Dr. Rob Dillon, Coordinator

Friday, October 12, 2007

The Classification of the Physidae

Editor's Note.  This essay was subsequently published as: Dillon, R.T., Jr. (2019b) The classification of the Physidae.  Pp 189-192 in The Freshwater Gastropods of North America Volume 2, Essays on the Pulmonates.  FWGNA Press, Charleston.

I'm pleased to report that Amy Wethington's excellent 2004 dissertation has, at long last, found its way to publication (1). "A molecular phylogeny of Physidae (Gastropoda: Basommatophora) based on mitochondrial DNA sequences" is now available as a PDF download from the link below. Our congratulations go to Amy and to her advisor, Chuck Lydeard, for a job well done!

Amy sequenced fragments from both the CO1 and 16S mitochondrial genes (summing to 1,200 bp) from a sample of 65 individual physids, representing 28 nominal taxa (2). The results of her phylogenetic analyses dovetail nicely with her anatomical observations, as well as with the growing body of experimental evidence demonstrating little reproductive isolation among many physid populations formerly considered specifically distinct. Amy and Chuck propose a return to the simple two-genus classification system favored by Thiele and Zilch - Physa and Aplexa - the former with about ten species and the latter with but one.

Although their sample size within any single physid population was kept small by the exigencies of scale, Amy and Chuck demonstrate in their analysis the appreciation for interpopulation variation that characterizes all good evolutionary science. Amy has published at least 14 papers on the genetics, ecology, behavior, and reproductive biology of Physa over the last 15 years. She first familiarized herself thoroughly with her organism, then sequenced its genes and cranked out her phylogenetic trees. It shows.

Amy is currently an assistant professor at Chowan University in Murfreesboro, North Carolina (3). We'll look forward to many additional contributions from her in the future!

And keep in touch,


(1) Wethington, A.R., & C. Lydeard (2007) Journal of Molluscan Studies 73: 241 - 257. [PDF]

(2) Amy's sample of taxa was primarily North American, but did include fontinalis from The Netherlands, marmorata from Guadeloupe, and acuta from several spots around the world.

(3) Email Amy at wethia@chowan.edu