06 August 2009

What do philomycid slugs and poison ivy have in common?

They have similar worldwide distribution patterns.

The members of the slug family Philomycidae are found in eastern North America and southeast Asia. Here is their distribution range.

Verbreitungskarte der Philomyciden, the distribution map of the Philomycidae from Hoffmann (1924). Keep in mind that the taxonomy and the known ranges of the philomycid species may have since changed, but the overall distribution is probably still the same.

And here is the distribution range of the genus Toxicodendron.

From The Poisoned Weed by Donald G. Crosby (2004).

Toxicodendron radicans is the poison ivy. There are several subspecies of T. radicans in eastern North America and 2 subspecies in China, Taiwan and the Kurile Islands.

Is it a coincidence that a family of animals and a species of plants have roughly the same distribution ranges each characterized by 2 widely separated areas?

This peculiarity is not limited to the Philomycidae and Toxicodendron radicans. There are some other groups of animals and plants with similar shared ranges in eastern North America and Southwest Asia.

*Hoffmann, H. 1924. Zur Anatomie und Systematik der Philomyciden. Jenaische Zeitschrift für Naturwissenschaft 60: 364-396.


Christopher Taylor said...

The same pattern pops up a number of times in harvestmen - Caddo agilis, Caddo pepperella and (if I recall correctly) Crosbycus dasycnemus are all individual species that each show this kind of distribution (mind you, they're also all mostly parthenogens, so morphological conservatism may be hiding genetic diversity).

Neil said...

Magnolia and Alligator also come to mind...

Anonymous said...

Biogeographers need to be aware of the role of commerce in spreading the subjects of their research. Philomycids are not native to Hawaii nor, I suspect, to any of the other islands of Polynesia or Micronesia. Even by 1924, Hoffmann should have been aware of that.

Carl C. Christensen


That`s a good point, Carl.