Biology subjects

Schmitt, T.

Publications and source records attributed to Schmitt, T..

At least 19 recordsLinked to original sources

bioRxiv2026

Conserved task-specific profiles outweigh seasonal shifts in cuticular hydrocarbons of European honey bee subspecies

Cuticular hydrocarbons (CHCs) are essential for insect waterproofing, yet how they change seasonally in social insects remains poorly understood. Due to its distinct seasonal worker phenotypes (summer and winter bees) and diverse subspecies, the western honey bee (Apis mellifera) is an ideal model to study seasonal CHC plasticity across populations with distinct local adaptations. We performed a common garden experiment to investigate the seasonal plasticity in CHC profiles across five European subspecies (A. m. carnica, A. m. iberiensis, A. m. ligustica, A. m. macedonica, A. m. ruttneri). We compared the CHC composition of workers performing tasks inside ("in-hive") or outside ("out-hive") the colony during summer and winter. Notably, out-hive workers consistently exhibited more waterproofing CHC profiles compared to in-hive workers, regardless of season or subspecies. The persistence of this stereotypical task-related differentiation in long-lived winter bees, which largely lack an age-based division of labor, indicates a robust, age-independent regulatory mechanism linked to the environment faced by the workers rather than a simple response to seasonal desiccation pressure. Moreover, we demonstrate CHC seasonal plasticity for the first time in honey bees. However, these seasonal shifts in hydrocarbon classes and chain length were not uniform; they varied across subspecies and critically depended on the task the workers performed.

ecology↗

bioRxiv2025

Tolerance toward foreigners in ants requires chronic exposure for establishment but only sporadic exposure for maintenance

Social insects discriminate between foreigners and members of their own colony via complex olfactory cues. How plastic this discriminatory behavior is, and whether and under what circumstances ants can learn to accept genetically distinct individuals as nestmates, is poorly understood. Here, we study this question in the clonal raider ant, Ooceraea biroi, which provides unparalleled experimental control over the genotype of individuals and the genotypic composition of colonies. Using a cross-fostering design with mixed-genotype colonies of wild-type and transgenically labelled individuals, we show that ants become non-aggressive specifically toward their foster genotype. This tolerance is transient, and aggression resumes after two weeks of being isolated from the foster colony. However, even sporadic re-exposure to individuals from the foster colony is sufficient to maintain tolerance for over a month, while the same paradigm fails to establish tolerance in the first place. This shows that non-nestmate discrimination is remarkably plastic and that, once established, tolerance toward foreigners can be maintained by only intermittent contact. These dynamics echo general principles of social learning and contact-dependent tolerance described in other social species, including humans.

animal behavior and cognition↗

bioRxiv2025

Domain-Specific Functional Network Adaptations Supporting Dual-Task Performance in Older Adults

Aging is associated with declines in both motor and cognitive functions, which are well captured by dual-task gait paradigms. However, the functional brain network mechanisms supporting motor and cognitive aspects of dual-task performance in aging remain unclear. We examined 40 older adults (50-80 years) and 20 younger adults (20-40 years) who performed a motor single-task (pedaling), a cognitive single-task (Go/NoGo), and a combined cognitive-motor dual-task during functional magnetic resonance Imaging (fMRI) using a custom-built MRI-compatible pedaling device. Behaviorally, older adults showed significant dual-task costs in motor performance, while cognitive performance was preserved. Neurally, older adults showed selective increases in connectivity within executive and motor-planning regions of cognitive networks, consistent with compensatory recruitment, whereas motor networks underwent broader reorganization, with strengthened frontoparietal control circuits but weakened cerebello-parietal and sensorimotor pathways. Multivariate analyses further revealed age-related differences in latent connectivity- behavior relationships: motor-network patterns in older adults were more dispersed, reflecting heterogeneous reorganization, whereas cognitive-network patterns were more overlapping across groups, suggesting relative preservation. These findings suggest that aging involves a domain-specific balance of resilience and vulnerability across brain networks and highlight motor-network adaption as a promising target for understanding why some older adults maintain function while others decline.

neuroscience↗

bioRxiv2025

Evolution of first aid and social wound care in an army ant society

Injuries and infections pose a significant threat to fitness. Animals cope with this problem by performing self-medication or receiving social care from members of the group. While the benefits of wound care in increasing survival are clear, the forces driving the evolution of these behaviours are not fully understood. Contrary to the current hypothesis that social wound care is more likely to evolve in small groups due to the high relative value of an individual, we demonstrate that group size is not necessary for its evolution or retention. Instead, our theoretical model formalises how injury rate and lethality are fundamental drivers of care rather than group size. This is further evidenced by the presence of wound care in the army ant Eciton burchellii, a species with colonies of [~]1 million ants that hunts pugnacious prey. Here, wound care significantly increased survival in ants with infected wounds, occurring in two phases: direct care at the raiding site, and treatment with antimicrobial secretions in the bivouac. This species is the first to provide on-site care, thereby minimising the latency to receive care and thus potentially the likelihood of lethal wound infection. Our findings reject the notion that small group size is necessary for the evolution or retention of social wound care, revealing instead that injury-driven care can be a widespread and adaptive feature of even the largest insect societies. Significance StatementInjuries and infections threaten survival, but animals can counter these dangers through self-medication or social care. It has been suggested that helping behaviours directed towards vulnerable or injured individuals, such as social wound care, are more likely to evolve in small groups. This study in an army ant with [~]1 million workers shows otherwise, with injury frequency likely being the key component for the evolution or retention of wound-care behaviours. The unique strategy of on-site care at the raiding site, followed by antimicrobial care inside the bivouac, significantly improved survival outcomes. Our theoretical model further shows that even at low rates of care, fitness benefits are high, suggesting that social wound care may be far more widespread than previously thought.

evolutionary biology↗

bioRxiv2025

The Invisible Heterogeneity of a Forest -- Beta Diversity of Volatiles

Forest structural heterogeneity affects biodiversity, yet how changes in forest structure influence the spatial patterns of forest chemical heterogeneity remains poorly understood. Volatile organic compounds (VOCs) create invisible chemical landscapes that influence forest ecosystem processes, but whether VOC {beta}-diversity patterns respond to silviculture or disturbance caused heterogeneity remains unknown. We quantified how enhanced structural beta complexity (ESBC) treatments affect VOC {beta}-diversity patterns and investigated potential drivers and ecological effects in temperate production forests. Using the experimental BETA-FOR framework, we sampled ambient forest air at the forest floor and 1 m heights across 234 forest patches in six German regions using Tenax/Carboxen adsorbent traps analyzed via TD-GCMS. Results from generalized linear beta regression models showed that {beta}-diversity of VOCs increased significantly at 1 m height in ESBC forests compared to control forests, but this increase was not significant at the forest floor. In contrast to studies on plants, fungi and animals, the main driver for increasing beta-diversity in VOCs was not the heterogeneity of canopy openness, but the amount of deadwood. Using saproxylic beetles as a test group, we found that saproxylic beetle community dissimilarity increased with VOC dissimilarity, but only for forest floor VOCs. Our finding adds a new component to the framework of habitat heterogeneity, the invisible gradient of volatile diversity utilized by many forest organisms. Furthermore, we provide the first evidence that enhancing the heterogeneity of forests, and particularly of the dead wood, increase not only the structural heterogeneity but also the volatile {beta}-diversity.

ecology↗

bioRxiv2025

The potential role of volatile organic compounds on the colonisation of deadwood by saproxylic beetles

Volatile organic compounds (VOCs) emitted by deadwood are increasingly recognised as key olfactory cues used by saproxylic beetles to locate suitable substrates. However, how beetle communities respond to these cues during the colonisation of deadwood remains poorly understood. To address this gap, it is essential to quantify both VOC emissions and beetle assemblages, and to experimentally disentangle the main ecological drivers of the deadwood volatilome (i.e., tree species, sun exposure). To explore the potential role of VOCs on saproxylic beetle colonisation, we exposed 1200 freshly cut branches of oak, beech, spruce, and pine across Central Europe. To mimic natural variation in deadwood and disturbance processes, the bundles were experimentally manipulated either by sterilisation (to reduce endogenous fungi), fungal inoculation with a brown rot fungus (Fomitopsis pinicola), a white rot fungus (Fomes fomentarius), or burning. From each deadwood bundle, we sampled 448 substances, 89 of which were identified as VOCs and reared 134 saproxylic beetle species. We observed distinct VOC profiles emitted by broadleaf and conifer species, aligning with the beetles tree-type preferences. In conifers, bark beetles, longhorn beetles, and jewel beetles were associated with different chemical cues, whereas beetle taxonomic separation was not observed in broadleaf species. Although experimental treatments altered VOC composition, they could not explain beetle colonisation patterns. Our study highlights that VOCs emitted during the early decay stage of deadwood are associated with distinct saproxylic beetle assemblages. VOC composition varied across tree species and treatments, suggesting that chemical variation reflects multiple ecological factors. These findings indicate that deadwood diversity, particularly in tree species, contributes to chemical heterogeneity, which is linked to broader beetle assemblages. Forest conservation efforts may therefore need to consider the role of chemical variation in deadwood, as it could influence colonisation patterns of saproxylic beetles and affect the success of biodiversity management strategies.

ecology↗

bioRxiv2025

Better Safe Than Sorry: Leg Amputations as a Prophylactic Wound Care Behaviour in Carpenter Ants

Animals often sustain injuries, which are susceptible to lethal infections. In social insects, wound care behaviours have evolved to reduce these risks. But the limits of wound care behaviours remain unclear. Here we investigated the wound care behaviours of the ant Camponotus maculatus. Our findings show that amputation of legs infected with Pseudomonas aeruginosa significantly reduced mortality. However, nestmates do not differentiate between infected and sterile injuries, providing similar treatments regardless of infection. Even though we show that early amputation correlates with higher survival rates, nestmates amputate indiscriminately on legs with fresh or old wounds. Additionally, cuticular hydrocarbon profiles differed between ants with infected or sterile wounds only 24 hours post-injury, a timepoint when amputations are no longer effective. We propose that C. maculatus workers perform prophylactic amputations regardless of injury state or age. This is in sharp contrast to previous studies which showed clear capabilities to treat infected wounds differently in ants using antimicrobial compounds. This work therefore shows the limits of wound care behaviours in social insects, allowing us to better understand the evolutionary drivers of this unique behaviour.

animal behavior and cognition↗

bioRxiv2024

Recognition of an appropriate mating partner using cuticular hydrocarbons in a species with an extreme intra-sexual dimorphism

Attracting a mate at the right time is critical for many species that reproduce sexually. In insects, short-range communication between potential mates is often mediated by cuticular hydrocarbons (CHCs), which cover most of the insect cuticle. Although the CHC profiles of many insects have been studied, we know little about what aspects of a CHC profile cause changes in mate attractiveness over the lifetime of an individual. We addressed this question by studying the mason wasp Odynerus spinipes, whose females exhibit age-related quantitative changes in their CHC profile composition. First, we created an ethogram of the male mating behavior. We knew from preliminary investigations that males do not attempt to mate with recently eclosed adult females. By coating wasp dummies with different CHC extracts, we were able to show that the CHC profiles of 3-day-old females are indeed more attractive to males than those of 0-day-old females. The increased attractiveness of 3-day-old females compared to younger females was negatively correlated with the relative abundance of methyl-branched alkanes in the CHC profile of the females. These results, and the fact that the CHC profile of males is characterized by a high relative abundance of methyl-branched alkanes throughout the adult wasp lifetime, suggest that in O. spinipes, methyl-branched alkanes may act as anti-aphrodisiacs that reduce the harassment of females by males before the females are ready to mate.

ecology↗

bioRxiv2024

Variability in honey bee cuticular hydrocarbon composition can be understood as a function of gene expression

Most terrestrial insects have a layer of cuticular hydrocarbons (CHCs) protecting them from desiccation and mediating chemical communication. CHC composition is regulated by the expression of genes coding for enzymes in the biosynthetic pathway of hydrocarbons. The diversity and expression of these enzymes determine the abundance and richness of compounds in the CHC profile of an insect. For example, elongases are enzymes that lengthen the hydrocarbon chain, while desaturases introduce double bonds in it. CHC profiles of honey bees (Apis mellifera) vary among castes, task groups, and subspecies. This makes A. mellifera an excellent model to study the molecular mechanism underlying CHC biosynthesis. Here, we examined the expression of specific elongase- and desaturase-encoding genes and correlated gene expression with CHC composition in bees from two different task groups of two highly divergent A. mellifera subspecies: A. m. carnica and A. m. iberiensis. We show that in A. mellifera, the specificity of desaturases and elongases shapes the CHC profiles of different task groups. Our results shed light on the genetic basis for the task-specific CHC composition differences in social hymenopterans and lay the ground for further studies aiming to unravel the genetic underpinning of CHC biosynthesis. Moreover, these results underline the importance of investigating different subspecies of A. mellifera to better understand the mechanisms driving CHC composition.

ecology↗

bioRxiv2024

Deciphering the variation in cuticular hydrocarbon profiles of five European honey bee subspecies

The Western honey bee (Apis mellifera) subspecies exhibit local adaptive traits that evolved in response to the different environments that characterize their native distribution ranges. An important trait is the cuticular hydrocarbon (CHC) profile, which helps preventing desiccation and mediating communication. We compared the CHC profiles of six European subspecies (A. m. mellifera, A. m. carnica, A. m. ligustica, A. m. macedonica, A. m. iberiensis, and A. m. ruttneri) and investigated potential factors shaping their composition. We did not find evidence of adaptation of the CHC profiles of the subspecies to the climatic conditions in their distribution range. Subspecies-specific differences in CHC composition might be explained by phylogenetic constraints or genetic drift. The CHC profiles of foragers were more subspecies-specific than those of nurse bees, while the latter showed more variation in their CHC profiles, likely due to the lower desiccation stress exerted by the controlled environment inside the hive. The strongest profile differences appeared between nurse bees and foragers among all subspecies, suggesting an adaptation to social task and a role in communication. Foragers also showed an increase in the relative amount of alkanes in their profiles compared to nurses, indicating adaptation to climatic conditions.

evolutionary biology↗

bioRxiv2024

A chemically defined oviposition attractant and repellent of Black Soldier Flies (Hermetia illucens)

Black Soldier Flies (BSF), Hermetia illucens, are industrially important species. They can consume large amounts of spoilt organic material as larvae and bio-convert it to more useful biomass. Female BSF lay eggs in crevices adjacent to spoilt organic materials that serve as an oviposition attractant. These kairomones are central to maximising rearing efforts, yet the composition and origin of oviposition cues remain undefined, and no synthetic oviposition attractants are currently available. This work aimed to identify key components of naturally occurring oviposition attractants and to formulate an effective synthetic alternative for BSF. We have developed a novel oviposition assay and found larval food- and frass-based attractants to be the most effective at centralizing egg laying. We have identified the volatile compounds in the headspaces of putative attractants and established that the antennae of the female flies respond to some of these compounds. Behavioural validation using synthetic compounds allowed us to generate a mixture of 5 compounds (p-cresol, decanal, sulcatone, pentanoic acid, acetophenone) that cues oviposition as efficiently as currently used natural oviposition attractants. We also identified a synthetic mixture that deters oviposition in BSF. The synthetic attractant and repellent we generated are likely to simplify BSF rearing in research and industrial settings.

neuroscience↗

bioRxiv2023

Gut microbiota influences foraging onset without affecting division of labor and associated physiological hallmarks in honeybees

Gut microbes can impact cognition and behavior, but whether they regulate division of labor in animal societies is unknown. We addressed this question using honeybees since they exhibit division of labor between nurses and foragers and because their gut microbiota can be manipulated. Using automated behavioral tracking and controlling for co-housing effects, we show that gut microbes influence the age at which bees start foraging but have no effects on the time spent in a foraging area and number of foraging trips. Moreover, the gut microbiota did not influence hallmarks of behavioral maturation such as body weight, cuticular hydrocarbon (CHC) profile, hypopharyngeal gland size, and the proportion of bees maturing into foragers. Overall, this study shows that the honeybee gut microbiota does not affect division of labor but rather plays an important function in controlling the onset of bee foraging.

evolutionary biology↗

bioRxiv2023

Spatial transcriptomics of a parasitic flatworm provides a molecular map of vaccine candidates, drug targets and drug resistance genes

The spatial organization of gene expression dictates tissue functions in multicellular parasites. Here, we present the first spatial transcriptome of a parasitic flatworm, the common liver fluke Fasciola hepatica. We identified gene expression profiles and marker genes for eight distinct tissues and validated the latter by in situ hybridization. To demonstrate the power of our spatial atlas, we focused on genes with substantial medical importance, including vaccine candidates (Ly6 proteins), drug targets ({beta}-tubulins, protein kinases) and drug resistance genes (glutathione S-transferases, ABC transporters). Several of these genes exhibited unique expression patterns, indicating tissue-specific biological functions. Notably, the prioritization of tegumental protein kinases identified a PKC{beta}, for which small-molecule targeting caused parasite death. Our comprehensive gene expression map provides unprecedented molecular insights into the organ systems of this complex parasitic organism, serving as a valuable tool for both basic and applied research.

molecular biology↗

bioRxiv2023

Cuticular hydrocarbon profiles of Himalayan bumble bees (Hymenoptera: Bombus Latreille) are species-specific and show local and elevation related variation

Bumble bees are important pollinators in natural environments and agricultural farmlands and are in particular adapted to harsh environments like high mountain habitats. In these environments, animals are exposed to low temperature and face the risk of desiccation. The Eastern Himalayas are one of the recognized biodiversity hotspots worldwide. The area covers subtropical rainforest with warm temperature and high precipitation as well as high mountain ranges with peaks reaching up to 6000 m, shaping a diverse floral and faunal community at the different altitudinal zones. We investigated the cuticular hydrocarbon profiles of four bumble bee species occurring at different elevational ranges in Arunachal Pradesh, the northeast most state in India. At 17 locations along an elevational gradient we collected workers of two species from lower elevations (B. albopleuralis and B. breviceps; [~] 100m - 3000m asl) and two species from higher elevations (B. prshewalskyi and B. mirus; [~] 2800m - 4,500m asl). The CHC profiles of all four species showed a significant degree of variation in the composition of hydrocarbons, indicating species specificity. We also found clear correlation with elevation. The weighted mean chain length of the hydrocarbons significantly differed between the low and high altitudinal species, and the proportion of saturated hydrocarbons in CHC profiles significantly increased with the elevational range of the bumble bee species. Thus, these four species of bumble bees in the eastern Himalayas seem to adapt their CHC composition to elevation by decreasing water permeability of their cuticle, similar to insects living in dry mountains or deserts habitats.

ecology↗

bioRxiv2023

Behavioural individuality determines infection risk in clonal ant colonies

In social groups, disease risk is not distributed evenly across group members. Individual behaviour is a key source of variation in infection risk, yet its effects are difficult to separate from those of other factors. Here, we combine long-term epidemiological experiments and automated tracking in clonal raider ant colonies, where behavioural individuality emerges among identical workers. We find that: 1) division of labour determines the distribution of parasitic nematodes (Diploscapter) among hosts, showing that differences in infection can emerge from behavioural variation alone, 2) infections affect colony social organisation by causing infected workers to stay in the nest. By disproportionally infecting some workers and shifting their spatial distribution, infections reduce division of labour and increase spatial overlap between hosts, which is expected to facilitate parasite transmission. Thus, division of labour, a defining feature of many societies, not only shapes infection risk and distribution but can also be modified by parasites.

animal behavior and cognition↗

bioRxiv2022

The alarm pheromone and alarm response of the clonal raider ant

Ants communicate via an arsenal of different pheromones produced in a variety of exocrine glands. For example, ants release alarm pheromones in response to danger to alert their nestmates and to trigger behavioral alarm responses. Here we characterize the alarm pheromone and the alarm response of the clonal raider ant Ooceraea biroi, a species that is amenable to laboratory studies but for which no pheromones have been identified. During an alarm response, ants quickly become unsettled, leave their nest pile, and are sometimes initially attracted to the source of alarm, but ultimately move away from it. We find that the alarm pheromone is released from the head of the ant and identify the putative alarm pheromone as a blend of two compounds found in the head, 4-methyl-3-heptanone and 4-methyl-3-heptanol. These compounds are sufficient to induce alarm behavior alone and in combination. They elicit similar, though slightly different behavioral features of the alarm response, with 4-methyl-3-heptanone being immediately repulsive and 4-methyl-3-heptanol being initially attractive before causing ants to move away. The behavioral response to these compounds in combination is dose-dependent, with ants becoming unsettled and attracted to the source of alarm pheromone at low concentrations and repulsed at high concentrations. While 4-methyl-3-heptanone and 4-methyl-3-heptanol are known alarm pheromones in other more distantly related ant species, this is the first report of the chemical identity of a pheromone in O. biroi, and the first alarm pheromone identified in the genus Ooceraea. Identification of a pheromone that triggers a robust, consistent, and conserved behavior, like the alarm pheromone, provides an avenue to dissect the behavioral and neuronal mechanisms underpinning chemical communication.

animal behavior and cognition↗

bioRxiv2022

Infection signaling and antimicrobial wound care in an ant society

Infected wounds pose a major mortality risk in animals1,2. Injuries are common in the ant Megaponera analis, which raids pugnacious prey3,4. Here we show that M. analis can determine when wounds are infected and treat them accordingly. By applying a variety of antimicrobial compounds and proteins secreted from the metapleural gland to infected wounds, workers reduce the mortality of infected individuals by 90%. Chemical analyses showed that wound infection is associated with specific changes in the cuticular hydrocarbon profile, thereby likely allowing nestmates to diagnose the infection state of injured individuals and apply the appropriate antimicrobial treatment. This study demonstrates that the targeted use of antimicrobials to treat infected wounds, previously thought to be a uniquely human behavior, has evolved in insect societies as well.

animal behavior and cognition↗

bioRxiv2022

Anti-thrombotic treatment enhances antibiotic efficiency in a humanized model of meningococcemia

Meningococcal infections remain particularly difficult to treat. Despite antibiotic therapy, the state of the patients often rapidly deteriorates. Early clinical studies suggest that meningococci acquire a form of resistance to antibiotic treatments during infections. Taking advantage of a humanized animal model of infection, we confirm that adherent bacteria become highly resistant to antibiotic treatments as early as 3-6 hours post infection, although fully sensitive in vitro. Within this time frame, meningococci adhere to the endothelium via their type IV pili, proliferate and eventually fill the vessel lumen. Using intravital imaging, we show that rapidly upon infection blood flow is dramatically decreased, thus limiting antibiotic access to infected vessels. Concomitantly, fibrin is deposited inside infected vessels in proximity to bacterial aggregates. Pharmacologically impairing thrombin generation by inhibiting Factor X activity not only improves blood flow in infected vessels, but also enhances the efficacy of the antibiotic treatment. Our results indicate that the combined administration of anticoagulants together with antibiotics might represent a therapeutic approach to treat meningococcal sepsis more efficiently.

pathology↗