Spotted Seals, Phoca largha, in Alaska

The worldwide literature on management of spotted seals, Phoca largha, was reviewed and updated, and aerial surveys weref lown in 1992 and 1993 to determine the species' distribution and abundance in U.S. waters. In April, spotted seals were found only in the Bering Sea ice front. In June, they were seen along deteriorating ice floes and fast ice in Norton Sound. Surveys along most of Alaska's western coast in August and September found over 2,500 spotted seals in Kuskokwim Bay and concentrations of 100-400 seals around Nunivak Island, Scammon Bay, Golovnin Bay/Norton Sound, Cape Espenberg/Kotzebue Sound, and Kasegaluk Lagoon. All of these sites have been used by spotted seals in the past. The sum of the highest counts, irrespective of year, was 3,570 seals (CV =0.06). This is not an abundance estimate for all spotted seals in the Bering Sea, because it does not account for animals in the water, and we did not survey the Asian coast and some islands. Also, spotted seals and harbor seals, Phoca vitulina, are too similar in appearance to be identified accurately from the air, so our results probably include a mix of these species where their ranges overlap

Evolution of malaria virulence in cross-generation transmission through selective immune pressure

Theoretical arguments and some mathematical models of host-parasite coevolution (e.g. [1- 6]) suggest host immunity as the driving source for the evolution of parasite virulence. Imperfect vaccines in particular, can play the role and recent work [7] sets to test these ideas experimentally, using the mouse malaria model, Plasmodium chabaudi. To this end the authors evolve parasite lines in immunized and nonimmunized (“naïve”) mice using serial passage of infected blood samples. They find parasite lines evolved in immunized mice become more virulent than those evolved in naive mice. Furthermore, this feature persisted even when the evolved strains were transmitted through mosquitoes. 
Here we develop a mathematical model of parasite dynamics that qualitatively reproduces the experimental results of [7]. Our model accounts for the basic in-host processes: (i) production and depletion of red blood cells (RBC); (ii) immune-modulated parasite growth/ replication, (iii) immune stimulation and clearing of parasite. Besides we introduce multiple parasite strains with variable levels of virulence, and allow random mutations during replication process. The virulence is represented by a single parameter – immune stimulation threshold. So more virulent strains have higher “tolerance levels”, hence increased RBC depletion (anemia). 
Numeric simulations with our model exhibit, as in [7] the overall evolution of virulence in serial passage of parasite strains, and its enhancement through partial (imperfect) immunization