Millipedes Control Territory Borders With Inexplicable Precision

The distribution of a species is often limited by bodies of water or differences in climate or terrain. Why the clear-cut boundary between two particular species of Tasmanian millipede exists, however, is not so clear.
Millipedes Control Territory Borders With Inexplicable Precision
12/28/2011
Updated:
9/29/2015

The distribution of a species is often limited by environmental boundaries such as bodies of water or differences in climate or terrain. Why the clear-cut boundary between two particular species of Tasmanian millipede exists, however, is not so clear.

Dr. Robert Mesibov from the Queen Victoria Museum and Art Gallery in Launceston, Tasmania, identified the millipedes Tasmaniosoma compitale and Tasmaniosoma hickmanorum and noted that while they lived in the same habitat, the two species crossed only very slightly into each other’s territory, a phenomenon known as parapatry.

Over the course of the past two years, Dr. Mesibov collected samples of the two millipedes on the Australian island to map their distributions and found that the border between the two species’ territories did not seem to parallel any geographic or ecological features.

“The boundary runs up and down hills, crosses rivers and different bedrocks and soils, and ignores vegetation type and climate differences,” said Dr. Mesibov in a news release.

“Its position and its sharpness seem to be the result of an unexplained biological arrangement between the two millipede species.”

Along the boundary, the two species do co-occur. However, these zones are only about 100 yards wide.

“I have no idea why the line is so sharp,” remarked Dr. Mesibov.

“It is also longer than any other parapatric boundary I know about. At 230 km [143 miles], it is 50 percent longer than the boundary between England and Scotland, and the ‘border control’ is a lot better than what we humans can do.”

The findings were published online on Dec. 20 in ZooKeys.