Gene expression changes of seven stonefly species in responses to a latitudinal-environmental gradient.

Latitudinal variation has been known to create strong selection pressure for genomic variation that enables the adaptation and survival of organisms. By altering gene expression patterns, organisms can modify their adaptive potential to heterogeneous environmental conditions along a latitudinal gradient; however, there is a gap in our understanding of how physiological consequences in wild species are affected and how changing environmental conditions act on multiple species. Here, we investigated how seven stream stonefly species sampled from four geographical regions in Japan differ in their responses to latitudinal variations by measuring gene expression (RNA-sequencing) differences within species and gene co-expression among species. We found that a large number of genes (622) were differentially expressed along the latitudinal gradient. The high species-specific gene expression diversity found at higher latitude regions was probably associated with low temperatures and high water discharge, which suggests the adaptive potential of stonefly specie. In contrast, similar gene expression patterns among species was observed at lower latitudes, which suggests that strong environmental stress occurs in warmer regions. Weighted gene co-expression network analysis (WGCNA) identified 22 genes with similar expression patterns among species along the latitudinal gradient. Among the four geographical regions, high differential expression patterns in the co-expressed genes from two regions were found, suggesting that the local environment strongly affects gene expression patterns among species in these regions. Respiration, metabolism, and developmental co-expressed genes exhibited a latitudinal cline, showing clear evidence of divergent adaptive responses to latitude. Our findings demonstrate that stonefly species are differentially adapted to local environmental conditions, and imply that adaptation in gene expression could be shared by multiple species under environmental stress conditions. This study highlights the importance of considering multiple species when evaluating the consequences of environmental changes on aquatic insect communities, and possible mechanisms to cope with environmental changes.