During this fellowship, I conducted work using demographic, molecular and physiological data on Asian elephants in Myanmar. I contributed to strengthen the world’s largest studbook on elephants, by collecting, for each individual, data on date, place of birth/death, age, filiation, and origin. This represents the most comprehensive demographic data for any elephant population worldwide. I also collected physical measures (body weight, size, body condition), health and disease records, as well as blood and feacal samples to measure a range of molecular and physiological data. Blood samples were used to measure oxidative stress and telomere dynamics; faecal samples were used to assess parasites load and cortisol levels. While, thanks to our collaboration with the Chiang Mai University, measures of the levels of endocrinological stress and of parasites intensities were already optimized; I had to establish protocols to measure oxidative stress in elephants, to extract DNA, and to optimize qPCR telomere assays for elephant samples. Completion of these analyses is expected within the coming months.
The demographic data collected allowed me to determine factors influencing senescence patterns in the elephant population. First, I examined the effects of advanced maternal age at birth on offspring condition, age-specific reproductive success, and long-term survival. I show that offspring born to older mothers display reduced overall survival and higher age-specific reproductive success, but reduced survival of their own progeny. My results show rare evidence of a persistent effect of maternal age on fitness across generations in a long-lived mammalian population.
I then was interested in investigating how differential sex allocation might impact offspring condition, age-specific reproductive success, and long-term survival. I show that calves born after a male sibling display reduced body mass and lower survival compared with those born after females. The sex of the previous offspring also seems to impact the reproduction of the subsequent siblings, with females born after a male sibling reproducing more slowly. This is the first time such a long-term intergenerational cost has been shown in a mammal species.
Although senescence is often observed in the wild, its underlying mechanistic causes are still poorly understood. I was thus also interested in investigating age-related variations in biological markers of health and their interconnectedness with variations in environmental conditions. I examined how different physiological markers of health (body score index, blood cells count, liver and kidney functions) vary across age. In this study, we see a decline of body condition, immune and liver functions with age; which is the first evidence of senescence on physiological traits in Asian elephants.
The results of this project have been presented at several national and international conferences, including evolutionary biology and physiology symposiums in 2017, as well as invited talks in different Universities (Glasgow – Scotland, Turku – Finland) in 2016 and 2017, which were ideal opportunities to present my research to a broad range of scientists (from ecologists to epidemiologists) interested senescence and its mechanisms.
