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Aim: A detailed, comparative DNA‐barcoding and morphospecies‐based overview of the vertical and horizontal distribution of Lake Ohrid's endemic Gammarus species flock is provided. Re‐evaluation of the time frame for the onset of the species flock and identification of events that putatively influenced diversification processes. Location: Lake Ohrid, Balkan Peninsula, Europe. Taxon: Gammarus species flock (Amphipoda, Crustacea). Methods: Extensive sampling and DNA barcoding of 600 individuals was carried out. DNA sequences were analysed using species delimitation methods, haplotype network reconstructions, Bayesian molecular dating and demographic analyses. The COI‐based species delimitation results were validated with nuclear 28S RNA data. Results: The species flock distribution has a weak horizontal but clear vertical structure. The diversity along bathymetric gradients correlates with temperature and salinity; and the highest diversity is observed in sublittoral and springs on the lake's shore. Two new molecular units representing putatively new species are revealed and supported also by the nuclear marker. The onset of flock radiation overlaps with the time of lake formation. The COI gene shows signs of positive selection and an acceleration in substitution rate. The demographic changes within the flock happened during the last thousands years. Main Conclusions: Distribution of the Gammarus species flock is vertically structured, reflecting habitat zonation. Parapatric speciation is one of the possible mechanisms behind the flock's diversification. Detection of new MOTUs suggests that the flock's diversity is still not fully revealed. Simultaneously, failure to collect three previously known MOTUs suggests a loss of gammarid diversity in the lake. This represents, together with the current threats to the lake ecosystem (i.e. climate changes, development of tourism), a clear call for conservation efforts. The speciation events and demographic changes within the flock relate presumably to glacial and postglacial water level changes and to the colonisation of new depth ranges and the associated springs. [ABSTRACT FROM AUTHOR]

Evidence for cryptic diversity has been accumulated for many animal groups. In reply, effective tools for ordering this diversity by detecting and delimiting new species have been developed. Although molecular methods of species delimitation become fast means to order information upon hidden diversity, cryptic species discoveries are rarely followed by formal species descriptions and implementation of DNA data in species diagnoses, enhancing rather than reducing the taxonomic impediment. DNA-based diagnostic characters may serve as the backbone for a taxonomic description of cryptic species. In this article, we verify an established taxonomy of an ancient lake endemic species flock, through confrontation of the morphological taxonomy and molecular species delimitation methods. The endemic Gammarus species flock inhabiting Lake Ohrid was tested with several distance- and phylogeny-based delimitation methods using the mitochondrial cytochrome oxidase subunit I and 16S ribosomal RNA genes. We described three new species, including the Gammarus sywulai sp. nov., on the basis of morphological and molecular characters and two cryptic species, Gammarus cryptoparechiniformis sp. nov. and Gammarus cryptosalemaai sp. nov., diagnosed exclusively on the basis of molecular characters. A simple taxonomic key is provided for provisional morphological identification of the Lake Ohrid Gammarus species. [ABSTRACT FROM AUTHOR]

Aim Lake Ohrid is the oldest existing lake in Europe, dating back to the Tertiary. Given its surface area and the adjusted endemism rate, it seems to hold the greatest biodiversity of any ancient lake. Of all the animal groups endemic to this lake, gammarids form one of the largest species flocks. The goal of our study was (1) to develop the phylogenetic framework for the Ohridian endemic Gammarus species flock and place it within a regional palaeobiogeographical context, and (2) to interpret the data with respect to the putative origin of the Lake Ohrid fauna. Location Lake Ohrid, Balkan Peninsula. Methods Sequences of two mitochondrial genes (cytochrome c oxidase subunit I and 16S ribosomal RNA) and one nuclear gene (28S ribosomal RNA) of the Ohridian endemic Gammarus species and of other Balkan gammarids from 69 localities were analysed. The phylogenetic relationships of the group were studied using Bayesian methods. The biogeographical history and the chronology of diversification events were investigated using a relaxed molecular clock with two calibration points. Results It appears that the Lake Ohrid gammarids derive from an old local lineage of the Gammarus balcanicus complex. This lineage arrived from the northern part of the Proto-Balkans, after its emergence during the Tethys/Paratethys regression, and differentiated during the last 18 Myr of the Dinaric uplift (Alpine orogeny). It is also closely affiliated with the biota endemic to the neighbouring area of the former Miocene lake system and to lineages from the upper Vardar and Črni Drim river systems. Main conclusions The Lake Ohrid endemic fauna is closely affiliated to the local biota and its roots are more ancient than the lake itself. [ABSTRACT FROM AUTHOR]

Tentatively dated, the Plio-/ Pleistocene origin of the ancient Lake Ohrid on the Balkan Peninsula makes it the oldest ancient lake in Europe. Given the surface area of the lake and the adjusted endemicity rate, it may be also defined as the most diverse of all the ancient lakes in the world. From all the animal groups endemic to this lake, gammarids are amongst the most scarcely known in terms of their diversity and phylogenetic relationships. Partial DNA sequences of two mitochondrial genes, cytochrome oxidase subunit I ( cox1) and 16S ribosomal RNA ( 16 S r RNA) of eight known endemic Gammarus species from the Lake Ohrid valley were analysed. Phylogenetic analyses showed that endemic Gammarus species comprise an ancient species flock, with Gammarus sketi from the feeder springs being their sister taxon outside the lake. Amongst the species inhabiting the lake, Gammarus solidus and Gammarus salemaai are morphologically and molecularly well defined. By contrast, Gammarus ochridensis, Gammarus parechiniformis, Gammarus lychnidensis, and Gammarus stankokaramani revealed high discrepancy between morphological and genetic data. None of these morphospecies form a monophyletic clade and a significant degree of apparent gene flow occurs between them. This could be caused by incomplete lineage sorting and/or hybridization events. Two novel mtDNA lineages were found within the lake, possibly constituting two new species ( Gammarus sp. 1 and Gammarus sp. 2). Molecular clock analysis showed that the split between G. sketi and the Gammarus species flock from the lake occurred approximately 5-7 Mya, whereas within the flock there were at least two intralacustrine radiations: one estimated at 2-3 Mya and the second at less than 1 Mya. The first one could be associated with the origin of the lake and the second with the lake water-level fluctuations during Pleistocene. © 2013 The Linnean Society of London [ABSTRACT FROM AUTHOR]

Traditional morphological diagnoses of taxonomic status remain widely used while an increasing number of studies show that one morphospecies might hide cryptic diversity, i.e. lineages with unexpectedly high molecular divergence. This hidden diversity can reach even tens of lineages, i.e. hyper cryptic diversity. Even well-studied model-organisms may exhibit overlooked cryptic diversity. Such is the case of the freshwater crustacean amphipod model taxon Gammarus fossarum. It is extensively used in both applied and basic types of research, including biodiversity assessments, ecotoxicology and evolutionary ecology. Based on COI barcodes of 4926 individuals from 498 sampling sites in 19 European countries, the present paper shows (1) hyper cryptic diversity, ranging from 84 to 152 Molecular Operational Taxonomic Units, (2) ancient diversification starting already 26 Mya in the Oligocene, and (3) high level of lineage syntopy. Even if hyper cryptic diversity was already documented in G. fossarum, the present study increases its extent fourfold, providing a first continental-scale insight into its geographical distribution and establishes several diversification hotspots, notably south-eastern and central Europe. The challenges of recording hyper cryptic diversity in the future are also discussed. [ABSTRACT FROM AUTHOR]