Biology subjects

Kaiser, T. S.

Publications and source records attributed to Kaiser, T. S..

7 recordsLinked to original sources

bioRxiv2026

On the evolution of emergence patterns driven by environmental cycles

Regular environmental cycles such as day and night or the lunar cycle are ubiquitous and drive many biological processes. Many organisms have evolved endogenous time-keeping mechanisms to anticipate these cycles to accurately time their behavior or synchronize physiological processes. The evolution of such synchronization to environmental cycles and their variability is not very well understood. As an example, we use the marine insect Clunio (Diptera, Chironomidae), which synchronize adult emergence and reproduction with the lunar cycle, and show different emergence patterns across populations. We use a model constructed with replicator-mutator dynamics to provide a novel outlook at the evolution of these emergence patterns. In particular, we investigate the effect of two traits of individual phenotypic variability of emergence, the spread and shape, on population-wide emergence patterns. We find that the semilunar and lunar emergence patterns are alternatively stable and occur when the phenotypic distribution has a narrow and is roughly flat. Arrhythmic emergence occurs when the phenotypic distribution is wide and nearly flat. The semi-lunar pattern can only be observed when the parameter of rhythmicity is changed. With our model, we introduce the concepts of frequency-dependent selection and individual phenotypic variability into the theory of chronobiology, which gives us insights into the evolution of rhythmicity in these organisms.

evolutionary biology↗

bioRxiv2026

Lunar Reproductive Timing Acts as a Magic Trait and May Recruit Additional Isolating Barriers in Sympatric Marine Midge Populations

Population divergence with gene flow has proven more common than expected, but the underlying mechanisms are not fully understood. Magic traits (i.e. characters involved in both ecological adaptation and assortative mating) offer a tantalizing mechanism to explain the phenomenon, yet empirical demonstrations are rare. Moreover, speciation is assumed to involve genomic processes that couple multiple reproductive barriers, rather than being driven by a single barrier, and it re-mains unclear how magic traits interact with these processes. Here, we investigate the marine midge Clunio marinus, whose reproduction is timed to the extreme spring tide low tides during full moon or new moon. In Roscoff (Brittany, France) there are two sympatric chronotypes, i.e. subpopulations which reproduce only during full or new moons. Lunar reproductive timing is hypothesized to act as a magic trait, as it is both ecologically relevant and isolates reproduction in time. Based on wild-caught mating pairs and laboratory crosses, we show that lunar timing indeed is the major reproductive barrier (RI > 0.87). We also identify additional barriers which further increase reproductive isolation (total RI > 0.94). To explore the genomic basis of these barriers, we perform association testing on several high-FST loci. Two loci were associated with multiple barriers, and patterns of linkage disequilibrium suggest that these effects may arise from a combination of genetic link-age and pleiotropy. Together, our results indicate that lunar timing played a pivotal role in chronotype divergence, not only as a magic trait but also by promoting the recruitment of additional isolating barriers. We hypothesize that this recruitment is due to the polygenic and complex genetic architecture of lunar timing, highlighting the joint role of magic traits and genomic architecture in divergence with gene flow.

evolutionary biology↗

bioRxiv2025

How competition can drive allochronic divergence: a case study in the marine midge, Clunio marinus

Synchronizing mating to extrinsic environmental cycles can increase the chance of successful reproduction. However, the resulting temporally-assorted mating may precipitate speciation if coupled with divergent selection. This process might be particularly relevant to the marine midge Clunio marinus, which synchronizes its reproduction to different lunar phases. In Ro-scoff (France) two sympatric populations differ in reproductive timing but are still connected by gene flow. A previous study found a relationship between the timing of reproduction and larval depth in the intertidal zone. Building on this observation, we ask if the link between reproductive timing and depth could be a mechanism for divergence when coupled with competition-induced density-dependent fitness. We devise an individual-based model replicating the reproductive behavior of C. marinus and find that sympatric divergence can occur, even when we model sexual reproduction with recombination and an explicit genetic basis. Our results suggest this mechanism is a likely hypothesis for the allochronic divergence observed in the Roscoff populations. Additionally, our study provides insights into how density-dependent fitness and competition may play a role in allochronic divergence in general.

evolutionary biology↗

bioRxiv2024

How light at night sets the circalunar clock in the marine midge Clunio marinus

Many organisms inhabiting the interface between land and sea have evolved biological clocks corresponding to the period of the semilunar (14.77d) or the lunar (29.53d) cycle. Since tidal amplitude is modulated across the lunar cycle, these circasemilunar or circalunar clocks allow organisms to adapt to the tides. Biological clocks are synchronized to external cycles via environmental cues called zeitgebers. Here, we explore how light at night sets the circalunar and circasemilunar clocks of Clunio marinus, a marine insect that relies on these clocks to control timing of emergence. We first characterized how moonlight intensity is modulated by the tides by measuring light intensity in the natural habitat of C. marinus. In laboratory experiments, we then explored how different moonlight treatments set the phase of the clocks of two C. marinus strains, one with a lunar rhythm and one with a semilunar rhythm. Light intensity alone does not affect the phase or strength of the lunar rhythm. Presenting moonlight during different 2-hour or 4-hour windows during the subjective night shows that (1) the required duration of moonlight is strain-specific, (2) there are strain-specific moonlight sensitivity windows and (3) timing of moonlight can shift the phase of the lunar rhythm to stay synchronized with the lowest low tides. Experiments simulating natural moonlight patterns with moonrise and moonset confirm that the phase is set by the timing of moonlight. Light intensity within the ranges observed in the field leads to the best synchronization. Taken together, we show that there is a complex and strain-specific integration of intensity, duration and timing of light at night to precisely entrain the lunar and semilunar rhythms. The observed fine-tuning of the rhythms under the most natural moonlight regimes lays the foundation for a better chronobiological and genetic dissection of the circa(semi)lunar clock in C. marinus.

ecology↗

bioRxiv2022

Genetic analysis of a phenotypic loss in the mechanosensory entrainment of a circalunar clock

Genetic variants underlying traits that become either non-adaptive or selectively neutral are expected to have altered evolutionary trajectories. Uncovering genetic signatures associated with phenotypic loss presents the opportunity to discover the molecular basis for the phenotype in populations where it persists. Here we study circalunar clocks in populations of marine midge Clunio marinus. The circalunar clock synchronizes development to the lunar phase, and it is set by moonlight and tidal cycles of mechanical agitation. Two out of ten studied populations have lost their sensitivity to mechanical agitation while preserving sensitivity to moonlight. Intriguingly, the F1 offspring of the two insensitive populations regained the sensitivity to mechanical entrainment, implying a genetically independent loss of the phenotype. By combining quantitative trait locus mapping and genome-wide screens, we explored the genetics of this phenotypic loss. QTL analysis suggested an oligogenic origin with one prevalent additive locus in one of the strains. In addition, it confirmed a distinct genetic architecture in the two insensitive populations. Genomic screens further uncovered several candidate genes underlying QTL regions. The strongest signal under the most prominent QTL contains a duplicated STAT1 gene, which has a well-established role in development, and CG022363, an ortholog of the Drosophila melanogaster CG32100 gene, which plays a role in gravitaxis. Our results support the notion that adaptive phenotypes have a complex genetic basis with mutations occurring at several loci. By dissecting the most prevalent signals, we started to reveal the molecular machinery responsible for the entrainment of the circalunar clock.

genetics↗

bioRxiv2022

An oligogenic architecture underlying ecological and reproductive divergence in sympatric populations

The evolutionary trajectories and genetic architectures underlying ecological divergence with gene flow are poorly understood. Sympatric timing types of the intertidal insect Clunio marinus (Diptera) from Roscoff (France) differ in lunar reproductive timing. One type reproduces at full moon, the other at new moon, controlled by a circalunar clock of yet unknown molecular nature. Lunar reproductive timing is a magic trait for a sympatric speciation process, as it is both ecologically relevant and entails assortative mating. Here we show that the difference in reproductive timing is controlled by at least four quantitative trait loci (QTL) on three different chromosomes. They are partly associated with complex inversions, but differentiation of the inversion haplotypes cannot explain the different phenotypes. The most differentiated locus in the entire genome, with QTL support, is the period locus, implying that this gene could not only be involved in circadian timing but also in lunar timing. Our data indicate that magic traits can be based on an oligogenic architecture and can be maintained by selection on several unlinked loci.

evolutionary biology↗

bioRxiv2021

Polygenic adaptation from standing genetic variation allows rapid ecotype formation

Adaptive ecotype formation is the first step to speciation, but the genetic underpinnings of this process are poorly understood. Marine midges of the genus Clunio (Diptera) have recolonized Northern European shore areas after the last glaciation. In response to local tide conditions they have formed different ecotypes with respect to timing of adult emergence, oviposition behavior and larval habitat. Genomic analysis confirms the recent establishment of these ecotypes, reflected in massive haplotype sharing between ecotypes, irrespective of whether there is ongoing gene flow or geographic isolation. QTL mapping and genome screens reveal patterns of polygenic adaptation from standing genetic variation. Ecotype-associated loci prominently include circadian clock genes, as well as genes affecting sensory perception and nervous system development, hinting to a central role of these processes in ecotype formation. Our data show that adaptive ecotype formation can occur rapidly, with ongoing gene flow and largely based on a re-assortment of existing alleles.

evolutionary biology↗