Every homeowner knows that maintenance is a major expense, and our bodies are no different. Most species make significant investments in maintaining systems that are essential for survival, but sometimes the costs are too high, leading animals to cut back on maintenance at certain times of the year and make do with second best. Lisa Schwanz and her colleagues from Iowa State University and the University of Pennsylvania say, ‘Physiological maintenance has been widely studied in birds, mammals and invertebrate model systems, but much less is known about maintenance in ectothermic vertebrates’. Explaining that ectotherms tend to live longer than endotherms and experience significantly different physiological stresses, Schwanz and her co-workers decided to find out how painted turtles – ranging from hatchlings to aged adults – maintain their bodies throughout the year. The team measured the DNA damage repair efficiency and immune responses of painted turtles prior to hibernation, and then continued monitoring the immune response during hibernation and in the spring to find out how well they maintain two physiological systems that are essential for long-term survival (p. 88).
Collecting animals from the wild, the team took small blood samples from them before, after and during hibernation. Measuring the ability of the blood samples to repair DNA damage, the team exposed the pre-hibernation samples to UV light and analysed the amount of DNA damage sustained. They also counted the number of immune response cells – ranging from lymphocytes to heterophils – to find out how their levels vary at different times of year, as well as measuring the blood parasite levels, to find out how healthy the animals were, and several responses to infection.
Analysing a colossal amount of data, the team found that the hatchling's immune response was weaker than the adult's. However, when they looked at the older turtles' immune systems, they found that they were almost as well maintained as younger adults' immune systems – unlike the immune systems of elderly endotherms, which usually deteriorate with age. But, despite their well-maintained immune systems, the elderly turtles had higher levels of haemogregarine parasite infection, which could weaken them. And when the team compared the turtle's immune responses before, during and after hibernation they found seasonal fluctuations but no evidence that the immune response became stronger during hibernation.
Looking at the levels of DNA damage repair across the different age groups the team found that hatchlings had high levels of DNA damage repair, but juvenile and elderly turtles seemed to have no DNA damage repair mechanisms at all. The team suspect that the loss of DNA damage repair mechanisms is not a natural decline with age and suggest that turtles may have reduced levels of DNA damaging oxygen free radicals so they no longer require protection from DNA damage.
Schwanz and her colleagues say, ‘Physiological maintenance across different immunological and non-immunological systems is not consistently determined by age, sex or season in the long-lived painted turtle,’ and point out that the reptiles do not seem to suffer many of the ageing effects that elderly endotherms endure.