Genomic footprints of a biological invasion: Introduction from Asia and dispersal in Europe of the topmouth gudgeon (Pseudorasbora parva)

Spatio-temporal variation in reproductive characteristics of invasive fish Pseudorasbora parva (Temmick & Schlegel, 1846) in the lakes region of Türkiye

Invasive species present a serious peril to aquatic ecosystems worldwide, thus it is essential to have a comprehensive understanding of the reproductive dynamics, spreading characteristics, and biological properties of these species in order to effectively manage their population structure and mitigate both the ecological damage and economic loss they can cause. For this reason, we delved into the reproductive dynamics of Pseudorasbora parva, an invasive species of inland water fish found in Türkiye. We focused on three populations inhabiting Beyşehir (Konya, Isparta) and Eğirdir Lakes (Isparta) and Onaç Reservoir (Burdur). Sampling was carried out on a monthly basis from March 2021 to June 2022, utilizing a variety of tools such as multimesh nets, seine nets, and electrofishing. The developmental stages of gonads and reproductive cells were determined through morphological and microscopic examinations. A total of 1186 P. parva individuals were captured from all three lakes. Our results showed that the Beyşehir Lake population spawned from March to July, while the Eğirdir Lake population did so between May and October, and the Onaç Reservoir population laid their eggs from June to August. Female individuals in Beyşehir Lake, Eğirdir Lake, and Onaç Reservoir had initial breeding lengths of 3.49, 4.89, and 5.35 cm, respectively. In comparison, male individuals measured 5.56, 4.80, and 5.40 cm. Interestingly, the Beyşehir Lake population exhibited the highest egg fecundity, with each individual at 2 years producing a remarkable 2949 eggs. The present findings provide valuable information for us to further understand the reproductive biology and dynamics of P. parva, which could be useful in managing and preventing the spread of this invasive species in inland aquatic ecosystems.

Freshwater fish in mid and northern German rivers - Long-term trends and associated species traits

To understand biodiversity change and support conservation decision-making, estimates of species' long-term population trends at regional and national scales are essential. However, such estimates are missing for many freshwater taxa, despite the diverse range of threats that they face. For this study, we mobilised monitoring data on riverine freshwater fish abundance collected across different regions of Germany. We applied generalized mixed effect models to estimate the population trends for 55 native species and 11 non-native species between 2004 and 2020. In addition, we used boosted regression trees to identify trait-based predictors of species trends and assessed their predictive ability. We found evidence of increasing abundance trends for 14 species and decreasing trends for 15 species; while the remaining species were mostly stable (26 species). Native species were more typically decreasing than increasing (14 vs 10 species); while non-native species were more often increasing (4 vs 1 species). Important traits associated with trends were maximum length, spawning temperature, and water quality tolerance, with small species, those spawning at high temperatures, and those preferring unpolluted waters, being most likely to have positive trends. Despite these associations, overall trait-based models showed limited power to predict trends in terms of direction as well as magnitude. Our results highlight the ongoing change in riverine fish communities and the importance of on-going species-level monitoring. The trait-based associations also indicate climate change and invasive species as important drivers of change in European freshwater rivers.

Contrasting population genetic responses to migration barriers in two native and an invasive freshwater fish

Habitat fragmentation impacts the distribution of genetic diversity and population genetic structure. Therefore, protecting the evolutionary potential of species, especially in the context of the current rate of human-induced environmental change, is an important goal. In riverine ecosystems, migration barriers affect the genetic structure of native species, while also influencing the spread of invasive species. In this study, we compare genetic patterns of two native and one highly invasive riverine fish species in a Belgian river basin, namely the native three-spined stickleback (Gasterosteus aculeatus) and stone loach (Barbatula barbatula), and the non-native and invasive topmouth gudgeon (Pseudorasbora parva). We aimed to characterize both natural and anthropogenic determinants of genetic diversity and population genetic connectivity. Genetic diversity was highest in topmouth gudgeon, followed by stone loach and three-spined stickleback. The correlation between downstream distance and genetic diversity, a pattern often observed in riverine systems, was only marginally significant in stone loach and three-spined stickleback, while genetic diversity strongly declined with increasing number of barriers in topmouth gudgeon. An Isolation-By-Distance pattern characterizes the population genetic structure of each species. Population differentiation was only associated with migration barriers in the invasive topmouth gudgeon, while genetic composition of all species seemed at least partially determined by the presence of migration barriers. Among the six barrier types considered (watermills, sluices, tunnels, weirs, riverbed obstructions, and others), the presence of watermills was the strongest driver of genetic structure and composition. Our results indicate that conservation and restoration actions, focusing on conserving genetic patterns, cannot be generalized across species. Moreover, measures might target either on restoring connectivity, while risking a rapid spread of the invasive topmouth gudgeon, or not restoring connectivity, while risking native species extinction in upstream populations.

Environmental correlates of genetic variation in the invasive European starling in North America

Populations of invasive species that colonize and spread in novel environments may differentiate both through demographic processes and local selection. European starlings (Sturnus vulgaris) were introduced to New York in 1890 and subsequently spread throughout North America, becoming one of the most widespread and numerous bird species on the continent. Genome-wide comparisons across starling individuals and populations can identify demographic and/or selective factors that facilitated this rapid and successful expansion. We investigated patterns of genomic diversity and differentiation using reduced-representation genome sequencing of 17 winter-season sampling sites. Consistent with this species' high dispersal rate and rapid expansion history, we found low geographical differentiation and few F_ST outliers even at a continental scale. Despite starting from a founding population of ~180 individuals, North American starlings show only a moderate genetic bottleneck, and models suggest a dramatic increase in effective population size since introduction. In genotype-environment associations we found that ~200 single-nucleotide polymorphisms are correlated with temperature and/or precipitation against a background of negligible genome- and range-wide divergence. Given this evidence, we suggest that local adaptation in North American starlings may have evolved rapidly even in this wide-ranging and evolutionarily young system. This survey of genomic signatures of expansion in North American starlings is the most comprehensive to date and complements ongoing studies of world-wide local adaptation in these highly dispersive and invasive birds.

Genomic footprints of a biological invasion: Introduction from Asia and dispersal in Europe of the topmouth gudgeon (Pseudorasbora parva)

Facilitated by the intensification of global trading, the introduction and dispersal of species to areas in which they are historically non-native is nowadays common. From an evolutionary standpoint, invasions are paradoxical: not only non-native environments could be different from native ones for which introduced individuals would be ill-adapted, but also small founding population size should be associated with reduced adaptive potential. As such, biological invasions are considered valuable real-time evolutionary experiments. Here, we investigated the population structure and adaptive potential of the highly invasive topmouth gudgeon (Pseudorasbora parva) across Europe and East Asia. We RAD-sequenced 301 specimens from sixteen populations and three distinct within-catchment invaded regions as well as two locations in the native range. With 13,785 single nucleotide polymorphisms, we provide conclusive evidence for a genome-wide signature of two distinct invasion events, in Slovakia and Turkey, each originating from a specific area in the native range. A third invaded area, in France, appears to be the result of dispersal within the invasive range. Few loci showed signs of selection, the vast majority of which being identified in the Slovakian region. Functional annotation suggests that faster early stage development, resistance to pollution and immunocompetence contribute to the invasion success of the local habitats. By showing that populations in the invasive range have different evolutionary histories, our study reinforces the idea that populations, rather than species, are the units to consider in invasion biology.