Desert lizards modulate nutritional responses to match seasonal biological needs

Animals in extreme environments such as deserts experience severe seasonal fluctuations in abiotic conditions and resources. Under these conditions, they must obtain macronutrients in optimal amounts and ratios to meet their nutritional requirements, which themselves vary with seasonal changes in physiological and life-history processes. To understand whether nutritional intakes and retention align with key life-history events across seasons, we examined the nutritional ecology of the desert-dwelling lizard, Saara hardwickii. We first measured seasonal variation in the quantity and quality of plants available for these herbivorous lizards. By combining field observations of foraging behaviour with elemental analysis, we determined the carbon (C) and nitrogen (N) levels in dietary intakes and faecal matter across seasons. Intake C : N was lowest and faecal C : N was highest in June, reflecting greater proportional consumption and retention of N, likely meeting increased protein demands during breeding. Conversely, dietary C : N and faecal %N were highest in October, indicating greater consumption and retention of C prior to hibernation. Surprisingly, these putative herbivores consumed insects only around the breeding season, despite their year-round availability. Overall, we show that S. hardwickii use both behavioural diet choice and post-ingestive physiology to match seasonal nutritional needs by differentially consuming and retaining nutrients in an extreme environment.