The Ecological Impact of Stress on Grasshoppers
Paragraph 1
You are tense and wary, alert to every rustle and snapped twig. A predator is near, you can sense it. Your heart races; you sweat. Quietly, you reach for a doughnut. Stress speeds up the metabolism of grasshoppers, making them seek out easily digested sugars and carbohydrates for a quick energy boost. This and other results, published in three journals in the past month, could have big implications — not just for prospective prey, but also for the ecosystems they live in. In more relaxed conditions, many animals opt for high-protein foods that help them to grow and reproduce. But with a predator lurking, they need fuel to quickly feed their amped-up bodies — and to bolt, if needs be. Dror Hawlena, an ecologist at Yale University in New Haven, Connecticut, has been teasing out the ecological ramifications of this predation stress in meadows.
Paragraph 2
In cages placed on naturally growing vegetation, Hawlena added grasshoppers and, in some cases, spiders with their mouthparts glued shut, so that they could induce fear without killing the grasshoppers. Grasshoppers that were exposed to spiders switched from eating protein-rich grasses to munching on several species of sugary goldenrod plants. Initially, this diet shift was thought to be related to how easy it is for grasshoppers to hide from spiders in the branched and flowering goldenrod. To separate out the possible effects refuge-seeking, Hawlena also studied grasshoppers and muzzled spiders in indoor terrariums. Instead of plants, the grasshoppers were fed with an artificial diet of high-sugar or protein-rich 'biscuits' — and he saw the same trend. Fearful grasshoppers went for the high-sugar cookies rather than the protein-rich bars.
Paragraph 3
All that sugary food means that the stressed-out insects are ingesting foods richer in carbon and poorer in nitrogen than their calmer, protein-pumping cousins. Meanwhile, their bodies are breaking down proteins to make even more glucose. The result is a body that is made of significantly more carbon and less nitrogen — and thus makes poorer fertilizer when it dies and rots. Hawlena thinks that the ecosystem is likely to be changed in two ways by frightened grasshoppers. First, they eat more goldenrod and less grass, changing the ratio of these species in the landscape. Second, the soil is receiving less nitrogen, potentially influencing what can grow there. In ongoing experiments, Hawlena is getting intriguing results by looking at the different kinds of soil bacteria that thrive on stressed or unstressed grasshopper corpses. He expects to see a similar story in the bodies of most other animals. The stressed-out living are likely to alter their diet, and the relaxed and happy dead are likely to make better fertilizer.
Paragraph 4
It remains to be seen whether the physiological effects of stress on grasshoppers scale up to plants, soil, bacteria and onwards or whether the effect is too small and is swamped by all the other convoluted causal factors in ecosystems. "It is very intriguing that [Hawlena and colleagues] can detect these effects. What will determine the importance ecologically is how strongly these effects translate from one level of biological organization to another," says Matthew Kauffman of the US Geological Survey in Laramie, Wyoming.
