Evolutionary Ecology of Health in Asian Elephants

The definition of health is complex, involving the maintenance of a delicate balance between different physiological processes within an organism. The understanding of life-history traits and ecological factors affecting health in wild animal populations is still limited, especially in long-lived mammals. Here I investigated life-history traits and ecological factors affecting health in a semi-captive population of Asian elephants (Elephas maximus) from Myanmar. My study system is comprised of working timber elephants, employed by a government-owned company, the Myanma Timber Enterprise (MTE). These elephants are classified as semi-captive: they are managed during the day but free to roam in their natural habitat during the night without human supervision. I collected health measures from the elephants for a period of three years that encompass longitudinal quantification of several body systems and functions. Life-history data for these animals were obtained from detailed logbooks that are maintained for each individual from birth to death. My study first established reference intervals for several health parameters, describing for the first time in Asian elephants both body condition score (BCS) outside of zoos and blood pressure, and reinforced the importance of evaluating health separately for males and females (Chapter 2, Franco dos Santos et al., in press). In chapter 3 I observed a decline in health with age, both at the individual health parameter and global health levels, providing an example of senescence in this long-lived mammal. Chapter 4 shows how elephant health is affected by ecological variation across different seasons of the year, driven mainly by rainfall and food quality/quantity fluctuations (Chapter 4). Finally, Chapter 5 quantified the risk parasites pose for their host health, especially in heavily parasitized animals, driven mainly by immune system activation (Chapter 5). These results improve our knowledge of health variation in wild populations, and have implications for the management and conservation strategies of this endangered species.