Abstract
BackgroundOwing to its independence from the main Central European drainage systems, the Italian freshwater fauna is characterized by a high degree of endemicity. Three main ichthyogeographic districts have been proposed in Italy. Yet, the validity of these regions has not been confirmed by phylogenetic and population genetic analyses and a phylogeographic scenario for Italy's primary freshwater fish fauna is still lacking. Here, we investigate the phylogeography of the Italian vairone (Telestes muticellus).ResultsWe sampled 38 populations representing the species' entire distribution range and covering all relevant drainage systems, and genotyped 509 individuals at eight variable microsatellite loci. Applying various population genetic analyses, we identify five distinct groups of populations that are only partly in agreement with the proposed ichthyogeographic districts. Our group I, which is formed by specimens from Veneto and the Po River system draining into the Adriatic Sea, corresponds to the Padano-Venetian ichthyogeographic district (PV), except for two Middle Adriatic drainages, which we identify as a separate group (III). The Tuscano-Latium district (TL) is equivalent to our group V. A more complex picture emerges for the Ligurian drainages: populations from Central Liguria belong to group I, while populations from West (group II) and East Liguria (group IV) form their own groups, albeit with affinities to PV and TL, respectively.ConclusionsWe propose a phylogeographic scenario for T. muticellus in which an initial T. muticellus stock became isolated from the 'Alpine' clade and survived the various glaciation cycles in several refugia. These were situated in the Upper Adriatic (groups I and II), the Middle Adriatic (group III), (East) Liguria (group IV) and Tuscano-Latium (group V). The population structure in the vairone is, in principal, in agreement with the two main ichthyogeographic districts (PV and TL), except for the two populations in the Middle Adriatic, which we identify as additional major "district".
Highlights
Owing to its independence from the main Central European drainage systems, the Italian freshwater fauna is characterized by a high degree of endemicity
Two of the microsatellite markers could not be successfully amplified in a small number of populations and were coded as missing data for the subsequent analyses: Lsou09 in populations 20 and 21, and Lsou11 in populations 20, 21, 22 and 26 (Additional file 1)
Significant departures from Hardy-Weinberg equilibrium (HWE) were observed in a number of populations and mainly in two loci, Lsou09 and Lsou11. This was most likely due to problems with the amplification of these loci in a small subset of samples, which resulted in missing data in the evaluation of the departure from Hardy-Weinberg Equilibrium (HWE)
Summary
Owing to its independence from the main Central European drainage systems, the Italian freshwater fauna is characterized by a high degree of endemicity. The most important mountain chains bordering these glacial refugia limited areal reexpansion towards Central and northern Europe during the interglacial periods The combination of these two geographical features isolated populations of various taxa, thereby triggering genetic diversification and (allopatric) speciation [2]. Phylogeography, i.e. the integration of the phylogenetic inferences and/or population genetic relationships among individuals or taxa on one hand, and their geographic distribution on the other hand [5], offers the means to reconstruct the historical processes that triggered the geographic distribution of biodiversity In this context, freshwater fishes constitute an important model group because their dispersion, diversification and speciation are strictly related to the processes that shaped the landmass and the hydrogeographic systems, which they inhabit [6,7]. There are only few ways by which a primary freshwater fish can reach a new river basin: by river capture [8], by downstream river confluence when the sea level is lowered [9], by dispersal over the sea under lower salinity conditions ("lago-mare" phase; [10]), or by lakes formed during the retreat of glaciers [6]
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