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Sex allocation theory predicts that the proportion of daughters to sons will evolve in response to ecological conditions that determine the costs and benefits of producing each sex. All else being equal, the adult sex ratio (ASR) should also vary with ecological conditions. Many studies of subterranean species reported female-biased ASR, but no systematic study has yet been conducted. We test the hypothesis that the ASR becomes more female-biased with increased isolation from the surface. We compiled a data set of ASRs of 35 species in the subterranean amphipod Niphargus, each living in one of three distinct habitats (surface-subterranean boundary, cave streams, phreatic lakes) representing an environmental gradient of increased isolation underground. The ASR was female-biased in 27 of 35 species; the bias was statistically significant in 12 species. We found a significant difference in the ASR among habitats after correction for phylogeny. It is most weakly female-biased at the surface-subterranean boundary and most strongly female-biased in phreatic lakes. Additional modelling suggests that the ASR has evolved towards a single value for both surface-subterranean boundary and cave stream-dwelling species, and another value for 9 of 11 phreatic lake dwellers. We suggest that a history of inbreeding in subterranean populations might lower inbreeding depression such that kin selection favours mating with siblings. This could select for a female-biased offspring sex ratio due to local mate competition among brothers. The observed patterns in sex ratios in subterranean species make them a group worthy of more attention from those interested in sex allocation theory.

We characterized taxonomically, ecologically, and phylogenetically the amphipod community of Melissotrypa Cave (Central Greece), which comprises both freshwater and sulphidic lakes. We found four amphipod species: Niphargus jovanovici, Niphargus lindbergi, Niphargus gammariformis sp. nov. and an unknown species of Bogidiella. The three Niphargus species form a well-supported monophylum but differ in their ecology and morphology: N. jovanovici is a small and slender species inhabiting small freshwater voids, N. lindbergi is a large and stout species living in freshwater lakes, whereas N. gammariformis sp. nov. is a small and stout species found predominantly in a sulphidic lake. Available evidence suggests that diversification may have happened in a geographically restricted area and was driven by ecological differentiation. Niphargus gammariformis sp. nov. shows morphological convergences in diagnostic traits with two species hitherto classified into the genus Pontoniphargus. As molecular phylogenies show Pontoniphargus nested within Niphargus, we synonymize here Pontoniphargus with Niphargus. The species originally named Pontoniphargus ruffoi needed to be renamed into Niphargus pontoruffoi.http://www.zoobank.org/urn:lsid:zoobank.org:pub:4F5EED3B-DEB4-4402-BCE8-6AE2B65CCC3A., info:eu-repo/semantics/published

Subterranean animals are known for their highly evolved phenotypes. They are eyeless, depigmented and possess elongated appendages compared to their surface relatives. Increased antenna and leg length of cave species has traditionally been explained as a consequence of selection for non-visual senses and increased food-finding ability in an environment low in energy. Variation in appendage length between cave species is usually thought to result from differences in time since the colonization of the subterranean habitat. In this study, we analyzed appendage length variation in the Dinaric amphipod species Niphargus croaticus. Relative length of appendages varied substantially among populations. Using multilocus phylogenetic analysis, we showed that the species is nested within highly specialized N. steueri species complex and rejected the time hypothesis. Next, we explored the effects and strength of two environmental factors, water flow and presence of a competing species, N. subtypicus. Populations in caves with flowing water had shorter appendages than populations in cave lakes. Presence of the competing sister species did lead to longer appendages in stagnant water, but had no effect in flowing water. Abiotic factors had a stronger effect than biotic factors, but their relative strength differed among appendage pairs. High variation in appendage length between adjacent population shows that the morphology of cave arthropods is changing quickly and therefore cannot be used to predict species age. Rather than being a general adaptation to cave life, long appendages seem to be associated with the absence of water flow as well as character displacement when in sympatry with ecologically similar competing species.

The amphipod genusNiphargus(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 >425Niphargusspecies 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 ofNiphargusin Switzerland. First, we molecularly delimited, morphologically diagnosed, and formally described two new species, namelyNiphargusluchoffmannisp. n.andNiphargustonywhittenisp. n.Second, we updated and revised a checklist ofNiphargusin 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 Niphargus gebhardti belongs to the clade distributed between Central and Eastern Europe, whereas phylogenetic relationship of Niphargus 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.

Three new freshwater Amphipods of the family Niphargidae G. Karaman, 1962 are described from subterranean waters of Greece, Niphargus aitolosi sp. nov., Niphargus karkabounasi sp. nov. and Niphargus koukourasi sp. nov. Phylogenetic analysis based on 28S rDNA and H3 genes suggests that N. aitolosi sp. nov. belongs to N. longicaudatus species-complex. Species from that complex are distributed along both sides of Adriatic Sea and share roughly similar morphology, including the newly described species from Greece. Niphargus karkabounasi sp. nov., the second new species, belongs to a clade distributed broadly across Europe and the Middle East. Many species of this group, including N. karkabounasi, are small and likely live in small crevices. The third species, Niphargus koukourasi sp.nov. is phylogenetically related and morphologically similar to N. sanctinaumi and N. maximus from Lake Ohrid on the border of the Former Yugoslav Republic of Macedonia and Albania. In addition, this group of species may be related to species collected from Iran.

Subterranean species show a distinct morphology, yet the adaptive significance of some traits, like body size and shape, is poorly understood and cannot be explained solely by distinct environmental conditions (darkness, less food). We predicted that in females some morphological changes may have co-evolved with life history traits, and that co-evolving life history traits provide at least part of the explanation for evolutionary changes of morphology. Using museum material we tested this prediction on the subterranean amphipod genus Niphargus. We studied six species found in springs and eight species found in cave lakes. We treated them as two ecologically distinct groups, and the major ecological differences between them were the availability of nutrients and the water currents. Cave species were found to be larger and stouter (as inferred from the shape of coxal plates, which are part of the marsupium), they had larger eggs and lower reproductive effort per brood, whereas the egg number and brood volume if corrected for the body size were not different. Using phylogenetic independent contrasts, we found a positive correlation between body shape and egg volume, a positive correlation between body size and egg volume, and a negative correlation between body size and reproductive effort per brood. We tentatively conclude that evolutions of morphology and life histories are functionally connected and that co-evolving traits contribute to overall selective regime.

SUMMARY 1. Various groundwater habitats have exceptionally high levels of endemism caused by strong hydrographical isolation and low dispersal abilities of their inhabitants. More than 10% of macro-stygobiotic species nevertheless occupy relatively large ranges, measuring from some hundred to over 2000 km in length. These species represent a challenge because their distributions disregard hydrographical boundaries, and their means to disperse and maintain long-term gene flow are unknown. 2. Based on mitochondrial and nuclear gene sequences, we examined the phylogeographic structure of six formally recognised stygobiotic species (Niphargus virei, N. rhenorhodanensis, Troglocaris anophthalmus, T. hercegovinensis, Spelaeocaris pretneri, Proteus anguinus) and searched for cryptic lineage diversity in a genus-wide phylogeny of Niphargus. Using treebased criteria as well as comparative divergence measures, we identified cryptic lineages, which may tentatively be equated with cryptic species. 3. Fourteen analysed nominal stygobiotic species with large ranges emerged as highly diversified, splitting into 51 tentative cryptic lineages. The degree of divergence was within the range or larger than the divergence of other related pairs of sister species. A substantial part (94%) of the cryptic lineages had ranges

Niphargus steueri (Niphargidae) comprises a complex of four subspecies (N. s. steueri, N. s. kolombatovici, N. s. subtypicus, and N. s. liburnicus), the morphology and distribution of which have been poorly known until now. New diagnostic characters of the species and its four subspecies are presented and illustrated. The species is distributed along the major part of the Dinaric Karst, between Slovenia in the northwest and Bosnia and Herzegovina in the southeast. The distribution of the four subspecies approximately resembles the distribution of the evolutionary lineages of the subterranean amphibian Proteus anguinus and the Dinaric lineage of the cave shrimp Troglocaris agg. anophthalmus. Niphargus s. steueri is restricted to the Istran Peninsula; N. s. subtypicus is distributed in southeast Slovenia and northwest Croatia; N. s. liburnicus is known from two disjunctive localities, one on the island of Krk (Croatia) and the other in Gorizia (Italy); and N. s. kolombatovici is restricted to Dalmacija and Herzegovina. The somewhat variable putative synapomorphies of N. steueri probably suggest that the group is old and that the present distribution pattern is a result of historical events, possibly events in the Miocene Dinaride Lake system. Two populations of N. s. kolombatovici and one population of N. s. subtypicus deviate from the general distributional pattern and may belong to cryptic taxa that cannot be distinguished on the basis of morphology. Both hypotheses corroborate with the estimated times of divergence and with the number of independent lineages in the similarly distributed but unrelated stygobionts Proteus and Troglocaris.

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.