1. In the past decades, nocturnal temperatures have been playing a disproportionate role in the global warming of the planet. Yet, they remain a neglected factor in studies assessing the impact of global warming on natural populations. In ectotherms, physiological performance is influenced by thermal conditions and an increase in body temperature of a few degrees during night-time is sufficient to induce a disproportionate increase in metabolic expenditure.

2. Here, we question whether an intense augmentation of nocturnal temperatures is beneficial or deleterious to ectotherms. Warmer nights may expand a species thermal niche and open new opportunities for prolonged activities and improve foraging efficiency. However, increased activity may also have deleterious effects on energy balance if exposure to warmer nights reduces resting periods and elevates resting metabolic rate.

3. We assessed whether warmer nights affected an individual’s growth, dorsal skin colouration, thermoregulation behaviour, oxidative stress status and parasite load by exposing yearling common lizards (Zootoca vivipara) from four populations to either ambient or high night-time temperatures for approximately five weeks.

4. Warmer nocturnal temperatures increased the prevalence of ectoparasitic infestation and altered allocation of resources toward structural growth rather than storage. We found no change in markers for oxidative stress. The thermal treatment did not influence thermal preferences, but influenced dorsal skin brightness and luminance, in line with a predicted acclimation response in colder environments to enhance heat gain from solar radiation.

5. Altogether, our results highlight the importance of considering nocturnal warming as an independent factor affecting ectotherms life-history in the context of global climate change.