Population genetic relationships reveal the signatures of current processes such as reproductive behaviour and migration, as well as historic events including vicariance and climate change. We analyse population structure of native walleye Sander vitreus across North America, encompassing 10 nuclear DNA microsatellite loci, 26 spawning sites and 921 samples from watersheds across the Great Lakes, Lake Winnipeg, upper Mississippi River, Ohio River and Mobile Bay of the Gulf Coast. Geographical patterning is assessed using phylogenetic trees, pairwise F(ST) analogues, hierarchical partitioning, Mantel regression, Bayesian assignment and Monmonier geographical networks. Results reveal congruent divergences among population groups, corresponding to historic isolation in glacial refugia, dispersal patterns and basin divisions. Broad-scale relationships show genetic isolation with geographical distance, but reproductive groups within basins do not -- with some having pronounced differences. Greatest divergence distinguishes outlying Gulf Coastal and northwest populations, the latter tracing to dispersal from the Missourian refugium to former glacial Lake Agassiz, and basin isolation approximately 7000 ya. Genetic barriers in the Great Lakes separate groups in Lakes Superior, Huron's Georgian Bay, Erie and Ontario, reflecting contributions from Mississippian and Atlantic refugia, and changes in connectivity patterns. Walleye genetic patterns thus reflect vicariance among watersheds and glacial refugia, followed by re-colonization pathways and changing drainage connections that established modern-day northern populations, whose separations are maintained through spawning site fidelity. Conservation management practices should preserve genetic identity and unique characters among these divergent walleye populations.

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We compared the decomposition of sediment-associated litter of Typha angustifolia in 2 Lake Erie coastal wetlands, examining the effects of sedimentation on microbial biomass, production and litter decay dynamics. Experimental manipulations of sediment had no statistically significant effect (p > 0.05) on microbial biomass or metabolism. However, unforeseen differences between wetland sites (i.e. permanently inundated vs. exposed) had a major influence on microbial colonization and growth, litter mass loss, and nutrient dynamics. Litter-associated bacterial biomass and production were greater at the inundated site vs. the exposed wetland site (e.g. 487 vs. 158 µg C g -1 detrital C after 146 d, respectively). In contrast, fungal biomass and production were greater at the exposed site (e.g. 125 vs. 56 mg C g -1 detrital C after 146 d, respectively). Microbial degradative enzymes involved in the acquisition of phosphorus, nitrogen and carbon followed similar patterns as observed for fungal biomass and production, with higher activities associated with decaying litter at the exposed site. Microbial respiration rates were initially similar at both sites, but increased at the inundated site towards the end of the study period. Despite greater litter-associated microbial biomass, production and enzyme activities at the exposed wetland site, rates of litter mass loss were similar, suggesting that the greater metabolic potential of microbiota at the exposed site may have been offset by environmental conditions (e.g. fluctuations in water availability). Although mass loss rates were similar, significant differences in nutrient dynamics were observed, with higher N and P associated with higher litter-associated microbial biomass. These results illustrate how microbial decay dynamics can potentially interact with environmental variables (e.g. water availability) to modulate the carbon and nutrient dynamics of a litter resource that dominates many wetlands.

The parasitic fauna in the lower Volga River basin was investigated for four gobiid species: the nonindigenous monkey goby Neogobius fluviatilis (Pallas, 1814), the round goby N. melanostomus (Pallas, 1814), the Caspian bighead goby Ponticola gorlap (Iljin, 1949), and the tubenose goby Proterorhinus cf. semipellucidus (Kessler, 1877). In total, 19 species of goby parasites were identified, of which two - Bothriocephalus opsariichthydis Yamaguti, 1934 and Nicolla skrjabini (Iwanitzki, 1928) - appeared to have been introduced from other geographic regions. The monkey goby had significantly fewer parasitic species (6), but relatively high levels of infection, in comparison to the native species. Parasitism of the Caspian bighead goby, which is the only predatory fish among the studied gobies, differed from the others according to the results of discriminant analysis. The parasitic fauna of the tubenose goby more closely resembled those of Caspian Sea gobiids, rather than the Black Sea monkey goby.