Influence of geography, seasonality and experimental selection on Chironomus riparius recombination rates

BACKGROUND: , assessing causality through structural equation modeling. RESULTS: In natural populations, recombination rates showed no clear latitudinal pattern, likely due to interactions between climate-driven selection, demographic history and regional environmental heterogeneity. However, seasonal variation was evident, with higher recombination rates in autumn than winter, possibly due to temperature-induced plasticity or seasonal bottlenecks. A cold snap in March 2018 triggered a sharp recombination increase, potentially suggesting a stress-induced adaptive response. Across datasets, recombination rates were correlated with genetic diversity and other genomic parameters, with structural equation models (SEMs) indicating that recombination and selection jointly shape patterns of π and differentiation, while relationships with GC content and TEs counts varied among environmental and experimental contexts. In experimental populations, thermal regimes alone had little effect on recombination; instead, adaptation to laboratory conditions and specific stressors drove recombination changes. Exposure to microplastics led to a genome-wide reduction in recombination, likely due to stress-induced DNA repair prioritizing genome integrity, whereas cadmium exposure generally suppressed recombination. CONCLUSIONS: Our results demonstrate that recombination in C. riparius is a highly dynamic trait influenced by environmental conditions, selection, and genomic context. By integrating ecological variation, experimental evolution, and multivariate genomic analyses, this study highlights recombination as a context-dependent process that responds to both natural and anthropogenic stressors and interacts with multiple features of genome architecture.