiological, and social characteristics, skin depigmentation in these social rodents mirrors traits that presumably evolved as byproducts from selection against aggression in domestic animals, making them a potential candidate species for a self-domesticated wild mammal. Here we explored whether the expression of the white head patch, sexual dimorphism, and reproductive division of labor are reflected by different personalities in Ansell’s mole-rats. We tested locomotory activity and risk-taking as well as aggression and affiliative behavior in 51 individuals originating from nine captive families in various experimental set-ups. In line with the concept of animal personality, we recovered consistent individual responses over time. While sex had no influence on any tested variable, reproductive status was found to affect risk-taking behavior but not other personality dimensions. Discriminant function analysis revealed that family members clustered more closely together than expected by chance, suggesting that group affiliation rather than sex or social status determines behavioral profiles in this species. Finally, we failed to recover any consistent correlation between head patch expression and behavior, which conflicts with predictions of the self-domestication hypothesis. We argue that many domestication-like traits in Ansell’s mole-rat and its congeners evolved in the framework of subterranean adaptation and call for a cautious application of the self-domestication concept to wild mammals.

Evolution and functionalization of vitellogenin genes in the termite Reticulitermes speratus.

Eusociality has been commonly observed in distinct animal lineages. The reproductive division of labor is a particular feature, achieved by the coordination between fertile and sterile castes within the same nest. The sociogenomic approach in social hymenopteran insects indicates that vitellogenin (Vg) has undergone neo-functionalization in sterile castes. Here, to know whether Vgs have distinct roles in nonreproductive castes in termites, we investigated the unique characteristics of Vgs in the rhinotermitid termite Reticulitermes speratus. The four Vgs were identified from R. speratus (RsVg1-4), and RsVg3 sequences were newly identified using the RACE method. Molecular phylogenetic analysis supported the monophyly of the four termite Vgs. Moreover, the termites Vg1-3 and Vg4 were positioned in two different clades. The dN/dSratios indicated that the branch leading to the common ancestor of termite Vg4 was under weak purifying selection. Expression analyses among castes (reproductives, workers, and soldiers) and females (nymphs, winged alates, and queens) showed that RsVg1-3 was highly expressed in fertile queens. In contrast, RsVg4 was highly expressed in workers and female nonreproductives (nymphs and winged adults). Localization of RsVg4messenger RNAwas confirmed in the fat body of worker heads and abdomens. These results suggest that Vg genes are functionalized after gene duplication during termite eusocial transition and that Vg4 is involved in nonreproductive roles in termites.

Population genomics supports multiple hybrid zone origins of socially hybridogenetic lineages of Pogonomyrmex harvester ants.

Reproductive division of labor in the social insects is typically determined by environmental cues; however, genetic effects on caste have been discovered in a growing set of ant taxa. An extreme form of genetic caste determination is "social hybridogenesis," in which co-occurring genetic lineages obligately interbreed to produce workers, whereas daughter queens are of pure-lineage ancestry. In this study, we tested the hypothesis that social hybridogenesis in the genus Pogonomyrmex resulted from one or more interspecific hybridization events, and if so, whether individual lineages were of hybrid ancestry. We reconstructed evolutionary relationships of four lineage pairs to populations of two closely related non-hybridogenetic species, Pogonomyrmex barbatus and Pogonomyrmex rugosus, using nuclear SNP loci and mitochondrial sequencing. The nuclear phylogeny supported a hybridization hypothesis, with one member of each pair nested within P. rugosus, whereas the other was nested within P. barbatus. The source populations corresponded with two distinct geographic areas at the eastern and western edges of a zone of contact. Relatively little gene flow was detected between interbreeding lineages, either historically or currently. This suggests that shifts in reproductive caste determination may reinforce reproductive incompatibility, in a manner similar to the evolution of hybridogenesis in nonsocial systems.

Parasite resistance and immunity across female castes in a social insect

Living in a social group increases the risks of parasitism, especially in highly-related groups. In homogenous groups, with no reproductive division of labour, the impact of parasitism is unlikely to vary with host identity. Many social systems, however, do exhibit division of reproductive labour, most famously in social insects with their reproductive queens and generally infertile workers. In such systems, the impact of parasitism will differ for each group. Consequently, we predict that susceptibility to parasites will vary to reflect such differential impact. We tested this prediction using a trypanosome-bumble bee system, where Crithidia bombi infects both gynes and workers of Bombus terrestris. We studied both susceptibility to the parasite and relevant measures of the immune function. As predicted, gynes were significantly less susceptible to the parasite than workers, but while gynes and workers expressed different immune profiles, how these link to differential susceptibility remains unclear. In conclusion, our results suggest that differential selection pressures exerted by parasites may produce multiple phenotypes from a single genotype in order to maximise fitness in a social group context.Significance statementSocial insect colonies dominate terrestrial ecology, and as such are targets for parasites. How they defend themselves against such threats is a key question. Here, we show that bumble bee gynes — the reproductive individuals that overwinter and found colonies in this annual social system — are more resistant to a parasite that disproportionately affects reproductive fitness than their sister workers. Differential patterns of susceptibility may help to explain the success of these social insects.

The Extension of Foundress Life Span and the Evolution of Eusociality in the Hymenoptera.

AbstractThe evolution of effectively sterile workers in the aculeate Hymenoptera (ants, bees, and stinging wasps) requires that a female's life span largely overlap that of her daughters. The evolution of long nest foundress life spans in eusocial species from the short life spans of solitary species is investigated. Analyses that control for phylogeny show for the first time that foundress adult life span increases and first-brood offspring development time decreases with increasing colony size, resulting in the ratio of foundress adult life span to worker total life span increasing with increasing colony size. These patterns support the hypothesis that the reproductive division of labor increases with increasing colony size, explaining the evolution of effectively sterile workers in species with large colonies. However, there is a discrete increase in foundress adult life span in the transition from noneusociality to eusociality that is independent of colony size. An analysis of life history characters suggests that this increase is explained by nests being founded by multiple females and progressive feeding of larvae as they develop. A reduced rate of senescence of a dominant cofoundress may be selected as a plastic response to social status if high-risk tasks performed by subordinate cofoundresses reduce the dominant's extrinsic mortality rate. Multiple-foundress nests in which one female is responsible for most or all of the reproduction (semisociality) and in which foundresses are full sisters are favored by haplodiploidy, perhaps explaining why eusociality is so common in the Hymenoptera.

La división intrafamiliar del trabajo en el marco de los procesos migratorios: entre ires y venires

This article analyzes some implications of migratory processes in the family world. Specifically, it investigates the division of reproductive labor into families where at least one of the parents returned to Colombia from Spain. The biographical method is used to examine the family organizational system before emigration and after the return. The results show changes, permanence, and resistance to the traditional division of labor, even though staying in Spain seems to have introduced some balance, after returning, the findings point to the provisional nature of some of these arrangements. The consolidation of female co-suppliers is evident, while men do not end up assuming their role in domestic chores. It is concluded that slowly and without contradictions, progress is being made in the transition process towards more democratic relations, where factors beyond migration combine withit to encourage the emerging processes of change.

The build-up of dominance hierarchies in eusocial insects.

Reproductive division of labour is a hallmark of eusocial insects. However, its stability can often be hampered by the potential for reproduction by otherwise sterile nest-mates. Dominance hierarchy has a crucial role in some species in regulating which individuals reproduce. Compared with those in vertebrates, the dominance hierarchies in eusocial insects tend to involve many more individuals, and should require additional selective forces unique to them. Here, we provide an overview of a series of studies on dominance hierarchies in eusocial insects. Although reported from diverse eusocial taxa, dominance hierarchies have been extensively studied in paper wasps and ponerine ants. Starting from molecular physiological attributes of individuals, we describe how the emergence of dominance hierarchies can be understood as a kind of self-organizing process through individual memory and local behavioural interactions. The resulting global structures can be captured by using network analyses. Lastly, we argue the adaptive significance of dominance hierarchies from the standpoint of sterile subordinates. Kin selection, underpinned by relatedness between nest-mates, is key to the subordinates' acceptance of their positions in the hierarchies. This article is part of the theme issue 'The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies'.

Foraging gene expression patterns in queens, workers, and males in a eusocial insect

Reproductive division of labour is based on biased expression of complementary parental behaviours, brood production (egg-laying) by queens and brood care (in particular, brood-provisioning) by workers. In many social insect species, queens provision brood when establishing colonies at the beginning of a breeding season and reproductive division of labour begins with the emergence of workers. In many social insect species, the expression of foraging (for) mRNA is associated with the intensity of foraging behaviour and therefore brood-provisioning. However, only two studies have compared queen and worker for expression levels and neither accounted for transcript splice variation. In this study, we compare the expression level of the for-α transcript variant across four life stages of the queen caste, two behavioural groups of workers, and males of a eusocial sweat bee Lasioglossum laevissimum (Smith, 1853). Foundresses collected prior to the onset of the foraging season and males had the highest for-α expression levels. All active (post-hibernatory) queens and workers had similar for-α expression levels independent of behaviour. These results suggest that the for gene in L. laevissimum acts as a primer before foraging activity and that caste-specific expression patterns correlate with the timing of foraging activity in queens and workers.

Non-kin Cooperation in Ants

Eusociality represents an extreme form of social behavior characterized by a reproductive division of labor. Eusociality necessarily evolved through kin selection, which requires interactions among related individuals. However, many eusocial taxa also show cooperation between non-kin groups, challenging the idea that cooperative actions should only occur among relatives. This review explores the causes and consequences of non-kin cooperation in ants. Ants display a diversity of behaviors that lead to non-kin cooperation within and between species. These interactions occur among both reproductive and non-reproductive individuals. The proximate and ultimate mechanisms leading to non-kin cooperative interactions differ substantially depending on the biotic and abiotic environment. We end this review with directions for future research and suggest that the investigation of non-kin cooperative actions provides insight into processes leading to social evolution.

Molecular underpinnings of division of labour among workers in a socially complex termite

Division of labour characterizes all major evolutionary transitions, such as the evolution of eukaryotic cells or multicellular organisms. Social insects are characterized by reproductive division of labour, with one or a few reproducing individuals (queens) and many non-reproducing nestmates (workers) forming a colony. Among the workers, further division of labour can occur with different individuals performing different tasks such as foraging, brood care or building. While mechanisms underlying task division are intensively studied in social Hymenoptera, less is known for termites, which independently evolved eusociality. We investigated molecular mechanisms underlying task division in termite workers to test for communality with social Hymenoptera. We compared similar-aged foraging workers with builders of the fungus-growing termite Macrotermes bellicosus using transcriptomes, endocrine measures and estimators of physiological condition. Based on results for social Hymenoptera and theory, we tested the hypotheses that (i) foragers are in worse physiological conditions than builders, (ii) builders are more similar in their gene expression profile to queens than foragers are, and (iii) builders invest more in anti-ageing mechanism than foragers. Our results support all three hypotheses. We found storage proteins to underlie task division of these similar-aged termite workers and these genes also characterize reproductive division of labour between queens and workers. This implies a co-option of nutrient-based pathways to regulate division of labour across lineages of termites and social Hymenoptera, which are separated by more than 133 million years.

Experimental increase of worker diversity benefits brood production in ants

BackgroundThe reproductive division of labor of eusocial insects, whereby one or several queens monopolize reproduction, evolved in a context of high genetic relatedness. However, many extant eusocial species have developed strategies that decrease genetic relatedness in their colonies, suggesting some benefits of the increased diversity. Multiple studies support this hypothesis by showing positive correlations between genetic diversity and colony fitness, as well as finding effects of experimental manipulations of diversity on colony performance. However, alternative explanations could account for most of these reports, and the benefits of diversity on performance in eusocial insects still await validation. In this study, we experimentally increased worker diversity in small colonies of the ant Lasius niger while controlling for typical confounding factors.ResultsWe found that experimental colonies composed of workers coming from three different source colonies produced more larvae and showed more variation in size compared to groups of workers coming from a single colony.ConclusionsWe propose that the benefits of increased diversity stemmed from an improved division of labor. Our study confirms that worker diversity enhances colony performance, thus providing a possible explanation for the evolution of multiply mated queens and multiple-queen colonies in many species of eusocial insects.

Analisis Peran Gender Suami Dan Istri Dalam Rumah Tangga Penenun Kain Songket (Studi Kasus Di Kelurahan Tuan Kentang Kecamatan Seberang Ulu 1 Kota Palembang)

This study aims to analyze and describe gender equality in the household of female songket weavers in Tuan Kentang Village, Seberang Ulu 1 District, Palembang City. This study uses Harvard Analysis. The method used in this research is qualitative research methods. Data collection methods are observation, in-depth interviews and documentation. There are 7 informants in this study. The activity profile includes a description of the reproductive, productive and social division of labor. The access and control profile includes a description of the level of equity in access to resources, access to benefits, control over resources and control over benefits in the household. The results showed that, the household activities profile of women weaving Songket fabrics in Tuan Kentang Village is dominated by activities that are gender biased or have not provided equality for women (including the division of productive labor and the division of social labor). Meanwhile, the division of reproductive labor has a gender perspective in which control of benefits is carried out jointly between male and female. The access and control profile of resources and benefits in the household is generally responsive or women have a high degree of equality in access to and control of resources and benefits.

Eusociality in snapping shrimps is associated with larger genomes and an accumulation of transposable elements

Despite progress uncovering the genomic underpinnings of sociality, much less is known about how social living affects the genome. In different insect lineages, for example, eusocial species show both positive and negative associations between genome size and structure, highlighting the dynamic nature of the genome. Here, we explore the relationship between sociality and genome architecture in Synalpheus snapping shrimps that exhibit multiple origins of eusociality and extreme interspecific variation in genome size. Our goal is to determine whether eusociality leads to an accumulation of repetitive elements and an increase in genome size, presumably due to reduced effective population sizes resulting from a reproductive division of labor, or whether an initial accumulation of repetitive elements leads to larger genomes and independently promotes the evolution of eusociality through adaptive evolution. Using phylogenetically informed analyses, we find that eusocial species have larger genomes with more transposable elements (TEs) and microsatellite repeats than noneusocial species. Interestingly, different TE subclasses contribute to the accumulation in different species. Phylogenetic path analysis testing alternative causal relationships between sociality and genome architecture is most consistent with the hypothesis that TEs modulate the relationship between sociality and genome architecture. Although eusociality appears to influence TE accumulation, ancestral state reconstruction suggests moderate TE abundances in ancestral species could have fueled the initial transitions to eusociality. Ultimately, we highlight a complex and dynamic relationship between genome and social evolution, demonstrating that sociality can influence the evolution of the genome, likely through changes in demography related to patterns of reproductive skew.