Rapid evolution of an ancient lake species flock: Freshwater limpets (Gastropoda : Ancylidae) in the Balkan Lake Ohrid

Ancient lakes have long been recognized as evolutionary theatres and hot spots of endemism; the evolution of their morphologically often highly diverse species flocks has received much attention. However, as each ancient lake has its own geological and evolutionary history, modes of speciation may differ from system to system. Ancient lakes can act as evolutionary reservoirs that assure the survival of relict species, but at the same time extant species may evolve through intralacustrine speciation. Other aspects of interest are the actual rates of immigration, diversification or extinction as well as the temporal framework of morphological change. Many of these questions have been addressed in the African (e.g. Lake Tanganyika) and Asian (e.g. Lake Baikal) ancient lakes. For an European ancient lakes (e.g. Lakes Ohrid and Prespa), such studies are largely missing. In the present paper. extraordinarily shaped endemic freshwater limpets of the genus Ancylus from the Balkan Lake Ohrid are used in a phylogeographic and phylogenetic context to test whether they represent an ancient lake species flock, to study the mode of speciation, and to assess the timing of morphological change. Based on DNA data from two mitochondrial genes (COI, LSU rDNA), it has been found that the Lake Ohrid Ancylus species form an endemic monophyletic group. In addition, the lake's feeder springs are inhabited by another, undescribed Ancylus species. All other studied waterbodies within the watershed do not support their own Ancylus lineages but are inhabited by a widespread Mediterranean taxon. The split between the species endemic to the take and its sister taxon is dated to 1.4 +/- 0.6 million years ago. The study presents the first genetic confirmation for the existence of a species flock in a European ancient lake. Contrary to the prevailing opinion it shows that, concerning Ancylus, Lake Ohrid represents a site of intralacustrine speciation rather than an evolutionary reservoir, Moreover, it provides the first evidence for rapid morphological change in an European ancient lake species flock. (c) 2006 Gesellschaft fur Biologische Systematik. Published by Elsevier GmbH. All rights reserved.