The invasive bighead goby Ponticola kessleri displays large-scale genetic similarities and small-scale genetic differentiation in relation to shipping patterns.

Colonization events, range expansions and species invasions leave genetic signatures in the genomes of invasive organisms and produce intricate special patterns. Predictions have been made as to how those patterns arise, but only very rarely, genetic processes can be monitored in real time during range expansions. In an attempt to change that, we track a very recently established invasive population of a fish species, the bighead goby Ponticola kessleri, with high temporal and spatial resolution through 2 years to identify patterns over time. We then compare Swiss and German samples of bighead goby along the river Rhine using microsatellites, mitochondrial D-loop sequences and geometric morphometrics to investigate geographic patterns. We detect weak temporal and strong geographic patterns in the data, which are inconsistent with isolation by distance and indicate long range transport. In search of an explanation for our observations, we analyse the vector properties and travel patterns of commercial vessels on the river Rhine. We present evidence that freshwater cargo ships and tankers are plausible vectors for larvae of invasive goby species. We also present indications that cargo ships and tankers act as differential vectors for this species. In summary, we present genetic data at unique temporal resolution from a vertebrate invasion front and substantiate the paramount role of commercial shipping in freshwater fish translocations.

Genetically distinct colour morphs of European perch Perca fluviatilis in Lake Constance differ in susceptibility to macroparasites.

The unusual yellow-finned morph of European perch Perca fluviatilis found in Lake Constance suffers more severely from macroparasite infections, including the tapeworm Triaenophorus nodulosus and the gill worm Ancyrocephalus percae, than conspecifics elsewhere. Microsatellite analysis of yellow-finned P. fluviatilis and red-finned variant recently discovered in Lake Constance revealed significant genetic differentiation. Red-finned P. fluviatilis and fish with mixed fin colour, suggested backcrosses between red and yellow-finned colour morphs, exhibit better resilience to parasite infection, suggesting that the inability of the yellow-finned morph to reject macroparasites may have a genetic basis.

Multiple isotope analyses of the pike tapeworm Triaenophorus nodulosus reveal peculiarities in consumer-diet discrimination patterns.

Previous studies of dietary isotope discrimination have led to the general expectation that a consumer will exhibit enriched stable isotope levels relative to its diet. Parasite-host systems are specific consumer-diet pairs in which the consumer (parasite) feeds exclusively on one dietary source: host tissue. However, the small numbers of studies previously carried out on isotopic discrimination in parasite-host (ΔXP-HT) systems have yielded controversial results, showing some parasites to be isotopically depleted relative to their food source, while others are enriched or in equilibrium with their hosts. Although the mechanism for these deviations from expectations remains to be understood, possible influences of specific feeding niche or selection for only a few nutritional components by the parasite are discussed. ΔXP-HT for multiple isotopes (δ13C, δ15N, δ34S) were measured in the pike tapeworm Triaenophorus nodulosus and two of its life-cycle fish hosts, perch Perca fluviatilis and pike Esox lucius, within which T. nodulosus occupies different feeding locations. Variability in the value of ΔXP-HT calculated for the parasite and its different hosts indicates an influence of feeding location on isotopic discrimination. In perch liver ΔXP-HT was relatively more negative for all three stable isotopes. In pike gut ΔXP-HT was more positive for δ13C, as expected in conventional consumer-diet systems. For parasites feeding on pike gut, however, the δ15N and δ34S isotope values were comparable with those of the host. We discuss potential causes of these deviations from expectations, including the effect of specific parasite feeding niches, and conclude that ΔXP-HT should be critically evaluated for trophic interactions between parasite and host before general patterns are assumed.

Postglacial colonization shows evidence for sympatric population splitting of Eurasian perch (Perca fluviatilis L) in Lake Constance.

Previous microsatellite analysis showed that two subpopulations of perch (Perca fluviatilis L) exist in Lake Constance. This raises questions of whether (i). Lake Constance was colonized by two populations that diverged in allopatry, or (ii). the two subpopulations diverged in sympatry. Sequence analysis of a 365 bp mtDNA fragment (5'-end of the D-loop) of perch from Lake Constance and adjacent waters revealed 10 haplotypes. We suggest colonization via the Danube river, based on the frequency and dispersion of haplotypes, and knowledge of the lake's palaeohydrological development. Pairwise FST-values using mitochondrial DNA sequences showed no significant population subdivision. Our study provides strong evidence that subpopulations of perch in Lake Constance have diverged in sympatry.