Data from: Gene expression under thermal stress varies across a geographic range expansion front

Many ectothermic species are currently expanding their distributions polewards due to anthropogenic global warming. Molecular genetic mechanisms facilitating range expansion under these conditions are largely unknown, but understanding these could help mitigate expanding pests and disease vectors, or help explain why some species fail to track changing climates. Here, using RNA-seq data, we examine genome-wide changes in gene expression under heat and cold stress in the range-expanding damselfly Ischnura elegans in northern Europe. We find that both the number of genes involved and levels of gene expression under heat stress have become attenuated during the expansion, consistent with a previously-reported release from selection on heat tolerances as species move polewards. Genes upregulated under cold stress differed between core and edge populations, corroborating previously-reported rapid adaptation to cooler climates at the expansion front. Expression of sixty-nine genes exhibited a region x treatment effect; these were primarily upregulated in response to heat stress in core populations but in response to cold stress at the range edge, suggesting that some cellular responses originally adapted to heat stress may switch to cold stress functionality upon encountering novel thermal selection regimes during range expansion. Transcriptional responses to thermal stress involving heat shock and neural function genes were largely geographically conserved, while retrotransposon, regulatory, muscle function and defence gene expression patterns were more variable. Flexible mechanisms of cold stress response and the ability of some genes to shift their function between heat and cold stress might be key mechanisms facilitating rapid poleward expansion in insects.

受人为全球变暖影响，诸多变温物种目前正向极地扩张其分布范围。在此类环境下助力分布扩张的分子遗传机制大多尚未明确，但阐明此类机制既有助于防控扩张的害虫与病媒生物（disease vectors），也能帮助解释为何部分物种无法追踪气候变化的轨迹。本研究利用RNA测序（RNA-seq）数据，针对北欧范围内正进行分布扩张的长叶异痣蟌（Ischnura elegans），分析其在冷热胁迫下的全基因组基因表达变化。本研究发现，在扩张过程中，受热胁迫时参与应答的基因数量以及基因表达水平均已减弱，这与此前报道的“物种向极地迁移时，其耐热性相关的选择压力得以释放”的结论相符。冷胁迫下上调表达的基因在核心种群与边缘种群间存在差异，佐证了此前报道的“扩张前沿种群对较冷气候产生快速适应”的结论。共有69个基因的表达呈现出区域×处理交互效应；此类基因在核心种群中主要受热胁迫诱导上调，而在分布边缘种群中则主要受冷胁迫诱导上调，这表明部分原本适配热胁迫的细胞应答，在分布扩张过程中遭遇新的热选择条件时，可能会转向冷胁迫相关功能。涉及热休克基因（heat shock genes）与神经功能基因的热胁迫转录应答在地理上大体保守，而反转录转座子（retrotransposon）、调控基因、肌肉功能基因及防御基因的表达模式则更为多变。冷胁迫应答的灵活机制，以及部分基因在冷热胁迫间转换功能的能力，或许是推动昆虫快速向极地扩张分布的关键机制。