Thermal regimes effects over stress indicators in rattlesnakes, Crotalus durissus (Serpentes: Viperidae)
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Data
2018-10-26
Autores
Fabrício Neto, Ailton [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Animais ectotérmicos têm suas funções fisiológicas fortemente influenciadas pela temperatura. Por exemplo, taxas metabólicas e de crescimento destes animais podem ser afetadas pela temperatura corpórea. Estudos com foco na medição de taxas metabólicas em serpentes, por exemplo, geralmente são realizados através da submissão dos animais a regimes constantes de temperatura. No entanto, ectotérmicos (serpentes inclusas) são conhecidos por apresentarem variações amplas de sua temperatura corpórea ao longo do ciclo circadiano. Esta discordância entre biologia termal e condições experimentais poderia funcionar como um potencial agente estressor para os ectotérmicos, o que poderia comprometer os resultados e interpretações de estudos, pois um aumento nos níveis de glucocorticóides pode afetar diversos atributos de vertebrados, como taxas metabólicas e resposta imune. O presente estudo testou os efeitos de diferentes regimes térmicos, constante e flutuante, ao longo do ciclo circadiano sobre indicadores de estresse em cascavéis (Crotalus durissus). Para tanto, um grupo de animais foi exposto ao tratamento constante-flutuante, composto por um regime constante de temperatura (30°C) seguido por um flutuante (25°C, 1800 às 0600h; 35°C, 0600h às 1800h, média de 30°C); o segundo grupo foi submetido ao tratamento flutuante-constante, composto por um regime flutuante e, após, o constante. Os animais foram expostos aos tratamentos por um período de 24 dias, sendo que no 12° dia ocorreu a mudança de regime termal. Efetuamos coletas de sangue nos dias 2, 10, 14 e 22 para medição da taxa heterófilo:linfócito (H:L), capacidade bactericida do plasma (CBP) e níveis plasmáticos de corticosterona (CORT). A mudança entre o regime termal constante e o flutuante agiu como um agente estressor para as serpentes, causando um aumento nos níveis plasmáticos de CORT. A exposição a um regime flutuante no início do experimento causou uma diminuição na CBP das cascavéis que persistiu por todo o experimento, e machos também apresentaram maior CBP do que fêmeas. H:L não foi afetada por nenhuma das variáveis independentes, portanto é possível que a mudança entre regimes termais agiu como um estressor de baixa intensidade. Nossos resultados demonstram que mudanças agudas em regimes termais podem causar uma resposta ao estresse em serpentes, mesmo após longos tempos de manutenção em cativeiro.
Ectothermic animals have their physiological functions closely related to temperature. For example, metabolic and growth rates of these animals may be affected by body temperature. Studies focusing on the measurement of metabolic rates in snakes, for example, are usually performed by subjecting animals to constant temperature regimes. However, ectotherms (snakes included) are known to exhibit wide variations in their body temperature throughout the circadian cycle. This disagreement between thermal biology and experimental conditions could act as a potential stressor agent for ectotherms. The present study tested the effects of different thermal regimes, constant and fluctuating, throughout the circadian cycle on stress indicators in rattlesnakes (Crotalus durissus). A group of animals was exposed to the constant-to-fluctuating treatment, composed by a constant temperature regime (30°C) followed by a fluctuating regime (25°C, 1800 to 0600h, 35°C, 0600h to 1800h, mean 30°C); the second group was subjected to the fluctuating-to-constant treatment, composed of a fluctuating regime and, after, the constant. The animals were exposed to the treatments for a period of 24 days, and on the 12th day the change of thermal regime occurred. We collected blood samples on days 2, 10, 14 and 22 to measure heterophil:lymphocyte ratio (H:L), plasma bacteria killing ability (BKA) and corticosterone plasmatic levels (CORT). The shift between constant and fluctuating thermal regime acted as an acute stressor for snakes, promoting an increase in plasma CORT levels. Exposure to a fluctuating thermal regime at the onset of the experiment induced a decrease in the BKA of rattlesnakes that persists for the whole experiment, and males also present higher levels of BKA than females. H:L was not affected by any of the treatments, therefore it is possible to postulate that the shift between constant and fluctuating thermal regimes acted as a low intensity stressor. Our results highlight that acute shifts in thermal regimes can promote a stress response in snakes, even after long times of maintenance in captivity.
Ectothermic animals have their physiological functions closely related to temperature. For example, metabolic and growth rates of these animals may be affected by body temperature. Studies focusing on the measurement of metabolic rates in snakes, for example, are usually performed by subjecting animals to constant temperature regimes. However, ectotherms (snakes included) are known to exhibit wide variations in their body temperature throughout the circadian cycle. This disagreement between thermal biology and experimental conditions could act as a potential stressor agent for ectotherms. The present study tested the effects of different thermal regimes, constant and fluctuating, throughout the circadian cycle on stress indicators in rattlesnakes (Crotalus durissus). A group of animals was exposed to the constant-to-fluctuating treatment, composed by a constant temperature regime (30°C) followed by a fluctuating regime (25°C, 1800 to 0600h, 35°C, 0600h to 1800h, mean 30°C); the second group was subjected to the fluctuating-to-constant treatment, composed of a fluctuating regime and, after, the constant. The animals were exposed to the treatments for a period of 24 days, and on the 12th day the change of thermal regime occurred. We collected blood samples on days 2, 10, 14 and 22 to measure heterophil:lymphocyte ratio (H:L), plasma bacteria killing ability (BKA) and corticosterone plasmatic levels (CORT). The shift between constant and fluctuating thermal regime acted as an acute stressor for snakes, promoting an increase in plasma CORT levels. Exposure to a fluctuating thermal regime at the onset of the experiment induced a decrease in the BKA of rattlesnakes that persists for the whole experiment, and males also present higher levels of BKA than females. H:L was not affected by any of the treatments, therefore it is possible to postulate that the shift between constant and fluctuating thermal regimes acted as a low intensity stressor. Our results highlight that acute shifts in thermal regimes can promote a stress response in snakes, even after long times of maintenance in captivity.
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Palavras-chave
Snakes, Ectothermic, Circadian cycle, Corticosterone, Innate immunity, Serpentes, Ectotérmicos, Ciclo circadiano, Corticosterona, Imunidade inata