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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 (CTmax) or minimum (CTmin) followed by rapid recovery. We used RNA-sequencing to compare the transcriptomes of lizards exposed to CTmax, CTmin, 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. 

Vertebrates house dense and diverse communities of microorganisms in their gastrointestinal tracts. These communities shape host physiological and ecological phenotypes in diverse ways, with implications for animal fitness in nature. Exposure to microbes during the earliest stages of life is particularly important because, during critical developmental windows, the microbiome is exceptionally plastic and interactions with microbes can have long-lasting physiological impacts on the host. Despite our understanding that early-life microbial interactions are important to host function broadly, the majority of research in this area has been performed in human or model organisms that are not representative of animals in the wild. Specifically, most gut microbiome studies in wildlife are cross-sectional and compare microbial communities across life stages using different individuals, as opposed to tracking the microbial communities and phenotypes of the same individuals from early to later life. This knowledge gap may hinder wildlife microbiome research, as the current model lacks an early-life perspective that can contextualize host phenotypic and fitness differences observed between animals at later life stages. Further, considering early-life microbial dynamics may offer insights to applied research, such as determining the optimal age to manipulate microbiomes for desired conservation outcomes. In this Commentary, we consider current understanding of the importance of early-life host–microbe interactions to vertebrate physiology across the lifespan, discuss why this perspective is necessary in wildlife studies, and provide practical recommendations for experimental designs that can address these questions, including field and laboratory approaches.