Stress and herpes infections in the frigatebird (Fregata magnificens): an experimental physiological approach
6 December 2018
Campus Drie Eiken, O.05 - Universiteitsplein 1 - 2610 Antwerpen-Wilrijk (route: UAntwerpen, Campus Drie Eiken
Organization / co-organization:
Department of Biology
M. Eens, D. Costantini & O. Chastel
PhD defence Manrico Sebastiano - Faculty of Science, Department of Biology
Pathogens represent a major selective force for animal populations. Wildlife infectious diseases also have enormous implications for the conservation status of many species. Indeed, one main question in conservation physiology addresses the proximate and ultimate factors that underlie the appearance of clinical signs of a disease in free-living animals. In this thesis we have used correlative and experimental approaches to investigate the causes and the consequences of an outbreak of a viral disease in a population of Magnificent frigatebird Fregata magnificens (hereafter frigatebirds).
The first goal of the work has been to determine the extent to which herpesvirus infections are linked to changes in organisms’ oxidative status. To this end, we have reviewed all available literature and used meta-analytical techniques to quantify the size of the effect of herpesvirus infection on oxidative stress and the potential protective role of antioxidants against herpesviruses.
We have then investigated the link between herpesvirus infection and oxidative status in frigatebird chicks in Grand Connétable island, the study area located in French Guiana. Given that other important endogenous pathways might be affected by the disease, we have also assessed the differences between healthy and sick chicks in stress hormones (corticosterone), inflammation, immunity, and telomere length.
We then aimed to experimentally manipulate the diet of frigatebird chicks. Administration of specific dietary molecules proved fundamental in animals exposed to viral diseases, but results of previous work arise from a limited number of domestic and laboratory species, while this topic remains poorly covered in free-living animals. We have therefore carried out two different experiments to increase: i) the intake of a specific antioxidant (i.e. resveratrol) with antiviral proprieties; ii) and food intake.
Exposure to environmental stressors may play an important negative role on the physiology of wild birds. These negative effects, however, are reliant on the duration of the exposure and the trophic level of the considered species. Therefore, we have investigated the exposure to both organic and inorganic pollutants and the stable isotope signature (which indicates the trophic level) of the six seabird species breeding in Grand Connétable island. The objective of this final part of the thesis was to identify pollutants that exceed the threshold for safety and essential trace elements that might be deficient in the chicks’ diet and thus play a role in the appearance of clinical signs in our population.
The results of this thesis point to oxidative stress as one of the main mechanisms that underlie viral activity and impact on health. Implicit in our discovery is the central role that dietary molecules may have in reducing the impact of a viral disease on the survival perspectives of free-living animals. As an example, sick chicks showed significantly higher levels of oxidative damage to lipids than healthy chicks, and the administration of resveratrol was able to buffer the deleterious effects that this viral infection has on the oxidative status of nestlings.
Our results from the food supplementation experiment also indicated that frigatebird chicks may be undergoing nutritional stress. Furthermore, although the levels of persistent organic pollutants occur at a low level in the seabirds breeding in the study area, we found mercury concentrations of concern.
Our results point to exposure to mercury and food shortage as the environmental stressors that might underlie the appearance of clinical signs in our population (e.g. through an impairment of their immune and oxidative statuses, which in turn facilitates herpes infections), although a causal link has not been proved.
Our work demonstrates that outbreaks of infectious diseases likely favoured by environmental changes can have devastating effects on free-living animal populations. Our work also provides the first evidence in a wild vertebrate that a shortage of antioxidants and/or food in the diet reduces the capacity of the organism to cope with a viral disease.