Frightened grasshoppers can affect their environment

New Worlds: Grasshoppers under stress can behave like tense humans who overeat sweets.

By JUDY SIEGEL-ITZKOVICH
Grasshopper 390 (photo credit: Courtesy)
Grasshopper 390
(photo credit: Courtesy)
To the layman’s eye, grasshoppers seem happy-go-lucky creatures, able to go anywhere they want and have an adequate supply of food. In fact, according to researchers at the Hebrew University of Jerusalem and Yale University, grasshoppers tend to get frightened by spiders – and this can even affect the productivity of our soil and our ecosystem.
A fearful grasshopper, experiencing stress, will consume a greater quantity of carbohydrate-rich plants – similar to humans under stress who might eat more sweets. This will, in turn, cause chemical changes in the grasshopper and its excretions, affecting the ecosystem it inhabits.
When a scared grasshopper dies, its carcass – which contains less nitrogen as a result of its diet change – will have an effect on the microbes in the ground, which are responsible for breaking down animal and plant matter. With less nitrogen available, the microbes decompose the hard-to-break-down plant materials in the soil at a slower rate. Thus, fear of predation may slow down degradation of complex organic materials to the simpler compounds required for plant growth.
Research on this biological/ ecological phenomenon, carried out by Dr. Dror Halwena of the department of ecology, evolution and behavior at HU’s Alexander Silberman Institute of Life Sciences, in cooperation with US researchers, appears in a recent issue of the journal Science.
The scientists exposed grasshoppers to spiders to arouse a stress reaction and compared the results with a control group of nonstressed grasshoppers. They found the scared grasshoppers had a higher carbon-tonitrogen ratio in their bodies than non-frightened grasshoppers. In further laboratory and field tests, the researchers tested the influence of grasshopper remains on soil. After the microbes consumed the grasshopper remains, the researchers added plants to the surface.
They showed that the decomposition rate of the plants in the areas where stress-free grasshopper remains were introduced decomposed at a rate between 62 percent and 200% faster than those of the stressed grasshoppers.
In a further experiment, the researchers used “artificial grasshoppers” – a mixture of sugar, protein and chitin, the organic compound found in the grasshopper external skeleton – in varying quantities.
Here, too, they found that even the small amount of nitrogen found in the protein added to the soil significantly increases the functioning of the microbes responsible for breaking down the organic matter in plants.
“We are dealing here with an absolutely new kind of mechanism whereby every small chemical change in a creature can regulate the natural cycle, thus in effect affecting the ecology in total, such as the amount of carbon dioxide released into the atmosphere through decomposition and field crop productivity. This has tremendous consequences for our ecological understanding of the living world,” said Halwena. “We are gaining a greater understanding of the necessity of conserving all of the component parts of the ecosystem in general and of predators in particular. We are losing predators in nature at a much faster rate than other species.”
He said he hoped the research help scientists better predict changes in the biological system as a result of such human-induced phenomenon as overfishing, hunting or global warming that can undermine the entire ecosystem.
MARINE STOWAWAYS Marine scientists studying life around deep-sea vents have discovered that some hardy species can survive the extreme change in pressure that occurs when a research submersible rises to the surface. The team’s findings, published recently in Conservation Biology, reveal how a species can be inadvertently carried by submersibles to new areas, with potentially damaging effects on marine ecosystems.
After using the manned submersible Alvin to collect samples from the Juan de Fuca Ridge under the northeastern Pacific Ocean, the team discovered 38 deep-sea limpets (Lepetodrilus gordensis) among their sample. Intriguingly, this species is believed to occur only in the vents of the Gorda Ridge, which are 635 kilometers south of the dive site.
“The big question was, how did they get over 600 kilometers from their habitat?” said Dr. Janet Voight, from Chicago’s Field Museum of Natural History. “We discovered that the individuals must have been transported from the Gorda Ridge by our submersible.
Even though we clean the submersibles after sampling we had assumed that the extreme pressure change would kill any species which are missed.”
The introduction by humans of new species to an ecosystem – often inadvertently – is a big challenge to conservation, as how a new species will react to new surroundings and its effects are unpredictable.
Increases in deep-sea drilling and submersible activity can raise the probability of introductions, but until now hydrothermal vents have been considered too extreme and too isolated to be a source of introduced species.
In coastal environments, one of the biggest threats posed by invasive species to native species is disease, as newly introduced pathogens and parasites can cause mass mortality. Diseases that may exist in the extreme environments created by hydrothermal vents have not been well studied.
“We’ve discovered that it is possible to accidentally introduce a species, and any potential diseases it may carry, from a deep-sea vent to a new location,” concluded Voight. “This has implications for the future exploration of hydrothermal vents as it reveals the potential risk of human-driven change to the ecosystem.”


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