ИСТИНА

After invading a vertebrate host, the parasite imposes its energetic demands on the host, forcing it to reallocate its energy resources between the immune response and other life-history traits reducing its fitness. The opposite energetic consequences of infestation of the organism with Plasmodium (Haemosporida) can be expected: an increase of the metabolic rate due to the cost of the immune response or its decrease because of the destruction of the erythrocytes by hemoparasite. The degree of changes in metabolic rate may also depend on the duration of host-parasite coevolution. In our study, we infected two groups of juvenile Siskins Spinus spinus: one with locally transmitted Plasmodium relictum (lineage SGS1), and the other with an African P. ashfordi (GRW2). We used flow-through respirometry to estimate resting metabolic rate (RMR) of infected siskins. One week after infection, the RMR of all experimental birds decreased. However, by the next measurement, there was a sharp increase in RMR followed by a further slight increase, which continued until the end of the experiment. Birds from the group infected with P. ashfordi had a higher RMR compared to birds from the P. relictum group. Birds with an initially high RMR tended to reduce it, while individuals with a low initial RMR tended to increase it. It seems that a malarial parasite, new to the host, causes the mobilization of energy resources in naïve birds, which may lead to rapid depletion and even death. This work was supported by the Russian Science Foundation (20-14-00049).