Transcriptomics at the thermal limits of an urban introduced lizard

Rapid changes in gene expression can result in physiological plasticity that assists animals in coping with environmental stressors. Increased capacity for physiological plasticity may then facilitate adaptation to stressful habitats like urban heat islands or invasion into novel ranges. Currently, temperature stress is a leading threat to organisms, especially ectotherms. While exposure to changing temperatures is known to shift gene expression patterns in ectothermic animals, many studies are conducted after lengthy acclimation times. However, exposure to thermal stress in nature can occur rapidly. We assessed the capacity for gene expression plasticity in response to a brief exposure to extreme thermal stress in an urban, introduced species, the common wall lizard (Podarcis muralis). Lizards were ramped to their critical thermal maximum (CT_max) or minimum (CT_min) followed by rapid recovery. We used RNA-sequencing to compare the transcriptomes of lizards exposed to CT_max, CT_min, or control conditions using heart, liver, and large intestine tissue. Exposure to heat stress induced a much stronger gene expression response across tissues than cold exposure. In response to heat, there was systemic upregulation of heat shock proteins and stress response pathways. Heat also induced changes in transcription, translation, and metabolic processes but these effects were more tissue specific. Although fewer gene expression changes were observed in response to cold, some genes were upregulated that could be beneficial under cooling stress. Our data suggests gene expression plasticity could facilitate range expansion in this species, but more work is needed to assess the transcriptomic response to temperature stress in nature.