Regionalization of Cutaneous Water Loss in Two European Lizards

AbstractSkin resistance to evaporative water loss (EWL) is essential for terrestrial organisms to maintain water balance. In squamate reptiles, cutaneous EWL (CEWL) represents a significant fraction of total EWL. Recent studies found differences in CEWL among body regions of the same species, which may be due to region-dependent selection to modulate water loss or indirect selection on other skin functions such as resistance to abrasion. Regionalization might also be linked to scale size or number, as scales are a major component of a reptile's integument. We measured CEWL and scale morphology across four body regions (venter, dorsum, throat, and head) in two lacertid lizard species, Zootoca vivipara and Podarcis muralis, from mesic and semiarid habitats, respectively. We estimated individual repeatabilities with and without experimental covariates to investigate the scope for consistent individual regional CEWL variation. Dorsal surface temperature always had positive effects on CEWL. Body size positively influenced CEWL in P. muralis. Our results further demonstrated differences among body regions in each species. The head and dorsum had the highest CEWL rates, while the venter and throat had the lowest CEWL. Accounting for covariates, we found that P. muralis exhibited lower CEWL than Z. vivipara on the throat and dorsum. We found differences in scale sizes among regions, scale types, and species and significant individual variation and correlations between individual scale sizes of different regions. However, a positive relationship between CEWL and mean scale size occurred only for the throat region. Regions with higher CEWL in Z. vivipara had larger scales than those in P. muralis, but the reverse was not the case. These findings contradict previous observations that less exposed regions (throat and venter) would exhibit higher water loss rates in lizards and reject a single general relationship between scale morphology and regional CEWL.