The exposition to urban habitat is not enough to cause developmental instability in the common wall lizards (Podarcis muralis)

Abstract

Developing trustworthy biomarkers is of primary importance in monitoring impacts of environmental stressors on biological systems. Recently, fluctuating asymmetry in morphological traits of the common wall lizard (Podarcis muralis) has been proposed as useful tools for assessing environmental disturbance in urban habitats. However, the experimental design used in previous studies lacked both site replication (only one urban area was sampled) and independent assessment of the physiological conditions of lizards. Hence, we replicated the analysis involving three large cities in Northern Italy and measured lizards’ health conditions as assessed by blood sampling analyses. We found a weak statistical association between fluctuating asymmetry and urban habitat. No significant differences occurred for white blood cell concentration and heterophils-to-lymphocytes ratio, whereas parasite load was significantly lower in urban than natural populations. Finally, somewhat of the variability in fluctuating asymmetry correlated with one or more latent variables not directly observed, but still not related to the habitat. Contrary to previous studies, we concluded that fluctuating asymmetry cannot be regarded as a reliable measure of urban environmental stresses. Despite this, fluctuating asymmetry in the morphology of common wall lizards has a real potential for working as biomarkers, but we need to clarify first the developmental mechanisms, the true effectors of the stress, their interactions and their effects on individual fitness in order to solve the inconsistencies occurring among different studies.