Caste Ratios Research Articles

Sex- and caste-specific developmental responses to juvenile hormone in an ant with maternal caste determination.

Juvenile hormone is considered to be a master regulator of polyphenism in social insects. In the ant Cardiocondyla obscurior, whether a female egg develops into a queen or a worker is determined maternally and caste-specific differentiation occurs in embryos, so that queens and workers can be distinguished in a non-invasive manner from late embryogenesis onwards. This ant also exhibits two male morphs - winged and wingless males. Here, we used topical treatment with juvenile hormone III and its synthetic analogue methoprene, a method that influences caste determination and differentiation in some ant species, to investigate whether hormone manipulation affects the development and growth of male, queen- and worker-destined embryos and larvae. We found no effect of hormone treatment on female caste ratios or body sizes in any of the treated stages, even though individuals reacted to heightened hormone availability with increased expression of krüppel-homolog 1, a conserved JH first-response gene. In contrast, hormone treatment resulted in the emergence of significantly larger males, although male morph fate was not affected. These results show that in C. obscurior, maternal caste determination leads to irreversible and highly canalized caste-specific development and growth.

Wählen mit Kübeln und Kaskaden: Wie sich das Personenstimmen- paradox bei Wahlen in Bremen, Hamburg und Niedersachsen auf einfache Weise vermeiden lässt

In state elections in Bremen and Hamburg and local elections in Lower Saxony, voters have the opportunity to vote directly for one or more candidates or to confirm the order of the lists proposed by the parties . The ratio of votes cast for the candidates and the list deter- mines how many seats are filled according to the order of the list and how many seats are filled according to the order of the votes cast for the candidates . It may be the case that an additional vote for a candidate leads to him not receiving a seat at all . This phenomenon, which is reminiscent of the negative weight of votes in Bundestag elections, is a nuisance from the point of view of democratic theory because it violates the fundamental require- ment that a vote for a candidate always leads to an increase in his chances of getting elected . Probst and Schröder speak of the personal vote paradox or external-utilization paradox . The aim of this article is to present three simple procedures that avoid the personal vote paradox without fundamentally changing the logic of the current electoral system . The effects of the proposed procedures are illustrated using the election results of the Bremen state election in 2023 . [

Functional heterogeneity facilitates effectual collective task performance in a worker-polymorphic ant

Abstract Effective coordination of group actions underlies the success of group-living organisms. Recent studies of animal personality have shown that groups composed of individuals with different behavioral propensities can outperform uniform groups in a range of different tasks, but we have only a rudimentary understanding of how differences in individual behavior influence the behavior of the group as a whole. In this study, we use natural variation in behavioral propensity among morphologically distinct worker castes of the small carpenter ant Camponotus yamaokai to shed new light on this. Iterative testing indicated that ants displayed consistent behavioral differences among individuals and between castes, with major workers exhibiting a lower exploratory tendency than minors. By constructing groups of different caste composition and quantifying their performance in the task of colony emigration, we show that group performance is an asymmetric humped function of caste ratio, with optimal performance achieved by groups with natural caste ratios. Using a simulation model based on our empirical data, we demonstrate that interindividual differences in social attraction and exploratory tendency are sufficient to explain the observed patterns. Our results provide new insights into how group performance in collective tasks can vary with group composition.

Cover Caption

The social aphid Pseudoregma bambucicola can produce morphologically and behaviorally specialized sterile soldiers and reproductively normal nymphs, and represents a good model system for studying social evolution. The cover photo shows a colony of this species on bamboo, in which several parthenogenetic viviparous mothers are producing offspring. Remarkable reproductive plasticity in parthenogenetic mothers and a novel strategy of regulating caste ratio via maternal reproductive differentiation were found in this social hemipteran (see pages 582‐586). Photo provided by Xiaolei Huang.

Association between parasite microbiomes and caste development and colony structure in a social trematode.

Division of labour through the formation of morphologically and functionally distinct castes is a recurring theme in the evolution of animal sociality. The mechanisms driving the differentiation of individuals into distinct castes remain poorly understood, especially for animals forming clonal colonies. We test the association between microbiomes and caste formation within the social trematode Philophthalmus attenuatus, using a metabarcoding approach targeting the bacterial 16S SSU rRNA gene. Clonal colonies of this trematode within snail hosts comprise large reproductive individuals which produce dispersal stages, and small, non-reproducing soldiers which defend the colony against invaders. In colonies extracted directly from field-collected snails, reproductives harboured more diverse bacterial communities than soldiers, and reproductives and soldiers harboured distinct bacterial communities, at all taxonomic levels considered. No single bacterial taxon showed high enough prevalence in either soldiers or reproductives to be singled out as a key driver, indicating that the whole microbial community contributes to these differences. Other colonies were experimentally exposed to antibiotics to alter their bacterial communities, and sampled shortly after treatment and weeks later after allowing for turnover of colony members. At those time points, bacterial communities of the two castes still differed across all antibiotic treatments; however, the caste ratio within colonies changed: after antibiotic disruption and turnover of individuals, new individuals were more likely to become reproductives than in undisturbed control colonies. Our results reveal that each caste has a distinct microbiome; whether the social context affects the microbiota, or whether microbes contribute to modulating the phenotype of individuals, remains to be determined.

A High Soldier Proportion Encouraged the Greater Antifungal Immunity in a Subterranean Termite.

Termites possess a mighty social immune system, serving as one of the key obstacles to controlling them biologically. However, the dynamic mechanism coordinating the social immunologic defense and caste distribution of the termites remains elusive. This study used the Coptotermes formosanus Shiraki and an entomopathogenic fungus as a host–pathogen system and experimentally manipulated a series of groups with different caste compositions of workers and soldiers. Then, the impact of demography on the behavior and innate immunity of termites was explored by analyzing the fungus susceptibility of the respective caste, efficiencies, and caste preferences of sanitary care, as well as the expression of the immune genes and phenoloxidase activity. Overall, to ensure the general health and survival of a group, the infected workers were found to sacrifice their survivorship for maintaining the soldier proportion of the group. If soldier proportion was limited within a threshold, both the survivorship of the workers and soldiers were not significantly affected by the infection. Correspondingly, the infected group with a higher proportion of soldiers stimulated the higher efficiency of a non-caste-biased sanitary care of the workers to the nestmate workers and soldiers. Moreover, the innate immunities of the infected workers were found to be more intensely upregulated in the group with higher soldier proportions. This suggested that the adjustable non-caste-biased sanitary care and innate immunity of the workers would contribute to the flexibility of the worker–soldier caste ratio in C. formosanus. This study, therefore, enhanced our understanding of the functional adaptation mechanism between pathogen-driven social immunity and the demography of the termites.

GERMINATION OF RADISH (RAPHANUS SATIVUS) IN EARTHWORM CASTING

Fecal content or castings of earthworms are used as organic manure with soil to evaluate the growth of radish (Raphanus sativus). Earthworm castings were used as manure mixed with soil at different ratios like 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90,100%, and normal soil without earthworm cast were used as a control. The rate of red radish growth increases with the percentage of cast manure increases and maximum growth is observed in 90% and 100% ratio of soil and cast. In pot containing 100%, earthworm casting has a high water holding capacity and density is also high.

The influence of new and used formwork coated with different release agents on the appearance of the formed concrete surface

The influence of silicon oil and liquid wax based release agents on the formation of surface voids and colour variation in cast-in-place concrete was studied. The performance of the said release agents was compared to conventional release agents based on water-soluble emulsion and mineral oil. In addition, new and used formwork panels made of plywood and steel were used in the research to determine the effect of release agents on contact angle values. The quality of surface finish was evaluated in terms of concrete surface void ratio using the standard image analysis methodology, and in terms of colour variation using a new digital colour reading method. The formed concrete surface category was evaluated according to CIB, ACI, DBV and ÖVBB standards in order to know the applicability limits of liquid wax and silicon oil based release agents. The results revealed that the amount of release agent used and the contact angle values on the facings analysed depend on the formwork surface roughness, i.e. the release agents can lodge inside the formwork surface asperities and trap air bubbles at the formwork/concrete interface. Furthermore, the results showed that plywood coated with silicon oil and liquid wax limited the achievement of the formed concrete surface category that is higher than the surface finish satisfying normal requirements. Steel coated with liquid wax did not produce the formed concrete surface of higher than normal quality either, while the surface voids ratio of concrete cast against steel formwork coated with silicon oil did not satisfy the requirements even of the lowest classification according to ACI, DBV and ÖVBB standards. Colour variation analysis revealed that the formwork with higher absorbing capacity produced a darker colour with visual blackness varying in the range from 45% to 60%, whereas the formwork with low absorbing capacity produced a lighter colour with visual blackness varying in the range from 25% to 35%. Rougher surfaces of the formwork absorb more hydrophilic release agents. This has an effect on concrete surface colour variation and on concrete's hue, mainly on the yellow hue with redness or the green hue with yellowness.

Regulatory Mechanisms Underlying the Differentiation of Neotenic Reproductives in Termites: Partial Release From Arrested Development

Eusocial insects exhibit reproductive division of labor, in which only a part of colony members differentiates into reproductives. In termite colonies, the division of labors is performed among multiple types of individuals (i.e., castes), such as reproductives, workers, and soldiers to organize their society. Caste differentiation occurs according to extrinsic factors, such as social interactions, leading to developmental modifications during postembryonic development, and consequently, the caste ratio in a colony is appropriately coordinated. In particular, when the current reproductives die or become senescent, some immature individuals molt into supplementary reproductives, also known as “neotenics,” that take over the reproductive task in their natal colony. Neotenics exhibit variety of larval features, such as winglessness, and thus, immature individuals are suggested to differentiate by a partial release from arrested development, particularly in the reproductive organs. These neotenic features, which have long been assumed to develop via heterochronic regulation, provide us opportunities to understand the developmental mechanisms and evolutionary origin of the novel caste. This article overviews the accumulated data on the physiological and developmental mechanisms that regulate the neotenic differentiation in termites. Furthermore, the evolutionary trajectories leading to neotenic differentiation are discussed, namely the acquisition of a regulatory mechanism that enable the partial release from a developmentally arrested state.

Late-Life Fitness Gains Explain the Absence of a Selection Shadow in Ants

A key hypothesis for the occurrence of senescence is a decrease in the selection strength because of low late-life fitness - the so-called selection shadow. However, in social insects, aging is considered a plastic trait and senescence seems to be absent. By life-long tracking of 102 ant colonies, we find that queens increase the production of sexuals in late life regardless of their absolute lifespan or worker investment. This indicates a genetically accommodated adaptive shift towards increasingly queen-biased caste ratios over the course of a queens life. Furthermore, mortality decreased with age, supporting the hypothesis that aging is adaptive. We argue that selection for late life reproduction diminishes the selection shadow of old age and leads to the apparent absence of senescence in ants, in contrast to most iteroparous species.

Metallic Fuel Fabrication Process Development in Remote Fuel Fabrication Mock-Up at KAERI

This paper presents a remote testbed for metallic fuel fabrication using surrogates or depleted uranium. The testbed named “remote fuel fabrication mock-up (RFFM)” was created at the Korea Atomic Energy Research Institute and specifically designed to incorporate remote operation and maintenance. The subsystems of the RFFM are described, and test results regarding remotely conducted metallic fuel slug fabrication at the RFFM are also presented. After fabricating fuel slugs using copper ingots, their specifications and properties were analyzed and evaluated using chemical analysis, radiographic tests, and diameter and weight measurements. Analysis results showed that the fabricated metallic fuel slugs have an acceptance rate of more than 90% and a casting ratio (ratio of weight of injected metal to charged metal) of more than 0.7. Moreover, operations involving remote handling of in-cell equipment were also satisfactory.

Ant Collective Behavior Is Heritable and Shaped by Selection.

AbstractCollective behaviors are widespread in nature and usually assumed to be strongly shaped by natural selection. However, the degree to which variation in collective behavior is heritable and has fitness consequences-the two prerequisites for evolution by natural selection-is largely unknown. We used a new pharaoh ant (Monomorium pharaonis) mapping population to estimate the heritability, genetic correlations, and fitness consequences of three collective behaviors (foraging, aggression, and exploration), as well as of body size, sex ratio, and caste ratio. Heritability estimates for the collective behaviors were moderate, ranging from 0.17 to 0.32, but lower than our estimates for the heritability of caste ratio, sex ratio, and body size of new workers, queens, and males. Moreover, variation in collective behaviors among colonies was phenotypically correlated, suggesting that selection may shape multiple colony collective behaviors simultaneously. Finally, we found evidence for directional selection that was similar in strength to estimates of selection in natural populations. Altogether, our study begins to elucidate the genetic architecture of collective behavior and is one of the first studies to demonstrate that it is shaped by selection.

Impact of environmental temperatures on mortality, sex and caste ratios in Melipona interrupta Latreille (Hymenoptera, Apidae).

Temperature is a major driver of biological phenomena, from metabolism to ecological interactions and rates of evolutionary diversification. However, species vary greatly in their thermal tolerance, as well as the temperature under which they perform best. This study aimed to investigate the effect of experimental manipulation of environmental temperatures on the individual mortality and phenotypic composition of colonies of Melipona interrupta. To fulfill these objectives, 30 colonies in equivalent developmental conditions were artificially subjected to different temperatures. Temperatures were monitored by thermo-hygrometers, and immature mortality and sex and caste ratios were observed in brood combs during 14months. A strong effect of external temperature on immatures was detected on deviations from 28 to 30°C (the natural average temperature inside the colony), causing an increase in mortality. Likewise, a significant effect of temperature on sex ratio was detected, with male:female ratio decreasing at temperatures below and above 28-30°C. Lastly, there was no clear evidence for an effect of temperature on caste ratio, although queens appeared to become relatively more frequent at warmer temperatures. The results of this study allow us to conclude that anthropogenic changes, whose effect can be extrapolated to the similar natural changes, that modify the environmental temperatures to which M. interrupta colonies are exposed are likely to compromise their survival, mainly through individual mortality.

Caste ratio adjustments in response to perceived and realised competition in parasites with division of labour.

Colonial organisms with division of labour are assumed to achieve increased colony-level efficiency in task performance through functional specialisation of individuals into distinct castes. In social insects, ratios of individuals in different castes can adjust adaptively in response to external threats. However, whether flexibility in caste ratio also occurs in other social organisms with division of labour remains unclear. Some parasitic trematodes, in which clonal colonies within the snail intermediate host comprise a reproductive caste and a soldier caste, offer good systems to test the general nature of adaptive caste ratio adjustments. Using the trematode Philophthalmus sp. as model, we test whether trematode colonies shift their composition towards more soldiers when exposed to a sustained risk of invasion by a competitor parasite species, and/or when experiencing sustained, active competition. We also quantify the colony-level fitness impact of caste ratio adjustments, measured as the colony's output of larval infective stages. We conducted two long-term laboratory experiments on within-snail trematode colonies. First, snails harbouring Philophthalmus colonies were exposed to different levels of invasion risk by another trematode species, Maritrema novaezealandense. Second, the structure of Philophthalmus colonies was quantified after a year-long period of within-snail competition with the other trematode species. When facing the risk of invasion by a competitor, independently of the level of risk, Philophthalmus colonies showed a significant shift towards producing more soldiers, resulting in altered caste ratio. Similarly, when experiencing actual competition by another trematode established in the same snail, Philophthalmus colonies also adjusted by producing significantly more soldiers. Greater investments in defense via more soldiers had negative impacts on the establishment and size of the competitor's colonies. Nevertheless, the presence of the competitor reduced the fitness (output of infective stages) of Philophthalmus colonies, although the production of more soldiers mitigated that effect. Our findings demonstrate that trematode colonies with division of labour are capable of adaptive caste ratio adjustments in response to both the perceived threat of competition and actual competition, with trade-offs against reproductive success only apparent when soldier numbers are very high. Combined with results on social insects, our study suggests parallel adaptations of colonial organisms in phylogenetically disparate organisms.

Camponotusfloridanus Ants Incur a Trade-Off between Phenotypic Development and Pathogen Susceptibility from Their Mutualistic Endosymbiont Blochmannia.

Various insects engage in microbial mutualisms in which the reciprocal benefits exceed the costs. Ants of the genus Camponotus benefit from nutrient supplementation by their mutualistic endosymbiotic bacteria, Blochmannia, but suffer a cost in tolerating and regulating the symbiont. This cost suggests that the ants face secondary consequences such as susceptibility to pathogenic infection and transmission. In order to elucidate the symbiont’s effects on development and disease defence, Blochmannia floridanus was reduced in colonies of Camponotus floridanus using antibiotics. Colonies with reduced symbiont levels exhibited workers of smaller body size, smaller colony size, and a lower major-to-minor worker caste ratio, indicating the symbiont’s crucial role in development. Moreover, these ants had decreased cuticular melanisation, yet higher resistance to the entomopathogen Metarhizium brunneum, suggesting that the symbiont reduces the ants’ ability to fight infection, despite the availability of melanin to aid in mounting an immune response. While the benefits of improved growth and development likely drive the mutualism, the symbiont imposes a critical trade-off. The ants’ increased susceptibility to infection exacerbates the danger of pathogen transmission, a significant risk given ants’ social lifestyle. Thus, the results warrant research into potential adaptations of the ants and pathogens that remedy and exploit the described disease vulnerability.

When predator odour makes groups stronger: effects on behavioural and chemical adaptations in two termite species

1. Being able to detect a predator before any physical contact is crucial for individual survival. Predator presence can be detected thanks to several types of signal, such as chemical cues. Chemical signals are produced by predators for their protection against desiccation, for their communication, or possibly as a side‐effect of their activity. In insects, chemical communication plays a key role in diverse biological processes, including prey‐predator or plant‐insect interactions, courtship behaviour, and kin or species recognition.2. Cuticular hydrocarbons (CHCs) are specifically involved in recognition processes and social organisation (division of labour, caste ratios) in social insects. Here, the questions raised are whether termites can detect a predator with their cuticular compounds and whether the predator‐produced compounds can influence their prey.3. The responses of termites Reticulitermes grassei (Clément, 1978) and Reticulitermes flavipes (Kollar, 1837) to the presence of the cuticular compounds produced by a predator, the ant species Lasius niger (Linnaeus, 1758), were investigated. More specifically, the study quantified termite traits such as caste ratios, mortality rates, CHC profile homogeneity and aggressiveness of workers after 2 months' exposure to predator‐produced compounds.4. The results show that the predator odour did affect the aggressiveness of the native species R. grassei but not of the invasive R. flavipes. The caste ratios and the mortality rates were not affected for both species.5. Differences between species are discussed around the native or invasive status of each species, along with the role played by chemical cues on behavioural and chemical adaptations.

The scaling of growth, reproduction and defense in colonies of Amazonian Termites

Phenotypes can evolve through life-history tradeoffs. Termites have been the first eusocial insects on Earth, prompting life history evolution at the colony level. Despite this, termite life-history allocation strategies are poorly known. Here, we addressed this issue using novel data on three common species from the diverse, yet understudied Amazonian termite fauna: Neocapritermes braziliensis, Labiotermes labralis and Anoplotermes banksi. Using Oster and Wilson’s optimal caste ratio theory and Higashi et al.’s termite caste allocation theory as frameworks, we assessed how termite colonies should invest in growth (immatures), reproduction (alates) and defense (soldiers) as they accumulate workers. We also examined whether soldier loss in soil-feeding Apicotermitinae (A. banksi) may have affected allocation strategies. We found that: (1) the scaling of immature number was isometric in the three species, contrary to the leveling off expected under resource limitation; (2) colonies of all sizes were equally likely to produce any number of alates, rather than having a size threshold for reproduction; (3) the scaling of soldier number was unrelated to alate production, but varied from isometry in N. braziliensis to negative allometry in L. labralis despite their similar defense strategies; (4) A. banksi had more immatures per worker and a higher maximum alate number per worker than the other species, suggesting that soldier loss may have allowed higher relative investment in colony growth and, possibly, reproduction. Termites can provide novel insights into life-history allocation strategies and their relation to social evolution, and should be better incorporated into sociobiological theory.

Political leanings and social capital

The research shows that the political leanings and social capital of the region around firms’ headquarters affect corporate and individual decisions. What remains unexplored is whether social capital and political leanings are associated with each other. To fill this gap, we use the ratio of votes cast for Democratic candidates to those cast for Republican candidates in presidential elections to measure the Democratic political leanings in the United States. We find that counties with more social capital lean toward the Democratic Party. A one standard deviation increase in social capital is associated with a 0.30 standard deviation increase in the vote ratio. Additional tests show that this positive association is stronger in counties that have higher incomes and less religiosity.

Copidosoma floridanum (Hymenoptera: Encyrtidae) Rapidly Alters Production of Soldier Embryos in Response to Competition.

Most social insects are free living and produce castes that develop in response to extrinsic environmental cues. Caste-forming polyembryonic insects, in contrast, are all endoparasitoids that form social groups inside the bodies of host insects. The best studied polyembryonic wasp is Copidosoma floridanum (Ashmead), which produces ∼3,000 clonal offspring that develop into two castes named reproductive and soldier larvae. Caste determination in this species is mediated by whether or not embryos inherit primary germ cells (PGCs). Prior results showed that C. floridanum increases the proportion of female soldier larvae it produces per host in response to other parasitoids like Microplitis demolitor. Here we show that caste ratio shifts occur through increased formation of embryos lacking PGCs. Our results further indicated that increased soldier production was a specific response to multiparasitism elicited by the chorion of M. demolitor eggs.

Artificial selection on ant female caste ratio uncovers a link between female-biased sex ratios and infection by Wolbachia endosymbionts.

Social insect sex and caste ratios are well-studied targets of evolutionary conflicts, but the heritable factors affecting these traits remain unknown. To elucidate these factors, we carried out a short-term artificial selection study on female caste ratio in the ant Monomorium pharaonis. Across three generations of bidirectional selection, we observed no response for caste ratio, but sex ratios rapidly became more female-biased in the two replicate high selection lines and less female-biased in the two replicate low selection lines. We hypothesized that this rapid divergence for sex ratio was caused by changes in the frequency of infection by the heritable bacterial endosymbiont Wolbachia, because the initial breeding stock varied for Wolbachia infection, and Wolbachia is known to cause female-biased sex ratios in other insects. Consistent with this hypothesis, the proportions of Wolbachia-infected colonies in the selection lines changed rapidly, mirroring the sex ratio changes. Moreover, the estimated effect of Wolbachia on sex ratio (~13% female bias) was similar in colonies before and during artificial selection, indicating that this Wolbachia effect is likely independent of the effects of artificial selection on other heritable factors. Our study provides evidence for the first case of endosymbiont sex ratio manipulation in a social insect.