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Grasshoppers change coats to beat the heat.

Many people head to southern California in search of a laid-back, sun-and-surf lifestyle. For insects, however, the living appears far from easy. To cope with the region's hot, dry conditions, grasshoppers in southern California develop special adaptations, biologists report in the Aug. 15 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES.

By studying one such trait--the ability to resist desiccation (drying) -- the researchers have determined that populations of the lesser migratory grasshopper, Melanoplus sanguinipes, in different parts of Claifornia evolved varying abilities to withstand their local climates. "IT tells us there's a lot of variation for a very important physiological trait previously thought to be fixed within a species," says study coauthor Timothy A. Mousseau, an evolutionary bilogist at the University of South Carolina in Columbia.

With their relatively small size and large surface area, insects could dry out quite rapidly in hot, arid climates. But a thin, invisible, waxy coat over their hard outer skeleton protects against water loss -- at least until the insect gets so warm that the lipids in the coating melt, says physiologist Allen Gibbs of the University of California, Davis, who directed the study.

He and his colleagues describe two types of adaptations by which M. sanguinipes can maintain its waterproofing even in harsh weather. In the short run, an individual, grasshopper can acclimatize somewhat to its environment. In the long run, entire populations evolve to become better suited for their local conditions. This "implies they have genetic diversity so they could evolve fairly quickly," says Mousseau.

"It's evidence of evolutionary change that can occur within a species," comments George N. Somero, an environmental physiologist at the University of California, San Diego. "That's novel."

Both he and Gibbs' team speculate that such fine-scale tuning of the genetic makeup of populations within a single species may occur more often than scientists realize.

For their laboratory study, Gibbs and his co-workers established breeding colonies of lesser migratory grasshoppers gathered from 18 sites throughout California. They collected the eggs and raised the emerging young at one of three temperatures -- 34[degrees]C, 32[degrees]C or 29[degrees]C -- to simulate field conditions at collection sites. When the young grasshoppers molted, the researchers collected the shed "Skins" and analyzed them.

Using a technique called Fourier-transform infrared spectroscopy, the team monitored changes in the physical properties of the lipids as the skins were gradually warmed.

The melting points of the lipids in the samples ranged from 39.1[degrees]C to 49.6[degrees]C, they found. Some lipids liquefied over a range of about 5[degrees]C, while others did so over a range of nearly 25[degrees]C, while others did so with the lower melting points tended to liquefy over wider temperature ranges and came from the offspring of the more northern grasshoppers.

The scientists found that all the insects could alter their lipid coats in response to new environmental conditions. However, the higher melting point of lipids in skins shed by the southern offspring "suggests that the grasshoppers can [also] adapt to their local environment in an evolutionary sense," says Gibbs.

Insects can moderate the effects of sunlight by hiding under a leaf, but in summer even the soil can reach 50[degrees]C in the hottest parts of California, the researchers note. Thus, they say, melting point could make a difference in a grasshopper's ability to survive.

Other studies have focused on variations in body size or color within and among populations of a given species, but the grasshopper's lipid protection against deciccation "is a trait within important consequences for the fitness of the individual," says Mousseau.

"It's only been with recent technical developments that people have been able to delve into these properties, which are not easy to measure," he adds.
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Title Annotation:grasshoppers' adaptations for coping with the hot, dry climate in southern California
Author:Pennisi, Elizabeth
Publication:Science News
Date:Aug 24, 1991
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