Mysterious Border Between Two Millipede Species Runs for Over 140 Miles

Two species of millipede, Tasmaniosoma compitale and T. hickmanorum, maintain an invisible border in northwest Tasmania that runs for over 140 miles and has better border control than any border maintained by man. Dr. Bob Mesibov, a millipede specialist and a research associate at the Queen Victoria Museum and Art Gallery in Launceston, Tasmania, mapped the border, which is 230 kilometers (142.9 miles) long. The millipedes cross very little into each other's territory. The mixing zone - or parapatry - where the two species meet is less than 100 meters wide.

It is not yet known how the millipedes manage this border. Parapatric boundaries between two species usually parallel a geographical feature, such as a ridgeline, or a steep rainfall gradient, but the border between the millipede species runs along different types of terrain and crosses rivers.

Dr. Mesibov says, "I have no idea why the line is so sharp. The boundary runs up and down hills, crosses rivers and different bedrocks and soils, and ignores vegetation type and climate differences. Its position and its sharpness seem to be the result of an unexplained biological arrangement between the two millipede species."

Dr. Mesibov also says, "There does not seem to be an ecological or a geographic explanation for this particular boundary, or for any part of it. It is also longer than any other parapatric boundary I know about. At 230 km, it is 50% longer than the boundary between England and Scotland, and the 'border control' is a lot better than what we humans can do."

This photograph shows the two species of millipedes preserved in alcohol.

Dr. Mesibov's research was published here in the journal, ZooKeys.

Photos: Dr. Bob Mesibov

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