Abstract
The increase in human activities that leads to wildlife decline and species extinction poses an urgent need for simple indicators of environmental stress in animal populations. Several studies have suggested that fluctuating asymmetry (FA) can be an easy, direct measure of developmental instability because it is associated to environmental stress and, as such, it can be a useful indicator of population disturbance. We examined three different morphological traits in urban and rural populations of the common wall lizard (Podarcis muralis) to test whether anthropogenic disturbance causes an increase in FA. Compared to rural populations, urban ones showed higher levels of FA in all analyzed traits, thus providing evidence that FA can respond to anthropogenic disturbance. However, we also found significant differences in FA among traits, where femoral pores and subdigital lamellae, traits with a functional relevance, were more stable developmentally compared to supracilliar granules which have no evident function. Unsigned FA [abs(right-left)] exhibited significant, but weak, positive correlations among traits, indicating that developmental noise does not have a uniform effect across characters and thus questioning the view of developmental stability as an organism-wide property. The degree of signed FA (right-left) was more similar between structurally associated traits, possibly as an outcome of morphological integration. In conclusion, our results demonstrate that FA can be a reliable indicator of disturbance provided that it is analyzed on multiple traits simultaneously and examined at the population level.
Highlights
Environmental stress caused by human activities can have significant detrimental effects on animal populations [1,2]
In the present study we examined the degree of fluctuating asymmetry (FA) in three morphological traits in urban and rural populations of the common wall lizard, Podarcis muralis (Laurenti, 1768)
In order to explore this hypothesis, we followed a sequential design to address the following questions: 1) Do populations of the common wall lizard show FA in the examined traits, when taking measurement error into account? 2) Does FA vary across populations, sexes and traits? 3) If so, are these patterns consistent with an increased level of FA in urban populations? we examined whether functional traits are more developmentally stable in which case they are predicted to show lower levels of FA compared to nonfunctional ones
Summary
Environmental stress (considered here as those environmental changes disrupting homeostasis and, leading to decline in fitness of an individual) caused by human activities can have significant detrimental effects on animal populations [1,2]. Anthropogenic pressures have been increasing in the past decades and they are affecting wildlife at all levels of biological organization, often leading to population decline and even to the extinction of entire species [3] It is crucial for conservation biologists to have a sensitive indicator, which can be implemented to detect signs of population disturbance before components of fitness have been affected and before irreversible demographic damage has occurred. In this context, a wide range of indicators of stress have been used in animals to detect disturbance by examining molecular, cellular, histological and/or morphological traits, at the individual or population level [4]. Because developmental precision is affected by a wide range of environmental stressors, the degree of developmental instability (DI) has been suggested as a reliable indicator [5] that can be assessed using methodologies that fulfill the above requisites
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