Relationship between preferred temperature, metabolic rate and lipopolysaccharides of gram-negative bacteria (LPS) immune challenge in Rhinella icterica (Anura: Bufonidae)

Anfíbios tem a habilidade de manifestar febre comportamental em ambientes heterotermais durante infecção a um custo metabólico associado à elevação da temperatura corpórea e à ativação do sistema imune. Apesar do custo metabólico, a temperatura corpórea febril otimiza a resposta imune no combate à infecção e aumenta as chances de sobrevivência do indivíduo. Contudo, devido à limitada capacidade de termorregular, os anfíbios enfrentam variações diárias e sazonais na temperatura corpórea e na resposta metabólica de reação à infecção. O nosso objetivo foi medir a variação da resposta metabólica à infecção dentro da variação de temperaturas ecológicas relevantes do sapo Cururu. Testamos a hipótese de que a infecção aumenta as taxas metabólicas do sapo Cururu, mas o custo energético da resposta imune deve ser menor na temperatura febril dos sapos infectados. Para testarmos as hipóteses, nós medimos a temperatura operacional dos sapos no campo, a preferencia termal dos sapos hígidos e a temperatura preferencial dos sapos infectados. Depois, medimos a taxa metabólica e a resposta metabólica dos sapos antes e depois da infecção por LPS nessas temperaturas. Nossos resultados mostraram que as temperaturas ecológicas relevantes dos sapos variaram entre 17°C e 26°C. A temperatura influenciou a taxa metabólica dos sapos, mas só na temperatura preferencial dos sapos hígidos houve custo metabólico associado à infecção. Contudo, na temperatura corpórea dos sapos infectados a resposta metabólica de reação à infecção foi menor, indicando que o controle regulado no ponto de ajustes \"set-point\" da temperatura corpórea durante a infecção coevoluiu com um custo energético otimizado da resposta imuneAnphibians have the ability of manifested behavioral fever in heterothermal environments during infection with a metabolic cost associated to elevated body temperature set-point and due to activation of immune system. Despite the metabolic cost, fever body temperature optimizes immune response to combat infection and increase the survival of the host. However, because of the limited capacity for thermoregulation, amphibians can confront daily and seasonal variation in body temperature and in the metabolic response of reaction to combat infection. So, we measured the variation in metabolic response of reaction to infection at ecology relevant body temperature range in Cururu toads. We hypothesized that infection increases metabolic rates of the Cururu toads due to the activation of the immune system at different temperatures, but the energetic cost of immune response is lower at preferred body temperature of infected toads (behavioral fever). To test these hypotheses we measured the operative body temperature in the field, the preferred body temperature of higid toads, and the preferred body temperature of infected toads. After, we measured metabolic rate and metabolic response of the toads before and after injection of LPS at these temperatures. Our results showed that the ecology relevant temperature range of Cururu toads (R. icterica) varies between 17°C and 26°C, respectively, at operative temperature and at preferred body temperature in infected toads when exposed to heterothermal environment. The temperature had the major impact on metabolic rate of the toads during infection. But, at fever body temperature toads decrease the metabolic response of reaction to infection, indicating that the regulated control of body temperature set-point during infection coevolved with an optimized energetic cost of immune respons