Biology subjects

Bulut, B.

Publications and source records attributed to Bulut, B..

5 recordsLinked to original sources

bioRxiv2026

Local Adaptation of the Spontaneous Mutation Rate: Divergent Thermal Reaction Norms in Chironomus riparius

The germline mutation rate {micro} is a fundamental evolutionary parameter, yet its plasticity in response to environmental factors, particularly temperature, remains poorly understood. While often modeled as a species-specific constant, we tested whether {micro} evolves in response to local thermal regimes. Using whole-genome sequencing of mutation accumulation lines in the non-biting midge Chironomus riparius, we demonstrate divergent thermal reaction norms between populations from climatically distinct regions: Central Europe (Germany) and the Mediterranean (Spain). The Central European population displays a highly plastic, U-shaped reaction norm, whereas the Mediterranean population exhibits a more canalized, temperature-insensitive response. This divergence conforms to theoretical expectations: the higher thermal variance of high-latitude habitats selects for plasticity, while thermally more stable Mediterranean habitats favour robustness and optimises the mutational load in the respective thermal regimes. Furthermore, population-specific mutational spectra (Ts/Tv ratios) indicated evolved differences in DNA repair machinery. However, this is only partially mirrored by Reactive Oxygen Species (ROS) dynamics, where Mediterranean larvae maintain lower ROS levels and a buffered response to thermal extremes. These findings provide evidence for evolution of the mutation rate itself, challenging the assumption of constancy.

evolutionary biology↗

bioRxiv2025

A Trade-off Between Developmental Speed and Replication Fidelity Governs the Spontaneous Mutation Rate

The spontaneous mutation rate () is shaped by two potentially opposing forces: the passage of chronological time, which is inevitably associated with mutation accumulation, and the speed of development, which may compromise replication fidelity. Disentangling these forces has been a major challenge, particularly in ectotherms. Testing the competing predictions of the classic time-dependent Generation Length Hypothesis and the replication-dependent speed-fidelity trade-off model, we experimentally assessed individuals with short (mean 15 days) and long (mean 37.7 days) generation time (GT) in the midge Chironomus riparius under constant temperature and estimated the de novo mutation rates by whole genome sequencing. We found that long-GT lines accumulated 1.3-fold more mutations per generation (/gen), consistent with time-dependent mutagenic processes. Conversely, short-GT lines exhibited a nearly two-fold higher mutation rate per day (/day) and a trend towards a transition-biased mutational spectrum (Ts/Tv ratio = 1.28 vs. 0.95), a pattern consistent with a speed-fidelity trade-off in DNA replication. These results suggest that two distinct processes shaped the overall mutation rate. Integrating our data with previous studies and life-history data, we show that the daily mutation rate followed a non-linear relationship with respect to generation time, and that the species generation time mode coincides with its minimum. This suggests that the generation time is, amongst other factors, selected to optimise the mutational load by balancing between replication accuracy and developmental speed. Teaser TextThe spontaneous mutation rate () is governed by a fundamental trade-off between the passage of time and the speed of development. We used the midge Chironomus riparius to experimentally disentangle these forces. We show that rapid development comes with a cost: compromised DNA replication fidelity and a high daily . Conversely, prolonged development accumulates mutations over time. Crucially, the species optimal generation time balances these opposing forces, falling precisely at the developmental speed that minimizes the overall mutational load, suggesting that selection for replication accuracy helps shape life-history evolution.

evolutionary biology↗

bioRxiv2025

Pervasive and dynamic release of Cryptic Genetic Variation in Chironomus riparius: Rethinking adaptation in fluctuating environments

The interplay between phenotypic plasticity and cryptic genetic variation (CGV) is crucial for understanding adaptation, yet the prevailing paradigm suggests CGV is primarily exposed under novel or extreme conditions. By examining gene expression responses along a natural temperature gradient in Chironomus riparius, we challenged this view. We found that the vast majority of expressed genes (63%) exhibit dynamic CGV, where interindividual expression variability scales continuously with distance from the selectively optimal temperature, a pattern also observed in higher-level traits like mutation rate and ROS levels. Genes with lower overall expression levels were less temperature-regulated, and thermal reaction norm shapes varied with gene function. Unexpectedly, thermally plastic genes were more pleiotropic, often acting as hub genes, while CGV in gene expression was associated with lower pleiotropy. This pattern, and the observed strong recurrent selection on plastic genes with CGV, aligns with C. ripariuss adaptation to its highly fluctuating environment through selective tracking. We propose that this continuous, dynamic release of genetic variation is a necessary and inherent outcome of the polygenic nature of traits. This model fundamentally reshapes our understanding of adaptation, implying that populations can gradually and continuously adapt without requiring harsh conditions to expose hidden diversity. This leads to smoother adaptive landscapes, enhancing rapid adaptation and facilitating evolutionary innovation in the face of ongoing environmental change.

evolutionary biology↗

bioRxiv2025

Dissecting Oxidative Stress and Organismic Response to various Temperature Regimes in the midge C. riparius

Oxidative stress, driven by reactive oxygen species (ROS), poses a major challenge for organisms facing temperature fluctuations. This study provides the first direct in vivo measurements of ROS production in an insect, Chironomus riparius, across a broad range of ecologically relevant temperatures. We observed a U-shaped pattern of oxidative stress, with minimal ROS levels within an optimal thermal window (12-18{degrees}C) and significantly elevated stress at both cold and warm extremes. Crucially, our findings reveal distinct underlying molecular mechanisms for ROS generation at these extremes: at low temperatures, ROS production is predominantly of the superoxide group, linked to hypoxia-induced hemoglobin autoxidation. Conversely, at high temperatures, the hydrogen peroxide group dominates, associated with increased metabolic rate and heat stress signaling pathways. Transcriptomic analysis shows that C. ripariuss antioxidant defense system adapts accordingly, selectively upregulating mechanisms to counteract the specific dominant ROS type at different temperatures. This mechanistically differentiated oxidative stress and the modulated organismic response profoundly impacts the overall ecological success and evolution of C. riparius as a model for thermal stress in ectotherms. Summary StatementThis study shows that cold and heat stress activate different oxidative damage pathways in midge larvae, explaining how organisms face unique physiological limits in thermal extremes.

ecology↗

bioRxiv2024

Transcriptomics predicts Artificial Light at Night's (ALAN) impact on fitness: nightly illumination alters gene expression pattern and negatively affects fitness components in the midge Chironomus riparius (Diptera:Chironomidae)

The emission of artificial light at night (ALAN) is rapidly increasing worldwide. Yet, evidence for its detrimental effects on various species is accumulating. While the effects of ALAN on phenotypic traits have been widely investigated, effects on the molecular level are less well understood. Here we aimed to integrate the effects of ALAN at the transcriptomic and the phenotypic level. We tested these effects on Chironomus riparius, a multivoltine, holometabolous midge with high ecological relevance for which genomic resources are available. We performed life-cycle experiments in which we exposed midges to constant light and control conditions for one generation. We observed higher EmT50 and reduced fertility under ALAN. From the observed decline in population size due to the reduced fertility, we predicted the population size to decline to 1% after 200 days. The transcriptomic analysis revealed expression changes of genes related to circadian rhythmicity, moulting, catabolism and oxidative stress. From the transcriptomic analysis we hypothesised that under ALAN, oxidative stress is increased, and that moulting begins earlier. We were able to confirm both hypotheses in two posthoc experiments, showing that transcriptomics are a powerful tool in predicting physiological outcomes before they are even observable.

molecular biology↗