Missing Genomic Resources for the Next Generation of Environmental Risk Assessment

Environmental risk assessment traditionally relies on a wide range of in vivo testing to assess the potential hazards of chemicals in the environment. These tests are often time-consuming and costly and can cause test organisms' suffering. Recent developments of reliable low-cost alternatives, both in vivo- and in silico-based, opened the door to reconsider current toxicity assessment. However, many of these new approach methodologies (NAMs) rely on high-quality annotated genomes for surrogate species of regulatory risk assessment. Currently, a lack of genomic information slows the process of NAM development. Here, we present a phylogenetically resolved overview of missing genomic resources for surrogate species within a regulatory ecotoxicological risk assessment. We call for an organized and systematic effort within the (regulatory) ecotoxicological community to provide these missing genomic resources. Further, we discuss the potential of a standardized genomic surrogate species landscape to enable a robust and nonanimal-reliant ecotoxicological risk assessment in the systems ecotoxicology era.

Holistic evaluation of long-term earthworm field studies with a fungicide

Plant protection products to be placed on the market in the European Union need to meet rigorous safety criteria including the testing of lumbricid earthworms, the functionally most important soil organism group in Central European agricultural ecosystems. To address uncertainties and investigate the potential long-term in-crop effects of the fungicide Cantus^® containing 50% boscalid as an active substance, a series of standardized earthworm field studies with an overall duration of 5 years per study program was carried out in four German agricultural fields under realistic crop rotation conditions. A two-step approach was chosen to analyze the potential overall long-term effects on earthworms in agricultural fields: (i) an assessment of the earthworm abundance development in the course of the four study programs in relation to the determined actual content of boscalid in soil and (ii) an effect size meta-analysis of earthworm abundance 1 year after treatment for each consecutive year and study program. Measured boscalid concentrations in the soil after multiple applications were well above the maximum boscalid residues observed in agricultural soils across Central Europe. There were isolated statistically significant reductions of earthworm abundance for some species and groups at some time points during the studies, but no consistent relationship to the Cantus^® treatments was observed. These results were supported by the meta-analysis, indicating no adverse effects on earthworm populations. Therefore, fluctuations of abundance reflect the natural variation of the populations rather than a concentration-related response. Based on this comprehensive analysis, we conclude that there is no application rate-related effect of the 5-year use of Cantus^® on the development of the earthworm communities. The four study programs, paired with a comprehensive evaluation, directly address the concerns about the potential long-term effects of boscalid on earthworms in the field and suggest that multiyear applications do not adversely affect earthworm populations. Integr Environ Assess Manag 2022;18:1399-1413. © 2021 ECT Oekotoxikologie GmbH and BASF SE. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Investigating the role of soil mesofauna abundance and biodiversity for organic matter breakdown in arable fields

Intact soil food webs are pivotal to maintaining essential soil functions, such as carbon recycling, sequestering, and biomass production. Although the functional role of micro- (e.g., bacteria and fungi) and macrofauna (e.g., earthworms) is comparatively well established, the importance of the mesofauna community (e.g., abundance and diversity of Acari and Collembola) in maintaining soil functionality is less clear. We investigated this question in a six-month field experiment in arable soil by actively manipulating mesofauna abundance and biodiversity through the application of two legacy insecticides (lindane and methamidophos) at sufficiently high doses to reduce mesofauna abundance (well above previously registered application rates; 2.5 and 7.5 kg a.s./ha for lindane, and 0.6 and 3 kg a.s./ha for methamidophos) and measure the impact on organic matter degradation. Our results demonstrate that both insecticides had reduced Collembola and Acari abundances by up to 80% over the study's six-month duration. In addition, we observed less pronounced and more complex changes in mesofauna biodiversity over time. These included insecticide-dependent temporal fluctuations (both reduction and increase) for different estimates (indices) of local (alpha)-diversity over time and no lasting impact for most estimates after six months. Even at these exceptionally high field rates, Collembola and Acari diversity was observed to generally recover by six months. In contrast, considering organic matter breakdown, we found no evidence of a treatment-related effect. These results suggest that organic matter breakdown in arable soils is likely driven by other trophic levels (e.g., microorganisms or earthworms) with only a limited influence of the mesofauna community. We discuss these findings with regard to their implications for our current understanding of soil food web function and future European soil risk assessments. Integr Environ Assess Manag 2022;18:1423-1433. © 2021 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Establishing realistic exposure estimates of solitary bee larvae via pollen for use in risk assessment

Bees foraging in agricultural habitats can be exposed to plant protection products. To limit the risk of adverse events, a robust risk assessment is needed, which requires reliable estimates for the expected exposure. The exposure pathways to developing solitary bees in particular are not well described and, in the currently proposed form, rely on limited information. To build a scaling model predicting the amount of protein developing solitary bees need based on adult body weight, we used published data on the volume of pollen solitary bees provide for their offspring. This model was tested against and ultimately updated with additional literature data on bee weight and protein content of emerged bees. We rescaled this model, based on the known pollen protein content of bee-visited flowers, to predict the expected amount of pollen a generalist solitary bee would likely provide based on its adult body weight, and tested these predictions in the field. We found overall agreement between the models' predictions and the measured values in the field, but additional data are needed to confirm these initial results. Our study suggests that scaling models in the bee risk assessment could complement existing risk assessment approaches and facilitate the further development of accurate risk characterization for solitary bees; ultimately the models will help to protect them during their foraging activity in agricultural settings. Integr Environ Assess Manag 2022;18:308-313. © 2021 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Assessment of the Vulnerability to Pesticide Exposures Across Bee Species

In many countries, the western honey bee is used as surrogate in pesticide risk assessments for bees. However, uncertainty remains in the estimation of pesticide risk to non-Apis bees because their potential routes of exposure to pesticides, life histories, and ecologies differ from those of honey bees. We applied the vulnerability concept in pesticide risk assessment to 10 bee species including the honey bee, 2 bumble bee species, and 7 solitary bee species with different nesting strategies. Trait-based vulnerability considers the evaluation of a species at the level of both the organism (exposure and effect) and the population (recovery), which goes beyond the sensitivity of individuals to a toxicant assessed in standard laboratory toxicity studies by including effects on populations in the field. Based on expert judgment, each trait was classified by its relationship to the vulnerability to pesticide exposure, effects (intrinsic sensitivity), and population recovery. The results suggested that the non-Apis bees included in our approach are potentially more vulnerable to pesticides than the honey bee due to traits governing exposure and population recovery potential. Our analysis highlights many uncertainties related to the interaction between bee ecology and the potential exposures and population-level effects of pesticides, emphasizing the need for more research to identify suitable surrogate species for higher tier bee risk assessments. Environ Toxicol Chem 2021;40:2640-2651. © 2021 SETAC.

Extrapolating Acute Contact Bee Sensitivity to Insecticides Based on Body Weight Using a Phylogenetically Informed Interspecies Scaling Framework

Plant protection products, including insecticides, are important for global food production but can have adverse effects on nontarget organisms including bees. Historically, research investigating such effects has focused mainly on the honeybee (Apis mellifera), whereas less information is available for non-Apis bees. Consequently, a comprehensive hazard (sensitivity) assessment for the majority of bees is lacking, which in turn hinders accurate risk characterization and consequently bee protection. Interspecies sensitivity extrapolation based on body weight might be a way to improve the situation, but in the past such approaches often ignored the phylogenetic background of the species used, which in turn potentially reduces the robustness of such results. Published acute contact sensitivity data (median lethal dose per bee) of bees to insecticides, their body weight, and their phylogenetic background were used to build interspecies scaling models to predict bee sensitivity based on their weight. The results indicate that 1) bee body weight is a predictor of acute contact bee sensitivity to a range of insecticides, and 2) phylogeny (nonindependence of data points) needs to be considered in cross-species analysis, although it does not always confound the observed effects.  Environ Toxicol Chem 2021;40:2044-2052. © 2021 SETAC.

Multiple stressors interact to impair the performance of bumblebee Bombus terrestris colonies

Bumblebees are constantly exposed to a wide range of biotic and abiotic stresses which they must defend themselves against to survive. Pathogens and pesticides represent important stressors that influence bumblebee health, both when acting alone or in combination. To better understand bumblebee health, we need to investigate how these factors interact, yet experimental studies to date generally focus on only one or two stressors. The aim of this study is to evaluate how combined effects of four important stressors (the gut parasite Nosema ceranae, the neonicotinoid insecticide thiamethoxam, the pyrethroid insecticide cypermethrin and the EBI fungicide tebuconazole) interact to affect bumblebees at the individual and colony levels. We established seven treatment groups of colonies that we pulse exposed to different combinations of these stressors for 2 weeks under laboratory conditions. Colonies were subsequently placed in the field for 7 weeks to evaluate the effect of treatments on the prevalence of N. ceranae in inoculated bumblebees, expression levels of immunity and detoxification-related genes, food collection, weight gain, worker and male numbers, and production of worker brood and reproductives. Exposure to pesticide mixtures reduced food collection by bumblebees. All immunity-related genes were upregulated in the bumblebees inoculated with N. ceranae when they had not been exposed to pesticide mixtures, and bumblebees exposed to the fungicide and the pyrethroid were less likely to have N. ceranae. Combined exposure to the three-pesticide mixture and N. ceranae reduced bumblebee colony growth, and all treatments had detrimental effects on brood production. The groups exposed to the neonicotinoid insecticide produced 40%-76% fewer queens than control colonies. Our findings show that exposure to combinations of stressors that bumblebees frequently come into contact with have detrimental effects on colony health and performance and could therefore have an impact at the population level. These results also have significant implications for current practices and policies for pesticide risk assessment and use as the combinations tested here are frequently applied simultaneously in the field. Understanding the interactions between different stressors will be crucial for improving our ability to manage bee populations and for ensuring pollination services into the future.

Are honeybees suitable surrogates for use in pesticide risk assessment for non-Apis bees?

Historically, bee regulatory risk assessment for pesticides has centred on the European honeybee (Apis mellifera), primarily due to its availability and adaptability to laboratory conditions. Recently, there have been efforts to develop a battery of laboratory toxicity tests for a range of non-Apis bee species to directly assess the risk to them. However, it is not clear whether the substantial investment associated with the development and implementation of such routine screening will actually improve the level of protection of non-Apis bees. We argue, using published acute toxicity data from a range of bee species and standard regulatory exposure scenarios, that current first-tier honeybee acute risk assessment schemes utilised by regulatory authorities are protective of other bee species and further tests should be conducted only in cases of concern. We propose similar analysis of alternative exposure scenarios (chronic and developmental) once reliable data for non-Apis bees are available to expand our approach to these scenarios. In addition, we propose that in silico (simulation) approaches can then be used to address population-level effects in more field-realistic scenarios. Such an approach could lead to a protective, but also workable, risk assessment for non-Apis species while contributing to pollination security in agricultural landscapes around the globe. © 2019 Society of Chemical Industry.

Pollen report: quantitative review of pollen crude protein concentrations offered by bee pollinated flowers in agricultural and non-agricultural landscapes

To ease nutritional stress on managed as well as native bee populations in agricultural habitats, agro-environmental protection schemes aim to provide alternative nutritional resources for bee populations during times of need. However, such efforts have so far focused on quantity (supply of flowering plants) and timing (flower-scarce periods) while ignoring the quality of the two main bee relevant flower-derived resources (pollen and nectar). As a first step to address this issue we have compiled one geographically explicit dataset focusing on pollen crude protein concentration, one measurement traditionally associated with pollen quality for bees. We attempt to provide a robust baseline for protein levels bees can collect in- (crop and weed species) and off-field (wild plants) in agricultural habitats around the globe. Using this dataset we identify crops which provide sub-optimal pollen resources in terms of crude protein concentration for bees and suggest potential plant genera that could serve as alternative resources for protein. This information could be used by scientists, regulators, bee keepers, NGOs and farmers to compare the pollen quality currently offered in alternative foraging habitats and identify opportunities to improve them. In the long run, we hope that additional markers of pollen quality will be added to the database in order to get a more complete picture of flower resources offered to bees and foster a data-informed discussion about pollinator conservation in modern agricultural landscapes.

Immunity of leaf-cutting ants and its role in host-parasitoid relationships

Parasites are an important selection pressure for all organisms, and host immune responses are key in shaping host-parasite interactions. Host species with strong immune defences may be expected to experience lower parasitism; on the other hand, investment in immune function is costly, so hosts that have evolved to invest more in immune defence may be expected to have been under greater selection pressure from parasites. Disentangling the coevolutionary dynamics requires comparative studies that quantify the immune responses of potential hosts of parasites in a community, but such studies are rare. Here, we studied the immune defences of six leaf-cutting ant species in a community for which their relationships with phorid fly parasitoid species are known. We tested whether the strength of the baseline immune defences of the different ant species correlated positively or negatively with parasitoid load (number and abundance of parasitoid species exploiting the ant species), and host specialization of parasitoid species (the proportion of specialist parasitoids using each host). We measured four immune variables: i) the encapsulation response to a standard challenge, levels of ii) phenoloxidase (PO) and iii) prophenoloxidae (PPO) immune enzymes, and iv) the number of haemocytes. We found that ant species differed in their encapsulation response, PO levels and number of haemocytes, and that there was a positive, not negative, correlation across ant species between the strength of several of the immune variables and parasitoid load, but not for host specialization. This is in keeping with the hypothesis that higher parasitoid load selects for greater investment in immune defences. Our results suggest that immunity may be an important factor accounting for the dynamics of host-parasitoid interactions in this community. Similar community-level studies may be insightful, both for understanding host-parasite community ecology and for applications such as biocontrol.

The role of juvenile hormone in regulating reproductive physiology and dominance in Dinoponera quadriceps ants

Unequal reproductive output among members of the same sex (reproductive skew) is a common phenomenon in a wide range of communally breeding animals. In such species, reproductive dominance is often acquired during antagonistic interactions between group members that establish a reproductive hierarchy in which only a few individuals reproduce. Rank-specific syndromes of behavioural and physiological traits characterize such hierarchies, but how antagonistic behavioural interactions translate into stable rank-specific syndromes remains poorly understood. The pleiotropic nature of hormones makes them prime candidates for generating such syndromes as they physiologically integrate environmental (social) information, and often affect reproduction and behaviour simultaneously. Juvenile hormone (JH) is one of several hormones that occupy such a central regulatory role in insects and has been suggested to regulate reproductive hierarchies in a wide range of social insects including ants. Here we use experimental manipulation to investigate the effect of JH levels on reproductive physiology and social dominance in high-ranked workers of the eusocial ant Dinoponera quadriceps, a species that has secondarily reverted to queenless, simple societies. We show that JH regulated reproductive physiology, with ants in which JH levels were experimentally elevated having more regressed ovaries. In contrast, we found no evidence of JH levels affecting dominance in social interactions. This could indicate that JH and ovary development are decoupled from dominance in this species, however only high-ranked workers were investigated. The results therefore confirm that the regulatory role of JH in reproductive physiology in this ant species is in keeping with its highly eusocial ancestors rather than its secondary reversion to simple societies, but more investigation is needed to disentangle the relationships between hormones, behaviour and hierarchies.

The nectar report: quantitative review of nectar sugar concentrations offered by bee visited flowers in agricultural and non-agricultural landscapes

There is growing concern that some bee populations are in decline, potentially threatening pollination security in agricultural and non-agricultural landscapes. Among the numerous causes associated with this trend, nutritional stress resulting from a mismatch between bee nutritional needs and plant community provisioning has been suggested as one potential driver. To ease nutritional stress on bee populations in agricultural habitats, agri-environmental protection schemes aim to provide alternative nutritional resources for bee populations during times of need. However, such efforts have focused mainly on quantity (providing flowering plants) and timing (during flower-scarce periods), while largely ignoring the quality of the offered flower resources. In a first step to start addressing this information gap, we have used literature data to compile a comprehensive geographically explicit dataset on nectar quality (i.e., total sugar concentration), offered to bees both within fields (crop and weed species) as well as outside fields (wild species) around the globe. Social bees are particularly sensitive to nectar sugar concentrations, which directly impact calorie influx into the colony and consequently their fitness making it an important resource quality marker. We find that the total nectar sugar concentrations in general do not differ between the three plant communities studied. In contrast we find increased variability in nectar quality in the wild plant community compared to crop and weed community, which is likely explained by the increased phylogenetic diversity in this category of plants. In a second step we explore the influence of local habitat on nectar quality and its variability utilizing a detailed sunflower (Helianthus annuus L.) data set and find that geography has a small, but significant influence on these parameters. In a third step we identify crop groups (genera), which provide sub-optimal nectar resources for bees and suggest high quality alternatives as potential nectar supplements. In the long term this data set could serve as a starting point to systematically collect more quality characteristics of plant provided resources to bees, which ultimately can be utilized by scientist, regulators, NGOs and farmers to improve the flower resources offered to bees. We hope that ultimately this data will help to ease nutritional stress for bee populations and foster a data informed discussion about pollinator conservation in modern agricultural landscapes.

Social environment affects the transcriptomic response to bacteria in ant queens

Social insects have evolved enormous capacities to collectively build nests and defend their colonies against both predators and pathogens. The latter is achieved by a combination of individual immune responses and sophisticated collective behavioral and organizational disease defenses, that is, social immunity. We investigated how the presence or absence of these social defense lines affects individual-level immunity in ant queens after bacterial infection. To this end, we injected queens of the ant Linepithema humile with a mix of gram+ and gram- bacteria or a control solution, reared them either with workers or alone and analyzed their gene expression patterns at 2, 4, 8, and 12 hr post-injection, using RNA-seq. This allowed us to test for the effect of bacterial infection, social context, as well as the interaction between the two over the course of infection and raising of an immune response. We found that social isolation per se affected queen gene expression for metabolism genes, but not for immune genes. When infected, queens reared with and without workers up-regulated similar numbers of innate immune genes revealing activation of Toll and Imd signaling pathways and melanization. Interestingly, however, they mostly regulated different genes along the pathways and showed a different pattern of overall gene up-regulation or down-regulation. Hence, we can conclude that the absence of workers does not compromise the onset of an individual immune response by the queens, but that the social environment impacts the route of the individual innate immune responses.

The evolution of caste-biasing symbionts in the social hymenoptera

The separation of individuals into reproductive and worker castes is the defining feature of insect societies. However, caste determination is itself a complex phenomenon, dependent on interacting genetic and environmental factors. It has been suggested by some authors that widespread maternally transmitted symbionts such as Wolbachia may be selected to interfere with caste determination, whilst others have discounted this possibility on theoretical grounds. We argue that there are in fact three distinct evolutionary scenarios in which maternally transmitted symbionts might be selected to influence the process of caste determination in a social hymenopteran host. Each of these scenarios generate testable predictions which we outline here. Given the increasing recognition of the complexity and multi-faceted nature of caste determination in social insects, we argue that maternally transmitted symbionts should also be considered as possible factors influencing the development of social hymenopterans.

The effects of juvenile hormone on Lasius niger reproduction

Reproduction has been shown to be costly for survival in a wide diversity of taxa. The resulting trade-off, termed the reproduction-survival trade-off, is thought to be one of the most fundamental forces of life-history evolution. In insects the pleiotropic effect of juvenile hormone (JH), antagonistically regulating reproduction and pathogen resistance, is suggested to underlie this phenomenon. In contrast to the majority of insects, reproductive individuals in many eusocial insects defy this trade-off and live both long and prosper. By remodelling the gonadotropic effects of JH in reproductive regulation, the queens of the long-lived black garden ant Lasius niger (living up to 27 years), have circumvented the reproduction-survival trade off enabling them to maximize both reproduction and pathogen resistance simultaneously. In this study we measure fertility, vitellogenin gene expression and protein levels after experimental manipulation of hormone levels. We use these measurements to investigate the mechanistic basis of endocrinological role remodelling in reproduction and determine how JH suppresses reproduction in this species, rather then stimulating it, like in the majority of insects. We find that JH likely inhibits three key aspects of reproduction both during vitellogenesis and oogenesis, including two previously unknown mechanisms. In addition, we document that juvenile hormone, as in the majority of insects, has retained some stimulatory function in regulating vitellogenin expression. We discuss the evolutionary consequences of this complex regulatory architecture of reproduction in L. niger, which might enable the evolution of similar reproductive phenotypes by alternate regulatory pathways, and the surprising flexibility regulatory role of juvenile hormone in this process.

The effects of disturbance threat on leaf-cutting ant colonies: a laboratory study

The flexibility of organisms to respond plastically to their environment is fundamental to their fitness and evolutionary success. Social insects provide some of the most impressive examples of plasticity, with individuals exhibiting behavioral and sometimes morphological adaptations for their specific roles in the colony, such as large soldiers for nest defense. However, with the exception of the honey bee model organism, there has been little investigation of the nature and effects of environmental stimuli thought to instigate alternative phenotypes in social insects. Here, we investigate the effect of repeated threat disturbance over a prolonged (17 month) period on both behavioral and morphological phenotypes, using phenotypically plastic leaf-cutting ants (Atta colombica) as a model system. We found a rapid impact of threat disturbance on the behavioral phenotype of individuals within threat-disturbed colonies becoming more aggressive, threat responsive, and phototactic within as little as 2 weeks. We found no effect of threat disturbance on morphological phenotypes, potentially, because constraints such as resource limitation outweighed the benefit for colonies of producing larger individuals. The results suggest that plasticity in behavioral phenotypes can enable insect societies to respond to threats even when constraints prevent alteration of morphological phenotypes.

Hygienic food to reduce pathogen risk to bumblebees

Bumblebees are ecologically and economically important pollinators, and the value of bumblebees for crop pollination has led to the commercial production and exportation/importation of colonies on a global scale. Commercially produced bumblebee colonies can carry with them infectious parasites, which can both reduce the health of the colonies and spillover to wild bees, with potentially serious consequences. The presence of parasites in commercially produced bumblebee colonies is in part because colonies are reared on pollen collected from honey bees, which often contains a diversity of microbial parasites. In response to this threat, part of the industry has started to irradiate pollen used for bumblebee rearing. However, to date there is limited data published on the efficacy of this treatment. Here we examine the effect of gamma irradiation and an experimental ozone treatment on the presence and viability of parasites in honey bee pollen. While untreated pollen contained numerous viable parasites, we find that gamma irradiation reduced the viability of parasites in pollen, but did not eliminate parasites entirely. Ozone treatment appeared to be less effective than gamma irradiation, while an artificial pollen substitute was, as expected, entirely free of parasites. The results suggest that the irradiation of pollen before using it to rear bumblebee colonies is a sensible method which will help reduce the incidence of parasite infections in commercially produced bumblebee colonies, but that further optimisation, or the use of a nutritionally equivalent artificial pollen substitute, may be needed to fully eliminate this route of disease entry into factories.

The influence of space and time on the evolution of altruistic defence: the case of ant slave rebellion

How can antiparasite defence traits evolve even if they do not directly benefit their carriers? An example of such an indirect defence is rebellion of enslaved Temnothorax longispinosus ant workers against their social parasite Temnothorax americanus, a slavemaking ant. Ant slaves have been observed to kill their oppressors' offspring, a behaviour from which the sterile slaves cannot profit directly. Parasite brood killing could, however, reduce raiding pressure on related host colonies nearby. We analyse with extensive computer simulations for the Temnothorax slavemaker system under what conditions a hypothetical rebel allele could invade a host population, and in particular, how host-parasite dynamics and population structure influence the rebel allele's success. Exploring a wide range of model parameters, we only found a small number of parameter combinations for which kin selection or multilevel selection could allow a slave rebellion allele to spread in the host population. Furthermore, we did not detect any cases in which the reduction of raiding pressure in the close vicinity of the slavemaker nest would substantially contribute to the inclusive fitness of rebels. This suggests that slave rebellion is not costly and perhaps a side-effect of some other beneficial trait. In some of our simulations, however, even a costly rebellion allele could spread in the population. This was possible when host-parasite interactions led to a metapopulation dynamic with frequent local extinctions and recolonizations of demes by the offspring of few immigrants.

Behavioural development, fat reserves and their association with productivity in Lasius flavus founding queens

Reproduction-related behaviours are key components determining individual fitness. Many behavioural traits are linked, and such trait associations often affect fitness. Here, we combine behavioural and physiological data during two critical time points of founding queens (early and late nest-founding stage) in the claustral ant Lasius flavus to assess how these factors affect their initial productivity. We show that most behavioural traits, except brood care behaviour, are plastic during queen development and demonstrate that there are alternative behavioural pathways to achieve high productivity under standardised conditions. These results indicate that queens can utilise multiple behavioural trait combinations to maximise reproductive output at the earliest, and arguably most critical, time of colony foundation.

Pleiotropic effects of juvenile hormone in ant queens and the escape from the reproduction-immunocompetence trade-off

The ubiquitous trade-off between survival and costly reproduction is one of the most fundamental constraints governing life-history evolution. In numerous animals, gonadotropic hormones antagonistically suppressing immunocompetence cause this trade-off. The queens of many social insects defy the reproduction-survival trade-off, achieving both an extraordinarily long life and high reproductive output, but how they achieve this is unknown. Here we show experimentally, by integrating quantification of gene expression, physiology and behaviour, that the long-lived queens of the ant Lasius niger have escaped the reproduction-immunocompetence trade-off by decoupling the effects of a key endocrine regulator of fertility and immunocompetence in solitary insects, juvenile hormone (JH). This modification of the regulatory architecture enables queens to sustain a high reproductive output without elevated JH titres and suppressed immunocompetence, providing an escape from the reproduction-immunocompetence trade-off that may contribute to the extraordinary lifespan of many social insect queens.

Oh sister, where art thou? Spatial population structure and the evolution of an altruistic defence trait

The evolution of parasite virulence and host defences is affected by population structure. This effect has been confirmed in studies focusing on large spatial scales, whereas the importance of local structure is not well understood. Slavemaking ants are social parasites that exploit workers of another species to rear their offspring. Enslaved workers of the host species Temnothorax longispinosus have been found to exhibit an effective post-enslavement defence behaviour: enslaved workers were observed killing a large proportion of the parasites' offspring. As enslaved workers do not reproduce, they gain no direct fitness benefit from this 'rebellion' behaviour. However, there may be an indirect benefit: neighbouring host nests that are related to 'rebel' nests can benefit from a reduced raiding pressure, as a result of the reduction in parasite nest size due to the enslaved workers' killing behaviour. We use a simple mathematical model to examine whether the small-scale population structure of the host species could explain the evolution of this potentially altruistic defence trait against slavemaking ants. We find that this is the case if enslaved host workers are related to nearby host nests. In a population genetic study, we confirm that enslaved workers are, indeed, more closely related to host nests within the raiding range of their resident slavemaker nest, than to host nests outside the raiding range. This small-scale population structure seems to be a result of polydomy (e.g. the occupation of several nests in close proximity by a single colony) and could have enabled the evolution of 'rebellion' by kin selection.

Worker personality and its association with spatially structured division of labor

Division of labor is a defining characteristic of social insects and fundamental to their ecological success. Many of the numerous tasks essential for the survival of the colony must be performed at a specific location. Consequently, spatial organization is an integral aspect of division of labor. The mechanisms organizing the spatial distribution of workers, separating inside and outside workers without central control, is an essential, but so far neglected aspect of division of labor. In this study, we investigate the behavioral mechanisms governing the spatial distribution of individual workers and its physiological underpinning in the ant Myrmica rubra. By investigating worker personalities we uncover position-associated behavioral syndromes. This context-independent and temporally stable set of correlated behaviors (positive association between movements and attraction towards light) could promote the basic separation between inside (brood tenders) and outside workers (foragers). These position-associated behavior syndromes are coupled with a high probability to perform tasks, located at the defined position, and a characteristic cuticular hydrocarbon profile. We discuss the potentially physiological causes for the observed behavioral syndromes and highlight how the study of animal personalities can provide new insights for the study of division of labor and self-organized processes in general.

Temnothorax pilagens sp. n. - a new slave-making species of the tribe Formicoxenini from North America (Hymenoptera, Formicidae)

A new species of the ant genus Temnothorax Forel, 1890 – Temnothorax pilagens sp. n. is described from eastern North America. T. pilagenssp. n. is an obligate slave-making ant with two known hosts: T. longispinosus (Roger, 1863) and T. ambiguus (Emery, 1895). A differential diagnosis against Temnothorax duloticus (Wesson, 1937), the other dulotic congener from the Nearctic, is presented and a biological characteristics of the new species is given.

Raiders from the sky: slavemaker founding queens select for aggressive host colonies

Reciprocal selection pressures in host-parasite systems drive coevolutionary arms races that lead to advanced adaptations in both opponents. In the interactions between social parasites and their hosts, aggression is one of the major behavioural traits under selection. In a field manipulation, we aimed to disentangle the impact of slavemaking ants and nest density on aggression of Temnothorax longispinosus ants. An early slavemaker mating flight provided us with the unique opportunity to study the influence of host aggression and demography on founding decisions and success. We discovered that parasite queens avoided colony foundation in parasitized areas and were able to capture more brood from less aggressive host colonies. Host colony aggression remained consistent over the two-month experiment, but did not respond to our manipulation. However, as one-fifth of all host colonies were successfully invaded by parasite queens, slavemaker nest foundation acts as a strong selection event selecting for high aggression in host colonies.

Two pathways ensuring social harmony

Reproductive division of labour is a characteristic trait of social insects. The dominant reproductive individual, often the queen, uses chemical communication and/or behaviour to maintain her social status. Queens of many social insects communicate their fertility status via cuticle-bound substances. As these substances usually possess a low volatility, their range in queen-worker communication is potentially limited. Here, we investigate the range and impact of behavioural and chemical queen signals on workers of the ant Temnothorax longispinosus. We compared the behaviour and ovary development of workers subjected to three different treatments: workers with direct chemical and physical contact to the queen, those solely under the influence of volatile queen substances and those entirely separated from the queen. In addition to short-ranged queen signals preventing ovary development in workers, we discovered a novel secondary pathway influencing worker behaviour. Workers with no physical contact to the queen, but exposed to volatile substances, started to develop their ovaries, but did not change their behaviour compared to workers in direct contact to the queen. In contrast, workers in queen-separated groups showed both increased ovary development and aggressive dominance interactions. We conclude that T. longispinosus queens influence worker ovary development and behaviour via two independent signals, both ensuring social harmony within the colony.

Increased host aggression as an induced defense against slave-making ants

Slave-making ants reduce the fitness of surrounding host colonies through regular raids, causing the loss of brood and frequently queen and worker death. Consequently, hosts developed defenses against slave raids such as specific recognition and aggression toward social parasites, and indeed, we show that host ants react more aggressively toward slavemakers than toward nonparasitic competitors. Permanent behavioral defenses can be costly, and if social parasite impact varies in time and space, inducible defenses, which are only expressed after slavemaker detection, can be adaptive. We demonstrate for the first time an induced defense against slave-making ants: Cues from the slavemaker Protomognathus americanus caused an unspecific but long-lasting behavioral response in Temnothorax host ants. A 5-min within-nest encounter with a dead slavemaker raised the aggression level in T. longispinosus host colonies. Contrarily, encounters with nonparasitic competitors did not elicit aggressive responses toward non-nestmates. Increased aggression can be adaptive if a slavemaker encounter reliably indicates a forthcoming attack and if aggression increases postraid survival. Host aggression was elevated over 3 days, showing the ability of host ants to remember parasite encounters. The response disappeared after 2 weeks, possibly because by then the benefits of increased aggression counterbalance potential costs associated with it.