Testing the spatial and temporal framework of speciation in an ancient lake species flock: the leech genus Dina (Hirudinea: Erpobdellidae) in Lake Ohrid

[摘要] Ancient Lake Ohrid on the Balkan Peninsula is considered to be the oldestancient lake in Europe with a suggested Plio-/Pleistocene age. Its exactgeological age, however, remains unknown. Therefore, molecular clock data ofLake Ohrid biota may serve as an independent constraint of availablegeological data, and may thus help to refine age estimates. Suchevolutionary data may also help unravel potential biotic and abiotic factorsthat promote speciation events.

Here, mitochondrial sequencing data of one of the largest groups of endemictaxa in the Ohrid watershed, the leech genus Dina, is used to test whether itrepresents an ancient lake species flock, to study the role of potentialhorizontal and vertical barriers in the watershed for evolutionary events,to estimate the onset of diversification in this group based on molecularclock analyses, and to compare this data with data from other endemicspecies for providing an approximate time frame for the origin of LakeOhrid.

Based on the criteria speciosity, monophyly and endemicity, it can beconcluded that Dina spp. from the Ohrid watershed, indeed, represents an ancientlake species flock. Lineage sorting of its species, however, does not seemto be complete and/or hybridization may occur. Analyses of populationstructures of Dina spp. in the Ohrid watershed indicate a horizontal zonation ofhaplotypes from spring and lake populations, corroborating the role oflake-side springs, particularly the southern feeder springs, forevolutionary processes in endemic Ohrid taxa. Vertical differentiation oflake taxa, however, appears to be limited, though differences betweenpopulations from the littoral and the profundal are apparent. Molecularclock analyses indicate that the most recent common ancestor of extantspecies of this flock is approximately 1.99 ± 0.83 million years (Ma)old, whereas the split of the Ohrid Dina flock from a potential sister taxonoutside the lake is estimated at 8.30 ± 3.60 Ma. Comparisons with othergroups of endemic Ohrid species indicated that in all cases, diversificationwithin the watershed started ≤2 Ma ago. Thus, this estimate mayprovide information on a minimum age for the origin of Lake Ohrid. Maximumages are less consistent and generally less reliable. But cautiously, amaximum age of 3 Ma is suggested. Interestingly, this time frame ofapproximately 2–3 Ma ago for the origin of Lake Ohrid, generatedbased on genetic data, well fits the time frame most often used in theliterature by geologists.

[学科分类] 地球化学与岩石