Insight into Danube sturgeon life history: trace element assessment in pectoral fin rays

Sturgeon populations in the Danube River have experienced severe decline during the last several decades, mostly due to the poorly regulated fishery, river fragmentation and water pollution. This study focuses on gaining better understanding of sturgeon life history primarily by addressing the assessment of microelement accumulation in sturgeon pectoral fin rays, especially of strontium and calcium, as a method that can reveal migration patterns of anadromous sturgeons. Analysis was performed on pectoral fin samples of three anadromous Danube sturgeon species (beluga, Russian sturgeon and stellate sturgeon) by the use of a Nuclear Microprobe technique. The most frequent pattern in analyzed samples was represented by a low Sr:Ca ratio in the innermost annuli, followed by an increased ratio in the middle annuli segment, and often with a decreased ratio in the outermost annuli. Probability density estimate has revealed three distinguished maxima of the Sr:Ca ratio, 7.08 × 10⁻³, 8.98 × 10⁻³ and 9.90 × 10⁻³, which might correspond, respectively, to fresh, brackish and saltwater. Although the analysis of the Sr:Ca ratio in sturgeon pectoral fin rays has revealed changes that might indicate probable migration between habitats with different water salinity, further studies are needed for improvement of this method. This study represents the first analysis of this kind that was conducted on sturgeon species from the Black Sea basin.     

Sturgeon re‐introduction in the Upper and Middle Danube River Basin

All six sturgeon species naturally occurring in the Danube River from the Black Sea (BS) to the upstream reaches in Germany today are under severe pressure and classified as either vulnerable, critically endangered or already extinct in the Danube River Basin (DRB). This sharp decline of populations is the result of two major drivers: habitat alteration and unsustainable harvest. The Danube River Basin can be divided in three functionally separated sections by its hydromorphology and character: The Lower Danube (LD) and BS, now also separated ecologically from the Middle Danube (MD) by two hydropower stations at the Iron Gate gorge, 800 km from the sea, currently restricting the remaining anadromous sturgeon species (A. gueldenstaedtii, A. stellatus, Huso huso) to the LD and BS also restraining migrations of potamodromous species. The Upper Danube (UD) is nowadays disconnected from the approx. 850 km long MD by Gab?ikovo Dam. The UD itself, as well as many tributaries along the Danube, are fragmented by numerous barriers, leaving no more than a total of 300 km free flowing river out of 700 km. Overharvest led to disappearance of most sturgeon species in the UD already in the Middle Ages, with populations in the MD following in the subsequent centuries. Today the potamodromous sterlet (A. ruthenus) still exists in small decreasing populations in the UD and MD basins, where its occurrence is supported by stocking. Most probably the potamodromous ship sturgeon (A. nudiventris) is extirpated in the whole basin. The Danube basin comprises 19 countries, being the most international river basin in the world, rendering coordinated conservation efforts a challenge. Strategic guidelines for the conservation of the Danube sturgeons are available in form of several action plans, but implementation remains insufficient as of yet. This paper attempts an analysis of the potential for sturgeon restoration in the UD and MD basin and highlights the need for concerted approaches when it comes to ex situ actions and reintroductions.     

Genetic variation of European grayling (Thymallus thymallus) populations in the Western Balkans

In order to elucidate genetic composition of European grayling (Thymallus thymallus) populations in the Western Balkans, the partial mitochondrial DNA (mtDNA) control region was sequenced and 12 microsatellite loci genotyped in 14 populations originating from tributaries of the Adriatic and Danube drainages. Eleven mtDNA haplotypes were found, one confined to the Adriatic clade, one to the Alpine group and the rest to the ‘Balkan’ grayling phylogenetic clade. Haplotypes from the Balkan clade were confined to the Danube drainage and constituted two groups: northern group with haplotypes found in the Slovenian part of the Danube drainage, and southern group, consisting from Bosnia–Herzegovina and Montenegro. Substantial genetic distance between northern and southern groups of haplotypes (0.75–1.8%) and well supported divisions within the northern group indicate very structured grayling population within the studied Danube basin that most probably did not evolve due to vicariance but rather as a consequence of multiple colonization waves that might have occurred during the Pleistocene. Furthermore, genetic distance of ~4% between Adriatic and Danube populations’ haplotypes, suggest that their separation occurred in mid-Pliocene. These findings imply a complex colonization pattern of the Western Balkans drainages. Microsatellite data also confirm high genetic diversity in Western Balkans populations of grayling (on average 7.5 alleles per microsatellite locus and H _exp 0.58). Limited stocking activities were detected based on microsatellites and mtDNA data. Regarding current knowledge of grayling phylogeography appropriate management strategies were proposed to preserve unique, autochthonous grayling populations in Western Balkan.     

Cross-species amplification of microsatellite markers in the invasive spiny-cheek crayfish (Orconectes limosus): Assessment and application

The North American spiny-cheek crayfish,Orconectes limosus (Cambaridae), endangered in its native range, is a widespread invasive species in European waters and conservationally important carrier of crayfish plague. However, its population structure is poorly known, and no informative genetic markers for the species are available. We tested cross-species transfer of microsatellite loci to spiny-cheek crayfish from 5 other crayfish species. Variability of 10 successfully amplifying loci derived from 4 species was then tested in 60 individuals ofO. limosus originating from 3 natural populations: the river Danube at Bogyiszló in Hungary, a pond in Stary Klíčov, and the brook Černovicky, both in the Czech Republic. The allele number within the populations ranged from 4 to 10 alleles per locus, while heterozygosity levels varied from 0.650 to 0.900 forHo and from 0.660 to 0.890 forHe. No linkage disequilibrium and no null alleles were detected. The selected markers are useful for assessing population structure, intraspecific variation, and paternity studies in spiny-cheek crayfish.     

The distribution and the abundance of hydrophytes along the Danube River in Serbia

The Danube River runs through Serbia with flow 588 km long. Different hydrological, geological and ecological conditions occuring along the Danube in Serbia enables its division into four sections: The upper region, Đerdap I accumulation, Đerdap II accumulation, and the lower region. Each section is characterized by unique plant species diversity, frequency of occurrence and distribution pattern. The species diversity ranged from low in the upper reach, to high or very high in the impoundments and decreased in the lower reach. This paper provides a basis for a detailed study on the influence of large power plant impoundments over the aquatic vegetation of rivers.     

Pterygodermatites variabilis n. sp. (Nematoda: Rictularioidea) from the Indian gerbils of Pakistan

Pterygodermatites variabilis n. sp. (Nematoda: Rictulalarioidea) from the Indian gerbils Tatera indica collected from Sind and Baluchistan Provinces of Pakistan is described and compared with closely related species of the genus recovered from small mammalian hosts. The new species is characterised by a combination of the following characters: it possesses a regular crown of 26 and 14–38 denticles in male and female specimens respectively, 40–47 pairs of pre-vulvar spines, and a variable position of the vulva in specimens collected from different localities: it also differs in the size of the spicules and gubernaculum.     

Morphology and postembryonic development of males and females of Bosmina longispina Leydig (Crustacea, Anomopoda) from a North Iceland population

We investigated the morphology of adult and juvenile stages of females and males of Bosmina longispina Leydig from a North Icelandic population. There are additional setae near the basis of the second antenna and between its branches in adult males, not described in Bosmina, but known from other Anomopoda. New features of female morphology are also found. The development of the first limb and postabdomen of the male is described in detail. In juvenile males of B. longispina (belonging to subgenus Eubosmina), characteristics of morphology, similar to those in adult males of other subgenera are found.Abbreviations af antennal flap - as additional setae of male - bs basis of seta of clasper - bc basis of postabdominal claws - ch clasper hook - cl clasper - cs seta of clasper - cw claws of postabdomen - de distal endite of the first limb - dr dorsal row of denticles on male postabdomen - df dorsal fold of carapace - eh ejector hooks of limb I - ep epipodite - ex exopodite - fp frontal head pore - fs frontal seta - hs hair sensilla - in incision of juvenile male postabdomen - ir interrupted rows of setules on postabdomen - Ip lateral head pore - mp median head pore - mpr maxillar process of limb I - mr main row of denticles on postabdominal claws - pe predistal endite of limb I - pf preantennal fold of valve - pl plate above postabdominal setae - ps postabdominal setae - rs rudimentary setae - sr second row of denticles near basis of claws - vf ventral fold of valve - vr ventral row of denticles on male postabdomen     

Distribution and ecological preferences of noble crayfish in the Carpathian Danube basin: biogeographical insights into the species history

Widespread across Europe, the noble crayfish Astacus astacus has experienced many negative ecological and anthropogenic influences, mostly in western and northern Europe. We address the distribution and ecological affinities of this species in the geographical context of the Carpathian Danube basin, an area where these influences were limited and the distribution picture is expectedly a natural one. The main statistical method used to reveal the environmental factors that influence the distribution of noble crayfish was boosted regression trees. Crayfish presence was found to be favoured by a combination of a high percentage of riverbank tree coverage, moderate altitude and slow water velocity, to the detriment of dissolved oxygen. These results reveal the species requirements for river sectors offering the best long-term stability. An eastwards decrease in the probability of occurrence of noble crayfish populations was observed along the Danube tributaries. We hypothesise that this pattern is given by the early colonisation routes originating from southern Danube tributaries, after the Pleistocene glaciations. Including spatiality along with ecological data in the statistical models, this study comes to support the fact that a comprehensive approach can provide a better understanding of a species distribution pattern.     

Zooplankton in a Danube River Arm near Rusovce (Slovakia)

Poor quantity of zooplankton was recorded in a Danube arm situated on the right side of the Danube River in Slovakia (river km 1857) in 2002 and 2003. All over the year the arm is significantly influenced by groundwater by reason of seepage. Because of low mean water temperature (12°C) and poorly developed macrovegetation in particular, the arm reminds gravel pit-like. The annual average of zooplankton biomass was low and ranged from 0.35 g m⁻³ (2002) to 1.28 g m⁻³ (2003), because of low crustacean abundance. Total cladoceran abundance was excessively low in both years and ranged from 3.5 N L⁻¹ (2002) to 16.6 N L⁻¹ (2003). Small species, Bosmina longirostris and Chydorus sphaericus were dominant. Only four adult Copepoda — Cyclops vicinus, Thermocyclops crassus, Eurytemora velox and Eudiaptomus gracilis — were recorded in quantitative samples of both years. In the zooplankton assemblage dominated rotifers (Synchaeta pectinata, Synchaeta oblonga, Polyarthra dolichoptera and Keratella cochlearis) which represented 78% and 67% of total abundance respectively. The total of 19 species of rotifers, 34 Cladocera species and 16 taxa of Copepoda were found.     

Using morphological characters of subfossil daphniid postabdominal claws to improve taxonomic resolution within species complexes

Daphnia subfossils from lake sediments are useful for exploring the impacts of environmental stressors on aquatic ecosystems. Unfortunately, taxonomic resolution of Daphnia remains is coarse, as only a small portion of the animal is preserved, and so the identification of daphniid subfossils typically relies upon postabdominal claws. Daphniid claws can be assigned to one of two species complexes: D. longispina or D. pulex. Both complexes contain species with differing environmental optima, and therefore improved taxonomic resolution of subfossil daphniid claws would aid paleolimnological analyses. To identify morphological features that may be used to help differentiate between species within complexes, we used species presence/absence data from net tows to select lakes in central Ontario (Canada) containing only a single species from a particular complex, then used remains preserved in surface sediments of these lakes to isolate four Daphnia species: D. ambigua and D. mendotae from the D. longispina complex, and D. pulicaria and D. catawba from the D. pulex complex. Our analyses demonstrate that, within the D. longispina complex, postabdominal claw length (PCL) and spinule length can be used to distinguish D. mendotae from D. ambigua. In addition, within the D. pulex complex, there are differences between D. pulicaria and D. catawba in the relative lengths of the proximal and middle combs on the postabdominal claw. However, the number of stout spines on the middle comb is an unreliable character for differentiating species. Overall, our data demonstrate that greater resolution within Daphnia species complexes is possible using postabdominal claws; however, the process is arduous, and applicability will likely decrease with the number of taxa present.     

Assessing the range of newly established invasive species in rivers using probabilistic methods

Data on the presence of invasive species are often scarce, especially during the initial period following their introduction, when population abundance and species detectability are both still very low. In such cases, sporadic sightings in their newly occupied territory are often the only available information about their presence and distribution. Here, we demonstrate the potential of using probabilistic models for the assessment of the distribution of newly established invasive species in rivers, based on their sighting records. We have applied Solow’s equation to the sighting record of the Amur sleeper (Perccottus glenii) in the Danube River, to assess the probable range of its population. The method applied indicated that, at the time when the sightings have been made (2003–2008), the Amur sleeper population in the Danube most probably extended between the 704.5 and 1,178.5 river km, while it was highly improbable (P < 0.05) that it was present downstream from the 606 river km or upstream from the 1,277 river km. The application of this approach has, however, to be tested further on a larger number of scenarios and case studies in order to evaluate its reliability. What this method lacks in complexity, compared to more advanced species distribution assessments, it makes up by its ability to be easily used and quickly applied for preliminary assessments of the ranges of riverine species. As a result, the proposed approach might be of interest for scientists and managers dealing with invasive species.     

Success of the invasive Ponto-Caspian amphipod Dikerogammarus villosus by life history traits and reproductive capacity

Dikerogammarus villosus originates from the Ponto-Caspian basin. In the Austrian stretch of the River Danube it was not found before 1989, and not before 1992 in the Bavarian Danube. It very quickly spread to Germany, the Netherlands, and France via the so called “Southern Corridor”. The invader also migrates via the “Central Corridor”, reaching as far west as the Vistula River. The species has been reported from a number of lakes. Reasons for the quick spread and high abundance are, beside others, its life history traits. A population of this invasive species was studied from 2002 to 2004 in the Austrian stretch of the Danube. The following life-history traits are important in the invasion success: long reproductive period, early sexual maturity, short generation time, a life span not exceeding 1 year (up to three generations and 14 cohorts being present at the same time), high growth rates resulting in large body size, short duration of embryonic development, large numbers of comparatively small eggs in the brood pouch, large reproductive capacity, and optimal timing to release the maximum number of neonates per female in May/June (maximising rapid growth at high summer temperatures and at times of plentiful food), increasing mating privilege for large specimens of both sexes with decreasing water temperatures during winter. These life cycle characteristics together with its predatory behaviour and its ability to cope with variation in oxygen, temperature and salinity, give this invader a potential to become distributed in freshwater ecosystems of the temperate climate zone all over the world. Additionally, several indications seem to prove the tendency that biological invasion and global warming have a positive feed-back on each other. This combined scenario is a huge threat to the indigenous aquatic fauna, and might contribute to bio-monotony.     

Site heteroplasmy in the mitochondrial cytochrome b gene of the sterlet sturgeon Acipenser ruthenus

Sturgeons are fish species with a complex biology. They are also characterized by complex aspects including polyploidization and easiness of hybridization. As with most of the Ponto-Caspian sturgeons, the populations of Acipenser ruthenus from the Danube have declined drastically during the last decades. This is the first report on mitochondrial point heteroplasmy in the cytochrome b gene of this species. The 1141 bp sequence of the cytb gene in wild sterlet sturgeon individuals from the Lower Danube was determined, and site heteroplasmy evidenced in three of the 30 specimens collected. Two nucleotide sequences were identified in these heteroplasmic individuals. The majority of the heteroplasmic sites are synonymous and do not modify the sequence of amino acids in cytochrome B protein. To date, several cases of point heteroplasmy have been reported in animals, mostly due to paternal leakage of mtDNA. The presence of specific point heteroplasmic sites might be interesting for a possible correlation with genetically distinct groups in the Danube River.     

Vemakylindrus cantabricus, a new species of Diastylidae (Crustacea, Cumacea) from the northern Iberian coasts

Eleven species of the genusVemakylindrus Bacescu, 1961 are known at present. A hitherto unknown species is described herein asV. cantabricus, sp. nov., and is compared with the more closely related congeneric species:V. hastatus (Hansen, 1920) andV. stebbingi Day, 1980.Vemakylindrus cantabricus may be distinguished from its congeners by a combination of the following characters: (1) carapace densely covered by hooked denticles and hairs; (2) pseudorostrum shorter than carapace; (3) telson of “Diastylis type” with 5–6 pairs of lateral spines; and (4) external process of basis of third maxilliped with 4 long plumose setae.     

The denticle surface of thresher shark tails: Three-dimensional structure and comparison to other pelagic species

Shark skin denticles (scales) are diverse in morphology both among species and across the body of single individuals, although the function of this diversity is poorly understood. The extremely elongate and highly flexible tail of thresher sharks provides an opportunity to characterize gradients in denticle surface characteristics along the length of the tail and assess correlations between denticle morphology and tail kinematics. We measured denticle morphology on the caudal fin of three mature and two embryo common thresher sharks (Alopias vulpinus), and we compared thresher tail denticles to those of eleven other shark species. Using surface profilometry, we quantified 3D-denticle patterning and texture along the tail of threshers (27 regions in adults, and 16 regions in embryos). We report that tails of thresher embryos have a membrane that covers the denticles and reduces surface roughness. In mature thresher tails, surfaces have an average roughness of 5.6 μm which is smoother than some other pelagic shark species, but similar in roughness to blacktip, porbeagle, and bonnethead shark tails. There is no gradient down the tail in roughness for the middle or trailing edge regions and hence no correlation with kinematic amplitude or inferred magnitude of flow separation along the tail during locomotion. Along the length of the tail there is a leading-to-trailing-edge gradient with larger leading edge denticles that lack ridges (average roughness = 9.6 μm), and smaller trailing edge denticles with 5 ridges (average roughness = 5.7 μm). Thresher shark tails have many missing denticles visible as gaps in the surface, and we present evidence that these denticles are being replaced by new denticles that emerge from the skin below.     

Genetic analysis of the position of meiosis in <Emphasis Type="Italic">Porphyra haitanensis</Emphasis> Chang et Zheng (Bangiales,Rhodophyta)

Crossing experiments were carried out between artificial pigmentation mutants and the wild type in Porphyra haitanensis Chang et Zheng to ascertain where meiosis occurs in its life history by confirming whether the color segregation and the color-sectored blades appear in F₁ gametophytic blades developed from conchospores which are released from heterozygous conchocelis. Two red-type pigmentation mutants (R-10 and SPY-1) were used as the female parent. Their blades are red or red orange in color, thinner than the wild type and weak in elasticity, and have no denticles on their margins. The wild type (W) was used as the male parent; its blades are light brown in color, thick and good in elasticity, and have many marginal denticles. The F₁ gametophytic blades developed from conchospores which were released from heterozygous conchocelis produced in the crosses of R-10(♀)×W(♂) and SPY-1(♀)×W(♂) showed two parental colors (R and W) and two new colors (R', lighter in color than R; W', wild-type-like color and redder than W). Linear segregation of colors occurred in the F₁ blades, forming color-sectored blades with 2–4 sectors. In the color-sectored blades, R and R' sectors were thinner than W and W' sectors, and had weak elasticity and no denticles on their margins, whereas W and W' sectors were thick and had good elasticity and many marginal denticles. Of the F₁ gametophytic blades, 95.2–96.7% were color-sectored and only 3.3–4.8% were unsectored. These results indicate that meiosis of P. haitanensis occurs during the first two cell divisions of a germinating conchospore, and thus it is considered that the initial four cells of a developing conchosporeling constitute a linear genetic tetrad leading to the formation of a color-sectored blade. The new colors of R' and W' were recombinant colors due to the chromosome recombination during the first cell division in meiosis. It is considered that color phenotypes of the two mutants used in this paper were result of two (or more) recessive mutations in different genes, and that they also have mutations concerned with blade thickness and formation of marginal denticles, which are linked with the color mutations.     

15. Three Rumanian Mallomonas species (Synurophyceae), with special distribution patterns

Mallomonas is the largest genus of the Synurophyceae (chrysophytes) and includes more than 120 species. Most of them are cosmopolitan, living in freshwater habitats. The Rumanian taxa occur usually in spring or early summer at water temperatures ranging between 4 ° and 10 °C. They are most frequent in neutral or slightly acid, clear-watered, aquatic habitats of various types. However, Mallomonas paludosa Fott appears mostly in brown watered peatbog pools of low mineral contents, having a particular geographical area, with its southernmost limit in the Rumanian Eastern Carpathians. Its distribution, like that of other boreal elements, is strictly connected with the occurrence of genuine ombrogenic Sphagnum-bogs, which have their southern limit also in Romania. The other two species dealt with — M. cyathellata Wujek & Asmund and M. portae-ferreae Péterfi & Asmund —, occurring in circumneutral or moderately alkaline waters of eutrophic character, are apparently warm water forms, mostly distributed in tropical, subtropical or mediterranean zones. The Rumanian localities (in the Danube Delta and at Eşelniţa near the Danube, up stream Drobeta Turnu-Severin) might be the northern limits of M. portae-ferreae in Eastern Europe. The Danube Delta is the only locality of M. cyathellata in Europe, and its northernmost occurrence as well. The occurrence of both species in Rumania is presumably due to migratory waterfowl.     

Past and current status of sturgeons in the upper and middle Danube River

Of the six species of sturgeons native to the Danube basin, five occurred in the upper and middle Danube. Among anadromous sturgeons were the large winter races of beluga, Huso huso, Russian sturgeon, Acipenser gueldenstaedtii, and stellate sturgeon, A. stellatus, which ascended the middle, and sometimes also the upper Danube, to spawn. Due to overfishing, followed by severe habitat alteration including damming and pollution, these anadromous sturgeons are critically endangered or extirpated from the upper and middle Danube. Acipenser gueldenstaedtii and A. nudiventris are represented only as resident non-migratory races with very small populations. The most abundant and widely distributed species is the sterlet, A. ruthenus, although it is presently limited to the middle Danube. Its population increased in some sections of the middle Danube during the past 15 years, presumably because of improving water quality, but this species remains at risk because of continuing habitat degradation.     

Historic speciation and recent colonization of Eurasian monkey gobies (Neogobius fluviatilis and N. pallasi) revealed by DNA sequences,microsatellites, and morphology

Aim Hidden diversity within an invasive ‘species’ can mask both invasion pathways and confound management goals. We assessed taxonomic status and population structure of the monkey goby Neogobius fluviatilis across Eurasia, comparing genetic variation across its native and invasive ranges. Location Native populations were analysed within the Black and Caspian Sea basins, including major river drainages (Dnieper, Dniester, Danube, Don and Volga rivers), along with introduced locations within the upper Danube and Vistula river systems. Methods DNA sequences and 10 nuclear microsatellite loci were analysed to test genetic diversity and divergence patterns of native and introduced populations; phylogenetic analysis of mtDNA cytochrome b and nuclear RAG‐1 sequences assessed taxonomic status of Black and Caspian Sea lineages. Multivariate analysis of morphology was used to corroborate phylogenetic patterns. Population genetic structure within each basin was evaluated with mtDNA and microsatellite data using F_ST analogues and Bayesian assignment tests. Results Phylogenetic analysis of mitochondrial and nuclear sequences discerned a pronounced genetic break between monkey gobies in the Black and Caspian Seas, indicating a long‐term species‐level separation dating to c. 3 million years. This pronounced separation further was confirmed from morphological and population genetic divergence. Bayesian inference showed congruent patterns of population structure within the Black Sea basin. Introduced populations in the Danube and Vistula River basins traced to north‐west Black Sea origins, a genetic expansion pattern matching that of other introduced Ponto‐Caspian gobiids. Main conclusions Both genetic and morphological data strongly supported two species of monkey gobies that were formerly identified as subspecies: N. fluviatilis in the Black Sea basin, Don and Volga Rivers, and the Kumo‐Manych Depression, and Neogobius pallasi in the Caspian Sea and Volga River delta. Genetic origins of introduced N. fluviatilis populations indicated a common invasion pathway shared with other introduced Ponto‐Caspian fishes and invertebrates.