Research Lines
Local Adaptation & Ecological Speciation
Sensory Ecology & Neurobiology
Ecophysiology - Circalunar Clock Mechanisms
Biodiversity, Biogeography & Bioindicators
Local Adaptation & Ecological Speciation
The intertidal midge Clunio marinus (Diptera: Chironomidae) needs extreme low tides for reproduction. These recur predictably during the spring tides, around full moon and new moon. Thus, the development of C. marinus is controlled by circalunar (29.5 d) or circasemilunar (14.8 d) clocks, which ensure that adults only emerge at full moon and/or new moon. On these days, the circadian clock (24 h) ensures that the midges emerge into a receding tide. They reproduce immediately and die few hours later in the incoming tide.
Local adaptation. The timing of the tides can differ dramatically along the coastline (A, red lines). C. marinus displays genetic adaptations in both circadian and circalunar clocks to the local tidal regime (BMC Genetics 2011). We use genetic mapping, genome screens, and experiments to find genes underlying these adaptations. We have identified candidate genes for both circadian timing (Nature 2016) and circalunar timing (eLife 2023a).
Sympatric ecotypes. In several places in Brittany, there are sympatric chronotypes (=timing strains) of C. marinus which occupy different temporal niches for reproduction (Molecular Ecology 2021). In Roscoff, for example, there is a full moon strain (A,B: yellow) and a new moon strain (A,B: green). But as the long-lived larvae were assumed to compete for the same resources, their coexistence was not easily explained (Journal of Animal Ecology 2025). We found that suboptimal reproductive timing of the new moon strain (B: green) interacts with the tides, so that eggs and consequentially the benthic larvae are placed at different levels of the intertidal (panels B, C and D, Ecology Letters 2025). Modelling suggests that competition between the larvae leads to divergence into chronotypes across a wide range of ecological and genetic parameters (PLoS Computational Biology 2026). The intertidal is a strongly zonated habitat, and we found that the different chronotypes also differ in their preferred microhabitats and macroalgae, as well as their microbiome (E, manuscript in preparation). We have just started to investigate the chemical ecology of mate and oviposition site choice (collaboration with S Unsicker and A Ritter).
Baltic Ecotype. In the absence of notable tides, the Baltic ecotype of C. marinus - aka C. balticus - has lost the circalunar reproductive rhythm. Females oviposit on the open water surface and eggs sink to the bottom, where the larvae develop in red algae down to a depth of 20 m. Our genomic analyses suggest that this ecotype emerged after the Littorina transgression (<10.000 years), as a highly polygenic adaptation from standing genetic variation (eLife 2023b). The Atlantic intertidal and the Baltic Sea benthic zone pose fundamentally different ecological challenges. We now experimentally disentangle the biotic interactions and abiotic adaptations of the Baltic and Atlantic ecotypes. First experiments show they differ in oxygen consumption and salinity tolerance. Knowing that subfossil Clunio head capsules are conserved in sediment cores from the Baltic Sea, we also test if sediment ancient DNA (sedaDNA) allows us to reconstruct the sequence of ecological adaptations over the last 10,000 years, as well as evolutionary responses to the recent anthropogenic challenges of eutrophication, hypoxia and global warming.
Sensory Ecology & Neurobiology
Zeitgebers. The circalunar clock of C. marinus can be synchronized with the lunar cycle (a process called entrainment) via specific environmental cues (called zeitgebers). These are moonlight, as well as tidal cycles of water turbulence and temperature (A). C. marinus does not respond to tidal pressure cycles. We are currently exploring if other cues might play a role, e.g. tidal salinity cycles, social cues or biotic interactions within the benthic communities.
Insensitive strains. Some strains of C. marinus are insensitive to moonlight or tidal turbulence cycles. We have dissected these traits with genetic and genomic tools and have identified candidate genes involved in turbulence perception (PLoS Genetics 2023) and moonlight perception (in preparation). We are currently trying to confirm the functional relevance of these genes and their mutations in cell-based and in-vitro assays, as well as by expressing them heterologously in corresponding fruit fly knockout-lines.
Moonlight perception. Through experimental manipulation of moonlight intensity and patterns, we have obtained first insights into the quality of light that entrains the circalunar clock (JBR 2025). We are currently further exploring the sensitivity limits and spectral sensitivity of moonlight perception (B). In parallel, we assess the spectral sensitivites of C. marinus opsins (collaboration with P Senthilan) and cryptochrome (collaboration with E Wolf), aiming to narrow down the receptors potentially involved in moonlight perception. We also assess how artificial light at night (ALAN) affects moonlight entrainment and thus reproductive success.
Larval nervous system. The circalunar timing mechanism, including entrainment via different sensory modalities, is realised in the long-lived larvae. As a backbone for studying this timing system, we combine µ-CT scans (collaboration with Steffen Harzsch) and various staining techniques to achieve a 3D reconstruction of C. marinus’ larval nervous system (C). By localising and tracing the identified sensory inputs, we hope to find a convergence point, which might represent the cellular substrate of the circalunar clock. In parallel, we are currently trying to establish single-cell RNA sequencing to identify the neurons which co-express the identified circalunar clock candidate genes.
Ecophysiology - Circalunar Clock Mechanisms
A counter mechanism, evolutionary tinkering & convergent evolution. In 1962 Erwin Bünning suggested three possible mechanisms for circalunar clocks (A): a day-counter (red), a 29.5-day oscillator (yellow) or a beat phenomenon of superimposed circadian and circatidal clocks (blue). Our experiments indicate that the circalunar clock of C. marinus is based on counting circadian clock cycles (JBR 2024). Combined with other evidence, this suggests that the midge’s circalunar clock might have been derived from a photoperiodic diapause mechanism when the midge secondarily colonised the sea (BioEssays 2021 and manuscript in preparation). Interestingly, annelids (Platynereis, Syllis) and algae (Dictyota) seem to rely on an oscillator or beat phenomenon respectively, suggesting circalunar clocks have evolved several times independently (BioEssays 2021).
Circalunar developmental arrest (CDA) & temperature-compensated development. The development of C. marinus larvae is only synchronised with the lunar cyle in the last larval instar through a developmental arrest (CDA), followed by temperature-compensated development up to pupation (B). Gene regulation in CDA has some similarities to that in diapause (in preparation). A genome-wide association study of full moon vs. new moon emergence suggests that the timing of the CDA and/or the speed of subsequent developmental progression involve a specific cellular signalling cascade (in preparation).
Genetics & Genomics
Reference genomes. We published the first reference genome for C. marinus (CLUMA1.0, Nature 2016), and have added a new genome release (CLUMA2.0) and a reference genome for Clunio tsushimensis since (collaboration with A Betancourt; manuscript in preparation; genomes available on ClunioBase). For a better understanding of adaptations to marine habitats in the the genus Clunio and other marine chironomid genera (Pontomyia, Thalassosmittia & Telmatogeton), we are currently working on additional reference genomes, including related terrestrial or freshwater chironomids (collaboration with K Jaron). These efforts are embedded in international consortia, such as the Dipteran Comparative Genomics working group of the Darwin Tree of Life project (DToL) and the European Reference Genome Atlas (ERGA).
Germ-line restricted chromosomes (GRCs). As all members of the chironomid subfamily Orthocladiinae, Clunio marinus posesses GRCs. In a collaboration with C Hodson and K Jaron, we aim to elucidate their gene content and understand their function, as well as the mechanisms of germ-line maintenance and soma elimination. We also want to test if GRCs are causal to non-reciprocal cross-sterilities observed between certain Clunio marinus populations, which may help to generate or maintain ecological adaptations and diversity.
Sex determining locus. We are trying to identify the sex determining locus of C. marinus. As a by-product of our genetic mapping studies we know that it has several properties uncommon in Diptera: there are no degenerated sex chromosomes, it follows a ZW-like inheritance pattern, and its location differs between populations (in preparation).
Biodiversity, Biogeography & Bioindicators
Biodiversity. The genus Clunio currently has about 30 described species, all over the world. It is usually assumed that all Clunio species reproduce in a lunar rhythm. However, the few examples that have been studied besides C. marinus suggest there is probably a much greater diversity of rhythmic adaptations to the tides. C. takahashi is reported to rely solely on a tidal rhythm. C. tsushimensis switches its daily emergence time with photoperiod, emerging in the afternoon in winter and in the morning in summer.
Biogeography. To fully capture this “chronodiversity”, we are currently building a large collaborative network to obtain samples and reference genomes from all known species and from all over the world. At the same time, we have started a citizen science project - called Moonstruck Midges - aiming to collect comprehensive observations of Clunio adults. As adults only live for 1-2 hours, the time stamps of the obervations allow us to precisely monitor the emergence rhythm of the local Clunio population. We have given proof-of-principle for the Clunio midges of San Diego, likely C. californiensis. Combining genomics and citizen science, we aim to understand the evolution of timing adaptations and potential allochronic speciation, in relation to the local tidal regimes and environments, biogeographic factors (e.g. ocean currents, coastal profiles, latitudinal clines in benthic communities) and in a phylogenetic context.
Bioindicators. Chironomids are widely used as bioindicators for climate and pollution. On top of these, being a biofilm grazer, Clunio may also serve to monitor local microplastic contamination, as well as light pollution through a disturbance of its emergence rhythms. Our world-wide biogeographic, ecological and genomic analyses also aim to test if the genus Clunio can serve as a universal coastal benthos bioindicator.
Chironomids of Plön & global change. The beginnings of limnology are closely connected to Plön, where August Thienemann characterised lake types by trophic level, based on their characteristic chironomid assemblages, also laying the basis for their use as bioindicators. Unfortunately, the long tradition of chironomid research in Plön has dwindled away since the 1970s. We are now picking up basic species monitoring again, to see if and how chironomid communities have changed in the last 50 years in the face of climate change, eutrophication and insecticide influx. As a starting point, we are establishing a local DNA barcode library, based on chironomid samples taken by S Speth for monitoring according to the European Water Framework Directive and provided to us by the Landesamt für Umwelt (State Environment Agency). Based on these we aim to establish local chironomid monitoring based on environmental DNA (eDNA) metabarcoding, serving basic science, environmental monitoring and conservation.
Biophysics & Biomechanics
The genus Clunio secondarily colonised the sea and had to evolve adaptations to the unusual habitat. We are studying three of them in collaboration with different research groups at Kiel University:
Gas exchange (with T Roeder). Light microscopy and imaging at DESY show that Clunio’s larval tracheal system resembles that of a terrestrial chironomid (A). But the spiracles (openings to the outside) are closed. As Clunio larvae do also not have appendages for gas exchange, and the cuticle is very tough, the mechanism of gas exchange remains a mystery that we try to solve.
Water-gliding (with S Gorb). Clunio adults do not fly, but hover on the water surface. Their tarsi (~feet) show unusual structures (B), which at the same time allow the midge to stand on the water, anchor it in the surface, and allow it to walk on rocks and algae. Such a “multi-purpose foot” may serve as template in biomimetics.
Egg jelly (with A Tholey and S Gorb). Clunio eggs are laid in a gelatineous tube (C), which swells in water and usually is very sticky. These properties differ between Clunio species in adaptation to specific habitats (e.g. Atlantic vs. Baltic Sea). We try to identify the underlying protein matrices, as well as measure their mechanical properties. This may serve to develop a biodegradable glue or a swelling and bio-compatible buffering material for medical implants.