# Digestive Enzyme Activity and Temperature: Evolutionary Constraint or Physiological Flexibility?

## TL;DR

This study shows that island and mainland lizards have evolved different digestive strategies to adapt to their environments, with island lizards better at digesting fat but less tolerant to extreme heat.

## Contribution

The study reveals that digestive enzyme activity and morphology in lizards reflect ecological adaptation rather than evolutionary constraints.

## Key findings

- Island lizards have higher lipase activity and longer intestines, aiding fat digestion in resource-scarce environments.
- Island lizards show sharper declines in enzyme activity at high temperatures, indicating lower heat tolerance.
- Digestive differences between island and mainland lizards are due to ecological adaptation, not evolutionary constraints.

## Abstract

Lizards rely on external temperatures to regulate their body functions, including digestion. This study explored how rising temperatures affect the activity of digestive enzymes, (protease, lipase, and maltase) in eight Mediterranean wall lizard species living on the Greek mainland and islands. Our findings showed that enzyme activity generally increased with temperature up to about 50 °C and then declined. Island species showed higher lipase activity than mainland species in addition to longer intestines, suggesting better fat digestion, an advantage in environments of food scarcity or unpredictability. However, island species also showed sharper drops in enzyme activities at very high temperatures, indicating lower heat tolerance. These results suggest that island and mainland lizard species have developed different digestive strategies to cope with their environments. Understanding these physiological differences helps predict how reptiles might respond to future variations in climate in terms of food intake and energy assimilation.

Temperature strongly influences physiological processes in ectotherms, including digestion, yet its effects on digestive enzyme activity remain poorly understood. We examined the temperature dependence of digestive performance in eight Mediterranean wall lizard species (Podarcis spp.) from mainland and island populations. Under controlled laboratory conditions, we measured the activity of three key enzymes, protease, lipase, and maltase, across a temperature gradient (20–55 °C), alongside gastrointestinal (GI) morphology. Enzyme activity generally increased with temperature up to 50 °C and declined thereafter, reflecting typical thermal kinetics. Lipase activity was consistently higher in island species, while protease and maltase showed no significant geographic or phylogenetic trends. Island lizards also exhibited longer and heavier GI tracts relative to body size (SVL), suggesting enhanced nutrient absorption capacity. Phylogenetic signal analyses (Pagel’s λ and Abouheif’s Cmean) revealed no significant evolutionary constraints on digestive traits, indicating that observed differences reflect ecological adaptation rather than ancestry. Overall, island species appear to have evolved digestive traits that improve energy extraction under resource-limited conditions, but may be more sensitive to extreme heat. These findings highlight contrasting adaptive strategies between island and mainland reptiles and underscore the importance of digestive physiology in predicting the response of species to warming climates.