Continental-scale patterns of hyper-cryptic diversity within the freshwater model taxon Gammarus fossarum (Crustacea, Amphipoda).

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.

The effects of water diversion and climate change on hydrological alteration and temperature regime of karst rivers in central Croatia.

Karst rivers in Croatia have been heavily dammed in the past. However, long-term impacts of dams, water diversion and climate change on karst rivers in Croatia have rarely been examined. This study analyzes long-term trends of hydrological and temperature conditions, prior to closure of new large dam, in five connected karst rivers of central Croatia: the sinking rivers Gornja Dobra and Zagorska Mreznica that have underground connections with the Gojacka Dobra, Tounjcica and Mreznica Rivers. It was established that hydrological conditions of these rivers have been greatly changed after the Gojak HPP, located at spring of Gojacka Dobra, became operational in 1959. Water diversion from the reservoirs on Zagorska Mreznica and Gornja Dobra to the Gojak HPP has increased mean annual discharge (52-106%), causing great subdaily fluctuations and overall modification of natural flow regime along the whole course of Gojacka Dobra. By cutting the connection between Zagorska Mreznica and Tounjcica, water diversion has caused a reduction of mean annual discharges of the Tounjcica (-60%) and Mreznica (-29%) Rivers. Analyses of long-term trends in water temperature over the last 50 years have revealed significant positive trends in average annual temperature at three gauging stations on three rivers with increase of 0.17, 0.44 and 0.48°C per decade and climate change as the primary cause. The highest significant increasing trend was established at the lower course of Mreznica where discharge was reduced by water diversion. Mitigation measures for the improvement of hydrological conditions of affected rivers and underground systems are proposed and discussed.