Rheotaxis behavior of brown trout and grayling in the perspective of natural velocity variations

Fish rheotaxis, or alignment into flow currents, results from intertwined sensory, neural and actuation mechanisms, all coupled with hydrodynamics to produce a behaviour that is critical for upstream migration and position holding in oncoming flows. Among several sensory modalities, the lateral-line sensory system is thought to play a major role in the fish ability to sense minute water motions in their vicinity and, thus, in their rheotactic behaviour. Here, we propose a theoretical model consisting of a fishlike body equipped with lateral pressure sensors in oncoming uniform flows. We compute the optimal sensor locations that maximize the sensory output. Our results confirm recent experimental findings that correlate the layout of the lateral-line sensors with the distribution of hydrodynamic information at the fish surface. We then examine the behavioural response of the fishlike model as a function of its orientation and swimming speed relative to the background flow. Our working hypothesis is that fish respond to sensory information by adjusting their orientation according to the perceived difference in pressure. We find that, as in fish rheotaxis, the fishlike body responds by aligning into the oncoming flow. These findings may have significant implications on understanding the interplay between the sensory output and fish behaviour.

ABSTRACTAim Accumulating evidence indicates that species may be pre‐adapted for invasion success in new ranges. In the light of increasing global nutrient accumulation, an important candidate pre‐adaptation for invasiveness is the ability to grow in nutrient‐rich habitats. Therefore we tested whether globally invasive species originating from Central Europe have come from more productive rather than less productive habitats. A further important candidate pre‐adaptation for invasiveness is large niche width. Therefore, we also tested whether species able to grow across habitats with a wider range of productivity are more invasive.Location Global with respect to invasiveness, and Central European with respect to origin of study species.Methods We examined whether average habitat productivity and its width across habitats are significant predictors of the success of Central European species as aliens and as weeds elsewhere in the world based on data in the Global Compendium of Weeds. The two habitat productivity measures were derived from nutrient indicator values (after Ellenberg) of accompanying species present in vegetation records of the comprehensive Czech National Phytosociological Database. In the analyses, we accounted for phylogenetic relatedness among species and for size of the native distribution ranges.Results Species from more productive habitats and with a wider native habitat‐productivity niche in Central Europe have higher alien success elsewhere in the world. Weediness of species increased with mean habitat productivity. Niche width was also an important determinant of weediness for species with their main occurrence in nutrient‐poor habitats, but not for those from nutrient‐rich habitats.Main conclusions Our results indicate that Central European plant species from productive habitats and those species from nutrient‐poor habitat with wide productivity‐niche are pre‐adapted to become invasive. These results suggest that the world‐wide invasion success of many Central European species is likely to have been promoted by the global increase of resource‐rich habitats.

Introgressive hybridization is an important evolutionary process frequently contributing to diversification and speciation of angiosperms. Its extent in other groups of land plants has only rarely been studied, however. We therefore examined the levels of introgression in the genus Diphasiastrum, a taxonomically challenging group of Lycopodiophytes, using flow cytometry and numerical and geometric morphometric analyses. Patterns of morphological and cytological variation were evaluated in an extensive dataset of 561 individuals from 57 populations of six taxa from Central Europe, the region with the largest known taxonomic complexity. In addition, genome size values of 63 individuals from Northern Europe were acquired for comparative purposes. Within Central European populations, we detected a continuous pattern in both morphological variation and genome size (strongly correlated together) suggesting extensive levels of interspecific gene flow within this region, including several large hybrid swarm populations. The secondary character of habitats of Central European hybrid swarm populations suggests that man-made landscape changes might have enhanced unnatural contact of species, resulting in extensive hybridization within this area. On the contrary, a distinct pattern of genome size variation among individuals from other parts of Europe indicates that pure populations prevail outside Central Europe. All in all, introgressive hybridization among Diphasiastrum species in Central Europe represents a unique case of extensive interspecific gene flow among spore producing vascular plants that cause serious complications of taxa delimitation.

Unionid freshwater mussels need to attach to a host fish for completion of their life cycle. It remains unclear whether the relationship between these mussels and their host fishes can be considered parasitic, mutualistic, or commensal. Herein, we studied the effects of Margaritifera margaritifera infestation on Salmo trutta, the most important host of this endangered mussel species in Central Europe. Glochidial load of host fish increased with increasing glochidial concentration, but the highest ratios of encysted glochidia to exposed glochidia were found at low concentration (15,000 glochidia L(-1)) during infestation. Host fish mortality occurred at infestation rates of ~350 glochidia per g fish weight and was highest (60%) at the highest infestation rates (~900 glochidia per g fish weight). On a sublethal level, swimming performance of hosts was inversely related to infestation rates, with infestation of ~900 glochidia per g fish weight reducing critical swimming speed of S. trutta significantly by ~20% compared to infestation with 6 glochidia per g fish weight. The high mortality and the impaired swimming capability of highly infested hosts indicate a parasitic interaction between M. margaritifera and its host. For conservation and reintroduction of M. margaritifera via glochidia-infested S. trutta, we recommend glochidial loads of 5-100 glochidia per g fish weight, while for artificial breeding of juvenile M. margaritifera under laboratory conditions, higher infestation rates of up to 300 glochidia per g fish weight are ideal to balance high yields of mussels and welfare of host fishes.

Stipa capillata L. (Poaceae) is a rare grassland species in Central Europe that is thought to have once been widespread in post-glacial times. Such relict species are expected to show low genetic diversity within populations and high genetic differentiation between populations due to bottlenecks, long-term isolation and ongoing habitat fragmentation. These patterns should be particularly pronounced in selfing species. We analysed patterns of random amplified polymorphic DNA (RAPD) variation in the facultatively cleistogamous S. capillata to examine whether genetic diversity is associated with population size, and to draw initial conclusions on the migration history of this species in Central Europe. We analysed 31 S. capillata populations distributed in northeastern, central and western Germany, Switzerland and Slovakia. Estimates of genetic diversity at the population level were low and not related to population size. Among all populations, extraordinarily high levels of genetic differentiation (amova: phi(ST) = 0.86; Bayesian analysis: theta(B) = 0.758) and isolation-by-distance were detected. Hierarchical amova indicated that most of the variability was partitioned among geographic regions (59%), or among populations between regions when the genetically distinct Slovakian populations were excluded. These findings are supported by results of a multivariate ordination analysis. We also found two different groups in an UPGMA cluster analysis: one that contained the populations from Slovakia, and the other that combined the populations from Germany and Switzerland. Our findings imply that S. capillata is indeed a relict species that experienced strong bottlenecks in Central Europe, enhanced by isolation and selfing. Most likely, populations in Slovakia were not the main genetic source for the post-glacial colonization of Central Europe.

We investigated habitat use of wild brown trout Salmo trutta in Gilchrist Creek, Michigan, with and without a parallel cohort of introduced steelhead Oncorhynchus mykiss. This stream is typical of the region, having a low-gradient, stable discharge and a high sand bedload. By snorkeling, we evaluated seasonal habitat use in two stream reaches before and after steelhead introduction to one of the reaches. Age-0 brown trout occupied stream margins soon after emergence, using cover provided by aquatic vegetation growing on sand and silt substrates. By summer and fall, brown trout moved into deeper water and used more diverse cover types. From summer to fall, the smaller age-0 steelhead used lower current velocities than did age-0 brown trout. Similar water depth, substrate, and cover were used by the two species. At the densities studied, age-0 brown trout habitat use did not change in response to the presence of age-0 steelhead. We believe that three factors minimized the effect of steelhead: (1) the larger size of the brown trout, which gave them a competitive advantage; (2) vertical habitat segregation with steelhead suspended in the water column and brown trout near or at the bottom; and (3) temporal differences in habitat ontogeny with shifts of older, larger fish to deeper, faster water. These factors may permit these two species to coexist in low-gradient rivers.

The desaturation and elongation of [1- 14C]18:3n-3 was investigated in hepatocytes from different populations and three different species of salmonids indigenous to Scotland, brown trout, Atlantic salmon and Arctic charr. Two groups of fish were sampled, before and after they were fed two experimental diets, a control diet containing fish oil and a diet containing vegetable oil (a 1:1 blend of linseed and rapeseed oils) for 12 weeks. At each sampling time, fatty acyl desaturation and elongation activity was determined in isolated hepatocytes, and samples of liver were also collected for lipid compositional analysis. At the initiation of the dietary trial, the liver polar-lipid fatty acid compositions of salmon and brown trout were very similar to each other, and the two charr populations were similar to each other, having lower total n-3 polyunsaturated fatty acids (PUFA) and 22:6n-3, but higher 20:5n-3 than the other salmonids. Initially, hepatocyte desaturation activity varied, with the highest activity in brown trout, followed by salmon and then charr. Production of 20:5n-3 was particularly high in brown trout. Desaturation of [1- 14C]18:3n-3 was significantly greater in all fish fed the diet containing vegetable oil compared to fish fed the diet containing fish oil. The increase in activity was less in brown trout compared to the other groups of fish. Feeding the vegetable oil diet increased the levels of 18:2n-6, 20:3n-6, total n-6 PUFA, 18:3n-3, 18:4n-3, 20:3n-3 and 20:4n-3, and decreased 22:6n-3 and the n-3/n-6 ratio in salmon and brown trout. By contrast, in charr fed the vegetable oil diet, there was no increase in 18:3n-3, 18:4n-3, 20:3n-3 or 20:4n-3 in liver polar lipids and the level of 22:6n-3 was not decreased. In addition, there was only a modest increase in the levels of 18:2n-6 and total n-6 PUFA, and so the n-3/n-6 ratio was only slightly decreased. The percentage of 20:4n-6, which was not increased in salmon and brown trout fed vegetable oil, was increased in charr fed the vegetable oil diet. Overall, the results indicated that there were significant differences in liver PUFA metabolism between Arctic charr and the other salmonids, which could have important consequences, both physiologically and in their ability to be successfully cultured on diets containing vegetable oils.

The central aim of this paper is to clarify the picture of postglacial recolonisation and the reconstruction of refugia of Populus alba (L.) and Populus tremula (L.) in the light of hybridisation of the two species. We focussed our study on Central and Southeastern Europe including reference samples from Spain, Sweden and Northern Africa.We investigated 414 individuals of 26 populations using restriction fragment length polymorphisms (PCR-RFLPs) in six maternally inherited chloroplast markers. Altogether, 57 haplotypes were analysed of which four indicated hybridisation events in the past. Phylogeographic structure was found for P. alba with low diversity in Eastern Europe versus high diversity in Italy and Central Europe. A lack of phylogeographic structure was assessed for P. tremula as expected for a boreal forest tree, and diversity was evenly distributed in the studied populations. Two main refugia were identified for P. alba in Italy and Romania. A previously described hybrid zone between species in Central Europe turned out also to be a zone of contact between southern and eastern chloroplast lineages in P. alba. In contrast, P. tremula recolonised its present habitats in Central Europe from several refugia near the former ice cap. We assume separate disconnected refugia for P. alba and P. tremula and suggest an immigration scenario involving the mixing of colonisation routes and interspecific introgression to be responsible for the observed patterns.

An identification key to psychoactive bluing Psilocybe species growing on woody debris in Central Europe is presented. It is mainly based on microcharacters and includes 7 taxa (6 species and 1 variety) of the stirpes Serbica and Cyanescens (former “Psilocybe cyanescens complex“). Micro-, macroscopical, ecological and phenological characters and distribution of the taxa in Europe are presented and discussed.

The formation of dominance hierarchies within groups of salmonid fish is well documented and stream tanks are often used to create environmentally relevant conditions in which to study this aspect of fish behaviour. Although stream tanks simulate the natural environment of the fish in many ways, they have limitations in that they provide the fish with a rather predictable and constant habitat. The present study illustrates that under these constant conditions, the behaviour of fish in their natural environment may not be truly represented. Under constant conditions hierarchies were formed among groups of four brown trout, Salmo trutta, and the dominant fish displayed physiological advantages. However, when an environmental perturbation of increased water flow, simulating a spate, was imposed, the social behaviour of the fish was altered and the physiological advantages of dominance were lost. Clearly, environmental changes affect the behaviour, and consequently the physiology, of salmonid fish, therefore the importance of taking environmental disturbances into consideration in studies of salmonid behaviour should not be underestimated.

Gypsophila perfoliata (Caryophyllaceae) is a rare, only casually occurring species in Central Europe. Its native range spans from western Asian to the coast of the Black Sea. Several adventive occurrences of G. perfoliata were documented in Central Europe, especially in Germany where the naturalisation of the taxon occurred during the first decades of the 20th century. As a rare weed, it is suspected to have been introduced with iron ore from the former Soviet Union via railways (Kryvyi Rih region, now Ukraine). In this paper, we gathered information on the occurrence of G. perfoliata from its adventive range. These data indicate an ongoing and fast spread of the species across Central and Eastern Europe. For instance, prior to this study, G. perfoliata have two occurrence records from Hungary. Six new and recent records from Miskolc town and its surrounding areas are presented in this paper. The studied plant occurs in former industrial areas (steel factory, transshipment yards, external slag heaps) or along transport lines (esp. road verges, railway lines). We also describe 18 phytosociological relevés taken at the location of occurrences. All occurrences were documented on heavily modified anthroposols, where the populations flourish on bare ground (esp. road verges or parking areas) or on ground with admixture of metalliferous slag debris. With the help of available orthophotos the presumed land-use history of the locations has also been reconstructed. Based on data presented here we recommend modifying the species’ adventive status in Hungary from casual to naturalised. Further expansion of the species is expected not only 172 at industrial sites but also at locations where slag material was utilised (e.g. landfill, road and rail construction). Due to its halophyte characteristics the species might expand its range along roads where de-icing salt is used.

Temporary ponds are characterized as being in natural or close to natural states in Central and Eastern Europe, especially those located in forested landscapes. As these ponds function as breeding sites for many amphibians, they represent an ideal target to explore the terrestrial and aquatic habitat preferences of different species. We surveyed 133 small ponds in a forested, hilly region of North-Central Hungary. The occurrence of ten amphibian species and amphibian species richness were compared to six pond-related habitat variables and the extent of four terrestrial habitat types in the area surrounding the ponds. Our results suggest that most species’ occurrence and species richness are chiefly related to pond characteristics, although terrestrial habitat variables could also be a determining factor in particular species. Whereas the majority of amphibian species prefer larger, hence more permanent water bodies with abundant aquatic vegetation, the common frog (Rana temporaria) chooses small, shallow wallow pits for breeding and has special requirements concerning terrestrial habitat composition. This could explain its restricted distribution in the area. Our results suggest that maintaining a diverse set of ponds and forestry management which facilitates habitats’ structural heterogeneity are both important factors for the preservation of the rich amphibian fauna in Central Europe.

Leaf recognition of woody species in Central Europe

Sand flies are vectors of the protozoan Leishmania spp. and phleboviruses. In Europe, several species are widely distributed in the Mediterranean region and a northward spread can be observed. They can be found regularly also in some regions of Central Europe, with Phlebotomus mascittii being the most cold-tolerant and northerly distributed species, but the knowledge on their distribution in countries such as Germany, Austria, Czechia, Slovakia, and Hungary remains fragmentary because of a lack of comprehensive field studies and a poor understanding of the ecological requirements and phylogeographic history. A comprehensive literature review of sand fly occurrence in five Central European countries was complemented by entomological surveys, including sand fly and rodent screening for sand fly-borne pathogens. Nucleic acid extraction, COI barcoding, blood meal analysis, and phylogenetic and environmental analyses incorporating unsupervised machine learning techniques were conducted. This study significantly advances the understanding of the current distribution of six sand fly species in Central Europe. Among them, only Ph. mascittii was present in all analyzed countries, except Czechia, with its seasonal activity peaking in July. Phlebotomus papatasi, Ph. perfiliewi and Ph. neglectus were recorded in Hungary, while Ph. perniciosus and Phlebotomus simici were found in Germany and Austria, respectively. Although Leishmania DNA was absent in sand flies and rodents, DNA from two distinct Trypanosoma lineages was detected in several specimens, suggesting Ph. mascittii feeds on both birds and ruminants. Trypanosomatid lineages identified in local rodents differed, indicating distinct lineages between sand flies and rodents. Environmental analysis identified 15 Corine land cover classes associated with sand fly presence, with urban locations being the most frequently occupied. Linear regression models comparing presence versus absence revealed significantly higher sand fly presence in forested and urban landscapes. Furthermore, Ph. mascittii populations formed four distinct ecological clusters, which broadly grouped into two main geographic groups: one in the Upper Rhine Valley of southwestern Germany and the other spanning the Carpathian Basin. This study provides new insights into the current distribution, ecological preferences, seasonal activity, and potential vector capacity of sand fly species in Central Europe.

Higher susceptibility of beech to drought in comparison to oak