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.

SPREAD RATE OF ALIEN AMPHIPODS AND MYSIDS IN THE MAIN RIVERS OF BELARUS

The spread rates of alien species of Amphipoda and Mysida were calculated for the Dnieper, Pripyat and Neman rivers in the territory of Belarus. The maximal values of spread rate were obtained for Dikerogammarus villosus (in the Pripyat River - 37.8 km/year, in the Dnieper River - 17 km/year) and Dikerogammarus haemobaphes (in the Pripyat River - 53.6 km/year, in the Dnieper River - 17 km/year), while the minimal values of spread rate were calculated for mysids Paramysis lacustris (in the Dnieper River - 0.4 km/year) and Limnomysis benedeni (in the Dnieper River - 0.6 km/year), also for amphipods Chelicorophium robustum (in the Dnieper River - 0.5 km/year) and Echinogammarus trichiatus (in the Dnieper River - 1.3 km/year). The differences in the spread rates of species connected with the time of their first records at the monitoring points and the intensity of economic activities in the studied rivers.

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.

Ontogenetic shift in the trophic role of the invasive killer shrimp Dikerogammarus villosus: a stable isotope study

The introduction of the amphipod Dikerogammarus villosus in European fresh waters is to date recognized as a threat to the integrity of invaded communities. Predation by D. villosus on native benthic invertebrates is assumed as the key determinant of its ecological impact, yet available information describe the species as a primary consumer as well as a carnivore depending on local conditions. Here, we assessed the trophic position (TP) of D. villosus in Lake Trasimeno, a recently invaded lentic system in central Italy, using the CN isotopic signatures of individuals captured in winter spanning two orders of magnitude in body size. TP estimations were compared with those characterizing the native amphipod Echinogammarus veneris and other representative invertebrate predators. On average, D. villosus showed a trophic position higher than E. veneris, and comparable with that of odonate nymphs. An in-depth analysis revealed that large-sized individuals had a trophic position of 3.07, higher than odonates and close to that of the hirudinean predator Erpobdella octoculata, while small-sized specimens had a trophic position of 2.57, similar to that of E. veneris (2.41). These findings indicate that size-related ontogenetic shifts in dietary habits may per se vary the nature of the interaction between Dikerogammarus villosus and native invertebrates from competition to predation. Information collated from published isotopic studies corroborated the generality of our results. We conclude that intra-specific trophic flexibility may potentially amplify and make more multifaceted the impact of the species on other invertebrate species in invaded food webs.

Pilferer, murderer of innocents or prey? The potential impact of killer shrimp (Dikerogammarus villosus) on crayfish

Freshwater ecosystems worldwide are facing the establishment of non-native species, which, in certain cases, exhibit invasive characteristics. The impacts of invaders on native communities are often detrimental, yet, the number and spread of non-native invasive species is increasing. This is resulting in novel and often unexpected combinations of non-native and native species in natural communities. While the impact of invaders on native species is increasingly well-documented, the interactions of non-native invaders with other non-native invaders are less studied. We assessed the potential of an invasive amphipod, the killer shrimp Dikerogammarus villosus (Sowinsky, 1894), to cope with other established invaders in European waters: North American crayfish of the Astacidae family—represented by signal crayfish Pacifastacus leniusculus (Dana, 1852), and the Cambaridae family—represented by marbled crayfish Procambarus virginalis Lyko, 2017. The main goal of this study was to investigate if killer shrimp, besides their role as prey of crayfish, can significantly influence their stocks by predating upon their eggs, hatchlings and free-moving early juveniles. Our results confirmed that killer shrimp can predate on crayfish eggs and hatchlings even directly from females abdomens where they are incubated and protected. As marbled crayfish have smaller and thinner egg shells as well as smaller juveniles than signal crayfish, they were more predated upon by killer shrimp than were signal crayfish. These results confirmed that the invasive killer shrimp can feed on different developmental stages of larger freshwater crustaceans and possibly other aquatic organisms.

Genotoxic effects induced by glyphosate-based herbicide on two gammarid species: the invasive Dikerogammarus villosus (Sowinsky, 1894) (Crustacea, Amphipoda) and the native Echinogammarus veneris (Heller, 1865)

Freshwater communities all over the world suffer from anthropogenic stresses such as pesticide contamination. This stress acts as a selective force, inducing alteration in both the composition of species and their relative abundances. In the present work, we tested the genotoxic effect of the glyphosate-based herbicide Roundup® on two freshwater gammarid species. The tests were carried out on the native Echinogammarus veneris, and the invasive alien species, Dikerogammarus villosus. The latter is native to the Ponto-Caspian region and has now spread to many large European aquatic ecosystems. It has displaced native gammarids and is considered one of the most disruptive alien species in Europe. The genotoxic effect of Roundup® was measured by DNA fragmentation re- vealed by comet assay, after either 24 hours or 7 days of exposure. The results obtained demonstrate the genotoxic potential of Roundup® on both species and highlight the higher tolerance of D. villosus to its genotoxic potential.