Health News

Curious brain of spiders reaches down to the legs

Brain mass of small spiders distributed throughout the body

12/22/2011

In view of the complex structures that spiders use to create their nets, the question arises as to how the tiny creatures of the tiny creatures accommodate the brain mass they need in their bodies. Biologists from the Smithsonian Tropical Research Institute in Panama now report on the scientific online portal „Arthropod Structure and Development“, that little spiders use a special trick to accommodate their relatively large brain in their body.

While in the relatively large experimental animals from the genus Golden Spider Webs, the central nervous system was confined exclusively to the head, significantly smaller spiders store a large part of their brain in other parts of the body, report the scientists to study director William Wcislo. Thus, the central nervous system extends in the pinhead-sized spiders of the genus Mysmena over the entire body to the legs, said the experts. According to this, up to 78 percent of the body cavity and 25 percent of the limbs of the very small spiders are filled with brain matter.

The distribution of brain mass in the body of the spiders is, according to the researchers, directly related to their size. For example, in the approximately four-centimeter long and two-gram Golden Silk Spider (Nephila clavipes), the central nervous system is exclusively in the head, whereas the smaller spiders distribute their brain mass over the entire body. The scientists at the Smithsonian Tropical Research Institute have examined nine different spider species from the jungles of Central America. Among other things, they determined the weight of the animals, their brain mass and the distribution of the central nervous system in the body. The small spiders had a particularly large brain in relation to their body. The analysis under the microscope also revealed that their central nervous system is not only concentrated on the head, but extends into the body cavity and sometimes even into the legs.

The phenomenon of outsourcing brain mass to other parts of the body was the more pronounced the smaller the spiders were, write William Wcislo and colleagues. Thus, the brain formed in the very small spiders of the genus Mysmena up to 15 percent of the body mass. By comparison, the human brain makes up about two percent of the human body. In order to accommodate their relatively large brain, small spiders not only store a part of their brain in the body, but the young also form bumps on the shell, in which the required nerve cells can be accommodated. Study leader Wcislo explained the surprising trick of evolution is that spiders need a minimum of brain mass to weave their nets and perform other complex actions, so that small spiders have a huge brain relative to their body size, that in the tiny head of the animals would not find enough space. „The smaller the animal, the more it has to invest in his brain,“ said the expert from the Smithsonian Tropical Research Institute. For this purpose, large parts of the central nervous system in the body cavity or the legs are outsourced. (Fp)