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This manuscript summarizes the outcomes of the 6th EuroSpeleo Protection Symposium. Special emphasis was laid on presenting and discussing monitoring activities under the umbrella of the Habitats Directive (EU Council Directive 92/43/EEC) for habitat type 8310 "Caves not open to the public" and the Emerald Network. The discussions revealed a high level of variation in the currently conducted underground monitoring activities: there is no uniform definition of what kind of underground environments the "cave" habitat should cover, how often a specific cave has to be monitored, and what parameters should be measured to evaluate the conservation status. The variation in spatial dimensions in national definitions of caves further affects the number of catalogued caves in a country and the number of caves to be monitored. Not always participants are aware of the complete national monitoring process and that data sets should be freely available or easily accessible. The discussions further showed an inherent dilemma between an anticipated uniform monitoring approach with a coherent assessment methodology and, on the contrary, the uniqueness of caves and subterranean biota to be assessed – combined with profound knowledge gaps and a lack of resources. Nevertheless, some good practices for future cave monitoring activities have been identified by the participants: (1) Cave monitoring should focus on bio- and geodiversity elements alike; (2) Local communities should be involved, and formal agreements envisaged; (3) Caves must be understood as windows into the subterranean realm; (4) Touristic caves should not be excluded ad-hoc from regular monitoring; (5) New digital tools and open FAIR data infrastructures should be implemented; (6) Cave biomonitoring should focus on a large(r) biological diversity; and (7) DNA-based tools should be integrated. Finally, the importance of the 'forgotten' Recommendation No. 36 from the Bern Convention as a guiding legal European document was highlighted.

The Palaearctic genus Niphargus is a promising model system to understand subterranean fauna genesis in Europe. The Pannonian Plain (mainly covered by Hungary) in Central Europe, once being the area of the Paratethys, is a key area for Niphargus diversification. However, our knowledge on Hungarian species of Niphargus is primarily based on sporadic taxonomical works from the pre-molecular era. Here, we studied 14 localities, covering the eight valid Hungarian species of Niphargus and including nine previously unstudied populations. Based on sequences of three gene fragments, we reconstructed their phylogeny using maximum likelihood and Bayesian approaches. We found that not all Hungarian species of Niphargus are closely related, and even species sampled at the same localities can belong to different clades. Some Hungarian species form monophyletic clades, while others are nested in various non-Hungarian lineages. The new populations are all genetically distinct from the known species. Our results suggest that the Hungarian Niphargus fauna has originated from seven unrelated clades and its diversity is underestimated due to unknown populations and cryptic species. The detection of genetically distinct species of Niphargus from non-carbonate regions calls for further research efforts. The high diversity and the number of putative new species in the N. tatrensis clade warrants further, high-resolution phylogenetic studies.

The amphipod genus Niphargus (Amphipoda: Niphargidae Bousfield, 1977) is the most species-rich genus of freshwater amphipods in the World. Species of this genus, which live almost exclusively in subterranean water, offer an interesting model system for basic and applied biodiversity science. Their use, however, is often limited due to the hitherto unresolved taxonomy within the whole genus. As a comprehensive taxonomic revision of the currently >425 Niphargus species is too demanding, it has been suggested that the taxonomy of the genus could be advanced in smaller steps, by reviewing regional faunas, that would eventually integrate into a global revision. In this study, we provide such a revision of Niphargus in Switzerland. First, we molecularly delimited, morphologically diagnosed, and formally described two new species, namely Niphargus luchoffmanni sp. n. and Niphargus tonywhitteni sp. n. Second, we updated and revised a checklist of Niphargus in Switzerland with new findings, and prepared a list of reference sequences for routine molecular identification, available at BOLD and GenBank. All available specimens of 22 known species from the area were morphologically examined, and their morphological variation was compiled in a data file of DEscription Language for TAxonomy, which can be used for automated generation of dichotomous or interactive keys. The data file is freely available at the World Amphipoda Database. Together, the checklist, the library of reference sequences, the DELTA file, but also a list of hitherto unresolved aspects are an important step towards a complete revision of the genus within a well-defined and biogeographically interesting area in Central Europe.

A detailed redescription of two endemic, cave-dwelling niphargid species of the Hungarian Mecsek Mts., Niphargus molnari Méhely, 1927 and Niphargus gebhardti Schellenberg, 1934 is given based on newly collected material. Morphology was studied under light microscopy and with scanning electon microscopy. Morphological descriptions are complemented with mitochondrial cytochrome c oxidase subunit I (COI) sequences as barcodes for both species and with notes on their ecology. Using three independent molecular markers we showed that N. gebhardti belongs to the clade distributed between Central and Eastern Europe, whereas phylogenetic relationship of N. molnari to the rest of Niphargus species is not clear. The two species from the Mecsek Mts. are phylogenetically not closely related. Both species need to be treated as vulnerable according to IUCN Red List of Threatened Species.

Recent studies indicate that morphologically cryptic species may be ecologically more different than would be predicted from their morphological similarity and phylogenetic relatedness. However, in biodiversity research it often remains unclear whether cryptic species should be treated as ecologically equivalent, or whether detected differences have ecological significance. In this study, we assessed the ecological equivalence of four morphologically cryptic species of the amphipod genus Niphargus. All species live in a small, isolated area on the Istrian Peninsula in the NW Balkans. The distributional ranges of the species are partially overlapping and all species are living in springs. We reconstructed their ecological niches using morphological traits related to feeding, bioclimatic niche envelope and species' preference for epi-hypogean habitats. The ecological meaning of differences in niches was evaluated using distributional data and co-occurrence frequencies. We show that the species comprise two pairs of sister species. All species differ from each other and the degree of differentiation is not related to phylogenetic relatedness. Moreover, low co-occurrence frequencies in sympatric zones imply present or past interspecific competition. This pattern suggests that species are not differentiated enough to reduce interspecific competition, nor ecologically equivalent to co-exist via neutral dynamics. We tentatively conclude that the question of ecological equivalence relates to the scale of the study: at a fine scale, species' differences may influence dynamics in a local community, whereas at the regional level these species likely play roughly similar ecological roles.

In the last decade, several studies have shown that subterranean aquatic habitats harbor cryptic species with restricted geographic ranges, frequently occurring as isolated populations. Previous studies on aquatic subterranean species have implied that habitat heterogeneity can promote speciation and that speciation events can be predicted from species' distributions. We tested the prediction that species distributed across different drainage systems and karst sectors comprise sets of distinct species. Amphipods from the genus Niphargus from 11 caves distributed along the Western Carpathians (Romania) were investigated using three independent molecular markers (COI, H3 and 28S). The results showed that: 1) the studied populations belong to eight different species that derive from two phylogenetically unrelated Niphargus clades; 2) narrow endemic species in fact comprise complexes of morphologically similar species that are indistinguishable without using a molecular approach. The concept of monophyly, concordance between mitochondrial and nuclear DNA, and the value of patristic distances were used as species delimitation criteria. The concept of cryptic species is discussed within the framework of the present work and the contribution of these species to regional biodiversity is also addressed.

Using a comparative phylogeographic approach and different independent molecular clocks we propose a timescale for the evolution of troglobionts in the Dinaric Karst that is relatively consistent over a wide taxonomic range. Keystone events seem to belong to two age classes. (1) Major splits within holodinaric taxa are from the mid-Miocene. They present the potential upper limit for the age of cave invasions. (2) Regional differentiation, including speciation, which can at least in part be associated with a subterranean phase, took place from early Pliocene to mid-Pleistocene. We suggest two to five million years as the time when most of the analyzed lineages started invading the Dinaric Karst underground.