What doesn’t kill you doesn’t make you stronger: Parasites modify interference competition between two invasive amphipods

We used a freshwater amphipod-microsporidian model (Ponto-Caspian hosts: Dikerogammarus villosus and D. haemobaphes, parasite: Cucumispora dikerogammari) to check whether parasites affect biological invasions by modulating behaviour and intra- and interspecific interactions between the invaders. We tested competition for shelter in conspecific and heterospecific male pairs (one or both individuals infected or non-infected). In general, amphipods of both species increased their shelter occupancy time when accompanied by infected rather than non-infected conspecifics and heterospecifics. Infected amphipods faced lower aggression from non-infected conspecifics. Moreover, D. villosus was more aggressive than D. haemobaphes and more aggressive towards conspecifics vs. heterospecifics. In summary, infection reduced the intra- and interspecific competitivity of amphipods, which became less capable of defending their shelters, despite their unchanged need for shelter occupancy. Dikerogammarus haemobaphes, commonly considered as a weaker competitor, displaced by D. villosus from co-occupied locations, was able to compete efficiently for the shelter with D. villosus when microsporidian infections appeared on the scene. This suggests that parasites may be important mediators of biological invasions, facilitating the existence of large intra- and interspecific assemblages of invasive alien amphipods.

Mitochondrial Genomes, Phylogenetic Associations, and SNP Recovery for the Key Invasive Ponto-Caspian Amphipods in Europe

The Ponto-Caspian region is the main donor of invasive amphipods to freshwater ecosystems, with at least 13 species successfully established in European inland waters. Dikerogammarus spp. and Pontogammarus robustoides are among the most successful, due to their strong invasive impact on local biota. However, genomic knowledge about these invaders is scarce, while phylogeography and population genetics have been based on short fragments of mitochondrial markers or nuclear microsatellites. In this study, we provide: (i) a reconstruction of six mitogenomes for four invasive gammarids (D. villosus, D. haemobaphes, D. bispinosus, and P. robustoides); (ii) a comparison between the structure of the newly obtained mitogenomes and those from the literature; (iii) SNP calling rates for individual D. villosus and D. haemobaphes from different invasion sites across Europe; and (iv) the first time-calibrated full mitogenome phylogeny reconstruction of several Ponto-Caspian taxa. We found that, in comparison to other gammarids, the mitogenomes of Ponto-Caspian species show a translocation between the tRNA-E and tRNA-R positions. Phylogenetic reconstruction using the mitogenomes identified that Ponto-Caspian gammarids form a well-supported group that originated in the Miocene. Our study supports paraphyly in the family Gammaridae. These provided mitogenomes will serve as vital genetic resources for the development of new markers for PCR-based identification methods and demographic studies.

FEATURES OF THE SPATIAL DISTRIBUTION OF INVASIVE SPECIES OF AMPHIPODS IN THE LITTORAL OF LAKE LADOGA

The modern distribution of invasive amphipods of Baikal ( Gmelinoides fasciatus (Stebbing, 1899) , Micruropus possolskii Sowinsky, 1915) and Ponto-Caspian origin ( Pontogammarus robustoides Sars, 1894 , Chelicorophium curvispinum (Sars, 1895)) in Lake Ladoga was shown. The heterogeneity of the distribution of quantitative indicators of amphipods in different parts of the lake was established. The most widespread species in the littoral zone was G. fasciatus . A decrease in the contribution of G. fasciatus in the bottom communities of macrozoobenthos was noted. The dominant role of G. fasciatus was observed only in those parts of the lake where other species of invasive amphipods did not penetrated yet. The habitat of Ponto-Caspian amphipods is limited by the boundaries of the Volkhov Bay. A significant increase in the quantitative development of P. robustoides and active dispersal of M. possolskii to the South along the west coast of the lake indicate the ongoing structural restructuring of littoral biocenoses.

Superior predatory ability and abundance predicts potential ecological impact towards early-stage anurans by invasive ‘Killer Shrimp’ (Dikerogammarus villosus)

Invasive alien species negatively impact upon biodiversity and generate significant economic costs worldwide. Globally, amphibians have suffered considerable losses, with a key driver being predation by large invasive invertebrate and vertebrate predators. However, there is no research regarding the potential ecological impact of small invertebrate invaders. The invasive freshwater amphipod Dikerogammarus villosus can act as a top predator capable of displacing native amphipods and preying heavily upon a range of native species. Listed as one of Europe’s top 100 worst invaders, D. villosus has significantly restructured freshwater communities across western Europe and is expected to invade North America in the near future. Here we explore the ecological impact of invasive D. villosus upon UK native and invasive amphibians (Rana temporaria and Xenopus laevis respectively) using the “Relative Impact Potential” (RIP) metric. By combining estimations of per capita effects (i.e. functional response; FR) and relative field abundances, we apply the RIP metric to quantify the potential ecological impact of invasive D. villosus upon embryonic and larval amphibian prey, compared to the native amphipod Gammarus pulex. Both native and invasive amphipods consumed early-stage amphibians and exhibited potentially destabilising Type II FRs. However, larger body size in invasive D. villosus translated into a superior FR through significantly lower handling times and subsequently higher maximum feeding rates—up to seven times greater than native G. pulex. Higher invader abundance also drove elevated RIP scores for invasive D. villosus, with potential impact scores predicted up to 15.4 times greater than native G. pulex. Overall, D. villosus is predicted to have a greater predatory impact upon amphibian populations than G. pulex, due primarily to its larger body size and superior field abundance, potentially reducing amphibian recruitment within invaded regions.

The longitudinal pattern of crustacean (Peracarida, Malacostraca) assemblages in a large south European river: bank reinforcement structures as stepping stones of invasion

The spread of alien crustaceans has significantly contributed to the homogenization of macroinvertebrate fauna of European freshwaters. However, little is known about alien Peracarida crustaceans of the Sava River, which represents the most important corridor for the spread of invasive species into Dinaric rivers with highly endemic fauna. In this study, we investigated Peracarida (Amphipoda, Isopoda and Mysida) collected during three years (2011, 2012 and 2015) from a total of 61 sites along the entire course of the Sava River. Besides describing the longitudinal pattern of Peracarida assemblages, we tested the hypothesis that bank reinforcement structures facilitate peracarid invasions by comparing densities and assemblages on natural and artificial substrate at 15 sites. In a total, 14 peracarid crustacean species (5 native and 9 alien) were recorded. The Upper third of Sava was inhabited by native peracarids only, while the Middle and Lower Sava were dominated by alien species. The invasive amphipods Dikerogammarus haemobaphes, Chelicorophium sowinskyi and Chelicorophium curvispinum, and invasive isopod, Jaera istri, were the most abundant species along the middle course. Densities of alien peracarids in the Middle Sava were the highest and their share in macroinvertebrate assemblages was very variable, while the Lower Sava had the highest number of alien species in low densities. The densities of alien amphipods and isopods were in most cases significantly higher on bank reinforcement structures than on natural substrate. Therefore, artificial stony substrates act as stepping stones of invasion for alien peracarids and largely contribute to their success in large lowland rivers.