Host-Parasite Relations In Initiation Of Infection: I. Occurrence Of Listeriosis In Arctic Mammals,With A Note On Its Possible Pathogenesis

A lemming colony maintained at Fort Churchill was examined for the possibility of the presence of L. monocytogenes in latent form, but the organism was not isolated. Following transfer of the lemmings from Churchill to Kingston, L. monocytogens was isolated. In speculation on the pathogenesis of Listerosis, the author suggests that an upset carbohydrate metabolism may be involved in the trigger mechanism. The isolation of L. monocytogenes from a seemingly ill Arctic fox caught at Fort Churchill is reported for the first time.     

Notes On The Occurrence Of Clathrus Cancellatus,Tournf., In Argyllshire

Background: Estuaries are characterised by salinity gradients and regular flooding events. These environmental factors form stress gradients, along which species composition changes.

Aims: Analyse and compare patterns of plant species diversity along the estuarine salinity and flooding gradients of the Elbe and Connecticut Rivers.

Methods: Vegetation was sampled at three elevations (low, mid, high) in five sites of each marsh type (fresh, brackish, salt) in both estuaries. Patterns of species density (SD) and evenness (E) along the gradients were analysed and compared between the two estuaries with three-factor ANOVAs.

Results: The regional species pool was 33% higher for the Connecticut than for the Elbe. SD of fresh marshes (19 ± 2.2) was more than twice in the Connecticut than in the Elbe. We found an overall increase in SD from low to high elevation and from salt to freshwater marshes in both estuaries. However, SD and E were strongly depressed at intermediate elevations in the Elbe fresh and brackish marshes.

Conclusions: Although diversity patterns in the two estuaries show overall similarities, patterns of SD and E differ, when particular elevational zones and marsh types are compared. We hypothesise this to be due to evolutionary and historical influences on the regional species pools, shaping the impact of local biotic and abiotic processes.