Longevity Briefs: Penguins In Zoos Appear To Age Faster But Live Longer

Longevity briefs provides a short summary of novel research in biology, medicine, or biotechnology that caught the attention of our researchers in Oxford, due to its potential to improve our health, wellbeing, and longevity.

The problem:

Compared to wild animals, animals in captivity usually eat more and undertake less physical activity – both of which are associated with increased risk of age-related disease and death. Despite this, animals live longer in captivity on average. This is because even though wild animals live healthier ‘lifestyles’, animals in captivity are protected from predators, infectious diseases and environmental factors that may kill a wild animal regardless of how healthy they are. Thus it is possible for an organism to age at a slower pace, but still have a lower life expectancy due to factors unrelated to ageing.

One parallel to this is modern day hunter-gatherers, who are far more physically active throughout the day compared to us and consume a diverse, less calorie-rich diet. These hunter-gatherers do indeed seem to be healthier for their age (lower blood pressure, less risk of diabetes and so on) but also have poor life expectancy because when they do get ill, it is more often fatal due to lack of modern healthcare. However, these studies are hard to conduct and observational in nature – there are other things besides lifestyle, such as genetics and culture, that differentiate hunter-gatherers from humans living in industrialised societies. Animals in captivity provide an alternative way to study how lifestyle affects ageing. Since we have removed these animals from their natural habitat, this is a kind of controlled experiment in which we can be certain that the environment is responsible for differences in ageing patterns. In this study, researchers investigate the pace of ageing in king penguins in the wild and in captivity. King penguins don’t become overweight in captivity, but do eat significantly more and become less physically active than in the wild.

The discovery:

Researchers first compared the epigenetic age of wild and zoo-resident king penguins using an epigenetic clock. Epigenetic clocks are algorithms designed to give an approximation of the true biological age of an organism by looking at epigenetic modifications – changes to the DNA molecule that alter how genes are read without changing the genetic code itself. Since epigenetic changes occur in a predictable way throughout life, a 10 year-old penguin with epigenetic changes comparable to those of a 15 year-old penguin suggests that the penguin may be ageing at an accelerated pace.

When researchers compared wild penguins to zoo penguins of the same age, they found that captive penguins had epigenetic ages that were between 2.5 and 6.5 years older than the wild penguins. In other words, when you look at a 15 year-old zoo penguin, its epigenetic changes look like those of a 17.5 to 21.5 year-old wild penguin. Nevertheless, 50% of wild penguins die before 13.5 years of age, compared to 21 years of age for zoo penguins. Epigenetic age is not synonymous with biological age, so these measurements do not necessarily mean that zoo penguins are biologically older in all respects – it just means that their epigenetic state resembles that of an older animal.

Researchers then took a closer look at the genes with which the epigenetic modifications were associated. They found that the epigenetic differences between the zoo and wild penguins were primarily associated with genes that are important for cell growth and nutrient sensing (how cells sense and respond to the availability of nutrients from food). These included some molecular pathways already thought to be important in ageing, such as the mTOR pathway, a system that is activated when nutrients are plentiful and whose suppression by drugs has been shown to extend lifespan in mice.

The implications:

These findings suggest that the increased feeding of zoo penguins coupled with reduced physical activity could result in epigenetic changes that correlate with ageing. These epigenetic changes may be adaptations in response to increased nutrient availability; when nutrients are plentiful, cells divide faster and use more energy, which accelerates some of the hypothesised drivers of ageing such as telomere shortening, mitochondrial dysfunction and senescence. When nutrients are scarce, cells activate stress protection mechanisms that may slow down some drivers of ageing.

King penguins are unusual animals in that they regularly fast as a normal part of of their lives while incubating eggs, guarding chicks and when molting (because they can’t enter the water to hunt without their feathers), with fasts sometimes lasting 8 weeks. Fasting has consistently been shown to extend lifespan in various animals and fasting also appears to correlate with reduced epigenetic age in humans. However, we do not know if fasting increases lifespan in humans – many scientists suspect that fasting only extends lifespan in short-lived animals. This does not mean that fasting and other forms of calorie restriction aren’t beneficial practices that are associated with reducing the risk of age-related disease. Physical activity is of course strongly correlated with reduced risk of age-related diseases. Thus, it’s a relatively safe bet that living like a wild king penguin (but with fewer snowstorms and hungry orcas) will result in healthier ageing!