Population dynamics and biological connectivity among Italian smooth newt (Lissotriton vulgaris meridionalis) populations inhabiting a network of wetlands in a traditional landscape

Abstract

A growing number of studies suggest that anthropogenic factors more than natural fluctuations are responsible of the decline of amphibian populations all over the world. For Mediterranean amphibians, the major threats are represented by habitat loss, alteration and fragmentation caused, in particular, by agricultural intensification and urban development. Aquatic habitats, representing reproductive sites for many amphibian species, deserve a particular attention because their reduction in number and quality is alarming. However, in recent years it has clearly emerged that artificial aquatic sites as surrogates of natural ones represent an important contribution to the potential breeding habitats for amphibians. Even small artificial aquatic sites, extremely different in shape, structure, and size (e.g. tanks, drinking-troughs and reservoirs), associated with traditional agriculture and cattle breeding, have been identified as suitable habitats for amphibian reproduction. Several studies highlighted the importance of artificial water bodies for amphibians, especially in the Mediterranean, but most of them focused on artificial sites that simulate natural ponds. In this context, it has been suggested that in many areas drinking-troughs for cattle watering may represent the only permanent water points for amphibian reproduction and sheltering in human modified landscapes. To date, the persistence of such artificial systems is endangered by land reclamation, urbanisation and the abandonment of traditional farm practices in favour of modern agriculture and intensive farming. The disappearance of such artificial aquatic habitats may cause the local loss of small isolated amphibian populations, as was the case in Spain and Italy. Thus, the identification and protection of such key sites should be mandatory for amphibian survival, from an ecological and genetic point of view, especially when demes are structured in metapopulations, a dynamic population model observed frequently occurring in amphibians. The Italian smooth newt (Lissotriton vulgaris meridionalis) was selected as a model species in the present study, since it is widespread in Italy, is threatened by fragmentation and destruction of suitable habitats, especially of reproductive sites, and is known to colonize successfully artificial aquatic systems. The study site is located in the Tolfa Mountains, in Province of Rome, a hilly region showing a rural profile interested by traditional husbandry and agriculture, with medium to low urban and infrastructural development, where troughs for livestock watering are particularly common and widespread. The most bred species in the area is the Maremmana cow, a robust native breed of cattle in a semi-feral state, that indirectly provides additional aquatic resources represented by drinking-troughs built by farmers to facilitate its management. The aim of the present Ph.D. project is to investigate, for the first time, the role of drinking-troughs for the ecological and genetic conservation of the species in an area interested by traditional farming and agriculture. The present Ph.D. project is aimed at investigating the following main goals: q Provide a scenario on the basic demographic attributes of Italian smooth newt populations inhabiting drinking troughs and identify trough and landscape features favouring the persistence of the species in the long-term (CHAPTER ONE) q Test and optimize a panel of microsatellite markers, previously developed in other Lissotriton species and subspecies, on the Italian smooth newt in order to assess population structure and genetic variability at a local spatial scale (CHAPTER TWO) q Analyse the impact of drinking troughs on amphibian population connectivity and genetic variability within a patchy system by focusing on the Italian smooth newt, and determine whether drinking-troughs may provide alternative and/or complementary aquatic habitats for amphibian genetic conservation in a rural landscape (CHAPTER THREE) The first chapter of the present Ph.D. project highlights that even smaller and completely artificial aquatic habitats, such as drinking-troughs, linked to traditional farming practices, provide irreplaceable alternatives to pristine habitats for the reproduction, feeding and sheltering of L. vulgaris meridionalis. Moreover, the Italian smooth newt shows specific habitat requirements, and its populations were not uniformly distributed among the study sites but their occurrence and abundance were strongly related to some drinking-trough features. In this context, the Maremmana cow seems to act as an ecosystem engineer (i) directly by structuring landscape features (i.e., increasing habitat heterogeneity) and (ii) indirectly by providing suitable breeding sites crucial for the Italian smooth newt conservation. Indeed, traditional husbandry practices determine the increase of the total amount of aquatic habitats available to the Italian smooth newt, thus helping to sustain its populations in a region where natural aquatic sites are increasingly disappearing. The second chapter of the present Ph.D. project allows optimizing a panel of microsatellite markers (previously developed and tested for cross-species amplification in other Lissotriton species/subspecies) suitable for assessing Italian smooth newt population structure and genetic diversity across multi-scale levels, from meta-populations to full geographical range. For the Italian smooth newt, no microsatellite loci have been reported thus far and their development will be an important contribution to better understand the ecology and evolution of the species helping to assist its effective management and future conservation activities. In the third chapter of the present Ph.D. project highlights the importance of drinking-troughs on Italian smooth newt population connectivity within a network consisting of natural and artificial aquatic sites. Drinking-troughs supported structured populations, with a good level of genetic variability, connected by gene flow with neighbouring natural and/or artificial aquatic systems with a degree of cohesiveness concordant with the geographic distribution. Such detected connectivity suggests that both artificial and natural aquatic systems may constitute a metapopulation in which recolonization events subsequent to local extinctions are highly likely in the region. Therefore, the restored functionality of the natural network of wetlands by the integration of drinking-troughs in the rural/natural landscape is crucial for amphibian conservation as the ensemble of artificial and natural permanent aquatic systems provide breeding sites and safe migration routes in the current scenario of progressive and incessant process of aquatic habitat loss. In conclusion, the present Ph.D. research seems to be particularly valuable since it attempts to recognize firstly the ecological and genetic value of drinking-troughs for amphibian conservation, filling a gap of knowledge arising from the lack of empirical data on amphibians in such small artificial habitats that may have been neglected in research and policy in favour of natural aquatic systems.