Relationships among the three levels of biodiversity, genes, species and ecosystems: an empyrical study with Alpine amphibians from Trentino

In the ongoing global biodiversity crisis, amphibians are the most endangered group of vertebrate, with increasing reports of population declines and extinctions worldwide. Alpine ecosystems are heavily affected by climate change and habitat alteration: range shifts and contractions are predicted, particularly for cold-adapted species, leading to an increased fragmentation of populations. A growing body of evidence is showing that the different levels in which biological diversity may be divided (i.e. genes, species, and ecosystems) are broadly linked, and ecological processes result from the complex interactions between these levels. As a result, modern conservation biology is increasingly recognizing the need for an integrative approach. In this project, we adopted such approach, investigating the evolutionary and ecological processes affecting the amphibian populations and communities, within a systemic perspective. We focused on a south-eastern Alpine region, Trentino, choosing a model organism, the common frog (Rana temporaria), as target species for investigating patterns of diversity at the genetic level. In Chapter 2, we investigated the past evolutionary history of Rana temporaria in the Trentino region, by means of a phylogeographic study based on mtDNA data (540 individuals from 54 sites). We highlighted a complex scenario, with three different Pleistocene glacial refugia located in the southern slopes of the Alps, routes of post-glacial recolonization following irregular patterns (reflecting the complex orography of the region), and a contact zone among different evolutionary lineages in the eastern part of the region. Notably, different lineages exhibited different levels of genetic diversity at mtDNA. In Chapter 3, we conducted a population and landscape genetics study, using microsatellite markers (1522 individuals from 79 sites), for evaluating patterns of current genetic variability and genetic structure in Rana temporaria populations. We detected a main barrier to gene flow, the Adige river valley, separating the region in two genetically differentiated clusters. Comparing our findings with the pattern emerged from Chapter 2, we concluded that current levels of intra-population genetic variability seem to be shaped by a combination of past (e.g. recolonization processes) and present (e.g. isolation) factors. The two subregions, West and East Trentino, showed different spatial patterns for both genetic variability and fine-scale population structure. In Chapter 4, we studied the relationship between species diversity of amphibian communities and genetic diversity of the model species, Rana temporaria. We found a strong negative correlation, and we demonstrated that the recorded pattern was due to the opposite influence of environmental factors on the two levels of biological diversity. Genetic diversity is fundamental for the persistence of populations in the face of environmental change: in the context of the ongoing biodiversity declines, it is therefore of crucial importance monitoring its levels and understanding the underlying processes. Our approach, based on two different types of genetic markers (mtDNA and microsatellites), provided evidence that the legacy of past evolutionary history is still largely evident in the genetic patterns of small, low-vagility vertebrates such as amphibians, even at fine spatial scale. Identifying different evolutionary lineages, “hotspots” of genetic diversity, as well as evaluating current connectivity patterns should be considered an essential preliminary step for developing effective conservation strategies. In addition, the detected negative correlation between species and genetic diversity, perhaps the most important finding of this study, suggests that species diversity cannot be universally used as proxy for genetic diversity in conservation planning. Choosing a common, widespread species allowed us to capture a detailed (although not exhaustive) picture of amphibian biodiversity in the Trentino region, and this study may be used as a term of comparison with more endangered species, or for testing specific hypothesis in future research investigations.