Periodic Reporting for period 3 - Elephant Project (How elephants grow old)
Reporting period: 2019-01-01 to 2020-06-30
Improving the quality of life at old age and predicting future changes in longevity patterns of societies might depend on our ability to develop indicators of how old we really are and how many healthy years we have ahead, and how those indicators depend on our health history across several decades. Yet, most model species used in biology are short-lived and provide a poor comparison to long-lived mammals such as humans. Further, they do not often inform on the mechanisms of ageing alongside its fitness consequences in natural populations of long-lived mammals.
Elephant project integrates different ageing mechanisms with unique data on lifelong disease and reproductive history in the most long-lived non-human mammal studied so far, the Asian elephant. The project team will examine how different mechanisms of ageing (telomere dynamics, oxidative stress and telomerase activity) interact with lifelong disease and reproductive history, and current endocrinological measures of stress and reproductive status. This will help to better understand both the mechanisms of ageing and their consequences on senescence rates.
Understanding changes in health across life and its links to ageing rates, stress levels and life-history in a species as long-lived as humans will be relevant to a large range of end-users.
Given the considerable data collection so far, the team in Turku has begun statistical analysis of the data obtained so far to address several of the project main aims. These analyses have led to the following major discoveries:
1. By using the multigenerational demographic dataset of our semi-captive Asian elephants combined with measures of body size, we have quantified how maternal age affects offspring condition, age-specific reproductive success and long-term survival. We show that offspring born to older mothers display reduced overall survival, and higher age-specific reproductive success, but reduced survival of their own progeny. Our results suggest a persistent effect of maternal age on fitness across generations for the first time in a naturally occurring mammalian population.
2. We have also found that grandcalves from young mothers (<20 years) had 8 times lower mortality risk if the grandmother resided with her grandcalf compared to grandmothers residing elsewhere. Resident grandmothers also decreased their daughters’ inter-birth intervals by one year. Our findings that grandmother’s presence was highly beneficial for grandcalf survival particularly among young mothers and the daughters were also able to reproduce more rapidly in the presence of their mothers in elephants have implications for our understanding of the evolution and selection pressures on post-reproductive lifespan in general, as well as on dispersal and social system in elephants specifically.
3. We have shown that there was large variation in age at first reproduction in Asian elephants and only 81% of final weight had been reached by peak age of reproduction at the population level (19 years). Those females beginning reproduction early tended to be taller and lighter later in life, although these trends were not significant. We found that taller females were more likely to have reproduced by a given age, but such effects diminished with age, suggesting there may be a size threshold to reproduction which is especially important in young females. Our results suggest that although reproduction may not always impose significant costs on growth, height may be a limiting factor to reproduction in young female Asian elephants, which could have important implications for management.
4. We have shown that wild-captured elephants, suffering from adverse early events, had markedly lower survival compared to captive-born elephants in timber camps, and that the harmful effects of capture on survival lasted for several years or even decades.
First lifelong record of health and disease
Second, birth size, or subsequent individual size or body condition
Third, group (family) compositions
Fourth, reproductive and stress hormone samples, physiological ageing measures, parasite infection levels, longitudinal health monitoring including hematology, serum chemistry and clinical examination, and milk quality
Fifth, individual life-history data such as start of reproduction, lifelong records of births, death and its cause
Sixth, behavioural differences, personality variation and working task assays
Seventh, genomic data on e.g. inbreeding level and specific genetic markers
Using these data, we will be the first to determine how complementary measures of current health during 2011-2020 associate with telomere dynamics.
We will then examine how health at given ages across life (averaged over ~22 bi-monthly health reports/ year/ individual) and cumulatively across previous life are related to telomere dynamics.
We are revealing how reproductive investment (onset and rate of reproduction) affects the age-specific rate of decline in bi-monthly health status and increase in disease prevalence over entire lifespan of females. We also show how past reproduction is linked to a complementary correlates of current health, condition and ageing rate, measured by body mass and score, stress hormones and ageing markers (telomere dynamics and oxidative stress).
We have already produced a ""draft reference genome"" for the male Asian elephant (first one of its kind), produced using the 10X-linked reads technology, with a total coverage of 54X, a median effective coverage of 26X and a N50 of 40 kb so far. We are currently producing PacBio long reads to scaffold this further. Preliminary examination reveal at least 13 independent copies of P53 gene which is extremely exciting for research on ageing and unique cancer prevention mechanisms in this species. We expect first publications on this topic in 2019.