Response of wild aquatic insect communities to thermal variation through comparative landscape transcriptomics.

Fluctuations in temperature are recognized as a potent driver of selection pressure, fostering genomic variations that are crucial for the adaptation and survival of organisms under selection. Notably, water temperature is a pivotal factor influencing aquatic organism persistence. By comprehending how aquatic organisms respond to shifts in water temperature, we can understand their potential physiological adaptations to environmental change in one or multiple species. This, in turn, contributes to the formulation of biologically relevant guidelines for the landscape scale transcriptome profile of organisms in lotic systems. Here, we investigated the distinct responses of seven stream stonefly species, collected from four geographical regions across Japan, to variations in temperature, including atmospheric and water temperatures. We achieved this by assessing the differences in gene expression through RNA-sequencing within individual species and exploring the patterns of community-genes among different species. We identified 735 genes that exhibited differential expressions across the temperature gradient. Remarkably, the community displayed expression levels differences of respiration and metabolic genes. Additionally, the diversity in molecular functions appeared to be linked to spatial variation, with water temperature differences potentially contributing to the overall functional diversity of genes. We found 22 community-genes with consistent expression patterns among species in response to water temperature variations. These genes related to respiration, metabolism and development exhibited a clear gradient providing robust evidence of divergent adaptive responses to water temperature. Our findings underscore the differential adaptation of stonefly species to local environmental conditions, suggesting that shared responses in gene expression may occur across multiple species under similar environmental conditions. This study emphasizes the significance of considering various species when assessing the impacts of environmental changes on aquatic insect communities and understanding potential mechanisms to cope with such changes.

Spatial and phylogenetic structure of Alpine stonefly assemblages across seven habitats using DNA-species.

Stream ecosystems are spatially heterogeneous, with many different habitat patches distributed within a small area. The influence of this heterogeneity on the biodiversity of benthic insect communities is well documented; however, studies of the role of habitat heterogeneity in species coexistence and assembly remain limited. Here, we investigated how habitat heterogeneity influences spatial structure (beta biodiversity) and phylogenetic structure (evolutionary processes) of benthic stonefly (Plecoptera, Insecta) communities. We sampled 20 sites along two Alpine rivers, including seven habitats in four different reaches (headwaters, meandering, bar-braided floodplain, and lowland spring-fed). We identified 21 morphological species and delineated 52 DNA-species based on sequences from mitochondrial cox1 and nuclear ITS markers. Using DNA-species, we first analysed the patterns of variation in richness, diversity, and assemblage composition by quantifing the contribution of each reach and habitat to the overall DNA-species diversity using an additive partition analysis and distance-based redundancy analysis. Using gene-tree phylogenies, we assessed whether environmental filtering could lead to the co-occurrence of DNA-species using a two-step analysis to detect a phylogenetic signal. All four reaches significantly contributed to DNA-species richness, with the meandering reach having the highest contribution. Habitats had an effect on DNA-species diversity, where glide, riffle and, pool influenced the spatial structure of stonefly assemblage possibly due to the high habitat heterogeneity. Among the habitats, the pool showed significant phylogenetic clustering, suggesting high levels of evolutionary adaptation and strong habitat filtering. This assemblage structure may be caused by long-term stability of the habitat and the similar requirements for co-occurring species. Our study shows the importance of different habitats for the spatial and phylogenetic structure of stonefly assemblage and sheds light on the habitat-specific diversity that may help improve conservation practices.