Dispersione e flusso genico del vespertilio maggiore (Myotis myotis): le Alpi costituiscono una barriera riproduttiva?

The greater mouse-eared bat (Myotis myotis) is an insectivorous bat species that occurs throughout the Western Palearctic with a patchy distribution, due to its peculiar ecological requirements. Indeed, it relies on the availability of carabid beetles in open woodlands and of warm cavities where pregnant females roost and give birth. In the last few centuries, the greater mouse-eared bat has undergone a range expansion in continental Europe farther North and East with respect to the areas recolonized at the end of the last ice age, as revealed by phylogeographical studies, where it found new suitable roost sites in ancient buildings’ attics and cellars. Since the alteration of these sites (mainly due to building renovation works) is a major threat to the survival of this cave-dwelling species, genetic surveys that define its management units are urgently needed. This challenging task is traditionally accomplished by using clustering algorithms that rely on differences in allele frequencies at nuclear loci between samples gathered in different geographical areas; however, this method suffers from potential drawbacks, since it relies on the same data in order to define the populations and estimate the gene flow among them. For this reason in the present study I followed an alternative approach, based on the coalescent theory, by exploiting the information provided by two different genetic markers that do not evolve at the same pace. The analysis of the mitochondrial DNA sequence variation allowed me to compare different biogeographical hypothesis by computing their Bayes factors; the results of this comparison showed that the Alps likely represented an historical barrier to gene flow. This allowed me to unify thirteen nursery colonies into three main subpopulations, thus noticeably decreasing the number of the demographic parameters that ought to be estimated and, consequently, the time required by the program MIGRATE to carry out the analysis. The latter revealed a weaker gene flow between the Agliè nursery colony (and, perhaps, the population of northern Italy as a whole) and the Swiss population of canton of Valais, while the Piedmontese colony appeared more genetically connected to the French ones. Since the greater mouse-eared bat is a thermophilic species, unable to cross high mountain ridges, the gene flow rate between the three subpopulations may be related to the average height of the different parts of the Alpine range, that as a matter of fact reaches one of its maximum values between the Piedmont – Aosta Valley region and Switzerland.