Saving Water to Survive: Alternative Water Loss Strategies Could Explain Color Polymorphism Maintenance in a Lacertid Lizard

We investigated a potential new trade-off underlying the color polymorphism in the common wall lizard (Podarcis muralis). We tested the hypothesis that red males prioritize hydroregulation over fine thermoregulation, while white and yellow morphs are fine thermoregulators. This hypothesis was tested by experimentally measuring evaporative water loss (EWL) rates in 36 male lizards (12 for each morph) at a high temperature (37°C) under both dry and wet air conditions. Our results indicate that the red morph consistently exhibits a higher EWL rate compared to white and yellow morphs under both experimental conditions. No significant differences in EWL emerged between the white and yellow morphs. Since our experimental setup prevented behavioral adjustments and morphs did not differ in body size, the observed differences in EWL suggest underlying physiological mechanisms that allow white and yellow lizards to conserve water more efficiently. This finding supports our hypothesis and suggests that the red morph's strategy of finely regulating water balance may be favored in cooler, wetter environments. We propose that the thermo-hydroregulation trade-off, combined with the previously identified trade-off between aggression and survival, can explain the maintenance of a stable polymorphism with four distinct morphs in this species.