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Doctoral Thesis
DOI
https://doi.org/10.11606/T.41.2021.tde-14082021-155729
Document
Author
Full name
Adriana Maria Giorgi Barsotti
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 2021
Supervisor
Committee
Gomes, Fernando Ribeiro (President)
Andrade, Denis Otavio Vieira de
Carvalho, José Eduardo de
Fernandes, Pedro Augusto Carlos Magno
Title in Portuguese
Efeitos da desidratação sobre a secreção de glicocorticoides e a função imune em sapos
Keywords in Portuguese
1. Desidratação
2. Estresse
3. Corticosterona
4. Imunocompetência
5. Animais invasores
Abstract in Portuguese
A maior parte dos anfíbios apresenta alta permeabilidade hídrica e alto risco potencial de estresse hídrico. A desidratação pode representar um estressor, ativando o eixo hipotálamo- hipófise- adrenal/ interrenal (HHA/I), elevando a concentração plasmática de glicocorticoides (GC) e, consequentemente, modulando a resposta imune. Embora tenham clara implicação para o valor adaptativo, esses efeitos da desidratação sobre a imunocompetência permanecem pouco explorados na literatura, particularmente para anfíbios anuros. O objetivo dessa tese foi compreender o impacto da desidratação como estressor sobre aspectos da função imune inata em anfíbios anuros. Particularmente, foi investigado se indivíduos de Rhinella ornata, espécie de sapo associada a regiões mésicas e florestadas do Brasil, é capaz de ativar uma resposta de estresse quando desidratada, as consequências desse estresse hídrico sobre a imunocompetência e a capacidade de resposta a um estressor secundário. O impacto da desidratação como estressor sobre a função imune foi investigado também em populações nativas e invasoras do sapo Sclerophrys gutturalis da África do Sul, considerando-se as condições climáticas diferenciadas a que essas populações vivem. Brevemente, indivíduos foram submetidos à desidratação de 10% e 20% da massa corpórea padrão e tiveram amostra de sangue coletada para avaliar variáveis como a concentração plasmática de corticosterona (CORT), hematócrito (HCT), razão neutrófilo: linfócito (N:L), capacidade bactericida plasmática (CBP) e atividade fagocítica de leucócitos (AF). Em seguida, os animais foram submetidos à restrição de movimentos sob condições não-desidratantes (estressor secundário). Nossos resultados mostraram que a desidratação aumentou a CORT, HCT e N:L em sapos. O estresse de restrição secundário resultou em manutenção da concentração elevada de CORT no plasma e aumento da N:L e AF. Indivíduos de S. gutturalis da população invasora mostraram menor índice corpóreo, maior CBP e N:L em campo que indivíduos da população nativa. Após a submissão experimental aos estressores, sapos invasores e nativos mostraram aumento da CORT, e os invasores mantiveram CBP comparativamente maior que os nativos. Esses resultados indicam que a desidratação é um estressor para sapos, sendo capaz de ativar o eixo HHI, aumentando a secreção de CORT e estimulando a função imunitária. Adicionalmente, os sapos invasores apresentam uma função imune inata constitutivamente elevada se comparada à dos nativos, o que poderia aumentar seu valor adaptativo no novo ambiente e favorecer o sucesso de dispersão.
Title in English
Effects of dehydration on glucocorticoid secretion and immune function in toads
Keywords in English
1. Dehydration
2. Stress
3. Corticosterone
4. Immunocompetence
5. Invasive animals
Abstract in English
Among tetrapods, amphibians represent the group with the most permeable skin and the highest risk of water stress. Currently, it is known that dehydration can trigger a stress response in vertebrates, activating the hypothalamus-pituitary-adrenal/interrenal axis (HPA/I), increasing the levels of glucocorticoids (GC) and, consequently, modulating the immune response. Although they have a clear implication for the fitness, these effects of dehydration on immunocompetence remain little explored in the literature, particularly for anuran amphibians. The objective of this thesis was to understand the impact of dehydration as a stressor on aspects of innate immune function in anuran amphibians. Particularly, it was investigated whether individuals of Rhinella ornate, a species of toad associated with the mesic and forest regions of Brazil, is able to activate a stress response when dehydrated, the consequences of this water stress on immunocompetence and the ability to respond to a secondary stressor. The impact of dehydration as a stressor on immune function was also investigated in native and invasive populations of the toad Sclerophrys gutturalis in South Africa, considering the different climatic conditions in which these populations live. Briefly, individuals were subjected to dehydration of 10% and 20% of standard body mass and had a blood sample collected to assess variables such as plasma corticosterone concentration (CORT), hematocrit (HCT), neutrophil: lymphocyte ratio (N:L), bacterial killing ability (BKA) and phagocytic activity of leukocytes (PP). Then, the animals were submitted to movement restriction under non-dehydrating conditions (secondary stressor). Our results showed that dehydration increased CORT, HCT and N:L in toads. Secondary restriction stress resulted in the maintenance of a high plasma CORT concentration and an increase in N:L and PP. Individuals of S. gutturalis from the invasive population showed lower body index, higher BKA and N:L in the field than individuals from the native population. After experimental submission to stressors, invasive and native toads showed an increase in CORT, and the invaders maintained BKA comparatively higher than the native ones. These results indicate that dehydration is a stressor for toads, being able to activate the HHI axis, increasing the secretion of CORT and stimulating immune function. In addition, invasive toads have a constitutively high innate immune function compared to that of natives, which could increase their fitness in the new environment and favor the success of dispersion.
 
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Release Date
2023-08-14
Publishing Date
2021-09-10
 
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