Diet helps salamanders beat the heat

The Chinese giant salamander (Andrias davidianus) is one of the world's largest amphibians and can grow up to 1.8 m long. Unfortunately, its wild populations have suffered significant declines due to climate change and the destruction of its natural habitat. Temperatures above 20°C are already too high for these cold blooded (ectothermic) animals, negatively impacting their appetite and survival. However, diets rich in protein and oil might offer a helping hand. Previous studies found that Chinese giant salamanders fed diets high in protein and oil (fish-based diet) improved growth and the highest temperature that they can withstand compared to individuals fed high carbohydrate diets (worm-based diet). But why and how does diet mitigate the effects of elevated temperatures?To answer this question, Rui Zhai and colleagues from the Chinese Academy of Sciences, China examined the metabolites – such as amino acids, oils and other chemicals – involved in energy production in the livers of Chinese giant salamander larvae living at temperatures that they would experience during a summer heatwave of 20°C. They fed the youngsters two different diets: a fish-based diet (high in protein and fat) and a diet of worms (rich in carbohydrates) for 88 days. The researchers focused on the larvae's livers since the organ is a powerhouse of energy metabolism that converts amino acids and fatty acids into ATP for energy. While previous research has shown that the liver's metabolism is particularly vulnerable to high temperatures, including a decline in glycogen breakdown and ATP production, it remains unclear how dietary composition can offset these effects. By analysing metabolites in the liver, the researchers aimed to determine how a protein- and fat-rich diet could help the endangered larvae to survive high temperatures.The team discovered that diet significantly shaped how the young salamanders dealt with living at elevated temperatures. The salamander larvae on the fish-based protein- and oil-rich diet produced high levels of the metabolites that eventually go on to produce ATP at 20°C, suggesting a stronger ability to produce energy when the temperatures were dangerously high for the young salamanders. This means the fish-based diet better supported energy metabolism at high temperatures by enhancing the breakdown of amino acids and oils, which fuel ATP production. Interestingly, the salamanders on the worm-based carbohydrate-rich diet produced less energy and used fewer amino acids to fuel ATP production. However, when the team checked the metabolism of the salamander larvae on both diets living at 15°C, they were both producing ATP via similar mechanisms, indicating that the dietary benefits of a high-protein and high-fat diet are particularly important when the temperatures are high. So, diet plays a key role in influencing the resilience of Chinese giant salamander larvae as temperatures rise.Zhai and colleagues have found that salamander larvae fed a high-protein, oily diet could sustain efficient energy production by using these nutrients to produce ATP during a heatwave. The team suggests that adjusting the diets of captive giant salamander larvae, or those in managed protected areas, by providing the best prey with the ideal nutrient content of protein and fats could help this endangered species cope with rising temperatures. However, for wild populations, it is still unclear how they change their menu during summer, making it difficult for conservationists to develop strategies to give the salamanders access to prey that provide the optimum diet. By understanding how nutrition influences metabolism, ecosystem managers could implement conservation strategies that enhance the salamanders’ resilience to climate change. For the Chinese giant salamander, the right diet might be a lifeline in a warming world.