I am interested in the micro-evolutionary processes that generate, sustain, and—under human influence—sometimes threaten biological diversity and its geographic patterns of distribution. I have, therefore, used molecular markers to address the relevance of several of these processes, in particular, hybridisation and gene exchange, with respect to ecology, evolution, and conservation.
Current research projects aim at helping answer the following questions:
Why are hotspots of intraspecific diversity so hot?
Hotspots of genetic diversity have been observed in many species, often within areas of putative glacial refugia. Their existence has, therefore, mostly been considered the product of long-term stability of large refugial populations. However, growing evidence indicates genetic diversity is, often, not only higher within refugial areas, but also deeply structured, suggesting the involvement of micro-evolutionary processes other than long-term demographic stability. We use population genetic, phylogeographic, and historical demographic analyses to study the contribution of these processes to the current patterns of genetic diversity in several areas of the Mediterranean basin (including both mainland and islands) where hotspots of intra-specific diversity have been observed for multiple co-distributed species. Our results show that, in most cases, long-term persistence of populations in refugial areas could have been a necessary, but not sufficient, condition for the occurrence of intra-specific hotpots of diversity. Instead, other processes such as cycles of allopatric fragmentation and secondary admixture within refugia or range displacements toward the wider glacial coastlands (in some cases with a net demographic advantage) would have played a major role. These results point towards a central role for gene exchange in the formation of hotspots; they also change the perception of refugia as sanctuaries, which are long-term repositories of intra-specific diversity, and indicate that they, rather, are forges, hotspots exactly because they are melting pots. Currently, we are exploring the generality of these findings as well as their implications for other research areas such as the geographic mosaic of co-evolutionary interactions, development of ecological communities, and designing of long-term strategies for the conservation of populations and species.
How did glaciation-induced landscape variations affect the demographic and range dynamics of temperate taxa?
While it is now well established that glacial-interglacial cycles have deeply affected the demographic and range dynamics of temperate species, determining how they exert this influence is still an active field of research. There is growing evidence that a simple model of glacial contraction in the southern refugia followed by interglacial northward expansion does not adequately explain all the available data. We are investigating whether glaciation-induced increases in suitable habitats (e.g. along the coastline for lowland-adapted species) could have counterbalanced the glacial shifts of thermal optima in previously occupied areas, leading to net demographic stability or even expansions during these periods. Our first results, based on genetic data and paleo-distribution modelling, suggest that this could have actually occurred in various species from different areas.
What information can human-driven newly formed hybrid zones offer about the role of hybridisation in evolution?
Hybridisation can have a wide range of evolutionary and ecological consequences for both hybridising lineages and the ecological community. These consequences have traditionally been investigated by studying historically formed hybrid zones. Recently, however, the introduction of non-native species within the range of their close relatives and the variations in species ranges driven by recent environmental changes provide new windows on these processes. For instance, recently formed hybrid zones allow us to investigate the happenings during the early stages of secondary contacts, as well as the relevance of some transient processes—that, by definition, cannot leave detectable traces after the early stages of hybridisation—on the resulting patterns of diversity at the levels of population, species, and community. We are studying the genetic, ecological, and conservation consequences of the recent formation of secondary contact zones among lineages of frogs and small mammals in several areas of the Italian peninsula. These areas significantly differ in both their natural and human-driven disturbance features (from hilltops to lowlands and from weakly to strongly disturbed), which we hope will allow us to clarify the influence of environmental settings on the outcome of the diverse, recently established inter-specific interactions.
Are hotspots of intraspecific diversity areas of long-term resistance of host species to their pathogens?
Climate changes can affect the survival of populations in several ways, both directly and indirectly. Recent data on the causes of the current (i.e. the sixth) mass extinction show that the alteration of host–pathogen dynamics is one such way. However, it is also increasingly clear that populations of a host species can often show the entire range of potential responses to a new pathogen—from immunity to disappearance—which often leads to a geographic mosaic of outcomes of epidemics across a host species range. However, the factors underlying such a geographic mosaic are still poorly understood. We are evaluating the hypothesis that a contributing factor could be the geographic distribution of genetic diversity that ultimately influences the adaptive potential of a population to the ever-changing environmental (biotic and abiotic) conditions. In particular, we are exploring the hypothesis that host species’ populations from hotspots of diversity perform better in the evolutionary arms race with their pathogens. To this end, we are studying, both on field and under laboratory settings, several emerging infectious diseases, and their roles in amphibian population declines along the Italian peninsula, an area rich in both hotspots and cold spots of diversity.