@article{6552, abstract = {When animals become sick, infected cells and an armada of activated immune cells attempt to eliminate the pathogen from the body. Once infectious particles have breached the body's physical barriers of the skin or gut lining, an initially local response quickly escalates into a systemic response, attracting mobile immune cells to the site of infection. These cells complement the initial, unspecific defense with a more specialized, targeted response. This can also provide long-term immune memory and protection against future infection. The cell-autonomous defenses of the infected cells are thus aided by the actions of recruited immune cells. These specialized cells are the most mobile cells in the body, constantly patrolling through the otherwise static tissue to detect incoming pathogens. Such constant immune surveillance means infections are noticed immediately and can be rapidly cleared from the body. Some immune cells also remove infected cells that have succumbed to infection. All this prevents pathogen replication and spread to healthy tissues. Although this may involve the sacrifice of some somatic tissue, this is typically replaced quickly. Particular care is, however, given to the reproductive organs, which should always remain disease free (immune privilege). }, author = {Cremer, Sylvia}, issn = {09609822}, journal = {Current Biology}, number = {11}, pages = {R458--R463}, publisher = {Elsevier}, title = {{Social immunity in insects}}, doi = {10.1016/j.cub.2019.03.035}, volume = {29}, year = {2019}, } @inbook{7513, abstract = {Social insects (i.e., ants, termites and the social bees and wasps) protect their colonies from disease using a combination of individual immunity and collectively performed defenses, termed social immunity. The first line of social immune defense is sanitary care, which is performed by colony members to protect their pathogen-exposed nestmates from developing an infection. If sanitary care fails and an infection becomes established, a second line of social immune defense is deployed to stop disease transmission within the colony and to protect the valuable queens, which together with the males are the reproductive individuals of the colony. Insect colonies are separated into these reproductive individuals and the sterile worker force, forming a superorganismal reproductive unit reminiscent of the differentiated germline and soma in a multicellular organism. Ultimately, the social immune response preserves the germline of the superorganism insect colony and increases overall fitness of the colony in case of disease. }, author = {Cremer, Sylvia and Kutzer, Megan}, booktitle = {Encyclopedia of Animal Behavior}, editor = {Choe, Jae}, isbn = {9780128132517}, pages = {747--755}, publisher = {Elsevier}, title = {{Social immunity}}, doi = {10.1016/B978-0-12-809633-8.90721-0}, year = {2019}, } @phdthesis{6435, abstract = {Social insect colonies tend to have numerous members which function together like a single organism in such harmony that the term ``super-organism'' is often used. In this analogy the reproductive caste is analogous to the primordial germ cells of a metazoan, while the sterile worker caste corresponds to somatic cells. The worker castes, like tissues, are in charge of all functions of a living being, besides reproduction. The establishment of new super-organismal units (i.e. new colonies) is accomplished by the co-dependent castes. The term oftentimes goes beyond a metaphor. We invoke it when we speak about the metabolic rate, thermoregulation, nutrient regulation and gas exchange of a social insect colony. Furthermore, we assert that the super-organism has an immune system, and benefits from ``social immunity''. Social immunity was first summoned by evolutionary biologists to resolve the apparent discrepancy between the expected high frequency of disease outbreak amongst numerous, closely related tightly-interacting hosts, living in stable and microbially-rich environments, against the exceptionally scarce epidemic accounts in natural populations. Social immunity comprises a multi-layer assembly of behaviours which have evolved to effectively keep the pathogenic enemies of a colony at bay. The field of social immunity has drawn interest, as it becomes increasingly urgent to stop the collapse of pollinator species and curb the growth of invasive pests. In the past decade, several mechanisms of social immune responses have been dissected, but many more questions remain open. I present my work in two experimental chapters. In the first, I use invasive garden ants (*Lasius neglectus*) to study how pathogen load and its distribution among nestmates affect the grooming response of the group. Any given group of ants will carry out the same total grooming work, but will direct their grooming effort towards individuals carrying a relatively higher spore load. Contrary to expectation, the highest risk of transmission does not stem from grooming highly contaminated ants, but instead, we suggest that the grooming response likely minimizes spore loss to the environment, reducing contamination from inadvertent pickup from the substrate. The second is a comparative developmental approach. I follow black garden ant queens (*Lasius niger*) and their colonies from mating flight, through hibernation for a year. Colonies which grow fast from the start, have a lower chance of survival through hibernation, and those which survive grow at a lower pace later. This is true for colonies of naive and challenged queens. Early pathogen exposure of the queens changes colony dynamics in an unexpected way: colonies from exposed queens are more likely to grow slowly and recover in numbers only after they survive hibernation. In addition to the two experimental chapters, this thesis includes a co-authored published review on organisational immunity, where we enlist the experimental evidence and theoretical framework on which this hypothesis is built, identify the caveats and underline how the field is ripe to overcome them. In a final chapter, I describe my part in two collaborative efforts, one to develop an image-based tracker, and the second to develop a classifier for ant behaviour.}, author = {Casillas Perez, Barbara E}, issn = {2663-337X}, keywords = {Social Immunity, Sanitary care, Social Insects, Organisational Immunity, Colony development, Multi-target tracking}, pages = {183}, publisher = {Institute of Science and Technology Austria}, title = {{Collective defenses of garden ants against a fungal pathogen}}, doi = {10.15479/AT:ISTA:6435}, year = {2019}, } @article{413, abstract = {Being cared for when sick is a benefit of sociality that can reduce disease and improve survival of group members. However, individuals providing care risk contracting infectious diseases themselves. If they contract a low pathogen dose, they may develop low-level infections that do not cause disease but still affect host immunity by either decreasing or increasing the host’s vulnerability to subsequent infections. Caring for contagious individuals can thus significantly alter the future disease susceptibility of caregivers. Using ants and their fungal pathogens as a model system, we tested if the altered disease susceptibility of experienced caregivers, in turn, affects their expression of sanitary care behavior. We found that low-level infections contracted during sanitary care had protective or neutral effects on secondary exposure to the same (homologous) pathogen but consistently caused high mortality on superinfection with a different (heterologous) pathogen. In response to this risk, the ants selectively adjusted the expression of their sanitary care. Specifically, the ants performed less grooming and more antimicrobial disinfection when caring for nestmates contaminated with heterologous pathogens compared with homologous ones. By modulating the components of sanitary care in this way the ants acquired less infectious particles of the heterologous pathogens, resulting in reduced superinfection. The performance of risk-adjusted sanitary care reveals the remarkable capacity of ants to react to changes in their disease susceptibility, according to their own infection history and to flexibly adjust collective care to individual risk.}, author = {Konrad, Matthias and Pull, Christopher and Metzler, Sina and Seif, Katharina and Naderlinger, Elisabeth and Grasse, Anna V and Cremer, Sylvia}, journal = {PNAS}, number = {11}, pages = {2782 -- 2787}, publisher = {National Academy of Sciences}, title = {{Ants avoid superinfections by performing risk-adjusted sanitary care}}, doi = {10.1073/pnas.1713501115}, volume = {115}, year = {2018}, } @article{616, abstract = {Social insects protect their colonies from infectious disease through collective defences that result in social immunity. In ants, workers first try to prevent infection of colony members. Here, we show that if this fails and a pathogen establishes an infection, ants employ an efficient multicomponent behaviour − "destructive disinfection" − to prevent further spread of disease through the colony. Ants specifically target infected pupae during the pathogen's non-contagious incubation period, relying on chemical 'sickness cues' emitted by pupae. They then remove the pupal cocoon, perforate its cuticle and administer antimicrobial poison, which enters the body and prevents pathogen replication from the inside out. Like the immune system of a body that specifically targets and eliminates infected cells, this social immunity measure sacrifices infected brood to stop the pathogen completing its lifecycle, thus protecting the rest of the colony. Hence, the same principles of disease defence apply at different levels of biological organisation.}, author = {Pull, Christopher and Ugelvig, Line V and Wiesenhofer, Florian and Grasse, Anna V and Tragust, Simon and Schmitt, Thomas and Brown, Mark and Cremer, Sylvia}, journal = {eLife}, publisher = {eLife Sciences Publications}, title = {{Destructive disinfection of infected brood prevents systemic disease spread in ant colonies}}, doi = {10.7554/eLife.32073}, volume = {7}, year = {2018}, } @article{617, abstract = {Insects are exposed to a variety of potential pathogens in their environment, many of which can severely impact fitness and health. Consequently, hosts have evolved resistance and tolerance strategies to suppress or cope with infections. Hosts utilizing resistance improve fitness by clearing or reducing pathogen loads, and hosts utilizing tolerance reduce harmful fitness effects per pathogen load. To understand variation in, and selective pressures on, resistance and tolerance, we asked to what degree they are shaped by host genetic background, whether plasticity in these responses depends upon dietary environment, and whether there are interactions between these two factors. Females from ten wild-type Drosophila melanogaster genotypes were kept on high- or low-protein (yeast) diets and infected with one of two opportunistic bacterial pathogens, Lactococcus lactis or Pseudomonas entomophila. We measured host resistance as the inverse of bacterial load in the early infection phase. The relationship (slope) between fly fecundity and individual-level bacteria load provided our fecundity tolerance measure. Genotype and dietary yeast determined host fecundity and strongly affected survival after infection with pathogenic P. entomophila. There was considerable genetic variation in host resistance, a commonly found phenomenon resulting from for example varying resistance costs or frequency-dependent selection. Despite this variation and the reproductive cost of higher P. entomophila loads, fecundity tolerance did not vary across genotypes. The absence of genetic variation in tolerance may suggest that at this early infection stage, fecundity tolerance is fixed or that any evolved tolerance mechanisms are not expressed under these infection conditions.}, author = {Kutzer, Megan and Kurtz, Joachim and Armitage, Sophie}, issn = {1420-9101}, journal = {Journal of Evolutionary Biology}, number = {1}, pages = {159 -- 171}, publisher = {Wiley}, title = {{Genotype and diet affect resistance, survival, and fecundity but not fecundity tolerance}}, doi = {10.1111/jeb.13211}, volume = {31}, year = {2018}, } @article{426, abstract = {Sperm cells are the most morphologically diverse cells across animal taxa. Within species, sperm and ejaculate traits have been suggested to vary with the male's competitive environment, e.g., level of sperm competition, female mating status and quality, and also with male age, body mass, physiological condition, and resource availability. Most previous studies have based their conclusions on the analysis of only one or a few ejaculates per male without investigating differences among the ejaculates of the same individual. This masks potential ejaculate-specific traits. Here, we provide data on the length, quantity, and viability of sperm ejaculated by wingless males of the ant Cardiocondyla obscurior. Males of this ant species are relatively long-lived and can mate with large numbers of female sexuals throughout their lives. We analyzed all ejaculates across the individuals' lifespan and manipulated the availability of mating partners. Our study shows that both the number and size of sperm cells transferred during copulations differ among individuals and also among ejaculates of the same male. Sperm quality does not decrease with male age, but the variation in sperm number between ejaculates indicates that males need considerable time to replenish their sperm supplies. Producing many ejaculates in a short time appears to be traded-off against male longevity rather than sperm quality.}, author = {Metzler, Sina and Schrempf, Alexandra and Heinze, Jürgen}, journal = {Journal of Insect Physiology}, pages = {284--290}, publisher = {Elsevier}, title = {{Individual- and ejaculate-specific sperm traits in ant males}}, doi = {10.1016/j.jinsphys.2017.12.003}, volume = {107}, year = {2018}, } @article{194, abstract = {Ants are emerging model systems to study cellular signaling because distinct castes possess different physiologic phenotypes within the same colony. Here we studied the functionality of inotocin signaling, an insect ortholog of mammalian oxytocin (OT), which was recently discovered in ants. In Lasius ants, we determined that specialization within the colony, seasonal factors, and physiologic conditions down-regulated the expression of the OT-like signaling system. Given this natural variation, we interrogated its function using RNAi knockdowns. Next-generation RNA sequencing of OT-like precursor knock-down ants highlighted its role in the regulation of genes involved in metabolism. Knock-down ants exhibited higher walking activity and increased self-grooming in the brood chamber. We propose that OT-like signaling in ants is important for regulating metabolic processes and locomotion.}, author = {Liutkeviciute, Zita and Gil Mansilla, Esther and Eder, Thomas and Casillas Perez, Barbara E and Giulia Di Giglio, Maria and Muratspahić, Edin and Grebien, Florian and Rattei, Thomas and Muttenthaler, Markus and Cremer, Sylvia and Gruber, Christian}, issn = {08926638}, journal = {The FASEB Journal}, number = {12}, pages = {6808--6821}, publisher = {FASEB}, title = {{Oxytocin-like signaling in ants influences metabolic gene expression and locomotor activity}}, doi = {10.1096/fj.201800443}, volume = {32}, year = {2018}, } @article{55, abstract = {Many animals use antimicrobials to prevent or cure disease [1,2]. For example, some animals will ingest plants with medicinal properties, both prophylactically to prevent infection and therapeutically to self-medicate when sick. Antimicrobial substances are also used as topical disinfectants, to prevent infection, protect offspring and to sanitise their surroundings [1,2]. Social insects (ants, bees, wasps and termites) build nests in environments with a high abundance and diversity of pathogenic microorganisms — such as soil and rotting wood — and colonies are often densely crowded, creating conditions that favour disease outbreaks. Consequently, social insects have evolved collective disease defences to protect their colonies from epidemics. These traits can be seen as functionally analogous to the immune system of individual organisms [3,4]. This ‘social immunity’ utilises antimicrobials to prevent and eradicate infections, and to keep the brood and nest clean. However, these antimicrobial compounds can be harmful to the insects themselves, and it is unknown how colonies prevent collateral damage when using them. Here, we demonstrate that antimicrobial acids, produced by workers to disinfect the colony, are harmful to the delicate pupal brood stage, but that the pupae are protected from the acids by the presence of a silk cocoon. Garden ants spray their nests with an antimicrobial poison to sanitize contaminated nestmates and brood. Here, Pull et al show that they also prophylactically sanitise their colonies, and that the silk cocoon serves as a barrier to protect developing pupae, thus preventing collateral damage during nest sanitation.}, author = {Pull, Christopher and Metzler, Sina and Naderlinger, Elisabeth and Cremer, Sylvia}, journal = {Current Biology}, number = {19}, pages = {R1139 -- R1140}, publisher = {Cell Press}, title = {{Protection against the lethal side effects of social immunity in ants}}, doi = {10.1016/j.cub.2018.08.063}, volume = {28}, year = {2018}, } @article{29, abstract = {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.}, author = {Viljakainen, Lumi and Jurvansuu, Jaana and Holmberg, Ida and Pamminger, Tobias and Erler, Silvio and Cremer, Sylvia}, issn = {20457758}, journal = {Ecology and Evolution}, number = {22}, pages = {11031--11070}, publisher = {Wiley}, title = {{Social environment affects the transcriptomic response to bacteria in ant queens}}, doi = {10.1002/ece3.4573}, volume = {8}, year = {2018}, }