Pleistocene range disruption and postglacial expansion with secondary contacts explain the genetic and cytotype structure in the western Balkan endemic Alyssum austrodalmaticum (Brassicaceae)
Abstract
The western Balkans represents an area of significant topographic and environmental heterogeneity, harbouring high species and intraspecific diversity. Similar genetic and distributional splits observed in unrelated species have suggested some common features in their glacial response and biogeographic history.
Here, we studied the western Balkan endemic Alyssum austrodalmaticum with the aim to explore and understand its intraspecific structure and processes that shaped the present patterns. We employed data from AFLPs, two low-copy nuclear genes, genome size, morphometrics and species distribution modelling.
Four genetic lineages were identified within the species, which were geographically structured and showed cytotype-specific patterns. The observed phylogeographic structure is congruent with the predicted species distribution during the Last Glacial Maximum.
Two allopatric diploid lineages (referred to as N2x and S2x) reflect glacial range disruption and survival in distinct refugia inferred in north-western (Istria, Kvarner) and south-eastern Adriatic areas (northern Adriatic palaeo-coastline and southern Dinarides). AFLP analyses with in silico-generated polyploid genotypes and nuclear genes proved that the two tetraploid lineages (C4x, S4x) were genetic allopolyploids and arose independently.
The central tetraploids (C4x) originated through secondary contacts of the two diploid lineages. The origin of the southern tetraploids (S4x) is somewhat ambiguous.
Apart from the southern diploids (S2x), the involvement, either direct or through later introgression, of the central tetraploids (C4x) or even other Balkan relatives is possible. Our study highlights the role of glacial range dynamics and secondary contacts, triggering introgression and polyploid evolution, in the formation of genetic diversity and intraspecific patterns in the western Balkans.