Host-parasite interactions are associated with high selection pressures: parasites should evolve mechanisms to exploit their host, which leads to counter-adaptations by the host's immune system to reduce damage from the parasite. They are therefore ideal models to study evolution in action. We address this field using both natural populations of hosts and parasites, and with experimental evolution in the lab.
In our lab, we use the red flour beetle Tribolium castaneum as a model organism to study a variety of questions in evolutionary ecology. Our main focus is to understand how basic characteristics of the immune system are shaped by evolution. Specificity and memory are the hallmarks of the vertebrate immune system. For a long time, invertebrate immune systems were thought to completely lack these phenomena. However, this paradigm is currently being challenged (Kurtz & Franz 2003, Kurtz 2005, Netea et al. 2015). In the flour beetle, our group has demonstrated that individuals treated with heat-killed bacteria show improved survival when subsequently confronted with live bacteria. This protection was strongest when the bacteria were from the same strain, indicating an unexpected degree of specificity (Roth et al. 2009). Most astonishingly, this protection was even transmitted across generations, leading to enhanced survival of offspring when either the mother or the father was ‘vaccinated’ (Roth et al. 2010).
Recent projects further address the underlying mechanisms using the beetles' entomopathogen Bacillus thuringiensis tenebrionis (Btt) and have uncovered pathogen-associated molecules that induce these immune priming responses. Beside identifying the beetle-specific Cry3Aa toxin and other virulence factors as potential inducers (Länger, Baur et al. 2023), further work focusing on the primed host. Changed microbiome composition in primed beetles, points to a potential role of the microbiome in facilitating oral priming. Additional analysis of beetle guts revealed pathogen-induced damage, leading to a physiological stress response and the upregulation of a specific set of immune genes. These findings provide deeper insights into how pathogen encounters can lead to efficient protection against future infections (Baur et al. 2024).
Long term projects in our lab employ the host–parasite dynamics of Btt and T. castaneum to study host–parasite coevolution through experimental evolution. Such projects expose organisms to targeted selection pressure in the laboratory to study evolutionary consequences. Using this approach, we were able to show that controlled evolution of the pathogen Btt in primed hosts led to an increased variation in virulence compared to pathogens evolved in non-primed hosts (Korša, Baur et al. 2024).
Focusing on the host, instead of the pathogen, another selection line addresses the role of niche construction — the beneficial modification of the environment through an organism — in shaping host–parasite dynamics. For this, we have conducted 20 generations of selection to study how the experimental removal of niche construction, achieved via RNAi knockdown of a key gene required for the production of antimicrobial stink gland secretions, affects the beetles' adaptation to Btt. While all beetles exposed to Btt rapidly evolved bacterial resistance, beetles with intact niche construction did so faster and via different molecular routes, providing evidence for the importance of niche construction in the rapid evolution of resistance (Lo, Schulz et al. 2025).
Another mechanism that potentially enables rapid adaptation and is studied in our lab is the evolutionary capacitor heat shock protein 90 (HSP90). The term "evolutionary capacitor" refers to the ability of this chaperone to ‘store’ genetic variation in a cryptic manner, revealing associated phenotypes only under stressful conditions. Interestingly, in T. castaneum, the wounding of conspecifics led to the down-regulation of HSP90 in unharmed conspecifics housed in the same group, indicating that social cues mediate HSP90 regulation (Peuß, Eggert et al. 2015).
To study the potential consequences of HSP90 impairment, we experimentally impaired HSP90 function in T. castaneum, which led to the expression of a reduced-eye phenotype, providing fitness benefits under continuous light conditions (Sayed et al. 2025). This highlights a mechanism by which hidden genetic variation can contribute to adaptation.
In order to further identify mechanisms that enable rapid adaptation, we are also focusing on epigenetics in T. castaneum. Interestingly, T. castaneum has lost CpG DNA methylation, but the maintenance DNA methyltransferase 1 (Dnmt1) nevertheless seems essential for offspring development (Schulz et al. 2018). We are now investigating how such epigenetic mechanisms evolved among beetles by comparing T. castaneum to other beetle species. In doing so, we aim to uncover alternative functions of DNA methyltransferases and assess the interplay between DNA methylation and histone modification across species (Länger, Israel et al. 2025).
Lastly, we are interested in the evolution of temporal niches in T. castaneum. Like most organisms, the red flour beetle shows diel rhythms in locomotor activity, controlled by a circadian clock, with activity peaking during the late day. However, unlike most model species, these beetles show striking individual variation in their activity patterns (R et al. 2024). In our lab, we aim to exploit this variation to address key questions in the evolution of circadian clocks. In addition, based on these new insights into the beetles' circadian system, we are exploring whether the time of infection affects infection outcomes and whether infection itself alters diel behavioural patterns.
Dr. Nora Schulz (Lecturer)
Rascha Sayed (Postdoc)
Zoë Länger (PhD student)
Our research group investigates the intricate and fascinating dynamics of ecology and evolution in natural and semi-natural environments, focusing on the complex relationships between organisms and their ecosystems. Using the three-spined stickleback (Gasterosteus aculeatus), we explore how ecological factors like parasitism and competition shape evolutionary processes, species interactions, and community structure.
1. Eco-Evolutionary Dynamics and Individual Variation:
The central theme of our research is to understand how individual variation influences eco-evolutionary dynamics. We focus on how traits of individual organisms shape their interactions with the environment and other species. Our work aims to clarify the role of ecological factors—such as parasitism, competition, and predation—in shaping evolutionary processes and promoting species coexistence. Through detailed studies of the three-spined stickleback, we investigate how individual variation affects ecological outcomes and contributes to evolutionary trajectories.
2. Host-Parasite Coevolution in the Three-Spined Stickleback:
Our research on the three-spined stickleback (Gasterosteus aculeatus) primarily focuses on host-parasite interactions, with an emphasis on the evolutionary "arms race" between hosts and their parasites. This coevolutionary process is driven by genetic interactions (GxG), which we hypothesize are strongly influenced by environmental factors (GxGxE).
3. Ecological and Evolutionary Impact of Schistocephalus solidus on Host and Copepods:
A central component of our research involves studying the tapeworm Schistocephalus solidus, a highly adapted parasite of the three-spined stickleback. This parasite manipulates not only the immune system of its host but also alters its behavior in ways that increase the likelihood of predation by the parasite’s final host—a fish-eating bird. By influencing the host’s behavior, S. solidus enhances its transmission, contributing to a coevolutionary "arms race" between the parasite and its host.
In addition to studying the effects of S. solidus on the stickleback, we also investigate the ecological consequences of this parasite within the broader ecosystem. Specifically, we focus on its impact on copepods—small, crucial crustaceans in aquatic food webs. We examine how the presence of S. solidus affects copepod populations and, consequently, broader ecological dynamics, including species interactions, nutrient cycling, and food web structures. This research underscores how parasitism can extend beyond the host, influencing the entire ecosystem.
Our group employs a combination of field studies, controlled experiments, and genomic analyses to explore eco-evolutionary processes. Our research blends natural and semi-natural experimental settings, allowing us to investigate host-parasite dynamics in diverse ecological contexts. For example, we manipulate the exposure or infection levels of individuals to parasites and measure their effects at the individual, population, and community level.
Anke Große Brinkhaus (Technical assistant)
Julius Mersmann (Technical assistant)
Ilka Rauch (Technical assistant)
We study immunological niche conformance of different cave- and surface dwelling populations of Mexican tetras (Astyanax mexicanus) which differ in parasite abundance and diversity and immune investment strategy. Our research consists of field work taking physiological and environmental measurements from wild cave- and surface populations as well as experiments in the laboratory where we challenge the immune system of individual fish with different parasite antigen solutions from the field to test for their degree of niche conformance. This includes methods such as qPCR, image-based flow cytometry and single-cell RNA sequencing.
