Balaton Limnological Institute

Functional trait divergence underpins many biological invasions, yet its role in native- invasive fish interactions remains poorly understood. Invasive species significantly threaten the native biodiversity by disrupting the functional structure of aquatic communities. The widespread expansion of the invasive gibel carp ( Carassius gibelio ) throughout the European freshwater systems has potentially led to notable decline of the native crucian carp ( Carassius carassius ), yet the specific functional trait mechanisms driving this shift remains unclear. To address this unexplored aspect, we aimed to study the detailed morphometric measurements with a standardized functional trait approach to in order to understand whether divergence in the key morpho- functional ecological traits gives the invasive gibel carp a competitive edge. Samples for both native crucian carp and invasive gibel carp were collected across five sympatric pond systems in Czech Republic, wherein we quantified fourteen morpho-functional traits related to feeding and locomotion in both the species. Our analysis revealed that gibel carp consistently exhibited higher gut length ratios and larger oral gape surfaces than crucian carp, reflecting broader digestive capabilities and an increased ability to exploit diverse food resources, particularly plant and detrital material. Gibel carp also displayed significantly hightened values for the fin morphological traits, including pectoral fin aspect ratio and fin surface to body size ratio, suggesting enhanced maneuverability and habitat access. On the other hand, certain traits such as eye position and body shape showed substantial overlap between the two Carassius species, indicating convergence in certain ecological functions. The observed divergence in feeding and locomotory traits under sympatric conditions indicates that the invasion success of gibel carp is closely associated with increased trophic flexibility and resource acquisition. These functional trait advantages likely underpin rapid population growth and heightened competitive pressure on the native crucian carp population, which continues to decline in the invaded habitats. Our findings therefore, underscore the importance of trait-based analysis for elucidating the ecological processes underlying invasion and highlight the urgent need for targeted conservation actions to protect the critically endangered native crucian carp population.

The fauna of Lake Hévíz is unique due to its status as the world's only natural warm-water medicinal lake with a peat bed. A population of dwarf common carp (Cyprinus carpio carpio morpha hungaricus) forms an isolated, self-sustaining community in the lake, adapted to extreme thermal and chemical conditions. During continuous research conducted since 2007, we identified a hermaphroditic individual for the first-time following sampling during the winter period in 2024. Macroscopic examination revealed testicular tissue distinguishable from ovarian tissue. Histological analysis indicated that the small-bodied fish were in a pre-spawning phase, with gonads displaying traits of simultaneous hermaphroditism. In addition was capable of producing mature eggs and sperm concurrently. According to both literature and our experimental findings, this individual may have been capable of self-fertilization. Further investigation is required to ascertain whether specific or combined suboptimal environmental factors and/or endocrine-disrupting chemicals contributed to the emergence of hermaphroditism in this individual.

Snake genomes attract significant attention from multiple disciplines, including medicine, drug bioprospection, and evolutionary biology. However, genomic research within the Viperidae family has mostly focused on the subfamily Crotalinae, while the true vipers (Viperinae) have largely been overlooked. European vipers (Vipera) have been the subject of extensive research due to their phylogeographic and ecological diversification, as well as their venoms. Nevertheless, phylogeography and systematics in this genus have primarily relied on biased information from mitochondrial genes, which fail to capture the likely effects of introgression and are prone to biases. On the other hand, venom research in this group has been conducted predominantly through proteomics alone. In this study, we generated chromosome-level genome assemblies for three Vipera species and whole-genome sequencing data for 94 samples representing 15 Vipera lineages. This comprehensive dataset allowed us to disentangle the phylogenomic relationships of this genus, affected by mito-nuclear discordance and pervaded by ancestral introgression. Population-level analyses in the Iberian Peninsula, where the three oldest lineages within Vipera meet, revealed signals of recent adaptive introgression between old-diverged and ecologically dissimilar species, whereas chromosomal rearrangements isolate species occupying similar niches. Finally, using transcriptomic and proteomic data, we characterised the Vipera toxin-encoding genes, in which opposing selective forces were unveiled as common drivers of the evolution of venom as an integrated phenotype.

In this study, we present an updated checklist of alien fish species occurring in Hungarian natural waters. In addition, by analyzing the taxonomic, original range, and spatio-temporal occurrence data of the species in question, we also present current invasion trends and distribution patterns. For the database compilation, we used literature reports, validated occurrence data published by non-research contributors (e.g., anglers), and our own unpublished faunistic data. The occurrence of species shows an exponentially increasing trend, with 89 out of the 130 registered species and hybrids appeared in the last 24 years. Most of the new species are thermophilic aquarium species, belonging to the orders Cichliformes (39%) and Siluriformes (29%). Recently, five species from the Anabantiformes order have emerged, posing a significant threat to the native fish fauna of Hungary. Spatial data analysis indicates that the most important introduction hotspots are currently found in some thermal habitats (mostly spa outflows), especially in the capital of Hungary (Budapest), and Lake Hévíz. Due to ongoing global warming, heat-impacted stream and river stretches may serve as starting points for new invasions in the near future. This assumption is supported by the recent distribution of toothcarps (Cyprinodontiformes), as their acclimatized stocks released from warmwater habitats are likely to overwinter in temperate water bodies as well.

Anxiety, a behavioral consequence of stress, has been characterized in humans and some vertebrates but remains largely unexplored in invertebrates. Here, we demonstrate that after being exposed to fish water, which simulates the presence of predators, pond snails (Lymnaea stagnalis) exhibit a series of sustained fear responses. These include increased aerial respiration, changes in righting behavior, and reduced escape responses. Notably, these behaviors persist even after the stressor (fish water) is removed, indicating that they likely represent an anxiety-like state rather than a simple conditioned reflex. Additionally, exposure to fish water enhances long-term memory formation for the operant conditioning of aerial respiration, suggesting that the predator scent potentially induces a state of heightened alertness, which enhances memory consolidation processes. Furthermore, when snails experience fish water alongside an appetitive stimulus (carrot), they form configural learning—a higher form of learning – where the appetitive stimulus now triggers a fear response instead of eliciting feeding. Importantly, the anxiolytic drug alprazolam prevents these anxiety-like responses. Through dose-response experiments, we found that alprazolam at a concentration of 0.1 µM for 15 min effectively counteracts predator-induced anxiety without causing sedation. This treatment also prevents the effects of predator cues on learning and memory. However, consistent with data from vertebrates - alprazolam induces anterograde amnesia, impairing the formation of new memories for up to 3 h after treatment, though it does not cause long-term memory deficits. Overall, this is the first study showing that a molluscan model organism exhibits anxiety-like behaviors similar to those seen in vertebrates, and these behaviors can be mitigated by an anti-anxiety drug. This suggests that fundamental anxiety mechanisms are evolutionarily conserved across species. By using this simple invertebrate model, our research offers new insights into the biological basis of anxiety and sets the stage for future pharmacological studies.

The degradation of freshwater ecosystems due to land use changes is one of the major driver of global biodiversity loss and amphibian declines with these impacts varying across different spatial scales. Our study aimed to assess how natural and human-modified land affects smooth newt (Lissotriton vulgaris) abundance in the surrounding waterbodies of Lake Balaton, a highly urbanized area. We conducted aquatic trap surveys at 32 wetland sites during the breeding season and quantified land cover within 250, 500, and 1000-m radius buffer zones. We hypothesized that urban land use, cropland, and proximity to roads and railways would negatively correlate with newt abundance, while wetlands areas (marshes, swamps, periodically flooded grasslands) and natural terrestrial habitats (grasslands, forests and woodlands) would positively correlate, with effects varying across spatial scales. N-mixture models were used to analyse survey data, estimating abundance and examining relationships with covariates. Results revealed that wetland cover within a 500-m buffer zone increased newt abundance, probably due to supporting metapopulation connectivity. In contrast, cropland cover within 250 m and proximity to roads and railways negatively affected newt abundance. Conservation efforts should prioritize providing smooth newts with adequate breeding habitats and reducing disturbances from croplands, roads, and railways.

Microplastic contamination in freshwater systems poses serious ecological risks, yet the role of particle size in shaping these impacts remains underexplored. This study investigates the influence of microplastic size on bioturbation activities of Chironomus riparius larvae, a process essential for sediment dynamics and nutrient cycling. Employing luminophore sediment profile imaging (LSPI), we tracked the vertical distribution of polyethylene particles within sediment layers, focusing on two distinct size ranges: small (53-63μm) and large (250-300μm) spherical particles. Microplastics (MPs) were introduced at a 0.076% sediment ratio to reflect natural exposure scenarios. Initial findings reveal that both particle sizes undergo downward transport, though with different patterns. Notably, smaller particles demonstrated a more pronounced effect on larval behaviour, appearing frequently in digestive tracts and suggesting increased bioavailability. Temporal analysis showed distinct reworking dynamics for each particle size, with larger particles exhibiting a delayed reworking time compared to the smaller particles. This highlights the critical influence of particle size on the fate and behaviour of MPs in freshwater systems, with smaller particles potentially posing a greater ecological risk due to their quicker and more active incorporation into sedimentary processes. This study provides critical insights into size-specific interactions between MPs and freshwater organisms, enhancing our understanding of their impacts on ecosystem health and sedimentary processes.

Drying river networks include non-perennial reaches that cease to flow or dry, and drying is becoming more prevalent with ongoing climate change. Biodiversity responses to drying have been explored mostly at local scales in a few regions, such as Europe and North America, limiting our ability to predict future global scenarios of freshwater biodiversity. Locally, drying acts as a strong environmental filter that selects for species with adaptations promoting resistance or resilience to desiccation, thus reducing aquatic α-diversity. At the river network scale, drying generates complex mosaics of dry and wet habitats, shaping metacommunities driven by both environmental and dispersal processes. By repeatedly resetting community succession, drying can enhance β-diversity in space and time. To investigate the transferability of these concepts across continents, we compiled and analyzed a unique dataset of 43 aquatic invertebrate metacommunities from drying river networks in Europe and South America. In Europe, α-diversity was consistently lower in non-perennial than perennial reaches, whereas this pattern was not evident in South America. Concomitantly, β-diversity was higher in non-perennial reaches than in perennial ones in Europe but not in South America. In general, β-diversity was predominantly driven by turnover rather than nestedness. Dispersal was the main driver of metacommunity dynamics, challenging prevailing views in river science that environmental filtering is the primary process shaping aquatic metacommunities. Lastly, α-diversity decreased as drying duration increased, but this was not consistent across Europe. Overall, drying had continent-specific effects, suggesting limited transferability of knowledge accumulated from North America and Europe to other biogeographic regions. As climate change intensifies, river drying is increasing, and our results underscore the importance of studying its effects across different regions. The importance of dispersal also suggests that management efforts should seek to enhance connectivity between reaches to effectively monitor, restore and conserve freshwater biodiversity.

Although angler’s groundbaits (GBs) can be an important food resource for fish, we do not know much about the effects of GB consumption on the growth and health of fish. To fill this knowledge gap, we conducted a controlled, six-week long feeding trial (feeding ration: 2% of body weight) with common carp at 22 °C (Cyprinus carpio, mean initial body weight: 557 g) to test the effect of two GBs composed mostly of animal-derived ingredients (AN-GBs) and two plant-based GBs (PL-GBs) relative to one aquaculture feed, as a control (five treatment altogether). Consumption of PL-GBs resulted in lower growth rate than AN-GBs, presumably due to the low protein content. However, the unit biomass increment per unit nitrogen input was higher in PL-GBs. Although PL-GBs resulted in reduction of hepatic energy reserves, hepatosomatic index, viscerosomatic index, and body condition did not differ among the treatments. We did not find differences in expression of inflammatory cytokines in the liver. In conclusion, AN-GBs more effectively increases the carrying capacity of fisheries, but fish sequester a higher portion of nitrogen content of PL-GBs –PL-GB input can be more effectively counterbalanced by fish removal. Finally, the GB consumption does not pose a health risk to fish.