Anyone who has suffered jetlag will be uncomfortably familiar with the stubbornness of their internal body clock. Mis-timing a meal or nap after an intercontinental flight can play havoc with sleep for days. But few are aware of the ticking chronometer tucked away at the ends of our chromosomes. ‘Evidence is accumulating across species that the length of an individual’s telomeres [the protective structures at the ends of chromosomes] can predict an individual's remaining lifespan’, says Oscar Vedder from the Institute of Avian Research, Germany. Explaining that telomeres tend to shorten fastest in growing tissue where cells are dividing rapidly, Vedder and his colleagues – Simon Verhulst and Erica Zuidersma, from the University of Groningen, The Netherlands, and Sandra Bouwhuis, also from the Institute of Avian Research – approached the issue of telomere length from a different perspective. Would the telomeres of tern chicks developing in cold eggs with lower rates of cell division be longer than those of chicks developing in warm eggs?
Collecting freshly laid eggs from a tern colony near Wilhelmshaven, Germany, Vedder and Bouwhuis cautiously replaced each of the precious embryos with an imposter egg so that the parents would be none the wiser. Back in the lab, the duo divided the clutches and incubated half of the developing chicks at 37.5°C while the remaining eggs were incubated at a cooler 36.5°C until hatching. After collecting minute blood samples from each newborn, Vedder and Bouwhuis sneaked the youngsters back under their brooding parents as if nothing had happened, before analysing the length of the telomere capping structures at the ends of the chromosomes in the chicks’ red blood cells.
Knowing that the cooler chicks had hatched ∼1 day later and grown 5% more slowly than their warmer siblings, the team was pleased when it discovered that the chicks’ telomeres were 147 DNA base pairs (bp) longer than the 12,060 bp telomeres of the chicks that developed in the warm eggs. And Vedder explains that even this small difference could have implications for the chicks’ longevity. ‘Previous research on common terns showed that in adults a 50 bp reduction in telomere length was already associated with a 1 year shorter lifespan, so 147 bp is quite substantial for a species that on average lives for 10 years’, he says.
Now that Vedder knows that growth rate does affect telomere length, he is keen to understand how the difference might affect the birds’ lifespan, but he acknowledges that he will probably have to switch to a species with a shorter lifespan if he is to know the answer sooner rather than later.