Vertebrates, insects share the stress.

As it turns out, the spineless and the brave stand up to adversity the same way.

A key protein involved in animals' physiological responses to stress has carried out the same function since before any organism developed a backbone, a study of insects has revealed. That finding suggests that the entire "fight-or-flight" stress-response system based on corticotropin-releasing hormone (CRH) dates back to a common ancestor of vertebrates and insects. It lived at least 700 million years ago.

Mark O. Huising of Radboud University in Nijmegen, the Netherlands, and Gert Flik of Wageningen University in the Netherlands searched the honeybee's DNA for a sequence resembling the vertebrate gene that encodes CRH-binding protein. In mammals and other vertebrates, this substance influences the overall stress response.

The honeybee DNA segment that Huising and Flik found closely matches its vertebrate cousins in length, organization, and structure. Analysis of DNA sequences from a mosquito and a fruit fly show that both insects also have the CRH-binding protein.

That suggests that the endocrine stress system has existed since before insects and the ancestors of vertebrates parted evolutionary company, Huising and Flik conelude in the May Endocrinology.--B.H.