Biology subjects

Schulz, N. K. E.

Publications and source records attributed to Schulz, N. K. E..

12 recordsLinked to original sources

bioRxiv2026

An HSP90-released reduced-eye phenotype alters light-dependent behaviour in Tribolium castaneum

Heat Shock Protein 90 (HSP90) functions as an evolutionary capacitor, allowing populations to store cryptic genetic variation that can be released under stress. While former studies have described the release of morphological variation, its behavioural consequences remain unexplored. In the red flour beetle, Tribolium castaneum, HSP90 inhibition released a phenotype with much smaller, less defined eyes that confers fitness benefits in continuous light and was subsequently assimilated. We hypothesized that altered eye morphology affects light perception and thereby changes light-dependent behaviours. To test whether phenotypes released via evolutionary capacitance can beneficially alter behaviour, we examined locomotor activity rhythm entrainment to light-dark cycles as well as individual and group light choice behaviour. Males of the reduced-eye phenotype exhibited a diminished startle response to sudden light exposure in locomotor activity assays. We also found reduced negative phototaxis in groups of beetles with reduced eyes. This modified behaviour, indicating reduced light sensitivity, may stem from impaired light perception caused by altered eye morphology. Lower light sensitivity could be beneficial under stressful environmental conditions by promoting the exploration of alternative niches. Therefore, this study provides the first evidence for potentially beneficial behavioural changes in a HSP90-released phenotype, reinforcing HSP90s role as an evolutionary capacitor.

evolutionary biology↗

bioRxiv2025

Experimental Removal of Niche Construction Alters the Pace and Mechanisms of Resistance Evolution

Niche construction, a central eco-evolutionary process in which organisms modify their environment, is hypothesised to enhance evolutionary adaptability through feedback between genetic inheritance and the lasting effects of environmental change--known as ecological inheritance. However, while theoretically intriguing, direct empirical support for the effect of niche construction on adaptation is lacking. Red flour beetles modify their environment by releasing quinone-rich stink gland secretions, a form of external immunity. Here, we test in an evolution experiment how experimental removal of niche construction--using RNAi of a key gene needed to produce stink gland secretions--affects the beetles adaptation to the bacterial entomopathogen Bacillus thuringiensis. In each generation, beetles inhabited conditioned flour either with regular or drastically reduced stink gland secretion content. Compared to the non-exposed control, all bacteria-exposed regimes rapidly evolved bacterial resistance within only six generations. However, beetles evolving with intact niche construction acquired resistance as soon as after three generations, indicating that adaptation was initially facilitated by niche construction. RNAseq of evolved beetles showed that gene expression differed strongly between the selection regimes, revealing that the mechanisms underlying resistance were dependent on niche construction. Thus, our findings provide urgently needed empirical evidence on the role of niche construction for resistance evolution and its potential genetic basis.

evolutionary biology↗

bioRxiv2025

Three species, three labs, three experiments: testing the reproducibility of ecological studies on insect behaviour in a multi-laboratory setting

The reproducibility of studies involving insect species is an underexplored area in the broader discussion about poor reproducibility in science. Our study addresses this gap by conducting a systematic multi-laboratory investigation into the reproducibility of ecological studies on insect behaviour. We implemented a 3x3 experimental design, incorporating three study sites, and three independent experiments on three insect species from different orders: the turnip sawfly (Athalia rosae, Hymenoptera), the meadow grasshopper (Pseudochorthippus parallelus, Orthoptera) and the red flour beetle (Tribolium castaneum, Coleoptera). Using random-effect meta-analysis, we compared the consistency and accuracy of treatment effects on insect behavioural traits across replicate experiments. We successfully reproduced the overall statistical treatment effect in 83% of the replicate experiments, but overall effect size replication was achieved in only 66% of the replicates. Thus, though demonstrating sufficient reproducibility in some measures, this study also provides first experimental evidence for cases of poor reproducibility in insect experiments. Our findings further show that reasons causing poor reproducibility established in rodent research also hold for other study organisms and research questions. We believe that a rethinking of current best practices is required to face reproducibility issues in insect studies, but also across disciplines. Specifically, we advocate for adopting open research practices and the implementation of methodological strategies that reduce bias and problems arising from over-standardization. With respect to the latter, the introduction of systematic variation through multi-laboratory or heterogenized designs may contribute to improved reproducibility in studies involving any living organisms.

animal behavior and cognition↗

bioRxiv2024

Experimental evolution of a pathogen confronted with innate immune memory increases variation in virulence

Understanding the drivers and mechanisms of virulence evolution is still a major goal of evolutionary biologists and epidemiologists. Theory predicts that the way virulence evolves depends on the balance between the benefits and costs it provides to pathogen fitness. Additionally, host responses to infections, such as resistance or tolerance, play a critical role in shaping virulence evolution. But, while the evolution of pathogens has been traditionally studied under the selection pressure of host adaptive immunity, less is known about their evolution when confronted to simpler and less effective forms of immunity such as immune priming. In this study, we used a well-established insect model for immune priming - red flour beetles and their bacterial pathogen Bacillus thuringiensis tenebrionis - to test whether this form of innate immune memory favors the evolution of higher virulence. Through controlled experimental evolution of the pathogen in primed versus non-primed hosts, we found no change in average virulence after eight selection cycles in primed host. However, we found a significant increase in the variation of virulence (i.e., host-killing ability) among independent pathogen lines evolved in primed host, and bacteria were unable to evolve resistance against host priming. Whole genome sequencing revealed increased activity in the bacterial mobilome (prophages and plasmids). Expression of the Cry toxin - a well-known virulence factor - was linked to evolved differences in copy number variation of the cry-carrying plasmid, though this did not correlate directly with virulence. These findings highlight that innate immune memory can drive variability in pathogen traits, which may favor adaptation to variable environments. This underscores the need to consider pathogen evolution in response to innate immune memory when applying these mechanisms in medicine, aquaculture, pest control, and insect mass production.

evolutionary biology↗

bioRxiv2024

Immune priming in the insect gut: a dynamic response revealed by ultrastructural and transcriptomic changes

Research on forms of memory in innate immune systems has recently gained momentum with the study of trained immunity in vertebrates and immune priming in invertebrates. Immune priming provides protection against previously encountered pathogens. However, causes and mechanisms of immune priming are still not well understood in most organisms. In this work, we combine RNA sequencing with transmission electron microscopy to investigate the dynamic processes during priming in the gut of a well-established model for oral immune priming, consisting of the host Tribolium castaneum and its entomopathogen Bacillus thuringiensis tenebrionis (Btt). We show that priming with specific, pathogen-derived virulence-relevant factors causes damage in the gut of T. castaneum larvae, which leads to an early physiological stress response as well as the upregulation of a specific set of immune genes. This response diminishes over time yet enables the gut to upregulate genes known to interfere with Btt virulence when T. castaneum larvae are later exposed to infectious Btt spores. The identification of these processes increases our understanding of immune priming as a dynamic process where cellular responses in concert with specific gene regulation prepare the gut tissue and thereby enable more efficient protection against infection. Such work can further help us understand the origin and mechanism of innate immune memory. Author summaryInvertebrate animals do not possess a classical adaptive immune system. And yet, many of these animals show forms of immune memory, collectively called immune priming. In this work, we investigate the causes of oral immune priming in the red flour beetle Tribolium castaneum in response to its bacterial entomopathogen Bacillus thuringiensis tenebrionis. Primary exposure to Btt spent culture media supernatants enables the larvae of T. castaneum to better withstand a subsequent infection with infectious Btt spores. We show that exposing T. castaneum larvae to those supernatants leads to damage in the gut resulting in a strong stress and immune response early after priming and a targeted up-regulation of beneficial genes upon the secondary re-encounter with Btt. These results suggest fundamental stress responses can be involved in innate immune memory phenomena, which has implications in translational research across species.

evolutionary biology↗

bioRxiv2024

Resources modulate developmental shifts but not infection tolerance upon coinfection in an insect system

Energetic resources fuel immune responses and parasite growth within organisms, but it is unclear whether energy allocation is sufficient to explain changes in infection outcomes under the threat of multiple parasites. We manipulated diet in flour beetles (Tribolium confusum) infected with two natural parasites to investigate the role of resources in shifting metabolic and immune responses after single and co-infection. Our results suggest that gregarine parasites alter the within-host energetic environment, and by extension juvenile development time, in a diet- dependent manner. Gregarines do not affect host resistance to acute bacterial infection but do stimulate the expression of an alternative set of immune genes and promote damage to the gut, ultimately contributing to reduced survival regardless of diet. Thus, energy allocation is not sufficient to explain the immunological contribution to coinfection outcomes, emphasizing the importance of mechanistic insight for predicting the impact of coinfection across levels of biological organization.

ecology↗

bioRxiv2024

Deciphering a beetle clock: individual and sex-dependent variation in daily activity patterns

Circadian clocks are inherent to most organisms, including cryptozoic animals that seldom encounter direct light, and regulate their daily activity cycles. A conserved suite of clock genes underpins these rhythms. In this study, we explore the circadian behaviors of the red flour beetle Tribolium castaneum, a significant pest impacting stored grain globally. We report on how daily light and temperature cues synchronize distinct activity patterns in these beetles, characterized by reduced morning activity and increased evening activity, anticipating the respective environmental transitions. Although less robust, rhythmicity in locomotor activity is maintained in constant dark and constant light conditions. Notably, we observed more robust rhythmic behaviors in males than females with individual variations exceeding those previously reported for other insect species. RNA interference targeting the Clock gene disrupted locomotor activity rhythms. Our findings demonstrate the existence of a circadian clock and of clock-controlled behaviors in T. castaneum. Furthermore, they highlight substantial individual differences in circadian activity, laying the groundwork for future research on the relevance of individual variation in circadian rhythms in an ecological and evolutionary context.

animal behavior and cognition↗

bioRxiv2022

Female investment in terminal reproduction or somatic maintenance depends on infection dose

Immune responses are energetically costly to produce and often trade off with investment in reproduction and offspring provisioning. We predicted that hosts can interpret the magnitude of the infection threat from cues like initial bacterial load to adjust reproductive investment into offspring quantity and quality. To test this prediction, we exposed female flour beetles (Tribolium castaneum) to naive or sterile media controls or one of three increasing doses of heat-killed Bacillus thuringiensis (Bt). To estimate offspring quantity, we measured the number of eggs and hatched larvae from each maternal treatment group. To estimate offspring quality, we measured egg protein content, development to pupation, pupal weight, and offspring survival against Bt infection. Compared to naive controls, low and intermediate bacterial doses resulted in lower female fecundity, suggesting a shift to a somatic maintenance strategy. Meanwhile, in the highest-dose group, fecundity was negatively correlated with egg protein content, suggesting a trade-off between offspring quality and quantity that could mask terminal investment based on metrics of quantity alone. Our results underscore the need to account for the magnitude of environmental cue when quantifying plasticity and trade-offs among life history traits, and provide new insight into the trans-generational effects of immune responses.

evolutionary biology↗

bioRxiv2021

Experimental evolution of insect resistance to two pesticide classes reveals mechanistic diversity and context-dependent fitness costs

Does rapid adaptation to stressors evolve through similar underlying mechanisms among diverse populations, or are there many roads to a similar phenotype? The experimental evolution of pesticide resistance in insects provides a powerful model to study the diverse evolutionary signatures of adaptation and their associated costs. Here, we selected for resistance to two pesticides (organophosphates and pyrethroids) in six field-derived populations of the red flour beetle (Tribolium castaneum). After several generations of selection, we performed transcriptomic analyses and measured survival, development, and fecundity in the presence and absence of pesticides to detect fitness costs of resistance evolution. All pesticide-selected populations exhibited significantly improved survival after pesticide exposure without substantial fitness costs, compared to control populations. Populations that evolved to resist organophosphates had distinct gene expression in the presence and absence of organophosphates, supporting different detoxification mechanisms and cuticular modifications among populations. In contrast, pyrethroid resistant populations demonstrated common differential expression of cytochrome P450 transcripts. Furthermore, some populations evolved similar mechanisms against both pesticides while others showed little overlap in their evolved responses, suggesting variation in potential cross-resistance phenotypes. Overall, between populations, we observed both parallel and divergent patterns in gene expression associated with acquired pesticide resistance, without ubiquitous fitness costs.

evolutionary biology↗

bioRxiv2018

Dnmt1 has an essential function despite the absence of CpG DNA methylation in the red flour beetle Tribolium castaneum

Epigenetic mechanisms, such as CpG DNA methylation enable phenotypic plasticity and rapid adaptation to changing environments. CpG DNA methylation is established by DNA methyltransferases (DNMTs), which are well conserved across vertebrates and invertebrates. There are insects with functional DNA methylation despite lacking a complete set of Dnmts. But at least one of the enzymes, DNMT1, appears to be required to maintain an active DNA methylation system. The red flour beetle, Tribolium castaneum, lacks Dnmt3 but possesses Dnmt1 and it has been controversial whether it has a functional DNA methylation system.\n\nUsing whole genome bisulfite sequencing, we did not find any defined patterns of CpG DNA methylation in embryos. Nevertheless, we found Dnmt1 expressed throughout the entire life cycle of the beetle, with mRNA transcripts significantly more abundant in eggs and ovaries. A maternal knockdown of Dnmt1 caused a developmental arrest in offspring embryos.\n\nWe show that Dnmt1 plays an essential role in T. castaneum embryos and that its downregulation leads to an early developmental arrest. This function appears to be unrelated to DNA methylation, since we did not find any evidence for this modification. This strongly suggests an alternative role of this protein.

evolutionary biology↗

bioRxiv2018

Transgenerational developmental effects of immune priming in the red flour beetle Tribolium castaneum

Immune priming, the increased chance to survive a secondary encounter with a pathogen, has been described for many invertebrate species, which lack the classical adaptive immune system of vertebrates. Priming can be specific even for closely related bacterial strains, last up to the entire lifespan of an individual, and in some species, it can also be transferred to the offspring and is then called transgenerational immune priming (TGIP). In the red flour beetle Tribolium castaneum, a pest of stored grains, TGIP has even been shown to be transferred paternally after injection of adult beetles with heat-killed Bacillus thuringiensis.\n\nHere we studied whether TGIP in T. castaneum is also transferred to the second filial generation, whether it can also occur after oral and injection priming of larvae and whether it has effects on offspring development. We found that paternal priming with B. thuringiensis does not only protect the first but also the second offspring generation. Also, fitness costs of the immune priming became apparent, when the first filial generation produced fewer offspring. Furthermore, we used two different routes of exposure to prime larvae, either by injecting them with heat-killed bacteria or orally feeding them B. thuringiensis spore culture supernatant. Neither of the parental larval priming methods led to any direct benefits regarding offspring resistance. However, the injections slowed down development of the injected individuals, while oral priming with both a pathogenic and a non-pathogenic strain of B. thuringiensis delayed offspring development.\n\nThe long-lasting transgenerational nature of immune priming and its impact on offspring development indicate that potentially underlying epigenetic modifications might be stable over several generations. Therefore, this form of phenotypic plasticity might impact pest control and should be considered when using products of bacterial origin against insects.

evolutionary biology↗

bioRxiv2018

Paternal knockdown of Dnmt2 increases offspring susceptibility to bacterial infection

Intergenerational effects from fathers to offspring are increasingly reported from diverse organisms, but the underlying mechanisms remain speculative. Paternal trans-generational immune priming (TGIP) was demonstrated in the red flour beetle Tribolium castaneum: non-infectious bacterial exposure of fathers protects their offspring against an infectious challenge for at least two generations. Epigenetic processes, such as cytosine methylation of nucleic acids, have been proposed to enable transfer of information from fathers to offspring. Here we studied a potential role in TGIP of the Dnmt2 gene (renamed as Trdmt1 in humans), which encodes a highly conserved enzyme that methylates different RNAs, including specific cytosines of a set of tRNAs. Dnmt2 has previously been reported to be involved in intergenerational epigenetic inheritance in mice and protection against viruses in fruit flies. We first studied gene expression and found that Dnmt2 is expressed in various life history stages and tissues of T. castaneum, with high expression in the reproductive organs. RNAi-mediated knockdown of Dnmt2 in fathers was systemic, slowed down offspring larval development and increased mortality of the adult offspring upon bacterial infection. However, these effects were independent of bacterial exposure of the fathers. In conclusion, our results point towards a role of Dnmt2 for paternal effects, while elucidation of the mechanisms behind paternal TGIP needs further studies.

evolutionary biology↗