Small animals living in dry, harsh environments face the very real threat of desiccation. Many of them construct microenvironments -- not unlike an air-conditioned apartment on a heat island -- where they spend at least part of their life cycles. Some insect parents, for example, protect their eggs from drying using gels, casings, or cocoons. In an exceptional case of parental protection, tiny insects called thrips build wee little houses out of plant matter to prevent their larvae from drying out in the arid Australian outback. This is the first time anyone has demonstrated active parental protection of offspring from desiccation in insects.
Most thrips limit water loss by seeking out crevices, but acacia thrips are known to construct various kinds of niches. Some thrips from this family induce galls, or abnormal growths on plants, to house themselves. One Australian acacia thrip species called Dunatothrips aneurae live and breed within domiciles that they make from loosely glued phyllodes, winged leaf stalks that function like leaves. The glue is actually a silk-like secretion extruded from the insect’s anus, Science explains. When these little houses were first observed on acacia trees, their functions weren’t clear.
Here are a few examples of Dunatothrips aneurae domiciles on Acacia aneura (the squares measure 0.5 by 0.5 centimeters):
To see if these domiciles create favorable microenvironments, facilitate feeding, or protect from enemies, James Gilbert from the University of Sussex monitored larvae housed in intact domiciles as well as domiciles that have been destroyed. This was done in both high humidity (up to 80 percent) and in ambient low humidity (about 10 percent).
He found that regardless of humidity, most of the larvae survived in the intact domiciles. But with destroyed domiciles, survival depended on humidity -- suggesting that parents construct and maintain domiciles to prevent their offspring from desiccating. If and when the domicile wall gets damaged by wind, Science reports, the thrips rush over to fix the damage, preventing their offspring from drying out or falling out.
These domiciles are also commonly cofounded. The “cofoundresses” likely benefit from sharing the nest-building costs, and it also provides backup parental care if someone dies in what’s known as “deferred byproduct mutualism.”
The work was published in Behavioral Ecology.
Image: OpenCage (cropped) via Wikimedia CC BY-SA 2.5 (top), J.D.J. Gilbert 2014 (middle)