Species status and genetic isolation in the Subalpine Warbler complex: Insights from mitochondrial DNA analysis

This study investigates the genetic differentiation and gene flow within the Subalpine Warbler (Curruca cantillans) complex using mitochondrial DNA (mtDNA) analysis. We focused on three primary populations based on phylogenetic findings and geographical distributions. Pop1: Includes C. c. albistriata (distributed in extreme northeast Italy (Trieste), southern Slovenia, and south along the north Adriatic coast to Albania, as well as east to southern Bulgaria, Greece, Crete, and western Turkey, with non-breeding grounds in the central and eastern Sahel from eastern Mali to northwest Sudan) and C. c. cantillans (occurring in Sicily, central and southern Italy, and locally in north-central Italy, with non-breeding grounds presumably in the western Sahel). Pop2: Represents C. iberiae, found in Spain and western France. Pop3: Comprises C. subalpina, distributed across the Balearic Islands, Corsica, Sardinia, some Tuscan islands, and north and central Italy, with non-breeding grounds extending into the western Sahel, reaching northern Nigeria and Niger. Our genetic analysis indicates that all three populations have expanded recently but maintain unique genetic structures. Despite this recent expansion, the populations exhibit limited genetic diversity. Using AMOVA, we found that most genetic variation is between populations rather than within them, indicating significant genetic differentiation. This study uniquely combines population genetic data with advanced analyses to provide detailed insights into the genetic structure and connectivity of the Subalpine Warbler complex, highlighting the distinct genetic lineages within the Mediterranean biodiversity hotspot.