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Activation of immune response has been long assumed to be an energy-costly process but direct measures of changes in metabolic rate after eliciting immune response disputes the universality of this assertion. The acute phase response (APR) is the first line of defense of the vertebrate immune system against pathogens and is thought to be energetically costly. Measures of APR energetic cost in birds are higher than in rodents suggesting that this response is less expensive and important for mammals. However, large increase in metabolic rate after APR activation measured in a piscivorous bat species (Myotis vivesi) suggests that immune response is unusually costly for bats. Here we quantified the energetic cost and body mass change associated with APR in the nectarivorous Pallas’s long-tongued bat Glossophaga soricina and compared with values previously measured for piscivorous bats and other vertebrates. APR activation implied an energy cost for G. soricina as indicated by a short-term decrease in body mass and an increase in resting metabolic rate (RMR). However, the increase in RMR was far from the large increase detected in piscivorous bats and it was similar to the highest values measured in birds. Caloric cost of APR represented only 2% of the total daily energy expenditure estimated for G. soricina. Overall our results suggest that the costs of APR for bats may vary interespecifically probably in relation to feeding habits. Measurement of the energy cost of vertebrate immune response is limited to a few species and further work is warranted to evaluate its significance for the animal´s energy budget.
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Metabolic rate and body mass after immune response activation of Glossophaga socirina
Resting metabolic rate and body mass in bats injected with LPS and with PBS.