Athletic humpbacked conches leap to safety

When a predatory cone snail launches an attack, it is hardly a high-speed encounter. Lumbering towards an unsuspecting humpbacked conch, the cone snail looks likely to outpace its quarry; but then events take an unexpected turn. As soon as the conch gets a whiff of the approaching predator, it leaps out of reach. And Sjannie Lefevre from the University of Oslo, Norway, explains that the athletic conches can continue flipping for as long as 5 min to get clear of danger. Intrigued by the humble mollusc's remarkable escape reflex, Lefevre and her colleagues, Sue-Ann Watson and Philip Munday from James Cook University, Australia, and Göran Nilsson from the University of Oslo, wondered how the animals powered their gymnastics. Lefevre explains that the oxygen consumption of fish rockets when they exert themselves, but she was less sure that the conches – with their relatively simple hearts and circulatory systems – could rise to the challenge in quite the same way.

Collecting conches buried in the sand in the Lizard Island lagoon, the team headed back to the lab to measure the animals’ oxygen consumption rate while resting and leaping. However, before Lefevre could entice the conches to exert themselves, she had to collect some of the terrifying odour from the water bathing the predatory snails: ‘[The humpback conches] react very quickly; almost as soon as you inject the odour into the respirometer, they start jumping’, she says. And Lefevre was amazed to see the oxygen levels in the respirometer plummet as soon as the conches began jumping to evade the smell. ‘We had some conches increase their oxygen consumption six times’, she says, adding that this is similar to the metabolic boost measured in escaping fish. So, despite their unsophisticated circulatory systems, the conches were able to increase their oxygen consumption dramatically as their metabolism soared during an escape bid.

But then the team wondered how well the molluscs will cope as climate change takes hold and the planet's oceans become more acidic. Lefevre explains that the additional physical burden of increased temperature and acidity limits the performance of many ectotherms as they divert energy to cope with the physiological challenges. To test how well the conches may cope in the future, Lefevre turned up the thermometer – first to 33°C and then to 38°C – and measured their oxygen consumption while resting and leaping. However, the conches didn't miss a beat, successfully sustaining their athletic leaps at the highest temperature when other species would have diverted energy from their exertions to combat the heat. And when Lefevre turned up the pressure and increased the CO₂ level of the water from about 450 μatm to nearly 1000 μatm – to simulate conditions in 2100 – she was amazed to see that the conches barely suffered any ill effects and continued leaping. ‘These snails have aerobic capacity in excess of current and future needs’, she says.

However, this does not mean that the future will be all plain sailing for the athletic conches. Lefevre explains that increased levels of CO₂ in the water affect the ability of many aquatic species to react to predators, making them more vulnerable to predation. She suspects that the nimble conches may suffer the same fate, as she and her colleagues have found that the molluscs are reluctant to jump in high-CO₂ water. But, she is optimistic that enough of them will retain the ability to sniff-out a foe and take evasive action to keep the conches leaping into the future.