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

Understanding recombination rates is crucial in evolutionary biology, as recombination shapes genetic diversity, natural selection, and adaptation. We investigated recombination rate variation in Chironomus riparius across different latitudes, seasons, and experimental treatments using Pool-seq data from five studies and the ReLERNN neural network-based method. We examined its relationship with genetic diversity, GC content, and F_ST, assessing causality through structural equation modeling.

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.

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.